Claims:We claim the following from our invention,

Claim:
1. Micropatterned surfaces were fabricated on the stainless steel 304 surfaces using chemical etching process.
a) The chemical solutions and dwell time were fixed depending upon the required geometrical dimensions of the micropatterns.
b) The appropriate way to measure geometrical dimensions of the micropatterns was using 3D optical profilometer. The ridge width to channel width ratio (RW/CW) was taken as surface parameter to quantify its effect with wettability and ice formation.
c) Using High resolution camera wetting study was conducted on flat and micropatterned surface. Contact angle and contact diameter are taken as wetting parameters.
d) Using Icing chamber test rig, we quantified the amount of ice formed on the surface and proved our invention works successfully.
2. As mentioned in claim 1, the dimensions of the micropatterns taken are ridge width ranges between 60.31µm to 205.43µm and channel width ranges between 150.23µm to 255.74µm.The channel depth was maintained constant at 41µm for all cases. Within this geometrical dimension the optimized geometry to prevent wetting and ice formation was found in this invention
3. According to claim 1, micropillar patterned surface with ridge width to channel width ratio (RW/CW) 0.58078 shows better performance in terms of wetting and ice formation when compare to flat and microgroove patterned surface.
4. As per claim 1, wetting study was conducted on flat and micropatterned surface using high speed camera with the help of droplet generator and strobe lamp for illumination. Microgroove surface follows anisotropic wetting and micropillar surface follows isotropic wetting.
5. As per claim 1, our invention proves that micropatterning the surface with proper morphology and roughness will stand as a solution to reduce wetting which in turn reduces the ice formation on its surface.
6. As per claim 1, micropattern surface have better mechanical durability and chemical stability when compared to coatings.
7. As per claim 1, our invention proves that surface morphology, wetting and ice formation on the surface are strongly related to each other. , Description:Field of Invention
The present invention relates to, controlling ice formation on the structures working in ice cold environment (Polar climate). By choosing proper surface morphology, the surface can be turned into hydrophobic surface which in turn it can able to eradicate ice formation.
The objectives of this invention
The objective of this invention is to improve the life cycle of aerospace structures operating in ice cold conditions by means of reducing ice formation on the surfaces by enabling the surface as hydrophobic. Hydrophobicity was introduced on the surface by modifying its surface morphology and roughness for better durability.
Background of the invention
Recent technological developments and its need for developing the structures which can able to withstand for a prolong time period even in freezing cold atmospheric conditions. According to our national research perspective on anti-icing coatings, not much of works were done to the particular context. Some of the studies were focused on superhydrophobic behavior of surfaces and they did not look into the effect of icing on these surfaces (Yan Zhao et al. [2007], Langmuir, 23, p 6212-6217). Superhydrophobicity can be generated by incorporating the physio-chemical changes in the behavior on solid surfaces (Mohidus Samad Khan et al. [2011], Chemical Engineering Science, 66, p 6120-6127). Out of all these Superhydrophobicity enabling methods, the structural modification on the Teflon surfaces seems to have significant advantages to avoid ice aggregation on that. The ice formation, adhesion, and aggregation are directly linked with the friction and wear properties of the surface. A detailed review was done on the wear and tear properties of the Teflon surfaces (S K Biswas et al. [1992], Wear, 158, p 193-211). In addition to the superhydrophobic behavior of the surface, the impregnation of the super-cooled liquid drops impacting on the micro roughness asperities of the solid surfaces. The impregnation of impacting drops are directly linked to the surface micro asperities dimensions, chemical nature of the surface, impact velocity of the liquid drop, and properties of the liquid drop (Shaun Atherton et al. [2016], Chemical Engineering Research and Design, 110, p 200-208 & Hu Hai-Bao et al. [2013], Chinese Physics B, 22, p 084702). Other than that, GE Global research along with its US counterparts works on the anti-icing nano-structured surfaces and they have shown progress on delaying the ice aggregation time.
Across the globe, significant amount of works were done until now with the perspective of anti-icing surfaces using superhydrophobic coatings by various research institutes and industries. Most of the works are fundamental in nature and mostly looking into the superhydrophobic behavior and impregnation of impacting liquid drop on the solid surfaces (D Bartolo et al. [2006], Europhys. Lett., 74, p 299-305, Y C Jung et al. [2008], Langmuir, 24, p 6262-6269, I S Bayer et al. [2006], J. Fluid Mech., 558, p 415-449 & E G Engel [1955], J. Res. Natl. Bur. Stand., 54, p 281-298). Fundamental research studies were carried out to look at the superhydrophobic behavior of Teflon surfaces. From the understanding of phenomenon “Lotus effect”, the anti-icing behavior on the surfaces can be achieved by having a solid surface with high contact angle and low hysteresis to the liquid drop (R Furstner et al. [2005], Langmuir, 21, p 956-961, A B D Cassie et al. [1944], Trans. Faraday Soc., 40, p 546-551, R N Wenzel [1936], Ind. Eng. Chem., 28, p 988-994 & D Oner et al. [2000], Langmuir, 16, p 7777-7782 ). Recent study (Y Wang et al. [2013], Material Sciences and Applications, 4, p 347-356) suggests that the anti-icing behavior of aluminum surfaces can be achieved by the superhydrophobic tendency enabled through grafting of flourosilane molecule on the roughened surface.
All broad range of studies are looked at the static conditions of the liquid drop and not at the impregnation of the impacting drop into the solid surface microasperities. However, most of the situation involves the impact of ice cold drop or snow flurries impacting on the solid surfaces. The attention was given to focus on the surface resistance to impregnation of super-cooled impacting liquid drop in addition to their static configuration on the surface.
Description of Prior Art
Research findings on the anti-icing properties of the solid surfaces have received considerable importance as patents because of its direct industrial applications on aircraft surfaces, wind turbine blades, electrical transmission wires, etc. One of the recent patents describes about the drag reduction of the golf ball by treating the surface of the ball with superhydrophobic coating. According to this patent, superhydrophobic coating keeps moisture off the surface of the golf ball, due to this golf ball can achieve longer flight distance (US2013/0287967). Some of the other patents discuss about employing the coating of chemical like PDMS and other polymer combinations to achieve superhydrophobicity for anti-icing on the solid surfaces (WO2003/093357, US2013/0129982A1, US20100314575 & WO2005075112A1). Another one of recent patents talks about the controlling the ice aggregation through superhydrophobicity obtained using patterned micro structure solid surfaces as well as grafting of fluoro polymer on the surfaces (US20130227972)
The studies are focused on the anti-icing surfaces for aircraft applications (US8221847B2, US6153304A, NL2010504C2 & WO2011094508A1). The icephobic coating is developed by a Canadian research group using PTFE nanoparticles for wind turbine blades operating in freezing cold climate conditions (Rachid Karmouch et al. [2009], IEEE, Canada). Through systematic review of prior art in the area pertinent to the controlling of ice formation and its effect on hydrophobicity, there is still lack in the technologies required to achieve surfaces that avoids the formation of ice on the solid surfaces in the ice-cold conditions with better mechanical durability and chemical stability.
Summary of the invention
In the present innovative invention, the micropatterned surface is designed for eradicating ice formation on the structures and fabricated by chemical etching process.
The ultimate aim is to increase the life cycle of the structures operating in extreme cold environment by reducing ice formation on its surface. The role of surface morphology and roughness on controlling wettability and ice formation was found in this invention.
The key features of micropatterned surface observed in this invention was depending upon the surface morphology three phase contact line varies which impacts the ice formation on the surface of the structure.
Detailed description of the invention
Micro pillar and microgroove patterns with different ridge width (60.31µm – 205.43µm) and channel width (150.23µm – 255.74µm) were fabricated using chemical etching process on SS304 surface. The channel depth was maintained constant at 41µm. Photo mask was prepared in the desired dimensions of patterns and placed on SS304 surfaces. An etching solution, ferric chloride mixed with water taken in equal proportion was prepared and kept undisturbed for 2 hours to stabilize the chemical proportion. The solution gets heated with the subsequent addition of hydrofluoric acid in the ratio of 1:10 to the prepared solution. After a dwell time of 5 minutes, surface covered the masks were dipped in the prepared etchant solution. The surface area not covered by the masks undergoes etching and forms as channels on the surfaces. In contrast, those areas that were covered with masks, i.e. not exposed to etching solution forms as ridges. After the completion of the etching process, the micro patterned surfaces were cleaned with acetic acid mixed with distilled water in the ratio 1:10. The optical microscope image was taken on the fabricated micro patterned surfaces to check the presence of contaminants and it was shown in Fig.1. The images of the fabricated micropillar and microgroove patterns were captured using a 3D optical profilometer (WYKO NT 1100). The geometrical parameters, namely the ridge width, channel width and channel depth were extracted quantitatively from the captured images using the Veeco software.
The wettability study was conducted on flat, micropillar and microgroove patterned surfaces by the sessile drop method. The test samples were thoroughly cleaned with acetone to remove contaminants on their surfaces, before measuring the water contact angles. The customized setup to measure water contact angles encompasses a high speed camera (MotionXtra N3 with resolution 1280 x 1024 operating at 1000 frames per second) and precision controlled water dispensing system. Water droplets (volume 8µl) were gently placed on the surfaces of the test samples by means of a controlled droplet generator. The water droplets were placed on the surfaces and left undisturbed for 5-10 seconds to settle down, before their images were captured using the high speed camera. In case of microgroove images of each water droplet were taken in directions both perpendicular and parallel to the ridges, due to the geometrical anisotropy of the microgroove patterns. The static contact angle and static contact diameter of the water droplets were measured using an image analyzing software Image J from the droplets image taken by the high speed camera.
The static wetting characteristics of flat, microgroove and microgpillar patterned surfaces were studied by measuring their static contact angle and static contact diameter. The geometry of the micropatterns was quantified in two ways, namely: (i) ridge width to channel ratio (RW/CW) and (ii) solid fraction (Micropillar patterned surfaces (RW/CW = 0.58078 & Solid fraction 0.3674) shows less wettability (Contact Angle 164.89?) when compared to the flat surface and microgroove patterned surface. The water droplet sitting on the micropillar patterned surface was shown in Fig. 2. The icing study was conducted on the samples using customized icing setup. The CATIA V5 software is used to design icing test rig which is shown in Fig. 3. The flat, microgroove and micropillar surface samples are kept in the icing chamber (-10º C) to find the amount of ice formed on the surface. The ice formed is measured in terms of weight gain by the samples for different time periods. The corresponding average thickness of ice formed over the plate was theoretically calculated. In all the trials micropillar shows better performance when compare to other surfaces.

7 Claims & 3 Figures

Brief description of Drawing
In the figures which are illustrate exemplary embodiments of the invention.
Figure 1 Optical Microscope Image of a) Microgroove Patterned Surface and b) Micropillar Patterned Surface
Figure 2 Morphology of the Water Droplet Formed on MicroPillar Patterned Surface
Figure 3 Schematic Illustration of Icing Chamber Test Rig.

Detailed description of the drawing
As described above the present invention relates to optimizing the life cycle of the structures and components operating in ice cold environment by eradicating ice formation on its surface.
The optical microscope is used to capture the morphology of micropatterns formed on the surface and it is shown in figure 1. The geometrical parameters were measured using 3D optical profilometer and counterchecked by measuring the geometrical dimensions from the image captured using image J software.
The morphology of the liquid droplet formed on the flat and micropatterned surface was captured using high speed camera. The liquid droplet sitting on the micropillar surface was shown in Figure 2. Micropillar surface follows isotropic wetting where as microgroove surface follows anisotropic wetting. The image J software was preferred to quantitate the wetting parameters.
The fabricated icing chamber was shown in figure 3. Icing chamber works on the principle of single stage vapor compression refrigeration cycle. Compressor, condenser, expansion and evaporator sections forms the intrinsic part of refrigeration unit. Nozzle spray is located inside the chamber to simulate liquid spray over the samples. Motor, valve and pressure gauge arrangement is used to control flow in the nozzle. Icing chamber can generate and maintain temperature upto -15 °C.