DESC:FIELD OF THE INVENTION
The present invention describes exfoliation of layered materials in ionic liquids and use thereof. Particularly, the invention describes the ionic liquids consisting of phosphorous based cations and anions, the same being soluble in hydrocarbon oil.
BACKGROUND OF THE INVENTION
With the invention of graphene, two dimensional (2D) nanosheets have become a new breed of smart materials attracting ample interest for a range of applications. Low cost solution processing technique enables successful exfoliation and dispersion of graphene layers to fabricate various potentially useful graphene like materials, mostly lamellar inorganic materials such as WS2, MoS2, BN etc. Regarding this a number of reports have been published for exfoliating layered materials in solvents by sonication, where the delamination and stabilization is facilitated by similar surface energy of solvent and the nanosheets. For example Coleman et.al (WO 2012/101457 A1) described a method based on ultra-sonication of layered materials in solvents having specific range of dispersive Hansen solubility parameter. An aqueous surfactant based exfoliation method was described in another patent application (WO 2013/ 010211 A1) for delaminating layered materials such as graphene. Ionic liquids based exfoliation method was proposed for graphite in another report by Frazier et.al (WO 2010/ 065346 A1). In this patent various ionic liquids have been proposed, though it doesn’t describe other lamellar materials or any phosphorous based ionic liquids.

The described layered materials such as WS2, MoS2, BN in their nano dimension have promising application in lubricating oils owing to its lamellar structure. However, their solubility/ dispersibility in non-polar hydrocarbon oils have been a big disadvantage, where sufficiently longer storage stability is always desirable. Though a few solutions based exfoliation methods can be employed to make these inorganic nano sheets and, redispersing them in non-polar base oils, however their storage stability is still a challenge.

Ionic liquids based on Phosphorous containing cation and anion are mostly oil soluble/miscible and recently they have been proposed as very good lubricant additives with promising anti-wear performance (Appl Mat. & Interfaces, 2012, 4, 997). Hence, exfoliating the lamellar materials in these oil soluble ionic liquids would have a multifunctional advantage to intended lubricant applications.

SUMMARY OF THE INVENTION
The present invention discloses a dispersion comprising an ionic liquid medium and one or more layered material. The layered material exhibits exfoliation in the presence of the ionic liquid. The invention also discloses a stable composite liquid medium comprising a hydrocarbon oil and the liquid dispersion medium containing the exfoliated layered material.

An aspect of the present invention discloses a dispersion comprising a phosphorous based ionic liquid wherein the layered material is present in the composite liquid medium in an exfoliated form.

Another aspect of the invention discloses the process of preparing the said dispersion, wherein the layered material is present in the dispersion in an exfoliated form.

A further aspect of the present invention discloses the process of preparing a stable composite liquid medium, wherein the layered material is present in the composite liquid medium in an exfoliated form.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1: Shows TEM images of exfoliated materials (a) MoS2 (b) WS2 (c) BN

DETAILED DESCRIPTION OF THE INVENTION
The present invention discloses a dispersion comprising an ionic liquid medium and one or more layered material. The layered material exhibits exfoliation in the presence of the ionic liquid. The invention also discloses a stable composite liquid medium comprising a hydrocarbon oil and the liquid dispersion medium containing the exfoliated layered material.

The present invention discloses a dispersion comprising a phosphorous based ionic liquid wherein the layered material is present in the composite liquid medium in an exfoliated form. The invention discloses the process of preparing the said dispersion, wherein the layered material is present in the dispersion in an exfoliated form.

In accordance with the present invention, the phosphorous based ionic liquid has a minimum solubility of 0.05 % in hydrocarbon oil. Ionic liquid used in this invention are room temperature ionic liquid miscible in hydrocarbon matrix having cation or both cation and anion containing P moiety. The phosphorous based ionic liquid is selected from the group comprising of cation consisting of Phosphorous with long chain alkyl (R= C4-C14 or higher), alkoxy chains and anion may be phosphate, phosphinate, chloride, sulfonate, imide, sulfonimide etc. The hydrocarbon oil used in accordance with the present invention is selected from the group comprising Gr I, Gr II, Gr III, synthetic oils (i.e. PAO, PAG, diesters, polyesters, hydrotreated oils, silicone oils of different viscosity etc. ).

In accordance with the present invention, the layered material is present in about 0.1 to about 5 wt% in the dispersion. The layered material used in accordance with the present invention is selected from the group comprising transition metal di chalcogenides, transition metal tri chalcogenides, boron nitride and mixtures thereof. A list of layered materials used in the invention are the transition metal dichalcogenides namely molybdenum disulfide, tungsten disulfide, boron nitride but not limited to MX2, N2X3 where M is Mo, W, Ta, Re, Nb and N is Bi, Sb, As, P and X is S, Se, Te.

The dispersion is prepared by mixing from about 0.1 to about 5 wt% of one or more layered material in an ionic liquid medium to obtain a reaction mixture and subjecting the reaction mixture to sonication to obtain the dispersion.

The composite liquid medium is prepared by mixing from about 0.1 to about 5 wt% of one or more layered material in an ionic liquid medium to obtain a reaction mixture, then subjecting the reaction mixture to sonication to obtain a dispersion and mixing 0.05 to 10wt% of the dispersion with 99.95 to 90 wt% of a hydrocarbon oil.

The hydrocarbon matrix is selected from the group comprising base oil which include oils derived from mineral lubricating oils (Group I, Group II, Group III), and solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic or mixed paraffinic-naphthenic types. The oils may be biodegradable in nature. The polyalphaolefins (PAOs) derived from monomers having from about 4 to about 30 carbon atoms having a viscosity in the range from about 1.5 to about 150 mm2/s (cSt) at 100ºC have also used in this invention. The esters of dicarboxylic acids (e.g., adipic acid, phthalic acid, succinic acid etc.) with a variety of alcohols are also used. The base oil can be individual oil or may be a mixture of different proportion of these mentioned oils. In specific embodiment, the organic media is low viscosity mineral oil, or Polyalphaolefin or low viscosity di-iso decyl di-adipate (DIDA), or a mixture thereof.

In an embodiment of the present invention sonication was carried out for 1-2 hr. at a continuous stretch to get maximum exfoliation. In yet another embodiment, sonic amplitude for the process was kept in the range 20-70% amplitude and the beaker temperature was maintained around 50 °C.

Thermal stability of exfoliated nanodispersions of layered materials in ionic liquids are same as that of the base ionic liquids without any detoriation in lubricity property.

Exfoliated dispersion of MoS2 and WS2 in ionic liquid studied is stable up to 2% conc. Exfoliated dispersion of MoS2 is stable up to 1000 ppm concentration in hydrocarbon matrix. WS2 exfoliated dispersion is stable up to 200 ppm concentration in hydrocarbon matrix.

Having described the basic aspects of the present invention, the following non-limiting examples illustrate specific embodiment thereof.

Example 1
In a typical process 200 mg of MoS2 powder (~ 4µ) was added to 10 gm of ionic liquid (2% w/w). Maximum sonic amplitude (100% amplitude is 114 micron) for the process was kept at 50% and the beaker temperature was maintained at 50 °C. Sonication was carried out for 1 hr at a continuous stretch to get maximum exfoliation. The exfoliated sample in ionic liquid was kept overnight and decanted out to another beaker to discard little unexfoliated material. Exfoliation of WS2 and BN was done under similar conditions at same solid loading, keeping the amplitude at 40 % and duration for 2 hours.

Example 2
To check the dispersibility and stability of the exfoliated materials in base oils calculated amount of the dispersion was taken in mineral lubricating base oil, mildly sonicated for two minutes and kept in a cylinder for stability check by visual observation. The exfoliated MoS2 dispersion in this case was stable in the hydrocarbon oils in the range of 1-1000 ppm (based on MoS2 quantity), or more stable in the range of 1- 500 ppm, or most stable in the range of 1-100 ppm. However, despite good storage stability of exfoliated BN in ionic liquids, the dispersions in base oils were unstable.

Table 1: Extent of exfoliation of layered materials and stability of different P based Ionic Liquids in hydrocarbon Matrix:

Sr. No. P based Ionic Liquid (IL) Solubility in hydrocarbon matrix (5%) at room temperature Exfoliating efficiency to MoS2* Exfoliating efficiency to WS2* Exfoliating efficiency to BN Stability of exfoliated dispersion in hydrocarbon matrix*

1 Trihexyl tetradecyl phosphonium bis (2,4,4-trimethylpentyl) phosphinate Yes Yes Yes
2 Trihexyl tetradecyl phosphonium bis (2,4,4-trimethylpentyl) phosphinate Yes Yes Yes
3 Trihexyl tetradecyl phosphonium bis (2,4,4-trimethylpentyl) phosphinate Yes Yes No
4 Trihexyl tetradecyl phosphonium bis (trifluoromethylsulfonyl) amide Yes Yes Yes
5 Trihexyl tetradecyl phosphonium bis (trifluoromethylsulfonyl) amide Yes Yes Yes
6 Trihexyl tetradecyl phosphonium bis (trifluoromethylsulfonyl) amide Yes No No
7 Trihexyl tetradecyl phosphonium bis (2-ethyl hexyl) phosphate Yes Yes No
8 Trihexyl tetradecyl phosphonium bis (2-ethyl hexyl) phosphate Yes Yes No
9 Trihexyl tetradecyl phosphonium bis (2-ethyl hexyl) phosphate Yes No No
*For MoS2: up to 1000 ppm, WS2: up to 200 ppm
,CLAIMS:We Claim:
1. A dispersion comprising:
an ionic liquid medium; and
from about 0.1 to about 5 wt% of one or more layered material;
characterized in that:
the ionic liquid medium is a phosphorous based ionic liquid; and
the layered material is selected from the group comprising transition metal di chalcogenides and boron nitride and mixtures thereof.

2. The dispersion as claimed in claim 1, wherein the phosphorous based ionic liquid has a minimum solubility of 0.05 wt% in hydrocarbon oil.

3. The dispersion as claimed in claim 1, wherein the phosphorous based ionic liquid is selected from the group comprising of cation consisting of phosphorous with long chain alkyl (R= C4-C14 , alkoxy chains and anion may be phosphate, phosphinate, chloride, sulfonate, imide and sulfonimide.

4. The dispersion as claimed in claim 1, wherein the transition metal di chalcogenides is selected from the group comprising of molybdenum disulfide, tungsten disulfide, boron nitride.
5. The dispersion as claimed in claim 1, wherein the transition metal di chalcogenides is selected from the group comprising of MX2, N2X3 where M is Mo, W, Ta, Re, Nb and N is Bi, Sb, As, P and X is S, Se, Te.

6. The dispersion as claimed in claim 1, wherein the layered material transition is present in the composite liquid medium in an exfoliated form.

7. A composite liquid medium, comprising:
99.95 to 90 wt% of a hydrocarbon oil; and
0.05 to 10wt% of a dispersion comprising:
an ionic liquid medium; and
from about 0.1 to about 5 wt% of one or more layered material;
characterized in that:
the ionic liquid medium is a phosphorous based ionic liquid; and
the layered material is selected from the group comprising transition metal di chalcogenides and boron nitride and mixtures thereof.

8. The composite liquid medium as claimed in claim 7, wherein the hydrocarbon oil is selected from the group comprising mineral lubricating oils (Gr I, Gr II, Gr III), and solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic or mixed paraffinic-naphthenic types, synthetic oils selected from the group consisting of Poly Alpha Olefine (PAO), Poly Alkalyne Glycol (PAG), diesters, polyesters, hydrotreated oils, silicone oils of different viscosity.

9. A process for preparing the dispersion as claimed in claim 1, comprising the steps of:
a. mixing from about 0.1 to about 5 wt% of one or more layered material in an ionic liquid medium to obtain a reaction mixture; and
b. subjecting the reaction mixture to sonication to obtain the dispersion;
characterized in that:
the ionic liquid medium is a phosphorous based ionic liquid; and
the layered material is selected from the group comprising transition metal di chalcogenides and boron nitride and mixtures thereof.

10. A process for preparing the composite liquid medium as claimed in claim 6, comprising the steps of:
a. mixing from about 0.1 to about 5 wt% of one or more layered material in an ionic liquid medium to obtain a reaction mixture;
b. subjecting the reaction mixture to sonication to obtain a dispersion; and
c. mixing 0.05 to 10 wt% of the dispersion with 99.95 to 90 wt% of a hydrocarbon oil to obtain the composite liquid medium;
characterized in that:
the ionic liquid medium is a phosphorous based ionic liquid; and
the layered material is selected from the group comprising transition metal di chalcogenides and boron nitride and mixtures thereof.