Gelling nanofluids for dispersion stability

Abstract

A gelling nanofluid and methods for manufacture are provided. The composition and methods for manufacture produce nanofluid gels so that the settlement of nanoparticles in a base fluid is improved due to the inhibition of particle movement in the gel. The nanofluid gel is produced by using a gelling agent which is either coated on the nanoparticles prior to dispersion in the base fluid or directly introduced in the base fluid.

Claims

1. A nanofluid comprising: a base fluid; a nanoparticle component; and a gelling agent provided in an amount effective to cause the nanofluid to change from a liquid state to a gelled state at temperatures below at least about 10° C., the gelled state helping to maintain the nanoparticle component suspended throughout the base fluid, wherein the gelling agent is selected from the group consisting of sodium oleate, alginic acid, sodium linoleate, and mixtures thereof.

2. A nanofluid comprising: a base fluid; a nanoparticle component; and a gelling agent provided in an amount effective to cause the nanofluid to change from a liquid state to a gelled state at temperatures below at least about 10° C., the gelled state helping to maintain the nanoparticle component suspended throughout the base fluid, wherein the nanoparticle component is selected from the group consisting of diamond nanoparticles, MoS.sub.2 nanoparticles, WS.sub.2, and combinations thereof.

3. The nanofluid of claim 1 wherein the base fluid is a polar fluid.

4. The nanofluid of claim 3 wherein the base fluid is selected from the group consisting of water, long chain alcohol-base machining lubricant, oil-in-water emulsions, and mixtures thereof.

5. A nanofluid comprising: a base fluid; a nanoparticle component; and a gelling agent provided in an amount effective to cause the nanofluid to change from a liquid state to a gelled state at temperatures below at least about 10° C., the gelled state helping to maintain the nanoparticle component suspended throughout the base fluid, wherein the base fluid is a long chain alcohol-based machining lubricant.

6. The nanofluid of claim 1 wherein the gelling agent is provided in a range of about 0.2 to about 2.0 wt. %.

7. The nanofluid of claim 1 wherein the gelling agent is sodium oleate.

8. The nanofluid of claim 1 wherein the gelling agent is provided in an amount effective to cause the nanofluid to change from a liquid state to a gelled state at temperatures below at least about 20° C.

9. A method of preparing a gelling nanofluid, the method comprising the steps of: coating a first nanoparticle component with a gelling agent to form coated nanoparticles; and combining the coated nanoparticles with a base fluid to form the gelling nanofluid, the gelling agent provided in an amount effective to cause the nanofluid to change from a liquid state to a gelled state at temperatures below at least about 10° C., the gelled state helping to maintain the nanoparticle component suspended throughout the base fluid.

10. The method of claim 9 wherein the base fluid is a polar fluid.

11. The method of claim 10 wherein the base fluid is selected from the group consisting of water, long chain alcohol-base machining lubricant, oil-in-water emulsions, and mixtures thereof.

12. The method of claim 9 wherein the gelling agent is provided in a range of about 0.2 to about 2.0 wt. %.

13. The method of claim 9 wherein the gelling agent is selected from the group consisting of sodium oleate, alginic acid, sodium linoleate, and mixtures thereof.

14. The method of claim 13 wherein the gelling agent is sodium oleate.

15. The method of claim 9 wherein the gelling agent is provided in an amount effective to cause the nanofluid to change from a liquid state to a gelled state at temperatures below at least about 20° C.

16. A method of preparing a gelling nanofluid, the method comprising the steps of: combining a base fluid with a first nanoparticle component and a gelling agent to form a gelling nanofluid; and cooling the gelling nanofluid to a temperature of less than about 20° C., the gelling agent provided in an amount effective to cause the nanofluid to change from a liquid state to a gelled state at temperatures below at least about 10° C., the gelled state helping to maintain the nanoparticle component suspended throughout the base fluid.

17. The method of claim 16 wherein the base fluid is a polar fluid.

18. The method of claim 17 wherein the base fluid is selected from the group consisting of water, long chain alcohol-base machining lubricant, oil-in-water emulsions, and mixtures thereof.

19. The method of claim 16 wherein the gelling agent is provided in a range of about 0.2 to about 2.0 wt. %.

20. The method of claim 16 wherein the gelling agent is selected from the group consisting of sodium oleate, alginic acid, sodium linoleate, and mixtures thereof.

21. The method of claim 16 wherein the gelling agent is provided in an amount effective to cause the nanofluid to change from a liquid state to a gelled state at temperatures below at least about 20° C.

22. The nanofluid of claim 1 wherein the base fluid is a non-aqueous fluid having a moisture content less than about 20%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph representing nanoparticle size distribution in engine oil against time representing agglomeration of the nanoparticles when not in a gelled nanofluid;

(2) FIG. 2 is a representation of various concentrations of nanoparticles as the nanoparticles settle out of the fluid when in a standard, non-gelling nanofluid;

(3) FIG. 3 is a representation comparing a non-gelling nanofluid with a gelling nanofluid with diamond nanoparticles;

(4) FIG. 4 is a representation showing gelling nanofluids having MoS.sub.2 nanoparticles;

(5) FIG. 5 is a representation showing a gelling nanofluid that has been heated to turn from a gelled state to a fluid state;

(6) FIG. 6 is a graph representing the gelling time for various concentrations of gelling agents; and

(7) FIG. 7 is a graph representing the melting time for a gelled nanofluid to change to a fluid state for various concentrations of gelling agents and nanoparticles.

DETAILED DESCRIPTION

(8) In one approach it may be desirable to provide a long term substantially homogeneous, stable nanofluid using specified amounts of one or more gelling agents. In this regard, the nanofluid may include a fluid base, one or more nanoparticle components and a gelling agent. The combinations of these features may be used to provide a nanofluid that gels at a desired temperature, such as at a desired storage temperature. In this regard, the combination may help the nanoparticles remain in suspension when in storage such that the nanoparticles are still substantially suspended when used in a fluid state.

(9) Various forms of base fluids may be used to provide the desired properties and functionalities. In one form, the base fluid is a polar fluid such that when combined with the gelling agent, the combination will gel at a desired temperature. In one form, a suitable base fluid is Boelube®, a lubricant fluid manufactured by The Orelube Corporation. Such a base fluid generally is a long chain alcohol-base machining lubricant. Boelube® is a metalworking fluid that does not leave any residues on the workpiece after the machining process such that cleanup is easy.

(10) Other suitable polar base fluids include oil-in-water machining fluid emulsions. Other machining lubricants may also be used.

(11) Various forms of nanoparticles may be used in the gelling nanofluid composition. For example, such nanoparticles include, but are not limited to, MoS.sub.2, diamond, and WS.sub.2. Other nanoparticles may include aluminum oxide, silicon oxide, boron carbide, silicon carbide, and zirconium oxide.

(12) The size of the nanoparticles may also be modified to achieve desired properties and/or functionality. For example, in one form, the nanoparticles may have an average particle size in the range of about 5 nm to about 300 nm. According to one form, the nanoparticles may have an average size in the range of about 5 to about 100 nm.

(13) The concentration of the nanoparticles in the fluid may also be varied as desired. For example, the concentration of the nanoparticles may be in the range of about 0.1 to about 5 wt. %. In one form, the concentration of the nanoparticles may be in the range of about 1 to about 4 wt. %.

(14) In one form, MoS.sub.2 particles may be included having an average particle size of about 90 nm and a concentration of about 0.1 wt. %. In another form, diamond nanoparticles may be included having an average particle size of about 3-5 nm and a concentration of about 0.2 wt. %.

(15) It should be understood that the composition may include a plurality of different types of nanoparticles used in combination. For example, the composition may include both diamond nanoparticles and MoS.sub.2 nanoparticles. Other nanoparticles may also be used in combination with one another.

(16) The gelling agent may take a variety of forms to provide the desired properties and/or functionality. In one form the gelling agent can be a gelling surfactant. There are many surface active agents or surfactants that can be used as gelling surfactants. Such materials include, but are not limited to, castor oil derivatives, polyamides, organoclays, fumed silicas, and oil gelling polymers. These surfactants can be employed for different applications depending on activation temperatures, breakdown due to other components of the formulations, and handling difficulties. The surfactant may come in solid powder which can be dissolved at room or higher than room temperature in the base fluid.

(17) According to one form, the gelling agent is sodium oleate. Sodium oleate, a metal salt of oleic acid, is a compound with a double bond in the middle of chain as exhibited in the formula CH.sub.3—(CH.sub.2).sub.7—CH═CH—(CH.sub.2).sub.7—COONa. Sodium oleate is a molecule with a hydrophilic headgroup or polar head, and a hydrophobic tail. When dispersed in a liquid at concentration above their critical micelle concentration (CMC), it forms micelles. Sodium oleate micelles in aqueous solution form an aggregate with hydrophilic head regions in contact with surrounding solvent sequestering the hydrophobic single tail regions in the micelle center. The micelles grow to form long fibrils. These fibrils overlap or entangle to form the gel network. In this form, the sodium oleate may be suitable as a gelling agent in one or more nanofluids. Sodium linoleate is another exemplary form of a gelling agent.

(18) The concentration of the gelling agent may also be varied to achieve different properties and/or functionality. For example, the concentration of the gelling agent may be varied to provide different gelling temperatures. In one form, for some gelling agents, by increasing the concentration of the gelling agent, the temperature at which the fluid gels will increase. For example, by including a higher concentration of a particular gelling agent, the fluid may gel around room temperature (about 20° C.) while a lower concentration of the gelling agent may cause the fluid to gel at a lower temperature, such as about 10° C.

(19) The concentration of the gelling agent may also depend on the base fluid. Further, the ratio of the gelling agent to the base fluid may also impact the gel formation. For example, a ratio of 0.1 to about 5 of the gelling agent to the base fluid may be suitable to provide a gelling nanofluid at about 25° C.

(20) In one form, the concentration of the gelling agent may be in the range of about 0.1 to about 0.5. In another form, the concentration of the gelling agent may be in the range of about 0.05 to about 0.2 wt. %.

(21) The nanofluid gel may be produced in a number of different manners. For example, in one form, the gelling nanofluid may be prepared by using a gelling agent which is coated on the nanoparticles prior to dispersion in the base fluid. In this regard, the nanoparticles may be first dispersed in the methyl alcohol or other suitable solvent. Next, the gelling agent is added at the desired weight percentage. The solution can then be sonicated to separate particle agglomerates and help with dispersion. In one form, if necessary, the solution can then be heated up to about 90° C. so the alcohol is gradually evaporated. The base fluid, such as Boelube®, is then added with the desired weight percentage. The dispersion is again subjected to sonication for improved quality of dispersion.

(22) In another form, the gelling agent may be directly introduced in the base fluid. In this method, the gelling agent is added to the base fluid. In one form, if needed, the temperature is raised by 50° C. so that the gelling agent, which can be in powder form, can be completely dissolved. Then nanoparticles may then be added and the solution subjected to sonication for improved dispersion quality.

(23) FIG. 3 shows a non-gelled nano-Boelube® and gelled nano-Boelube® containing diamond nanoparticles. In the non-gelled nano-Boelube®, the diamond nanoparticles have completely settled after 24 hours. On the other hand, in the gelled nano-Boelube® the cross-linked structure of the gel has substantially prevented any particle settlement. As can be seen the gelled, homogeneous dispersion is sustained and stabilized.

(24) FIG. 4 shows the gelled nanofluid using MoS.sub.2 nanoparticles with an average particle size of 90 nm in Boelube®. The gelling process was similar to that used in preparation of diamond-based nanofluids, except that the nanoparticle concentration was 0.1% by weight.

(25) FIG. 5 shows a sample of the base fluid, i.e., Boelube®, which had been gelled at room temperature and then heated up beyond room temperature by 25° C. The gel was turned into the liquid state.

(26) Referring now to FIG. 6, gel formation time is plotted against sodium oleate concentration for nanofluids containing 0.1% by weight diamond nanoparticles. The overall composition was prepared by coating nanoparticles with sodium oleate, as described above. The gel formation time was measured after the nanofluid was prepared and its temperature became the room temperature.

(27) FIG. 7 illustrates the time it takes for a nanofluid gel to become liquid when subjected to an environmental temperature of about 60° C. A number sealed bottles of nanofluid gel containing 10 cc of gel with different particle concentrations and sodium oleate concentrations were dropped in a hot water bath with a temperature of 60° C. The time for the first sign of melting of the gel to appear was measured and plotted against time. The results are shown in FIG. 7.

(28) It is believed that when the nanofluid is in the form of a gel and maintained below the gelling temperature, the material can be stored for an infinite shelf life with a stable solution without particle settlement. Further, large volumes of gelling fluid can be brought above the gelling temperature for use and any unused portion can be re-cooled to a gel state for further storage.

(29) A number of exemplary compositions were prepared and tested to verify performance and gelling capabilities.

EXAMPLES

Example 1

(30) In Example 1, one form of a gelling nanofluid was prepared wherein the gelling agent is sodium oleate. The gelling process started by coating the diamond nanoparticles with sodium oleate. Initially, 0.5 wt. % of sodium oleate was dissolved in methyl alcohol. Then, 0.2 wt. % of diamond nanoparticles with an average particle size of 3-5 nm were added to the methyl alcohol solution. The solution was sonicated for 15 minutes. The solution was then heated up to about 90° C. until all the alcohol evaporated. Therefore, the diamond particles were covered by the sodium oleate coating.

(31) Next, the base fluid, which was Boelube®, was added to the composition and sonicated. The compound became a gel after one hour of remaining stationary in the container. It is hypothesized that the role of sodium oleate is to form a three-dimensional cross-linked network in the nanofluid which is the requirement for a gel.

Example 2

(32) Example 2 was prepared to analyze the gelling temperature of the nanofluid. In one form, the concentration of sodium oleate was in the range of 0.1-0.5% by weight and the gelling of the nanofluid occurred in temperatures below 10° C. The gelled nanofluid returned to the fluid state once it is brought to the room temperature environment.

Example 3

(33) Example 3 was prepared to compare different concentrations of the gelling agent on the gelling temperature. For example, the concentration of the gelling agent was in the range of about 0.5-5% by weight and the gelling of the nanofluid occurred at room temperature. The resulting nanofluid gel returns to the fluid state by increasing its temperature above the room temperature, such as about 20-100° C.

(34) The foregoing descriptions are not intended to represent the only forms of the compositions and methods in regard to the details of the overall composition and preparation. The percentages provided herein are by weight unless stated otherwise. Changes in form and in proportion of parts, as well as the substitution of equivalents, are contemplated as circumstances may suggest or render expedient.