FIELD OF INVENTION
The present invention relates to the field of material science, and more particularly to 5 a
simple and uniform method of synthesizing self-cleaning, superhydrophobic coating of
nano-micro carbon structures or carbon nanofiber (CNF) forest on different substrates.
Such coatings are widely used on steel-mesh for rust-resistance and water-containing
conduits.
10
BACKGROUND OF THE INVENTION AND PRIOR ART
Nanotechnology and hydrophobic surfaces have received tremendous attention in past
few years because of its different properties e.g. oil water separation, corrosion
resistance, self-cleaning, anti-icing property, drag reduction, anti-bacterial, transparency
15 and antireflection (Si, Y. & Guo, Z et al: Nanoscale 2015, 7, 5922–5946). The
combination of nano and micro hierarchical structures as disclosed in this prior art by
Si, Y. & Guo, Z et al. brought a great change in the field of super-hydrophobic nanocoatings.
The aim of these superhydrophobic coatings or surfaces is to provide unique
surfaces of superior functional properties with the long life survival. This prior art
20 further discloses different types of materials used for superhydrophobic coatings e.g.
Inorganic (Silica based, C based), Organic (Polymers based) and Inorganic – organic
(Metal oxide polymer composite based). These materials have their own benefits and
demerits with respect to the efficiency and cost of the production as well as the purity of
coating material. Inorganic coating shows excellent chemical resistance but is very
25 costly to produce. Organic material coatings are structurally flexible with high
transparency, easy to fabricate with desired thickness but these coatings are toxic in
nature and easily proven to corrosion. Further several methods have been developed for
fabrication of superhydrophobic coatings e.g. Sol-gel, Chemical vapour deposition
(CVD), spay process, electro spay, electro spinning, electro deposition, hydro thermal,
30 solution immersion, composite techniques, plasma electrolytic oxidation. Many
3
researchers have fabricated the superhydrophobic coatings of organic and inorganic
materials on different substrate by using different fabrication techniques.
Ma, M. & Hill, R. M. et al.: Superhydrophobic surfaces, 2006, 11, 193–202 discloses
non-wettable surface with higher contact angle > 150o and contact angle hysteresis 5 <
10o are referred to as superhydrophobic or ultra-hydrophobic surfaces.
Zhang, X. et al.: J. Mater. Chem.18, 2008, 621–633 discloses that the combination of
surface roughness and low-surface-energy modification leads to super hydrophobicity.
10
Roach, P. et al: Soft Matter 4 (2), 2008, 224-240 discloses that hydrophobicity of the
surface can be achieved by the creating texture or roughness on the surfaces. Two scale
roughness of the surfaces give rise to the super hydrophobicity effect like lotus leaf
which is a classic example of superhydrophobic surface.
15
Yazdanshenas et al.: Industrial & Engineering Chemistry Research, 2013, Res.52,
12846–12854 have reported ultrasound irradiation, a one-step fabrication method, for
producing silica based materials (TEOS and OTES) superhydrophobic coating on cotton
fabric having micro-nanostructure which shows the contact angle and sliding angle of
20 152.8° ± 2.6 and 8° respectively. The process in this prior art involves pre-treatment of
substrate by organic chemicals that affects the mechanical properties of fabric.
Seyedmehdi et al.: J. Appl. Polym. Sci.128, 4136–4140 (2013) discloses fabrication of
superhydrophobic coatings based on silica nanoparticles and fluoropolyurethane having
25 random structure which shows contact angle (CA) and sliding angle (SA) of greater
than 145o and ~ 3o respectively by spray, brush and dip coating.
Zhang et al.: RSC Adv.4, 2014, 33424 discloses a process of growing silicon
nanofilaments using tricholoromethylsilane on glass substrate having different contact
angle (36- 179.8 o) depending upon the type of solvent, its ratio and the thickness of
4
film by coating spread method. The process involved is time consuming and requires
pre-treating substrates chemically that may affect the properties of the substrate.
Choi, B. G. et al.: J. Phys. Chem. C116, 2012, 3207–3211 discloses a method of
fabricating graphene and nafion super hydrophobicity film having porous petal like
morphology with a 161o contact angle by supramolecular assembly method. Th5 e
process involved is time consuming (>1 week) and requires use of harmful organic /
inorganic chemicals.
Hong et al.: Phys Chem Chem Phys 15, 2013, 11862–11867 relates to a process of
preparing a superhydrophobic polymeric (polyurethane and polystyrene) surfaces
having long neck vase like structure (with a contact angle of 150.6 and 156.6o 10
respectively) on PET substrate by nanoimprinting method using AAO template.
Ivanova et al.: Appl. Surf. Sci.263, 2012, 783–787 prepared superhydrophobic chitosan
based nanoparticle coating with a contact angle of 157.2 o on cotton fabric through
electrostatic reaction by spraying method.
15 Chakradhar et al.: Appl. Surf. Sci.301, 2014, 208–215 fabricated superhydrophobic
coating of PVDF (polyvinylidene fluoride)-MWCNTs (multi walled carbon nanotubes)
on glass substrate by spray coating method having a contact angle of 154o.
Nguyen et al.: Energy Environ. Sci.5, 2012, 7908 fabricated superhydrophobic and
superoliophilic graphene based sponge using dip coating method followed by chemical
modification with PDMS by dip coating method having water contact angle of 162o20 .
Xu et al.: ACS Appl. Mater. Interfaces 5, 2013, 8915–8924 fabricated a
superhydrophobic TiO2-HDPE polymer nanocomposite surface via template lamination
method which exhibited water contact angle of 158o.
US6156389 relates to production of extremely high hydrophobic material composition
25 consisting of trifluoromethyl component and hardenable material (urethane resin or
Teflon AF) by spray coating or dip coating method.
5
Qi et al.: Sci Rep. 2015, 5 relates to a method of forming hydrophobiccomposite
coatings comprising of CNT and hydrophobic polymer (polytetrafluoroethylene,
perfluoroalkoxy polymer resin) through spray coating.
5
US6872441 discloses a method of forming self-cleaning, glass, ceramic and metal
surface by using layer of glass flux and structure forming particles (oxide and silicates
such as zirconium silicate, SiO2, ZrO2, TiO2 and Al2O3) by using printing process.
Macias-Montero, M. et al.: Plasma Process. Polym.11, 2014, 164–174 relates to
fabrication of Ag@TiO2 core shell nanorods having a contact angle of 156o 10 on different
substrates (fused silica and silicon wafers) via plasma deposition followed by PECVD
(Plasma enhanced chemical vapour deposition).
Bao, Xue-Mei et al.: Appl. Surf. Sci.303, 2014, 473–480 discloses a fabrication process
of superhydrophobic surfaces by coating of various metal oxide particles (zinc oxide,
15 iron oxide) on different substrates (fabric and paper) by dip coating or immerse solvent
followed by treatment with PDMS by CVD method to get different water contact angles
(154.8-162.4o), depending upon the type of nanoparticle on different substrate.
Crick et al.: J. Mater. Chem. A1, 2013, 4336 discloses a novel class of nanoparticulate
(Ti, Ni Au etc) incorporated in Si -elastomer superhydrophobic coating on glass
20 substrate fabricated by aerogel assisted chemical vapour deposition (AACVD) for oil
and water separation with water contact angle of 162o.
US2010/0330277 discloses nanocomposite materials comprising carbon nanotubes
(CNT) and oligo (p-phenylenevinylene) (OPV). Dispersion of CNT in the solution of
solution of oligo (p-phenylenevinylene) (OPV) in organic solvent results in the
25 formation of nanocomposite material. The nanocomposite solution can be drop casted
over glass or metallic surface for the preparation of superhydrophobic coating. The
resultant composite surface shows superhydrophobic nature even with corrosive liquids
6
and its contact angle is found167o, which is almost constant even after prolonged
contact with water.
Therefore, superhydrophobic coatings can be easily fabricated via above maintained
conventional techniques. But these techniques have some limitations such a5 s
involvement of multiple steps, use of harmful chemicals and being time consuming.
Among the conventional superhydrophobic materials, carbon based (graphene, CNT,
CNF) coatings have been most frequently used due to its superior property and simple
10 fabrication. Researchers have fabricated hydrophobic graphene surfaces having low
surface energy and appropriate surface roughness. Graphene sheets can be easily
produced by chemical vapour deposition (CVD) process by using Cu catalyst.
Reference is made to the contents of the pages 46-47 of the book titled “Physics and
15 Applications of Graphene – Experiments”, which discloses that the largest production
of roll-to-roll graphene can be achieved with Cu foil as catalyst by CVD technique.
Sreekar Bhaviripudi et, al: Nano Lett. 2010, 10, 4128–4133 discloses the role of
kinetics, in particular, the pressure of the reaction chamber in the chemical vapour
deposition (CVD) synthesis of graphene using low carbon solid solubility catalysts
20 (Cu), on both the large area thickness uniformity and the defect density are presented.
ETH ZURICH: a dissertation titled “Chemical Vapour Deposition of Graphene on
Copper” discloses that the composition and morphology of the copper catalyst strongly
influence the growth, by introducing defects, ripples and wrinkles. Careful selection and
25 high temperature (>800 °C) annealing of the copper foils are critical in order to avoid
nanoparticle-originated defects and to construct graphene crystals with well-connected
grains. It further discloses that copper sublimation is found to hinder the growth by
enhancing desorption of carbonaceous species from the surface. This hindrance is
shown to influence the crystal morphology of the carbon structures.
7
Yoon et al.: Chem. Commun. (Camb). 49, 2013, 10626–8fabricated transparent and
flexible 3D-graphene – PDMS (polydimethylsiloxane) electrode by a two-step
fabrication process. First, a 3D Cu structure is produced by high temperature annealing
(900- 1000oC) then a 3D graphene structure was grown by CVD. Then, this 3D
graphene structure was reconstructed with PDMS to get super hydrophobicity with th5 e
water contact angle of 154.2o.
Apart from 2D graphene structures,carbon nano fiber (CNF)and carbon nano-tube
(CNT) structureshave been most frequently used due to its simple fabrication and
10 inherent two length scale structure. Several efforts have been made to change the
surface chemistry of CNT and its array to build its wetting behaviour by controlling its
functional groups via CVD process.
US8277872 discloses a method of manufacturing multiscale carbon structures (carbon
15 fibers, films, foil, fabric, foams and bundles) using impregnation of catalytic salt
(palladium nitrate) followed by heating in CVD chamber to grow CNTs. The process
includes exposing a carbon fiber substrate to oxygen at a first predetermined
temperature and activating the carbon fiber substrate by exposure to oxygen at a second
predetermined temperature. The deposited catalyst on the carbon fiber structure is
20 exposed to a hydrocarbon at a third predetermined temperature to grow carbon
structures thereon. The carbon structures grown can be multimodal in nature with
structures that are nano-scale and/or submicron-scale.
US2012/0070667 relates to process for growing carbon nanotube on carbon fiber
25 substrate using deposition of transition metal catalyst and/or non-catalytic materials
such as aluminium salt, glass, silicate, silane and their combinations followed by CVD
based process.
Kakehi et al.: Appl. Surf. Sci.254, 2008, 6710–6714 relates to the effect of thickness
30 and structure of Co catalyst particles on morphology of CNT (grasses, forest) by using
alcohol catalytic chemical vapour deposition (AC CVD).
8
Yan Li et al.: Adv. Mater.22, 2010, 1508–1515 discloses that copper (Cu) acts as a
superior catalyst for growing SWCNT on quartz and silicon substrate in CVD process.
Weiwei Zhou et al.: Nano Res (2009) 2, 593 598 discloses that copper, which was onc5 e
considered the metal with the poorest catalytic efficiency for CNT growth, has been
experimentally proven to have high activity in catalyzing the growth of dense aligned
SWNT arrays on silicon or quartz wafers capable of producing large-area graphene.
US0250376 explained that to make CNT and its array super hydrobhobic, it needs to be
10 treated with non- wetting chemicals like PTFE, ZnO2, fluroalkylsilane etc. To make
hydrophilic CNT (change oxygenated functional group on CNT) processes like high
temperature annealing, UV ozone treatment, oxygen plasma treatment etc. have been
employed.
15 US0250376 discloses a simple method for producing superhydrophobic carbon
nanotube array, in which substrate photo lithographically patterned with thin film
(typically 1- 10 nm thick) of electron beam evaporated iron on quartz substrate that is
further processed by CVD at 750oC. The grown vertically aligned CNT post -treated to
get water contact angle of 160- 180oC, with the oxidation process to remove the
20 contamination (catalyst particles or amorphous carbon) followed by vacuum pyrolysis
(at 205 torr and 250oC for 3 hr.)
De Nicola F et la.: Nanotechnology. 2015 Apr 10;26(14) discloses the advantage of the
native surface roughness and the iron content of AISI 316 stainless steel to directly
grow super-hydrophobic multi-walled carbon nanotube (MWCNT) random networks by
25 chemical vapour deposition (CVD) at low-temperature (1000°C) without the addition of
any external catalysts or time-consuming pre-treatments.
Thus, in the above mentioned prior arts, carbon structures have been successfully
fabricated via CVD process by using different catalyst like palladium nitrate, aluminium
salt, glass-silicate, silane, copper etc. But these carbon structures do not exhibit super
30 hydrophobicity directly without any pre or post treatment. Furthermore, prior arts show
9
that 3D graphene structures are prepared at higher temperature (>750-800oC) for
imparting superhydrophobic behaviours, after being treated by chemicals. Two length
carbon structures like CNTs and carbon fibres prepared at higher temperature show
super hydrophobicity but involving various steps (oxidation to remove contamination,
vacuum pyrolysis etc.) or are limited to the type of substrates used5 .
Furthermore, EP2004353 discloses that superhydrophobic properties are desirable for
many industrial applications. For example, a durable superhydrophobic and selfcleaning
coating would be invaluable from the high voltage industry to limit or prevent
10 flashover, to the microelectromechanical systems (MEMS) industry to limit or prevent
stiction, to the anticorrosion of metal coatings. Other applications
for superhydrophobic surfaces are emerging all the time, such as the directed liquid flow
in microfluidics, antifouling in biomedical applications, and transparent coatings in
photovoltaics devices.”
15 Therefore, the production of superhydrophobic surface by different fabrication
techniques has been greatly increased in recent years. There are hundreds of patents
available on the fabrication of superhydrophobic surfaces via different techniques for
various applications.
20 US2006/0292360 discloses a manufactured coating of fuser or fixer member containing
CNT or its variant carbon nanofibers dispersed in polymeric binder (polyamide,
polyimide, PEEK, Teflon/ PFA etc.) which is suitable for use in an electrostatographic
printing roller.
25 US20060286305 relates to hydrophobic coatings comprising reactive inorganic nanoparticles
(nano silica particles) and polymer (PMMA, perflurooctyl chain etc.), which
shows self-cleaning with higher mechanical properties using spin, dip and spray
coating, as well as their use in industrial processes. These coatings combine
hydrophobic or even super-hydrophobic properties with superior mechanical properties
30 and easy proccessability. Some super-hydrophobic coatings may even have self10
cleaning properties. These hydrophobic and super-hydrophobic coatings may be applied
in the food industry, exterior or interior decoration, automobile industry and display
industry.
US8945409 relates to a porous medium with increased hydrophobicity and a method o5 f
manufacturing the same, in which a micro-nano dual structure is provided by forming
nanoprotrusions with a high aspect ratio by performing plasma etching on the surface of
a porous medium with a micrometer-scale surface roughness and a hydrophobic thin
film is deposited on the surface of the micro-nano dual structure, thus significantly
10 increasing hydrophobicity. When this highly hydrophobic porous medium is used as a
gas diffusion layer of a fuel cell, it is possible to efficiently discharge water produced
during electrochemical reaction of the fuel cell, thus preventing flooding in the fuel cell.
Some of the superhydrophobic surface material has been commercialized by various
15 companies e.g. Hirec by NTT-AT Corp. Japan that provides the communication and
radar antennae and receivers coated with superhydrophobic coating paint to reduce
water/ ice induced distortion. STO Corp, (USA) which manufactures the high quality
building material providing exterior paint since 1999 under trade name lotusan®.
Degussa GmbH (Germany) and TDk and Sony (Japan) provides some general coating
20 and resistance to scratching products respectively (Roach, P. et al: Soft Matter 4 (2),
2008, 224-240).
Thus, the process of fabricating desired superhydrophobic coatings with better
properties of water repellent and self-cleaning surfaces providing little resistance to
25 abrasion, as disclosed in the prior-art literatures suffer from the drawbacks of involving
multiple steps, prolonged time consumption, substrate limitation, higher operating
temperature and expensive production designs. Therefore, in view of the said
drawbacks of the prior art, there still remains a need in the art to develop a simple and a
straight forward process for preparing homogeneous hydrophobic coating at larger scale
30 with lesser number of steps at lower operating temperature as well as applicable to
various substrates.
11
OBJECTS OF THE INVENTION:
An object of the invention is to overcome the drawbacks of the prior art.
Another object of the present invention is to provide a simple and cost-effective process
for fabricating superhydrophobic coating on different substrates5 .
Another objective of the present invention is to provide a process for synthesizing and
growing hydrophobic coating of nano-micro carbon structure on activated carbon
fabric(ACF) / carbon nanofiber (CNF) forest on glass and stainless steel mesh.
Another objective of the present invention is to provide a process of fabricating
10 superhydrophobic coating on different substrates by means of selecting copper (Cu) as
the catalyst and controlling the various process parameters for coating deposition.
Another objective of the present invention is to provide a process of fabricating
superhydrophobic coating on different substrates by means of Direct Current (DC)
plasma sputtering of Cu catalyst film on different substrates, followed by the synthesis
15 and growing of nano-micro carbon structure/ carbon nanofiber (CNF) forest via
Chemical vapour deposition (CVD) process.
Another objective of the present invention is to provide a process of fabricating
superhydrophobic coating on different substrates by means of controlling different
parameters involved in the CVD process such as time, temperature and flow rate in
20 order to acquire hydrophobic behaviour.
Another object of the present invention is to provide a process of fabricating a
superhydrophobic surface with large scale productivity and better homogeneity.
Another object of the present invention is to provide a process for fabricating
superhydrophobic coatings that finds application in creating water-repellent steel-mesh
25 for rust-resistance and water-containing (and air-breathing) conduits.
12
SUMMARY OF THE INVENTION:
One aspect of the present invention provides a process for fabricating self-cleaning,
homogenous, super hydrophobic coating surface of carbon nano-micro structure, said
process comprising the steps of5 :
i. sputtering of copper (Cu) metal in inert gas atmosphere to deposit Cu
metal catalytic film on the surface of substrate;
ii. treating the Cu catalyst deposited substrate obtained in step (i) with
chemical vapour deposition (CVD) method with hydrogen gas at a
temperature range of 200-400o10 C, preferably between 290 - 310˚C;
iii. cracking the acetylene gas in the CVD chamber;
iv. decomposing the acetylene gas in the CVD chamber at a temperature of
290-310˚C; and
v. treating the substrate obtained from step (iv) in the CVD chamber with
nitrogen gas under cooling to room temperature (21-24o15 C), forming the
said carbon nano-micro structure on substrate.
Another aspect of the present invention provides a self-cleaning, super hydrophobic
coating of carbon nano-micro structure on different substrates (glass, active carbon
20 fabric, stainless steel mesh) by means of Cu catalyst film deposition on those substrates
via direct current (DC) plasma sputtering method, followed by synthesis and growing of
the said nano-micro carbon structures on the substrates via chemical vapour deposition
(CVD) process under controlled conditions.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
25 Figure 1 illustrates the schematic representation of the DC plasma sputter.
Figure 2 illustrates schematic representation of chemical vapour deposition (CVD)
system.
Figure 3 (a) illustrates schematic representation showing growth of carbon nano-micro
structure and wetting behaviour of uncoated & coated substrate (activated carbon fibre
13
and glass); Figure 3 (b) illustrates dynamic water contact angle on coated activated
carbon fibre (ACF); Figure 3(c, d) illustrate low and high magnification scanning
electron microscope (SEM) image of nano-micro hierarchical carbon nanofibers (CNF)
grown on ACF; and Figure 3 (e) illustrates Electrostatic discharge (ESD) spectra of
coated ACF5 .
Figure 4 (a) illustrates comparable digital images of stainless steel mesh with and
without hydrophobic coating - the descriptive views of figure 4(a) have been
schematically represented in figures 4 (a1, a2, a3, a4, a5 and a6), wherein Figure 4(a1)
illustrates steel mesh without hydrophobic coating; Figure 4(a2) illustrates substrate
10 steel mesh coated with present carbon nano-micro structure coatings; Figure 4(a3 and
a4) illustrate hydrophilic behaviour of the steel mesh in absence of the present
hydrophobic coating; Figures 4(a5 and a6) illustrate hydrophobic behaviour of steel
mesh after coating with present carbon nano-micro structures/nano-fibers; and
Figure 4 (b) illustrates dynamic water contact angle on coated stainless steel of (2x2)
15 mm open square mesh; Figures 4 (c and d ) illustrates low and high magnification
scanning electron microscope (SEM) image of carbon nanofiber (CNF) forest grown on
stainless steel mesh; Figure 4 (e) illustrates ESD spectra of coated stainless steel mesh;
and Figure 4 (f) illustrates dynamic water contact angle on coated stainless steel of
(1x1) mm open square mesh [a higher contact angle value (>146o) has been observed
20 for smaller (1x1) mm open square stainless steel mesh than stainless steel mesh of (2x2)
mm open square].
Figure 5 (a) illustrates comparable digital images digital images of glass with and
without hydrophobic coating - the descriptive views of figure 5(a) have been
schematically represented in figures 5 (a1, a2, a3, a4, a5 and a6)- Figure 5(a1) illustrates
25 glass without coating; Figure 5(a2) illustrates glass with coating; Figure 5(a3) illustrates
glass coating with mask (uncoated) in the centre; Figures 4(a4) illustrates wetting
behaviour (hydrophilic) of glass slide without coating; Figure 5(a5) illustrates wetting
behaviour (hydrophobic) of glass slide with coating; and Figure 5(a6) illustrates bulging
of water on coating with mask (uncoated) in the centre of glass slide; and Figure 5 (b)
30 illustrates dynamic water contact angles on coated glass; Figures 5(c) illustrates digital
14
images showing the effect of different temperatures on the quality and spreading of the
formed superhydrophobic coatings on glass substrates; Figure 5(d) illustrates digital
images showing the effect of different gas flow rates on the quality and spreading of the
formed superhydrophobic coatings on glass substrates; Figure 5(e) illustrates digital
images showing the effect of different time intervals on the quality and spreading of th5 e
formed superhydrophobic coatings on glass substrates.
Figures 6 (a, b, c, d, e) illustrate schematic representation of deposition performed by
controlling the processing temperature for superhydrophobic coating deposition on glass
slide in a temperature range of 200 – 400oC with an interval of 50oC by keeping
constant gas flow rate between 35 cm3/min- 55 cm310 /min and for a coating deposition
time of 30 mins.
Figures 6(a) and 6(b) illustrate deposition performed at high temperatures 400oC
and 350oC respectively , the resulting water contact angles (CA) is 143 o and 141o in
respective cases; Figure 6 (c) illustrates deposition performed at optimised controlled
temperature of 300oC), the water contact angle (CA) obtained is found to be 156o15 ; and
Figures 6 (d) and 6(e) illustrate deposition performed at temperatures lower than the
controlled temperatures such as at 250oC and 200oC respectively, the water contact
angle (CA) obtained is found to be 135o and 138o in respective cases;
Figures 6(f, g, h) illustrate overall schematic representation of deposition performed by
20 controlling the processing time for superhydrophobic coating deposition on glass slide
in the time range (15 – 45min) with the time interval of 15min by keeping constant gas
flow rate (35 cm3/min- 55 cm3/min) and temperature (300oC);
Figure 6 (f) illustrates deposition with a longer time than the controlled coating
deposition time (45min), the water CA obtained is found to be 140o; Figure 6 (g)
25 illustrates deposition with coating deposition time of 30mins., the water CA obtained is
found to be156o; and Figure 6 (h) illustrates deposition with a shorter time than the
controlled coating deposition time of 15mins., the water CA obtained is found to be
137o;
15
Figure 6 (i, j and k) illustrate overall schematic representation of deposition performed
by controlling the process gas flow rate for superhydrophobic coating deposition 35-55
cm3/min during coating deposition on glass slide by keeping constant temperature at
300oC and coating deposition time of 30 mins.
Figure 6(i) illustrates deposition with a faster gas flow rate than the higher limi5 t
of the range of controlled gas flow rate (55 cm3/min), when the water CA obtained is
found to be 137o; Figure 6 (j) illustrates the deposition with controlled gas flow rate
range between 35 cm3/min- 55 cm3/min when the water CA obtained is found to be
156o; and Figure 6 (k) illustrates deposition with slower gas flow rate than the lower
limit of the controlled gas flow rate i.e. 35 cm310 /min, the water CA obtained is found to
be 120o.
Figure 7(a, b, c, d, e, f, g, h, i, j, k) illustrate overall schematic representation of
deposition performed by controlling processing temperature, time and gas flow rate
respectively for activated carbon fabric (ACF);
15 Figure 7(a, b, c, d, e) illustrate schematic representation of deposition performed
by controlling processing temperature for superhydrophobic coating deposition on ACF
in the temperature range of 200 – 400oC with the interval of 50oC by keeping constant
gas flow rate of 35 cm3/min- 55 cm3/min and for a coating deposition time of 30 mins.
Figure 7 (a, b) illustrate deposition performed by deposition temperature higher than the
controlled temperatures of 400o and 350o20 C respectively, with water contact angle (CA)
obtained is 134o and 129o in respective cases; Figure 7 (c) illustrates deposition with the
controlled temperature (300oC), when the water CA obtained is 146o; and Figure 7 (d, e)
illustrate deposition with the temperature lower than the controlled temperatures of 250o
and 200oC respectively, the water CA obtained is 135o and 138o in respective cases;
25 Figures 7(f, g, h) illustrate overall schematic representation of deposition performed by
controlling processing time for superhydrophobic coating deposition on ACF in the time
range of 15 – 45min with the time interval of 15min by keeping constant gas flow rate
between 35 cm3/min- 55 cm3/min and temperature at 300oC;
16
Figure 7 (f) illustrates deposition with time longer than the controlled coating
deposition time of 45min, the water CA obtained is found to be 134o; Figure 7 (g)
illustrates deposition with controlled coating deposition time of 30min, the water CA
obtained is 146o; and Figure 7 (h) illustrates deposition with time shorter than the
controlled coating deposition time of 15mins, the water CA obtained is found to b5 e
135o.
Figure 7(i, j, k) illustrate overall schematic representation of deposition performed by
controlling processing gas flow rate for superhydrophobic coating deposition on ACF
by keeping constant temperature at 300oC and coating deposition time of 30 mins.
10 Figure 7 (i) illustrates deposition with faster process gas flow rate than the
higher limit of the controlled gas flow rate of 55 cm3/min) , the water CA obtained is
found to be 143o; Figure 7 (j) illustrates deposition with controlled gas flow rate in a
range between 35 cm3/min- 55 cm3/min, the water CA obtained is found to be 146o;
and Figure 7(k) illustrates deposition with slower process gas flow rate than the lower
limit of the controlled gas flow rate i.e. 35 cm315 /min, the water CA obtained is found to
be 138o.
Figure 8 (a, b, c, d, e, f) illustrate overall schematic representation deposition performed
by controlling Cu catalyst sputtering time in range between 20 – 60min with the time
interval of 20 mins on ACF by keeping constant gas flow rate between 35 cm3/min- 55
cm3/min) for a coating deposition time of 30 mins and temperature at 300o20 C;
Figure 8 (a) illustrates deposition with longer time than higher limit of the
controlled sputtering time of 60 min), the water CA obtained is 135o; Figure 8(b)
illustrates deposition with controlled sputtering time of 40mins, the water CA obtained
is 146 o; and Figure 8 (c) illustrates deposition with shorter time than the lower limit of
the controlled sputtering time i.e. 20min, the water CA obtained is 110o25 ;
Figure 8(d, e and f) illustrate schematic representation of deposition performed by
controlling Cu catalyst sputtering time in range between 20 – 60min with the time
interval of 20 mins on glass slide by keeping constant gas flow rate between 35
17
cm3/min- 55 cm3/min, for a coating deposition time of 30 mins and temperature at
300oC;
Figure 8 (d) illustrates deposition with time longer than the higher limit of the
controlled sputtering time of 60 mins, the with water CA obtained is found to be 144o;
Figure 8(e) illustrates deposition with controlled sputter time of 40 mins, the water 5 CA
obtained is found to be 156o; and Figure 8 (f) illustrates deposition with shorter time
than the lower limit of the controlled sputtering time of 20 mins, the water CA obtained
is found to be 119o.
10 DETAILED DESCRIPTION OF THE INVENTION:
The following description with reference to the accompanying drawings is provided to
assist in a comprehensive understanding of exemplary embodiments of the invention. It
includes various specific details to assist in that understanding but these are to be
regarded as merely exemplary.
15 Accordingly, those of ordinary skill in the art will recognize that various changes and
modifications of the embodiments described herein can be made without departing from
the scope of the invention. In addition, descriptions of well-known functions and
constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the
20 bibliographical meanings, but, are merely used by the inventor to enable a clear and
consistent understanding of the invention. Accordingly, it should be apparent to those
skilled in the art that the following description of exemplary embodiments of the present
invention are provided for illustration purpose only and not for the purpose of limiting
the invention as defined by the appended claims and their equivalents.
25 It is to be understood that the singular forms “a,” “an,” and “the” include plural
referents unless the context clearly dictates otherwise.
18
Features that are described and/or illustrated with respect to one embodiment may be
used in the same way or in a similar way in one or more other embodiments and/or in
combination with or instead of the features of the other embodiments.
It should be emphasized that the term “comprises/comprising” when used in this
specification is taken to specify the presence of stated features, integers, steps o5 r
components but does not preclude the presence or addition of one or more other
features, integers, steps, components or groups thereof.
The term “cost-efficient” as used in the specification refers to avoiding any need of
organic or inorganic chemicals and lesser number of steps make it cost effective.
10 The term “simple process” as used in the specification refers to a process having lesser
number of steps and using no harmful chemicals
The term “straight forward process” as used in the specification refers to process
without any post treatment of carbon structure to achieve super hydrophobicity
The term “self-cleaning” as used in the specification refers to removal of unwanted dirt
15 or dust particle from the surface on falling of water droplet.
The term “CNF forest” as used in the specification refers to microstructure of coated
entangled carbon nanofiber.
The term “nano-micro hierarchical” as used in the specification implies to carbon
nanofiber (~100 nm) grown on carbon fabric having dimension of micron range (10
20 μm).
The term “ACF” as used in the specification refers to activated carbon fiber.
The term “ESD” as used in the specification refers to Energy dispersive X-ray
spectroscopy.
The term “FESEM” as used in the specification refers to Field Emission Scanning
25 Electron Microscope.
The term “DC plasma sputtering” as used in the specification refers to Direct current
sputtering.
19
The term “CVD process” as used in the specification refers to Chemical vapour
deposition
The term “catalytic film” as used in the specification refers to Cu film deposition via
DC Sputtering.
The term “substrates” as used in the specification refers to Activated carbon fabric5 ,
glass, steel mesh.
The term “large scale” as used in the specification refers to process rate.
The term “better homogeneity” as used in the specification refers to uniform growth of
carbon fibers throughout the surface
10 The term “good catalytic film deposition” as used in the specification refers to Cu
catalyst coating at optimised range of DC sputtering.
The term “water contact angle” as used in the specification refers to the angle the water
droplet makes with the prepared surface (i.e. surface wettability with water).
A “hydrophobic” surface is generally defined as that which has a contact angle > 90o
15 A “super-hydrophobic” surface is generally defined as that which has a contact angle >
140o .
The terms ‘CK’ as used in the present specification refers to carbon content (atomic %
of C) during EDX analysis.
In accordance with the present invention, a simple and cost-effective process of
20 fabricating self-cleaning, superhydrophobic coating on different substrates based on
selection of the catalyst and controlling the process parameters for synthesis of
superhydrophobic nano-micro hierarchical carbon structures on various substrates have
been provided. Advantageously, the present process requires no additional posttreatment
steps such as treating with non-wetting chemicals (PDMS, PTFE,
25 fluroalkylsilane etc.) oxidation or chemical etching, therefore, is simple and economical.
The present process finds its application in creating water-repellent steel-mesh for rustresistance
and water-containing conduits.
20
An embodiment of the present invention provides a process for synthesizing
hydrophobic coating of hierarchical carbon structure i.e. carbon nanofiber (100-110 nm)
grown on active carbon fabric (ACF) / CNF forest (100-110 nm) grown on glass,
stainless steel mesh having dimension of micron range (10-30 μm). Carbon structures
deposited on the surface of substrates like fabric, glass or steel by means of proces5 s
performed by controlling various process parameters such as operating temperature, gas
flow rate, sputtering time exhibit super hydrophobic characteristics. The carbon nanomicro
structures thus formed are same but those grown on micrometer sized active
carbon fabric (ACF) are named as nano-micro hierarchical structure, whereas those
10 carbon nanofibers (100-110 nm) which are grown on glass/steel mesh looks like forest
of carbon fibers, so are also named as carbon nanofiber forest (CNF). Therefore, the
present invention provides a uniform process with controlled parameters which
facilitates superhydrohobic coatings on various substrates.
The process of fabricating superhydrophobic coating on different substrates in the
15 present invention is based on the copper (Cu) catalyst, which is responsible for
controlled preparation of carbon based nano-micro structures on different substrates by
Chemical Vapour Deposition method.
The substrates according to the invention are selected from stainless steel, glass, carbon
fabric, Al, alumina.
20 In another embodiment of present invention, a process of fabricating superhydrophobic
coating on different substrates is provided by means of controlling different parameters
involved in the sputtering and/or deposition process such as time, temperature and flow
rate in order to acquire hydrophobic behaviour. Such controlled process advantageously
results into synthesis and growth of nano-micro hierarchical carbon structures or carbon
25 nanofiber (CNF) forest on the surface of the substrates bearing catalytic film deposition.
In accordance with the present invention, the process of preparing superhydrophobic
coating on different substrates broadly comprises of the following steps -
21
i. depositing Cu catalytic film via Direct Current (DC) sputtering unit on
different substrates; and
ii. synthesizing carbon nano-micro structure on copper catalyst deposited
substrates via chemical vapour deposition (CVD) method:
5
In a further specific embodiment, a comprehensive process for fabricating self-cleaning,
homogenous, hydrophobic coating of hierarchical carbon structure i.e. carbon nanofiber
(100-110 nm) grown on carbon fabric / CNF forest (100-110 nm) grown on
glass/stainless steel mesh having dimension of micron range (10-30 μm) is provided
10 which comprises of the steps below:
i) sputtering of copper (Cu) metal in inert gas atmosphere to deposit Cu
metal catalytic film on the surface of the substrates;
ii) treating the substrates obtained in step (i) with chemical vapour
deposition (CVD) method with hydrogen gas at about 200 - 400˚C,
15 preferably 290-310 ˚C;
iii) cracking the acetylene gas in the CVD chamber;
iv) decomposing the acetylene gas in the CVD chamber at a temperature of
290-310˚C; and
v) treating the substrate obtained from step (iv) in the CVD chamber with
nitrogen gas under cooling to room temperature (21-24o20 C), forming the
said nano-micro hierarchical carbon structure.
In another embodiment of the present invention, the substrates on which deposition
happens are selected from glass, stainless steel mesh or activated carbon fabric (ACF).
25
In yet another embodiment of the present invention, a 99 % pure Cu disc is used as a
target in the sputtering unit. DC sputtering is performed in inert gas atmosphere under
controlled process parameters such as flow rate, time, current and voltage, in order to
achieve good catalytic film deposition. Inert gas within the sputtering unit is preferably
30 Argon (Ar). The sputtering of Cu is done for 20-60 mins, at a current of 1-100 mA and
voltage of 500-700V.The Cu catalyst film deposited on the substrates is then placed in a
22
chemical vapour deposition (CVD) chamber without any pre-treatment. Next, hydrogen
(H2), acetylene (C2H2) and nitrogen (N2) gas are introduced into the CVD chamber,
alternately, for predetermined period of time and flow rate. Initially hydrogen (H2) gas
is introduced in CVD chamber for 70min with the flow rate of (2-3 bubbles per second
coming out from 4 mm pipe or ~35-55 cm3/min) in a temperature range of 290 - 3105 oC.
Further acetylene gas is cracked in for decomposition at a temperature around 300oC for
30 min. After decomposition of acetylene gas, nitrogen gas is introduced up to the room
temperature (21-24oC) with the flow rate of (35-55 cm3/min).
10 In another embodiment of the present invention, the superhydrophobic coatings formed
on different substrates by the present process provides water contact angle for such
coated substrates ranging between 144- 156 o, thus confirming the hydrophobic behavior
of the coatings being formed.
15 In an important embodiment of the present invention, various process conditions have
been controlled in order to achieve the comprehensive process (as mentioned above)
which is capable of depositing coatings on substrates with the desired super
hydrophobic properties. The said process conditions have been defined by limited
parameters which are critical for achieving the desired hydrophobic coatings.
20 Accordingly, in the present process, the operational temperature is modulated within a
range of 200-400oC, preferably between 290-310oC. Experiments have been conducted
which shows that uniform carbon coating is obtained at a temperature between 290-
310oC with comparably good adherence and coverage along with superior super
hydrophobicity (CA of 146-156o). Further, the process gas flow rate is controlled
within a range of 35 -55 cm325 /min. Experiments have been conducted, wherein
temperature is maintained at 290-310oC and the process gas flow rate and time intervals
are varied. It has been observed that at the lower limit of the range of gas flow rate (<
35 cm3/min), superhydrophobic coating is not deposited and at higher limit of the gas
flow rate (>55 cm3/min) a poor carbon coating (rough and non-uniform deposition) is
30 deposited. Additionally, the time is maintained in the present process for 45 mins. It has
23
also been observed that for a lesser time i.e. for 15 mins than the controlled time
interval (<45mins), the superhydrophobic coating is not deposited and for a longer time
i.e. for 60 mins which is beyond the controlled time (>45 mins.), the said
superhydrophobic coating starts to peel off.
In a further important embodiment of the present invention, various process parameter5 s
are similarly controlled in order to achieve a comprehensive process capable of
depositing coatings on active carbon fibres (ACF) with the desired super hydrophobic
properties. Experiments are conducted as above and it is observed that for ACF, at (290-
310oC), a homogeneous superhydrophobic coating (CA of 146o) is obtained. Next,
keeping the said controlled temperature (290-310o10 C), constant, the deposition of carbon
coating has been observed by varying the process gas flow rate and time. It has been
found that below the lower limit of the range of gas flow rate i.e.< 35 cm3/min, the
superhydrophobic coating is not deposited, and above the higher limit of the range of
gas flow rate i.e. >55 cm3/min, the deposited coating exhibited a water CA of 143 o.
15 Moreover, it has been further observed that for a lesser time i.e. for 15 mins than the
controlled time interval (<45mins) and for a longer time i.e. for 60 mins which is
beyond the controlled time interval (>45 mins.), the superhydrophobic coating is not
deposited on ACF. Further experiments reveal that the quality of the present
hydrophobic coating is also dependent on the Cu sputtering time (20-60mins.) in the DC
20 sputtering unit. Therefore, based on the above information, it is evident that the
depositions of superhydrophobic coatings with desired water contact angles on
substrates depend on the various controlled parameters involved in such deposition
processes.
25 In a further embodiment of the present invention, the defined temperature range of 290-
310oC which is maintained during the deposition process in order to achieve coatings
with desired superhydrophibic properties (water contact angle (CA) of 146o-156o). The
said temperature range is advantageously lower than the temperature ranges for
deposition as mentioned in two of the closest prior arts such as in Yoon et al.: 2013
(process temperature reported- 1000o30 C) and De Nicola F et la.: 2015 (process
24
temperature reported- >750oC). Therefore, controlling the operating temperature at such
a lower level (290-310oC), as in the present deposition process and still achieving a
superior superhydrophobic coating (CA 146o-156o) is a technical advancement over
these prior arts.
5
Furthermore, the present process of fabrication superhydrophobic coating on substrates
is devoid of any additional, cost-incurring pre or post treatment steps with toxic
chemical agents such as non- wetting chemicals like PTFE, PDMS, fluroalkylsilane,
oxidative agents and chemical etchers. Hence, the present process with controlled
10 parameters as described above is economical, non-hazardous and at the same time
results into superior super hydrophobic coatings (water CA 146-156o).
The invention is now illustrated by way of non-limiting examples
15 EXAMPLES
Example 1: Process for fabricating superhydrophobic coating on substrate
I. Cu catalytic film deposition on substrates via DC sputtering:
A DC plasma sputter unit is used to deposit metal (Cu) catalyst on different
substrates (glass, stainless steel mesh and activated carbon fabric). Figure 1
20 demonstrates a schematic representation of the said DC plasma sputter unit. A
substrate selected from active carbon fibre (ACF) or glass or stainless steel mesh (1)
is placed inside the unit. An anode (2) and a cathode (3) are present in the sputtering
unit for conduction of current within the unit. A 3mm thick 99 % pure Cu disc (4) is
used as a target in the sputtering unit. DC sputtering performed in Argon (Ar) gas
25 atmosphere (8) with flow rate of 40-70 bar under vacuum pump (7). The sputtering
of Cu is done for 40min, at a current of 1-100 mA and voltage of 500-700V. Target
atoms (6) are produced within the unit under the influence of sputtered Ar ions (5).
The said target atoms (6) are then deposited on cu catalyst on substrates (9) placed
within the said sputtering unit.
25
II.Synthesis and growth of carbon structure on as Cu catalyst deposited substrates via
chemical vapour deposition (CVD):
Figure 2 demonstrates a schematic representation of a chemical vapour deposition
(CVD) setup. The Cu catalyst deposited substrate (10) obtained from the sputtering
process in above step I is placed within the said CVD chamber without any pre5 -
treatment. A heater (11) covered with Alumina tube jacketed with SS body (12)
acts as the heating source within the chamber. Next, hydrogen (H2), acetylene
(C2H2) and nitrogen (N2) gas are introduced in the CVD chamber, alternately, for
predetermined period of time and flow rate and under controlled temperature.
10 Initially hydrogen H2 gas is introduced in CVD chamber for 70min from the
hydrogen cylinder (13) attached to the chamber with the flow rate of (2-3 bubbles
per second coming out from 4 mm pipe or ~35-55 cm3/min) at a temperature range
of 290 - 310oC. Then after attaining a temperature of 300oC, acetylene gas is
cracked in from the attached acetylene gas cylinder (14) for 30 mins with a flow
rate of ~15-30 cm315 /min, 0.015-0.030 lpm. After decomposition of acetylene gas at
around 300oC, nitrogen gas from attached nitrogen cylinder (15) is introduced
within the CVD chamber at room temperature (21-24oC) with a gas flow rate of
~35-55 cm3/min. The gas conductions from the respective cylinders into the said
chamber occurs by means of a 1/8-inch flexible stainless steel pipe (16). The
20 various process conditions like maintaining the operating temperature low i.e.
between 290-310oC and/or each gas flow rate between 35-55 cm3/min are
controlled in the said CVD set-up by means of a one-way valve (18) and other
controls like moisture indicator (17), gas inlet control (19), outlet control (20), gas
bubbler i.e. a beaker containing Di-n-butylphthalate (21).
25
Example 2: Advantages of the present deposition process over those reported in
two of the closest prior arts
In the present invention, the operating temperature of the deposition process (as
mentioned in example 1 above) is controlled within the range of 290-310oC for super
30 hydrophobic coating to get deposited on substrates. Additionally, the present process is
26
simple as it does not require any pre or post treatment of substrates and also finds a
wider applicability. Most importantly, the defined process temperature is
advantageously low in comparison to those reported in two of the closest prior arts, as
described in table 1 below,
Table 5 1
Prior art Temperature involved in
the deposition process
Hydrophobic behaviour showed by
the carbon structure formed
Yoon et al.: Chem.
Commun. (Camb).
49, 2013, 10626–8
1000oC Carbon structures formed by the
process disclosed do not directly
show hydrophobicity without any
post treatment by PDMS. After post
treatment via PDMS, coating
deposition, superhydrophobicity was
obtained with water contact angle of
154.2o
De Nicola F et la.:
Nanotechnology
2015; Apr 10;26(14)
>750oC Carbon structure (MWCNT) formed
is limited to its deposition on
stainless steel only. Contact angle
observed by superhydrophobic steel
is 146-156o.
27
PRESENT PROCESS 290-310 o C Carbon nano-structures/nano-fibers
on substrates with
superhydrophobicity and water
contact angle (CA) of 146-156o; no
pre or post treatment of substrates
required; present process is a
uniform system applicable to various
substrates such as steel, glass, active
carbon fibers.
Generally, high operating temperature in carbon deposition processes suffers from the
drawback of forming carbon structures or films which tend to be inferior in quality.
However, it is evident from the above table 1 that the present deposition process with
lower operating temperature results into formation of carbon nano-structures/nano5 -
fibers on substrates with comparably good hydrophobic behaviours [water contact angle
(CA) of 146-156o]. Therefore, the present process shows technical advancement in
terms of its simplicity, wider applicability and low operating temperature when
compared with those reported in the prior arts as mentioned in the table above.
10 Example 3: Studies conducted on activated carbon fibre or ACF (substrate) –
uncoated or coated with superhydrophobic coating fabricated by the present
process
Figures 3(a) to 3(e) illustrate various studies conducted on activated carbon fibre
(ACF) substrate uncoated or coated with the superhydrophobic coating fabricated by
15 the present process. The data obtained are compared and analysed.
Figure 3(a) illustrates schematic representation showing growth of carbon nanomicro
structures and wetting behaviours of uncoated & coated substrates [e.g.
activated carbon fibres (ACF), glass]. A set of substrates (22) are kept uncoated and
the other set of substrates are coated with Cu sputtered carbon nano-structures (23)
28
or carbon nano-fibres (24) formed by the process as mentioned in example 1 above.
Comparative studies are conducted by putting water on the surfaces of the coated
and uncoated substrates in order to examine their hydrophobic behaviours. The
comparative images show that water spreading occur on the surfaces of the uncoated
hydrophilic substrates (25), whereas stay of water droplets are observed in case o5 f
carbon nano-structure/nano-fiber coated substrates (26). Thus it is evident from this
study that the hydrophobic characteristics of the substrates are obtained only after
they have been coated with carbon nano-structures formed by the controlled
deposition process of the present invention.
10 Figure 3(b) illustrates dynamic and static water contact angles that are measured to
confirm the hydrophobic behaviour of the superhydrophobic coating formed on
ACF. A contact angle for the uncoated ACF is measured to be 0o, which increases to
144o after ACF is coated with the said superhydrophobic coating fabricated by the
present process.
15 Figures 3(c, d) illustrate FESEM image of coated ACF surface which shows the
morphology and features of deposited superhydrophobic coating, confirming the
presence of nano-micro hierarchical carbon structures.
Figure 3(e) illustrates ESD spectra analysis of coated ACF samples which reveals
presence of 99.79 atomic % of carbon in ACF.
20 Example 4: Studies conducted on stainless steel mesh (substrate) – uncoated or
coated with superhydrophobic coating fabricated by the present process.
Figures 4(a) to 4(e) illustrate various studies conducted on stainless steel mesh
substrate, uncoated or coated with the superhydrophobic coating fabricated by the
present process. The data obtained are compared and analysed.
25 Figure 4 (a) illustrates comparable digital images of stainless steel mesh with and
without hydrophobic coating. The descriptive views of the said digital images have been
schematically represented in figures 4 (a1, a2, a3, a4, a5 and a6). Figure 4(a1) illustrates
steel mesh without hydrophobic coating (27). Figures 4(a3 and a4) show water falling
29
(31, 33) through the stainless steel mesh in absence of carbon-nanostructure coatings
(30, 32), exhibiting the hydrophilic character of the steel mesh. On contrary, figure
4(a2) illustrates steel mesh (28) with present hydrophobic coating (29). Figures 4(a5 and
a6) demonstrates staying of water droplets (36, 39) on the steel mesh (34, 37) coated
with the present carbon nano-structures/nano-fibers (35, 38) formed by the controlle5 d
deposition process as mentioned in example 1 above. Therefore, this study confirms that
the superhydrophobic behaviour is attributed to the present carbon nanostructure/nanofiber
based coatings on the steel mesh.
Figure 4(b) illustrates dynamic water contact angles that are measured to confirm
10 the hydrophobic behaviour of the superhydrophobic coating formed on stainless
steel made, (2x2) mm open square mesh. A water contact angle of (>128oC) is
observed for the (2x2) mm open square stainless steel mesh coated with the said
superhydrophobic coating fabricated by the present process.
Figures 4(c, d) illustrate low and high magnification scanning electron microscope
15 (SEM) image of coated stainless steel mesh surface. Figure 4(c) shows a
homogeneous growth of entangled carbon nano forest (CNF) on stainless steel
mesh, whereas figure 4(d) shows the magnified image of the as grown carbon nanofibres
on such mesh. These images are taken in order to confirm the formation of the
carbon nano-fibres on the stainless steel substrate and also to view the morphology
20 and features of such nano- carbon forest of the deposited superhydrophobic coating.
Figure 4(e) illustrates ESD spectra analysis of coated stainless steel mesh samples
which reveals presence of 99.71 atomic % of carbon for steel.
Figure 4(f) illustrates dynamic water contact angle on coated stainless steel of (1x1)
mm open square mesh. It is observed that a higher contact angle value (>146oC) is
25 obtained for smaller (1x1) mm open square stainless steel mesh than that of (2x2)
mm open square stainless steel mesh.
Example 5: Studies conducted on glass (substrate) – uncoated and coated with
superhydrophobic coating fabricated by the present process: -
30
Figures 5(a) and 5(b) illustrate the various studies conducted on glass substrate,
uncoated or coated with the superhydrophobic coating fabricated by the present
process. The data obtained are compared and analysed.
Figure 5(a) illustrates comparable digital images of glass substrate with and without
hydrophobic coating. The descriptive views of the said digital images have bee5 n
schematically represented in figures 5 (a1, a2, a3, a4, a5 and a6). Figure 5(a1) illustrates
glass without hydrophobic coating (40). On contrary, figure 5(a2) illustrates steel mesh
(41) with present hydrophobic coating (42). Figure 4(a3) illustrates glass (43) coating
with mask (uncoated) in the centre (44). Hydrophobic characteristics of each of coated
10 and uncoated glass substrates are now studied and compared by putting water on them.
Figure 4(a4) illustrates wetting behaviour (hydrophilic) (46) of glass slide without
coating (45), exhibiting the hydrophilic character of the steel mesh itself. On the other
hand, figure 4(a5) demonstrates staying of water droplets (49) on glass (47) coated with
the present carbon nano-structures/nano-fibers (48) formed by the controlled deposition
15 process as mentioned in example 1 above. Furthermore, figure 4(a5) shows bulging of
water (52) on coating with present carbon-nano-micro structures (51) with mask
(uncoated) in the centre of glass slide (50). Therefore, this study further confirms that
the superhydrophobic behaviour is attributed to the present carbon nanostructure/nanofiber
based coatings on the glass substrate.
20 Figure 5(b) illustrates that the water contact angle for the uncoated glass slide is
measured to be 36o, which increases to 156o after being coated with the said
superhydrophobic coating formed by means of the present process.
Figures 5(c) illustrates digital images showing the effect of different temperatures on the
quality and spreading of the formed superhydrophobic coatings on glass substrates.
25 From the said set of comparable digital images, it is confirmed that uniform spreading
and superior superhydrophobic behaviour (CA 156o) is exhibited by the carbon coating
which is formed by the present process under controlled temperature of 300oC.
Figure 5(d) illustrates digital images showing the effect of different gas flow rates on
the quality and spreading of the formed superhydrophobic coatings on glass substrates.
31
From the said set of comparable digital images, it is confirmed that uniform spreading
and superior superhydrophobic behaviour (CA 156o) is exhibited by the carbon coating
which is formed by the present process under controlled gas flow rate ~35-55 cm3/min.
Figure 5(e) illustrates digital images showing the effect of different time intervals on the
quality and spreading of the formed superhydrophobic coatings on glass substrates5 .
From the said set of comparable digital images, it is confirmed that uniform spreading
and superior superhydrophobic behaviour (CA 156o) is exhibited by the carbon coating
which is formed by the present process under controlled time interval of 30 mins.
Example 6: Studies conducted on the working of the present process within the
10 controlled process conditions and non-working outside those conditions in terms of
achieivng desired superhydrophobic coatings
Figures 6 (a, b, c, d, e, f, g, h, i, j, k), 7 (a, b, c, d, e, f, g, h, i, j, k) and 8 (a, b, c, d, e, f)
represents overall schematic representations for deposition of superhydrophobic
coatings (carbon nano-micro structures) on different substrates like glass, steel mesh
15 and ACF respectively, when performed by controlling various process conditions such
as processing temperature, time intervals and gas flow rate. The data obtained are
analysed and compared.
Figures 6 (a, b, c, d, e) illustrate schematic representation of superhydrophobic coatings
formed on glass slides by means of a process which is performed by controlling the
operational temperature within a range of 200-400o20 C, keeping constant gas flow rate
between 35 cm3/min- 55 cm3/min and for a coating deposition time of 30 mins.
Figures 6(a) and 6(b) show depositions performed on glass substrate (53, 55) at
high temperatures i.e. 400oC and 350oC respectively which resulted in formation of
excess and inhomogeneous growth of the carbon nano-micro structures (54, 56) with
water contact angles (CA) of 143 o and 141o 25 in respective cases.
Figure 6 (c) shows deposition performed at a controlled temperature of 300oC,
which resulted in homogeneous growth of carbon nano-micro structures (58) on glass
substrate (57) with super hydrophobic properties i.e. water contact angles (CA) of 156o.
32
Figures 6 (d) and 6(e) show deposition performed at temperatures lower than the
controlled temperature such as at 250oC and 200oC respectively, which resulted in
inhomogeneous growth of the carbon nano-micro structures (60, 62) on glass slides (59,
61) with water contact angles (CA) of 135 o and 138o in respective cases.
Figures 6(f, g, h) illustrate overall schematic representation of superhydrophobi5 c
coatings formed on glass slides by means of a process which is performed by
controlling the processing time within the range of 15 – 45min with the time interval of
15min, keeping constant gas flow rate (35 cm3/min- 55 cm3/min) and fixed temperature
(300oC).
10 Figure 6(f) shows deposition performed with a longer time than the upper limit
of the range of controlled coating deposition time (i.e. >45mins), which resulted in
inhomogeneous growth of the carbon nano-micro structures (64) on glass substrate (63)
with water contact angles (CA) of 140o.
Figure 6 (g) shows deposition performed within the range of controlled
15 deposition time i.e. at 30 mins (between 15-45mins), that resulted in homogeneous
growth of the carbon nano-micro structures (66) on glass substrate (65) with super
hydrophobic properties i.e. water contact angles (CA) of 156o.
Figure 6(h) shows deposition performed with a shorter time than the lower limit
of the range of controlled coating deposition time (i.e. <15mins), which resulted in
20 inhomogeneous growth of the carbon nano-micro structures (68) on glass substrate (67)
with water contact angles (CA) of 137o.
Figure 6 (i, j and k) illustrate schematic representation of superhydrophobic coatings
formed on glass slides by means of a process which is performed by controlling the gas
flow rate between 35-55 cm3/min, keeping operational temperature constant at 300oC
25 and for a coating deposition time of 30 mins.
Figure 6(i) shows deposition performed with a gas flow rate higher than the
upper limit of the controlled range i.e. >55 cm3/min, which resulted in inhomogeneous
33
growth of the carbon nano-micro structures (70) on glass substrate (69) with water
contact angles (CA) of 137o.
Figure 6 (j) shows deposition performed within the range of controlled gas flow
rate i.e. between 35- 55 cm3/min, which resulted in homogeneous growth of the carbon
nano-micro structures (72) on glass substrate (71) with super hydrophobic properties i.5 e.
water contact angles (CA) of 156o.
Figure 6(k) shows deposition performed with a gas flow rate below the lower
limit of the controlled flow rate i.e. <35 cm3/min, which resulted in inhomogeneous
growth of the carbon nano-micro structures (74) on glass substrate (73) with water
contact angles (CA) of 120o10 .
Figures 7 (a, b, c, d, e) illustrate schematic representation of superhydrophobic coatings
formed on activated carbon fabric (ACF) by means of a process which is performed by
controlling the operational temperature within a range of 200-400oC, keeping constant
gas flow rate between 35 cm3/min- 55 cm315 /min and for a coating deposition time of 30
mins.
Figures 7(a) and 7(b) show depositions performed on ACF (75, 77) at high
temperatures i.e. 400oC and 350oC respectively which resulted in formation of carbon
nano-micro structures (76, 78) with water contact angles (CA) of 134 o and 129o in
20 respective cases.
Figure 7 (c) shows deposition performed at a controlled temperature of 300oC,
which resulted in formation of homogeneous carbon nano-micro structures (80) on ACF
(79) with super hydrophobic properties i.e. water contact angles (CA) of 146o.
Figures 7(d) and 7(e) show deposition performed at temperatures lower than the
controlled temperature such as at 250oC and 200o25 C respectively, which resulted in
formation of carbon nano-micro structures (82, 84) on ACF (81, 83) with water contact
angles (CA) of 135 o and 138o in respective cases.
34
Figures 7(f, g, h) illustrate overall schematic representation of superhydrophobic
coatings formed on ACF by means of a process which is performed by controlling the
time within the range of 15 – 45min with the time interval of 15min, keeping constant
gas flow rate (35 cm3/min- 55 cm3/min) and a fixed temperature at 300oC.
Figure 7(f) shows deposition performed with a longer time than the upper limi5 t
of the range for controlled coating time (i.e. >45mins), which resulted in formation of
carbon nano-micro structures (86) on ACF (85) with water contact angles (CA) of 134o.
Figure 7 (g) shows deposition performed within the range of controlled coating
time i.e. at 30 mins (between 15-45mins), that resulted in formation of carbon nano10
micro structures (88) on ACF (87) with super hydrophobic properties i.e. water contact
angles (CA) of 146o.
Figure 7(h) shows deposition performed with a shorter time than the lower limit
of the range for controlled coating deposition time (i.e. <15mins), which resulted in
formation of carbon nano-micro structures (90) on ACF (89) with water contact angle
(CA) of 135o15 .
Figure 7(i, j and k) illustrate schematic representation of superhydrophobic coatings
formed on ACF by means of a process which is performed by controlling the gas flow
rate between 35-55 cm3/min, keeping operational temperature constant at 300oC and for
a coating deposition time of 30 mins.
20 Figure 7(i) shows deposition performed with a gas flow rate higher than the
upper limit of the controlled range i.e. >55 cm3/min, which resulted in formation of
carbon nano-micro structures (92) on ACF (91) with water contact angles (CA) of 143o.
Figure 7 (j) shows deposition performed within the range of controlled gas flow
rate i.e. between 35- 55 cm3/min, which resulted in formation of carbon nano-micro
25 structures (94) on ACF (93) with super hydrophobic properties i.e. water contact angles
(CA) of 146o.
35
Figure 7(k) shows deposition performed with a gas flow rate below the lower
limit of the controlled flow rate i.e. <35 cm3/min, which resulted in formation of carbon
nano-micro structures (96) on glass substrate (95) with water contact angles (CA) of
138o.
Figure 8 (a, b, c) illustrate overall schematic representation of deposition o5 f
superhydrophobic coatings on ACF by a process performed by controlling Cu catalyst
sputtering time in range between 20 – 60min with the time interval of 20 mins, keeping
constant gas flow rate between 35 cm3/min- 55 cm3/min and for a coating deposition
time of 30 mins at a fixed operational temperature of 300oC;
10 Figure 8(a) shows deposition performed with a longer time than the upper limit
of the range for controlled Cu sputtering time (i.e. >60 mins), which resulted in
formation of carbon nano-micro structures (98) on ACF (97) with water contact angles
(CA) of 135o.
Figure 8 (b) shows deposition performed within the range of controlled Cu
15 sputtering time i.e. at 40 mins (between 20-60mins), that resulted in formation of carbon
nano-micro structures (100) on ACF (99) with super hydrophobic properties i.e. water
contact angle (CA) of 146o.
Figure 8(c) shows deposition performed with a shorter time than the lower limit
of the range for controlled Cu sputtering time (i.e. <20mins), which resulted in
20 formation of carbon nano-micro structures (102) on ACF (101) with water contact angle
(CA) of 110o.
Figures 8(d, e, f) illustrate schematic representation of deposition of superhydrophobic
coating on glass slides by a process performed by controlling Cu catalyst sputtering
time in range between 20 – 60min with the time interval of 20 mins, by keeping
constant gas flow rate between 35 cm3/min- 55 cm325 /min, for a coating deposition time
of 30 mins and fixed operational temperature at 300oC;
36
Figure 8 (d) illustrates deposition on glass slide (103) with a time longer than the
higher limit of the controlled range of Cu sputtering time i.e. >60 mins, which resulted
in formation of carbon nano-micro structures (104) with water CA of 144o;
Figure 8 (e) illustrates deposition on glass slide (105) with a time within the
controlled range of Cu sputtering time i.e. between 20-60 mins, which resulted i5 n
formation of carbon nano-micro structures (106) with superhydrophobic properties i.e.
with water CA of 156o;
Figure 8 (f) illustrates deposition on glass slide (107) with a time shorter than
the lower limit of the controlled range of Cu sputtering time i.e. <20 mins, which
resulted in formation of carbon nano-micro structures (108) the water CA of 119o10 .
37
WE CLAIM:
1. A process for fabricating self-cleaning, homogenous, super hydrophobic coating
surface of carbon nano-micro structure, said process comprising the steps of:
i. sputtering of copper (Cu) metal in inert gas atmosphere to deposit 5 Cu
metal catalytic film on the surface of substrate;
ii. treating the Cu catalyst deposited substrate obtained in step (i) with
chemical vapour deposition (CVD) method with hydrogen gas at a
temperature range of 200-400oC, preferably between 290 - 310˚C;
10 iii. cracking the acetylene gas in the CVD chamber;
iv. decomposing the acetylene gas in the CVD chamber at a temperature of
290-310˚C; and
v. treating the substrate obtained from step (iv) in the CVD chamber with
nitrogen gas under cooling to room temperature (21-24oC), forming the
15 said carbon nano-micro structure on substrate.
2. The process as claimed in claim 1, wherein the substrates are selected from steel,
glass, carbon fabric, Al, alumina.
3. The process as claimed in claim 1, wherein said inert gas is argon (Ar).
20
4. The process as claimed in claim 3, wherein the Ar gas has a flow rate of 40-70 bar.
5. The process as claimed in claim 1, wherein the sputtering of Cu metal is done in a
Direct Current (DC) sputtering unit.
25
6. The process as claimed in claim 5, wherein the DC sputtering unit uses Cu metal
as a target which is of 99% purity.
7. The process as claimed in claim 1, wherein the sputtering of Cu is done for 20-60
30 minutes.
38
8. The process as claimed in claim 1, wherein the sputtering of Cu is done at a
current of 1-100 mA.
9. The process as claimed in claim 1, wherein the sputtering of Cu is done at a
voltage of 500-700V.
10. The process as claimed in claim 1, wherein acetylene gas cracked into the CV5 D
chamber is at a flow rate of 15-30 cm3/min.
11. The process as claimed in claim 1, wherein acetylene gas is decomposed in the
CVD chamber for 30 minutes.
12. The process as claimed in claim 1, wherein flow rate for hydrogen or nitrogen gas
in the CVD chamber is in a range of 35-55 cm310 /min.
13. The process as claimed in claim 1, wherein the deposition time of the said
superhydrophobic coating on substrate ranges between 15-45 minutes.
14. The process as claimed in any of the preceding claims, wherein said
superhydrophobic coating on substrate is having a water contact angle of 144o-
156o15 .
15. The process as claimed in any of the preceding claims, wherein said
superhydrophobic coating on substrate is with 99.71-99.79 atomic % of carbon.
16. A self-cleaning, superhydrophobic coating of carbon nano-micro structure on
substrate obtained by the process as claimed in claim 1.
20 17. The superhydrophobic coating as claimed in claim 16, wherein said carbon nanomicro
structure is having a particle size ranging from 100nm to 110nm.
18. The superhydrophobic coating as claimed in claim 16, wherein said carbon nanomicro
structure is having a dimension ranging between 10-30 μm.
19. The superhydrophobic coating as claimed in claim 16, wherein the growth of
25 carbon nano-micro structure on substrate is homogeneous.
39
20. The superhydrophobic coating as claimed in claim 16, wherein said carbon nanomicro
structure is a nanofiber or a nano-forest.