HEAT TRANSFER FLUIDS COMPRISING NANOMATERIALS AND METHODS OF MAKING AND USING THE SAME

BACKGROUND OF THE INVENTION Field of the Invention

[0001] The present invention is directed to heat transfer fluids comprising nanomaterials, methods for making the heat transfer fluids and nanomaterials, and products prepared by the methods.

Background

[0002] Fluids are often employed as the heat transfer media in cooling systems. In conventional cooling systems, the heat transfer coefficient can be improved by increasing the velocity of recirculation or by increasing the thermal conductivity of the heat transfer medium. Unfortunately, the extent to which the thermal conductivity of conventional fluids can be improved is minimal, leaving increased velocity as the only practical means of improving the efficiency. This option typically comes at the cost of greater power and energy consumption. Solids, on the other hand, generally have thermal conductivities that are orders of magnitude greater than fluids. As an example, the thermal conductivity of silver at room temperature is about 3000 times greater than that of engine oil, about 1700 times greater than that of ethylene glycol, and about 700 times greater than that of water.

[0003] Heat transfer fluids are of particular importance in transportation and cooling systems. Transportation-born emissions are the second largest source of man-made carbon and were responsible for more than 23% of total emissions in developed countries in 2001. Dedicated engine cooling systems are crucial components of all modern motor vehicles, preventing engine overheating and subsequent failure. Coolant in the engine absorbs heat and is pumped through a radiator, for example, where the coolant is air- cooled and then cycled back to the engine. Both the quantity and pumping speed of the coolant are determined by the thermal transfer coefficient of the fluid. Coolants with smaller coefficients require larger systems. Thus, increasing a thermal transfer coefficient of a fluid permits: 1) a lower quantity of coolant to be utilized; 2) reduction in radiator size (and weight); and 3) a lower power pump to be used for circulating the fluid. Approximately 2.5% to 5% of a vehicle's energy is used to power a cooling system. Thus, more efficient heat transfer fluids and smaller cooling systems can provide significant energy savings. In addition to direct energy savings, smaller radiators reduce weight and increase vehicle aerodynamics because radiators are a key source of drag, especially in large trucks.

[0004] Industrial cooling systems are typically closed loops in which water circulates to cool processing equipment, and chillers then remove heat from the cooling water. In these systems, the majority of energy is expended in the chilling and pumping processes, which account for about 1% to 2% of U.S. carbon emissions from manufacturing industries.

[0005] Finally, many proposed geothermal and solar-thermal energy systems utilize water as a heat-transfer liquid, and large energy savings in pumping power could be obtained by utilizing nanofluids instead of water and other traditional heat transfer fluids.

[0006] As early as 1881, Maxwell predicted that the effective thermal conductivity of a suspension of spherical particles would increase as the volume fraction of solids was increased. See J.C. Maxwell, A Treatise on Electricity and Magnetism 1, 435, 2d. ed., Clarendon Press (1881). Early studies focused on particles with micron-to-millimeter dimensions, but these materials worked poorly due to the large size of the particles. Even with constant agitation, the fluids routinely clogged small passages and, additionally, the suspensions were often abrasive. In the mid 1990's researchers at Argonne National Laboratory began working on suspensions of nanophase materials (materials having a dimension of about 100 nm or less) as advanced heat transfer fluids and termed these new materials nanofluids. See, e.g., S. Choi et ah, ASME Int. Mech. Eng. Cong. Exp. (Nov 12-17, 1995). In contrast to microparticles, nanoparticles can form stable suspensions that will typically do not clog even microscale passages. Moreover, nanoparticles have a much larger surface area-to-volume ratio than their microscale counterparts. This ratio is critical because thermal conductivity in a suspension is limited by the heat transfer between the base fluid and the particles, which occurs at the surface of the particles. For example, a mass of a material comprised of spheres with a diameter of 25 nm has 100- fold more surface area than the same mass of material composed of spheres with a diameter of 2.5 μηι. While nanofluid researchers have investigated the effects of particle size on fluid conductivity, the effects of particle geometry on conductivity are relatively unexplored. This is likely due to the difficulty of fabricating non-spherical particles. However., precise control over particle geometry is critical for maximizing surface area. The surface area of a 25 nm cubic nanoparticle is nearly twice that of a spherical nanoparticle with a 25 nm diameter. Likewise, the surface area of a hexagonal nanoplate with a ferret diameter of 25 nm and a thickness of 10 nm would be nearly five times greater than that of a 25 nm sphere. Thus, nanofluid design requires flexible fabrication processes that are capable of producing nanoparticles with well-controlled sizes and geometries.

[0007] A wide variety of nanoparticle compositions have been explored for nanofluid fabrication, including A1 ₂ 0 ₃ , Cu, Ag, Au, CuO, Ti0 ₂ , SiC, Si0 ₂ , and various forms of carbon nanotubes. Nanofluids containing metal oxide nanoparticles are attractive due to the ease with which these particles can be fabricated. However, in order for a resulting nanofluid containing the particles to have thermal conductivity greater than conventional fluids, a large volume fraction of particles must be used due to the limited intrinsic thermal conductivity of the oxide particles themselves. A large volume fraction of particles also causes a dramatic increase in the viscosity and abrasiveness of a suspension, even when nanoparticles are used, which greatly diminishes the utility of a nanofluid. Multi-walled carbon nanotubes dispersed in engine oil have also demonstrated impressive enhancements in the effective thermal conductivity (e.g., an enhancement of about 160% with a 1% volume fraction of nanotubes). However, the inherent difficulties with fabricating and handling nanotubes, and their propensity to aggregate, limits the practicality of these nanofluids.

BRIEF SUMMARY OF THE INVENTION

[0008] What is needed is a fluid having a high thermal conductivity that can be used as a direct replacement for currently used cooling fluids. In some embodiments, the fluids of the present invention have a thermal conductivity that is several times, or an order of magnitude, or more, greater than the thermal conductivity of currently used cooling fluids. The present invention is directed to a fluid composition comprising: a liquid carrier and a plurality of particles having an anisotropic shape. The fluid compositions of the present invention have a high thermal conductivity, and can be used as a direct replacement for many currently used heat-transfer fluids.

[0009] In some embodiments, the fibers have a cross-sectional dimension of 50 nm to 10 μπι, and at least one second dimension of 200 nm to 10 mm. In some embodiments, the particles have at least one dimension of 10 nm to 100 nm, and at least one second dimension of 10 nm to 250 nm.

[0010] In some embodiments, the particles have an aspect ratio of 1.5 : 1 or higher.

[0011] In some embodiments, at least a portion of the plurality of particles have a cage or porous structure.

[0012] In some embodiments, the particles comprise a metal. In some embodiments, the plurality of particles is a mixture of particles comprising a metal selected from: copper, silver, gold, palladium, and combinations thereof

[0013] In some embodiments, at least a portion of the plurality of particles comprise copper and have an anisotropic three dimensional shape selected from: a plate, a rod, a truncated prism, and combinations thereof.

[0014] In some embodiments, at least a portion of the plurality of particles comprise silver and have an anisotropic three dimensional shape selected from: a cube, a bar, a plate, a wire, a rod, a right bipyramid, and combinations thereof.

[0015] In some embodiments, at least a portion of the plurality of particles are silver nanocubes having a dimension of 100 nm or less per side.

[0016] In some embodiments, at least a portion of the plurality of particles are silver tetragnoal pyramids having a dimension of 120 nm or less per side.

[0017] In some embodiments, at least a portion of the plurality of particles are hollow silver-gold alloy nanocages having at least one dimension of 100 nm or less.

[0018] In some embodiments, at least a portion of the plurality of particles are silver nanobars having an aspect ratio of at least 1 :2 and lateral dimensions of 50 nm or less and

160 nm or less.

[0019] In some embodiments, at least a portion of the plurality of particles are silver nanorice having an aspect ratio of at least 1 :2 and lateral dimensions of 80 nm or less and 300 nm or less.

[0020] In some embodiments, at least a portion of the plurality of particles are palladium nanoplates having a diameter of 15 nm to 80 nm.

[0021] In some embodiments, at least a portion of the plurality of particles are silver nanoplates having a diameter of 20 nm to 200 nm.

[0022] In some embodiments, at least a portion of the plurality of particles are silver right bi-pyramids having a dimension of 50 nm to 150 nm.

[0023] In some embodiments, a fluid composition further comprises a solvent. In some embodiments, a fluid composition comprises a solvent selected from: water, an alcohol, a glycol, a glycol ester, a glycol ether, a ketone, an amide, an ester, an ether, a chlorinated solvent, an aromatic solvent, a petroleum grease, a petroleum oil, a silicone grease, a silicone oil, an ionic liquid, and combinations thereof.

[0024] In some embodiments, a fluid composition further comprises a polymer.

[0025] In some embodiments, at least a portion of the particles comprise a functional group. In some embodiments, at least a portion of the particles include a surface having a self-assembled monolayer thereon.

[0026] In some embodiments, the fluid composition has a thermal conductivity at least

1.5 times that of a fluid composition that lacks the particles.

[0027] The present invention is also directed to a fluid composition comprising: a liquid carrier comprising water and ethylene glycol, wherein the ethylene glycol is present in a concentration of 50% to 90% by volume of the liquid carrier; a polyvinylpyrrolidone polymer in a concentration of 1% by weight or less; and a plurality of particles comprising a metal selected from: gold, silver, and combinations thereof, wherein the particles are present in a concentration of 0.01% to 1% by weight, and wherein the particles have an anisotropic shape that includes at least one dimension of 10 nm to 100 ran, and at least one second dimension of 10 nm to 250 nm.

[0028] In some embodiments, a fluid composition has a thermal conductivity of 2 W/m-K or greater, or 5 W/m-K or greater.

[0029] Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.

[0031] FIGs. 1A-1B, 1C, ID, IE, IF and 1G provide images of metal nanoparticles suitable for use with the present invention.

[0032] One or more embodiments of the present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers can indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number can identify the drawing in which the reference number first appears.

DETAILED DESCRIPTION OF THE INVENTION

[0033] This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the claims appended hereto.

[0034] The embodiment(s) described, and references in the specification to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment(s) described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0035] References to spatial descriptions (e.g., "above," "below," "up," "down," "top,"

"bottom," etc.) made herein are for purposes of description and illustration only, and should be interpreted as non-limiting upon the fluids, materials, fibers, particles, methods, and products of the present invention, which can be spatially arranged in any orientation or manner.

[0036] The present invention is directed to nanomaterials (e.g., nanoparticles, nanofibers, and combinations thereof), nanofluids comprising the nanomaterials, methods to prepare the nanomaterials and fluids, and products prepared therefrom.

[0037] As used herein, a "nanomaterial" refers to a material having a discrete shape that includes at least one average lateral dimension (e.g., cross sectional dimension, width, height, diameter, and the like) less than 1 micron (μιη). In some embodiments, a nanomaterial has at least one cross-sectional dimension of 500 nm of less, 100 nm or less, or 50 nm or less.

[0038] As used herein, a "nanoparticle" refers to a material having a discrete shape and an aspect ratio between two dimensions (e.g., lengthiwidth, lengththeight, length:diameter, and the like) of 1.5 to 10, 2 to 10, 3 to 10, 5 to 10, 8 to 10, or about 10. Thus, nanoparticles for use with the present invention are anisotropic, which refers to an aspect ratio of 1.5 or greater.

[0039] In some embodiments, a nanoparticle of the present invention is a plate (i.e., has a flat or planar shape) in which at least one surface of the nanoparticle has a trigonal, square, rectangular, pentagonal, hexagonal, or octagonal shape.

[0040] In some embodiments, a nanoparticle of the present invention has a polyhedral shape that includes at least one side or facet having a trigonal, square, rectangular, pentagonal, hexagonal, or octagonal shape, or a combination thereof.

[0041] In some embodiments, a nanoparticle of the present invention has a ellipsoidal shape. In some embodiments, a nanoparticle of the present invention has a rod, platelet, wire, or ribbon shape. In some embodiments, a nanoparticle of the present invention has a right bi-pyramidal shape.

[0042] In some embodiments, a nanofluid of the present invention includes a plurality of nanoparticles having a single predominant shape such as, for example, a rod shape. In some embodiments, a nanofluid of the present invention includes a mixture of nanoparticles having different shapes. In both cases the plurality of nanoparticles can have the same or different compositions (e.g., a plurality of nanoparticles having the same shape, but different composition; a plurality of nanoparticles having a consistent composition, but different shapes; or a plurality of nanoparticles having diverse shapes and compositions).

[0043] In some embodiments, a nanoparticle of the present invention has a cage structure.

[0044] In some embodiments, the nanoparticles have at least one dimension (e.g., length, width, height, diameter, thickness, and the like) that has an average size of 10 nm to 100 nm, 10 nm to 80 nm, 10 nm to 75 nm, 10 nm to 70 nm, 10 nm to 65 nm, 10 nm to 60 nm, 10 nm to 50 nm, 10 nm to 45 nm, 10 nm to 40 nm, 10 nm to 35 nm, 10 nm to 30 nm, 10 nm to 25 nm, 10 nm to 20 nm, 20 nm to 100 nm, 20 nm to 80 nm, 20 nm to 75 nm, 20 nm to 70 nm, 20 nm to 65 nm, 20 nm to 60 nm, 20 nm to 50 nm, 20 nm to 45 nm, 20 nm to 40 nm, 20 nm to 35 nm, 20 nm to 30 nm, 30 nm to 100 nm, 30 ran to 80 nm, 30 nm to 75 nm, 30 nm to 70 nm, 30 nm to 65 nm, 30 nm to 60 nm, 30 nm to 50 nm, 30 nm to 45 nm, 30 nm to 40 nm, 40 nm to 100 nm, 40 nm to 80 nm, 40 nm to 75 nm, 40 nm to 70 nm, 40 nm to 65 nm, 40 nm to 60 nm, 40 nm to 50 nm, 50 nm to 100 nm, 50 nm to 80 nm, 50 nm to 75 nm, 50 nm to 70 nm, 50 nm to 65 nm, 50 nm to 60 nm, 60 nm to 100 nm, 60 nm to 90 nm, 60 nm to 80 nm, 60 nm to 75 nm, 75 nm to 100 nm, 75 nm to 100 nm, 10 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 75 nm, 80 nm, 90 nm, or 100 nm. [0045] Nanoparticles suitable for use with the present invention and methods of making the nanoparticles are also described in, for example, U.S. Pub. Nos. 2005/0056118, 2007/0289409, and 2008/0003130, the entire contents of which are incorporated herein by reference.

[0046] In some embodiments, a nanoparticle for use with a nanofluid of the present invention comprises silver and has a cube, bar, rice, plate, wire, or right bipyramid shape.

[0047] In some embodiments, a nanoparticle for use with a nanofluid of the present invention comprises copper Cu and has a plates or truncated prism shape having a ferret diameter of 10 nm to 100 nm and a thickness of 1 nm to 25 nm.

[0048] As used herein, a "nanofiber" refers to a material having a discrete wire, thread, hair and/or tube-like shape that is generally longer than a particulate. In some embodiments, a nanofiber has an aspect ratio of a length to a cross-sectional dimension (e.g., length:width, length:height, length: diameter, and the like) of 10:1 or greater, 15:1 or greater, 20:1 or greater, 25:1 or greater, 30:1 or greater, or 50:1 or greater.

[0049] In some embodiments, a nanofiber of the present invention has a cross-sectional shape selected from: a circle, an ellipse, a polyhedron (e.g., a trigonal, square, rectangular, pentagonal, hexagonal, or octagonal cross-section shape), a star, or a combination thereof.

[0050] In some embodiments, a nanofiber for use with the present invention has a cross- sectional dimension of 20 nm to 1 μηι, 50 nm to 900 nm, 100 nm to 800 nm, 150 nm to 700 nm, 200 nm to 600 nm, 250 nm to 500 nm, or 300 nm to 500 nm.

[0051] In some embodiments, a nanofiber for use with the present invention has a length of 500 nm to 50 μηι, 1 μηι to 25 μιη, 1 μιη to 10 μηι, or 1 μηι to 5 μη .

[0052] Nanofibers suitable for use with the present invention and methods of making the nanofibers are also described in, for example, U.S. Appl. Nos. 61/104,438, filed October 10, 2008, and 61/227,336, filed July 21, 2009, the entire contents of which are incorporated herein by reference.

[0053] In some embodiments, a nanomaterial for use with the present invention comprises a material selected from: a metal, a polymer, a conductive polymer, a ceramic, a composite thereof, and combinations thereof. Other presently known and later developed materials can also be employed.

[0054] Nanofluids comprising metallic nanomaterials are particularly preferred because metal nanoparticles show extremely high enhancements in effective thermal conductivity, even at low nanomaterial volume fractions. In some embodiments, a nanomaterial for use with the present invention comprises a metal selected from: a transition metal, a group IIIB metal, a group IVB metal, and combinations thereof. In some embodiments, a nanomaterial for use with the present invention comprises a metal selected from: silver, copper, gold, nickel, rhodium, palladium, platinum, iridium, cobalt, chromium, aluminum, titanium, tin, and the like, an oxide thereof, and an alloy thereo

[0055] In some embodiments, a nanomaterial for use with the present invention comprises a material selected from: a silver oxide (e.g., AgO), a titanium oxide (e.g., Ti0 ₂ ), a copper oxide (e.g., Cu ₂ 0), an aluminum oxide (e.g., A1 ₂ 0 ₃ ), a germanium oxide (e.g., GeO), a zirconium oxide (e.g., Zr0 ₂ ), a yttrium oxide (e.g., Y ₂ 0 ₃ ), a zinc oxide (e.g., ZnO), a vanadium oxide (e.g., V ₂ 0 ₅ ), an indium oxide (e.g., InO), a tin oxide (e.g., SnO), an indium tin oxide, a suboxide thereof, a doped and/or alloyed form thereof, and combinations thereof.

[0056] Metallic and metal oxide nanofibers for use the present invention can be prepared by electrospinning a metal salt-polymer nanofiber followed by reduction or oxidation of the metal salt to form a metal or metal oxide. Metallic and metal oxide nanofibers for use with the present invention include, but are not limited to, the metals and metal oxides listed above.

[0057] In some embodiments, a nanomaterial is conductive or semiconductive. As used herein, "conductive" and "semiconductive" materials include species, compounds, polymers, and the like capable of transporting or carrying electrical charge. Generally, the charge transport properties of a semiconductive material can be modified based upon an external stimulus such as, but not limited to, an electrical field, a magnetic field, a temperature change, a pressure change, exposure to radiation, and combinations thereof. Electrically conductive and semiconductive materials include, but are not limited to, metals, alloys, crystals, amorphous materials, polymers, and combinations thereof

[0058] In some embodiments, a nanofluid of the present invention is transparent, translucent, or opaque to visible, UV, and/or infrared light). In some embodiments, a nanofluid of the present invention is blue, green, red or black, and the nanofluid contains nanomaterials having an absorption in the visible, ultraviolet and/or infrared regions of the electromagnetic spectrum. In some embodiments, a nanomaterial absorbs electromagnetic radiation having at least one wavelength of 180 nm to 30 μηι. In some embodiments, a nanoparticle is substantially transparent to a light in a first region of the electromagnetic spectrum and has an absorption at a second wavelength range from 180 nm to 30 μηι. [0059] In some embodiments, nanomaterials present in a heat transfer fluid have approximately the same composition. In some embodiments, nanomaterials present in a heat transfer fluid of the present invention have compositions that differ from one another, or that differ substantially from one another.

[0060] In some embodiments, a nanoparticle and/or nanofiber for use with the present invention is porous. As used herein, "porous" and "porosity" are interchangeable and refer to a structure comprising void space. Nanoparticles and nanofibers for use with the present invention can have a porosity of 1% to 65% by volume, 5% to 60% by volume, 10% to 50% by volume, 15% to 40% by volume, or 20% to 30% by volume.

[0061] Nanomaterials for use with the present invention can be rigid or flexible. In some embodiments, a nanomaterial can undergo plastic deformation such that conformal contact can be made between a flexible nanomaterial and a curved or non-planar substrate.

[0062] In some embodiments, a nanomaterial of the present invention has a Young's

Modulus of 1 GPa to 1,000 GPa, 10 GPa to 1,000 GPa, 50 GPa to 1,000 GPa, 100 GPa to 1,000 GPa, or 500 GPa to 1,000 GPa. In some embodiments, the Young's Modulus of a nanomaterial of the present invention is substantially the same as the Young's Modulus a bulk material having the same composition as the nanomaterial.

[0063] In some embodiments, a nanofluid of the present invention has a thermal conductivity of 2 W/m-K or greater, 5 W/m-K or greater, 10 W/m-K or greater, 15 W/m-K or greater, 20 W/m-K or greater, 25 W/m-K or greater, 30 W/m-K or greater, 50 W/m-K or greater, 75 W/m-K or greater, or 100 W/m-K or greater. In some embodiments, a nanofluid of the present invention has a thermal conductivity 2 W/m-K to 100 W/m-K, 2 W/m-K to 50 W/m-K, 2 W/m-K to 25 W/m-K, 2 W/m-K to 10 W/m-K, 5 W/m-K to 100 W/m-K, 5 W/m-K to 50 W/m-K, 5 W/m-K to 25 W/m-K, 10 W/m-K to 100 W/m-K, 10 W/m-K to 50 W/m-K, 10 W/m-K to 25 W/m-K, 25 W/m-K to 100 W/m-K, or 25 W/m-K to 50 W/m-K.

[0064] In some embodiments, a nanofluid of the present invention exhibits an increase in thermal conductivity of 1.5-fold, two-fold, 2.5-fold, three-fold, four- fold, five-fold, sixfold, eight-fold, nine-fold, or ten-fold or more compared to a fluid lacking the nanoparticles but otherwise having the same composition.

[0065] The following table provides thermal conductivity values for various metallic and non-metallic materials. Table. The thermal conductivity of several solvents

[0066 J Thus, the intrinsic thermal conductivity of many commonly used solvents is below

1 W/m-K, and a nanofluid can exhibit significant increase in thermal conductivity at low nanomaterial loadings.

[0067] In some embodiments, a nanofluid of the present invention comprises a nanomaterial (i.e., nanoparticles and/or nanofibers) in a concentration of 0.5% to 80%, 0.5% to 75%, 0.5% to 70%, 0.5% to 60%, 0.5% to 50%, 0.5% to 40%, 0.5% to 30%, 0.5% to 25%, 0.5% to 20%, 0.5% to 15%, 0.5% to 10%, 0.5% to 7.5%, 0.5% to 5%, 0.5% to 4%, 0.5% to 3%, 0.5% to 2%, 0.5% to 1%, 1% to 50%, 1% to 25%, 1% to 10%, 5% to 80%, 5% to 70%, 5% to 60%, 5% to 50%, 5% to 40%, 5% to 30%, 5% to 25%, 5% to 20%, 5% to 15%, 5% to 10%, 10% to 80%, 10% to 50%, 10% to 25%, 15% to 80%, 15% to 50%, 15% to 40%, 15% to 30%, 20% to 80%, 20% to 70%, 20% to 60%, 20% to 50%, 25% to 75%, 25% to 50%, 30% to 80%, 30% to 60%, 40% to 80%, about 0.5%, about 1%, about 2%, about 3%, about 4%, about 5%, about 7.5%, about 10%, about 12.5%, about 15%, about 20%, about 25%, about 30%, about 40%, about 50%, about 60%, about 70%, or about 80% by volume.

[0068] In some embodiments, the nanomaterials within a heat transfer fluid of the present invention are not functionalized and/or derivatized. In some embodiments, nanomaterials of the present invention are functionalized and/or derivatized. As used herein, "functionalized" and "derivatized" refer to the attachment of a chemical group, ligand, species, moiety, and the like to a surface of a nanomaterial. In some embodiments, nanomaterials are derivatized with a molecular species as described herein.

[0069] In some embodiments, at least a portion of a nanomaterial surface is derivatized with a monolayer-forming species, for example a self-assembled monolayer forming species. Thus, in some embodiments at least a portion of the particles include a surface having a self-assembled monolayer thereon. A self-assembled monolayer can be formed on at least a portion of a metal nanomaterial surface using, for example, a thiol group.

[0070] Not being bound by any particular theory, functionalization and derivatization can be achieved via a covalent bonding interaction, an ionic bonding interaction, a hydrogen bonding interaction, a non-bonding interaction, an intercalation interaction, physical entanglement, a chiral interaction, a magnetic interaction, and combinations thereof. Furthermore, derivatization and/or functionalization of the anisotropic nanomaterials can be useful for modifying a chemical and/or thermal interface between the nanomaterials and a fluid. Thus, derivatization and/or functionalization of the anisotropic nanomaterials can increase the dispersibility of the nanomaterials in a fluid, increase the solubility of nanomaterials in a fluid, increase the hydrophobicity of nanomaterials, increase the hydrophilicity of nanomaterials, increase the thermal conductivity of the nanomaterials in a fluid, and combinations thereof.

[0071] In some embodiments, a self-assembled monolayer on at least a portion of a surface of a nanomaterial can also improve the chemical stability of the nanomaterial by, e.g., preventing oxidation, as well maintaining the stability of the nanofluid against agglomeration and/or sedimentation.

[0072] Functional groups suitable for imparting hydrophilicity to a nanomaterial of the present invention include, but are not limited to, hydroxyl, alkoxyl, thiol, thioalkyl, silyl, alkylsilyl, alkylsilenyl, siloxyl, primary amino, secondary amino, tertiary amino, carbonyl, alkylcarbonyl, aminocarbonyl, carbonylamino, carboxy, alkylenedioxy, and combinations thereof. Generally, increasing the length of an alkyl, alkenyl, or alkynyl chain will increase the hydrophobicity of a nanomaterial's surface.

[0073] As used herein, "alkyl," by itself or as part of another group, refers to straight and branched chain hydrocarbons of up to 60 carbon atoms, such as, but not limited to, octyl, decyl, dodecyl, hexadecyl, and octadecyl.

[0074] As used herein, "alkenyl," by itself or as part of another group, refers to a straight and branched chain hydrocarbons of up to 60 carbon atoms, wherein there is at least one double bond between two of the carbon atoms in the chain, and wherein the double bond can be in either of the cis or trans configurations, including, but not limited to, 2-octenyl, 1-dodecenyl, 1-8-hexadecenyl, 8-hexadecenyl, and 1-octadecenyl.

[0075] As used herein, "alkynyl," by itself or as part of another group, refers to straight and branched chain hydrocarbons of up to 60 carbon atoms, wherein there is at least one triple bond between two of the carbon atoms in the chain, including, but not limited to, 1-octynyl and 2-dodecynyl.

[0076] As used herein, "aryl," by itself or as part of another group, refers to cyclic, fused cyclic, and multi-cyclic aromatic hydrocarbons containing up to 60 carbons in the ring portion. Typical examples include phenyl, naphthyl, anthracenyl, fluorenyl, tetracenyl, pentacenyl, hexacenyl, perylenyl, terylenyl, quaterylenyl, coronenyl, fullerenyl and buckminsterfullereny 1.

[0077] As used herein, "aralkyl" or "arylalkyl," by itself or as part of another group, refers to alkyl groups as defined above having at least one aryl substituent, such as benzyl, phenylethyl, and 2-naphthylmethyl. Similarly, the term "alkylaryl," as used herein by itself or as part of another group, refers to an aryl group, as defined above, having an alkyl substituent, as defined above.

[0078] As used herein, "heteroaryl," by itself or as part of another group, refers to cyclic, fused cyclic and multicyclic aromatic groups containing up to 30 atoms in the ring portions, wherein the atoms in the ring(s), in addition to carbon, include at least one heteroatom. The term "heteroatom" is used herein to mean an oxygen atom ("O"), a sulfur atom ("S") or a nitrogen atom ("N"). Additionally, the term heteroaryl also includes TV-oxides of heteroaryl species that containing a nitrogen atom in the ring. Typical examples include pyrrolyl, pyridyl, pyridyl JV-oxide, thiophenyl, and furanyl.

[0079] Any one of the above groups can be farther substituted with at least one of the following substituents: hydroxyl, alkoxyl, thiol, alkylthio, silyl, alkylsilyl, alkylsilenyl, siloxyl, primary amino, secondary amino, tertiary amino, carbonyl, alkylcarbonyl, aminocarbonyl, carbonylamino, carboxy, halo, perhalo, alkylenedioxy, and combinations thereof.

[0080] As used herein, "hydroxyl," by itself or as part of another group, refers to an

(-OH) moiety.

[0081] As used herein, "alkoxyl," by itself or as part of another group, refers to one or more alkoxyl (-OR) moieties, wherein R is selected from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above. [0082] As used herein, "thiol," by itself or as part of another group, refers to an (-SH) moiety.

[0083] As used herein, "alkylthio," refers to an (-SR) moieties, wherein R is selected from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above.

[0084] As used herein, "silyl," by itself or as part of another group, refers to an (-Si¾) moiety.

[0085] As used herein, "alkylsilyl," by itself or as part of another group, refers to an

(-Si(R) _x H _y ) moiety, wherein 1 < x < 3 and y = 3-x, and wherein R is independently selected from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above.

[0086] As used herein, "alkylsilenyl," by itself or as part of another group, refers to a

(-Si(=R)H) moiety, wherein R is selected from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above.

[0087] As used herein, "siloxyl," by itself or as part of another group, refers to a

(-Si(OR) _x R ¹ _y ) moiety, wherein 1 < x < 3 and y = 3-x, wherein R and R ¹ are independently selected from hydrogen and the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above.

[0088] As used herein, "primary amino," by itself or as part of another group, refers to an

(-NH ₂ ) moiety.

[0089] As used herein, "secondary amino," by itself or as part of another group, refers to an (-NRH) moiety, wherein R is selected from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above.

[0090] As used herein, "tertiary amino," by itself or as part of another group, refers to an

(-NRR ¹ ) moiety, wherein R and R ¹ are independently selected from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above.

[0091] As used herein, "carbonyl," by itself or as part of another group, refers to a (C=0) moiety.

[0092] As used herein, "alkylcarbonyl," by itself or as part of another group, refers to a

(-C(=0)R) moiety, wherein R is independently selected from hydrogen and the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above.

[0093] As used herein, "aminocarbonyl," by itself or as part of another group, refers to a

(-C(™0)NRR ¹ ) moiety, wherein R and R ¹ are independently selected from hydrogen and the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above _* [0094] As used herein, "carbonylamino," by itself or as part of another group, refers to a

(-N(R)C(=0)R ¹ ) moiety, wherein R and R ¹ are independently selected from hydrogen and the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above.

[0095] As used herein, "carboxy," by itself or as part of another group, refers to a

(-COOR) moiety, wherein R is independently selected from hydrogen and the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described above.

[0096] As used herein, "alkylenedioxy," by itself or as part of another group, refers to a ring and is especially C _1-4 alkylenedioxy. Alkylenedioxy groups can optionally be substituted with halogen (especially fluorine). Typical examples include methylenedioxy (-OCH ₂ 0-) or difmoromethylenedioxy (-OCF ₂ 0-).

[0097] As used herein, "halo," by itself or as part of another group, refers to any of the above alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups wherein one or more hydrogens thereof are substituted by one or more fluorine, chlorine, bromine, or iodine atoms.

[0098] As used herein, "perhalo," by itself or as part of another group, refers to any of the above alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups wherein all of the hydrogens thereof are substituted by fluorine, chlorine, bromine, or iodine atoms.

[0099] In some embodiments, a nanomaterial of the present invention has a fluorinated surface. As used herein, a "fluorinated moiety" refers to a molecule, particulate, or molecular species that contains a bond to fluorine and can be used to derivatize a nanomaterial of the present invention. In some embodiments, a fluorinated moiety comprises a C-F bond and/or an Si-F bond. For example, in some embodiments, an outer surface of a nanomaterial is fluorinated (e.g., by exposure to F ₂ , SiF ₄ , SF ₆ , a fluorinated alkyl and/or alkoxy silane, and the like, as well as other fluorination processes that would be apparent to a person of ordinary skill in the art of surface fluorination) to provide a fluorinated surface.

[0100] In some embodiments, a nanomaterial is derivatized with a self-assembled monolayer forming species comprising any of the above alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups containing a functional group suitable for forming a bond with a metal. In some embodiments, a self-assembled monolayer forming species includes one or more hydroxyl, thiol, silyl, primary amino, secondary amino, and/or carboxyl groups.

[0101] In some embodiments, the nanomaterials are hydrophobic. In some embodiments, a nanomaterial is derivatized with a hydrophobic functional group. As used herein, "hydrophobic" refers to coatings that have a tendency to repel water, are resistant to water and/or cannot be wetted by water. In some embodiments, a hydrophobic nanomaterial comprises a surface that is at least 50%, at least 60%, at least 70%, or at least 80% covered by a hydrophobic molecular species.

[0102] In some embodiments, a hydrophobic molecular species comprises an optionally substituted Q-Ceo alkyl, an optionally substituted C ₂ -C ₆₀ alkenyl, an optionally substituted C ₂ -C ₆₀ alkynyl, an optionally substituted C ₆ -C ₆₀ aryl, an optionally substituted C ₆ -C ₆₀ aralkyl, an optionally substituted C ₆ -C ₆₀ heteroaryl, and combinations thereof, wherein these groups can be linear or branched. Optional substituents for hydrophobic molecular species include, but are not limited to, a halo and perhalo (i.e., wherein halo is any one of: fluorine, chlorine, bromine, iodine, and combinations thereof), alkylsilyl, siloxyl, tertiary amino, and combinations thereof.

[0103] In some embodiments, an optionally substituted hydrophobic molecular species is chosen from a Q-C60 fluoroalkyl, a Q-C60 perfluoroalkyl, and combinations thereof.

[0104] In addition to an anisotropic nanoparticle, a nanofluid of the present invention can further comprise a component selected from: an isotropic nanoparticle, a nanofiber, a solvent, a polymer, a surfactant, a dispersant, a stabilizer, an antioxidant, a chelator, and the like, and combinations thereof.

[0105] In addition to a nanofiber, a nanofluid of the present invention can further comprise a component selected from: an isotropic nanoparticle, an anisotropic nanoparticle, a nanofiber, a solvent, a polymer, a surfactant, a dispersant, a stabilizer, an antioxidant, a chelator, and the like, and combinations thereof.

[0106] In some embodiments, a nanofluid of the present invention comprises a solvent.

Solvents suitable for use with the present invention include both aqueous and nonaqueous solvents and solvent mixtures. In some embodiments, a composition of the present invention includes an aliphatic non-aqueous solvent, an aromatic non-aqueous solvent, or a combinations thereof. Solvents suitable for use with the present invention also include, but are not limited to, water, an alcohol (e.g., methanol, ethanol, propanol, butanol, pentanol, hexanol, and the like), a glycol (e.g., ethylene glycol, propylene glycol, diethylene glycol, tetraethylene glycol, and the like, and ethers and esters thereof such as, but not limited to, ethylene glycol dimethylether, ethylene glycol diethylether), a ketone (e.g., acetone, methylethylketone, butanone, and the like), an amide (e.g., dimethylformamide, dimethylacetamide, and the like), an ester (e.g., ethylacetate, and the like), an ether (e.g., dimethylether, dipropylether, and the like), N-methylpyrrolidone (NMP), a chlorinated solvent (e.g., methylenechloride, chloroform, 1 ,2-dichloroethane, and the like), aromatic solvents (e.g., benzene, chlorobenzene, furan, pyridine, quinoline, and the like), petroleum-based greases and oils (e.g., greases and oils derived from petroleum that contain 6 to 60 carbon atoms), silicone greases and oils (e.g., greases and oils having a siloxane backbone), an ionic liquid (e.g., l-alkyl-3-methylimidazolium, 1-alkylpyridinium, N-methyl-N-alkylpyrrolidinium, and the like complexed with e.g., tetrafluoroborate, hexafluorophosphate, bistriflimide, triflate, tosylate, and the like), and combinations thereof.

[0107] In some embodiments, a solvent is a glycol or an ether or ester thereof selected from: ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol methyl ether acetate, ethylene glycol monethyl ether acetate, ethylene glycol monobutyl ether acetate, and the like, and combinations thereof,

[0108] In some embodiments, the nanofluid comprises an aqueous solution that includes a glycol in a concentration of 50% to 90%, 50% to 75%, 60% to 90%, 75% to 90%, about 50%), about 60%, about 75%, or about 90% by volume. In some embodiments, the glycol is ethylene glycol.

[0109] In some embodiments, a nanofluid of the present invention comprises a polymer such as, but not limited to, a polyvinylpyrrolidone, a cellulose (e.g., a methylcellulose, ethylcellulose, a hydroxyethylcellulose, a hydroxypropylmethylcellulose, a carboxymethylcellulose, and the like), a polyethylene glycol, a polypropylene glycol, a polyacrylic acid, a polyvinylacetate, a polyvinylalcohol, and the like, and combinations thereof.

[0110] In some embodiments, a polymer is present in a concentration of 5% or less, 2.5% or less, 1% or less, 0.5%) or less, or 0.1% or less, by weight of a composition.

[0111] Not being bound by any particular theory, a polymer can function as a stabilizer in a nanofluid of the present invention, for example, to provide enhanced flowability and/or to prevent agglomeration, sedimentation, and/or oxidation.

[0112] In some embodiments, a nanofluid of the present invention comprises an anisotropic nanoparticle, a solvent and a polymer. In one embodiment, for example, the present invention is directed to a fluid composition comprising: a liquid carrier comprising water and ethylene glycol, wherein the ethylene glycol is present in a concentration of 50% to 90% by volume of the liquid carrier; a polyvinylpyrrolidone polymer in a concentration of 1% by weight or less; and a plurality of particles comprising a metal selected from: gold, silver, and combinations thereof, wherein the particles are present in a concentration of 0.01% to 1% by weight, and wherein the particles have an anisotropic shape that includes at least one dimension of 10 nm to 100 nm, and at least one second dimension of 10 nm to 250 nm.

[0113] In some embodiments, a nanofluid of the present invention comprises a nanofiber, a solvent and a polymer. In one embodiment, for example, the present invention is directed to a fluid composition comprising: an aqueous liquid carrier, a polyvinylpyrrolidone polymer in a concentration of 1% by weight or less, and a plurality of nanofibers comprising a metal selected from: nickel, copper, zinc, iron, an oxide thereof, and combinations thereof, wherein the nanofibers have an average cross-sectional dimension of 100 nm to 500 nm and an average length of 1 μηι to 25 μπι.

[0114] As used herein, "robust" refers to physical, dimensional and/or chemical stability.

For example, the nanofluids and nanomaterials of the present invention exhibit wear resistance, dimensional stability, and chemical stability that makes them suitable for use in a wide range of environments. Additionally, the nanofluids of the present invention are robust and stable for an extended period of time. In some embodiments, a nanofluid of the present invention is stable for at least 200 hours, at least 300 hours, at least 400 hours, at least 500 hours, at least 600 hours, at least 700 hours, at least 800 hours, at least 900 hours, at least 1,000 hours, at least 1,200 hours, at least 1,500 hours, or at least 2,000 hours without agitation.

[0115] The nanomaterials and nanofluids of the present invention are compatible with a variety of materials without inducing corrosion of the bulk and/or surface of a material. In some embodiments, a nanomaterials suspension and/or nanofluid of the present invention is compatible with 6061 aluminum, stainless steel, polycarbonate, silica, quartz, and the like.

[0116| The nanofluids of the present invention are suitable for application in cooling systems, solar energy conversion systems, photovoltaic systems, electrical systems, consumer electronics, industrial electronics, automobiles, military applications, space applications, and any other applications in which heat transfer fluids are required or desirable. [0117] Properties of the fluid compositions of the present invention that can be optimized and/or controlled include, but are not limited to, composition, stoichiometry, viscosity, thermal conductivity, density, light absorption, electrical conductivity, chemical stability, and the like, and combinations thereof. Properties of the nanomaterials and fluid compositions of the present invention can be measured using analytical tools and methods known to persons of ordinary skill in the art.

[0118] The nanofluids of the present invention are robust and can be used in a wide variety of industrial applications without undergoing physical and/or chemical degradation or resulting in damage to equipment. In some embodiments, a nanofluid of the present invention has a lifetime of 5,000 hours or more, 10,000 hours or more, 15,000 hours or more, or 20,000 hours or more. In some embodiments, a nanofluid of the present invention can be used with a heat transfer apparatus comprising at least one opening having a diameter of 100 μηι or less, 50 μηι or less, 25 μιη or less, 10 μιη or less, or 5 μπι or less without sedimentation and/or clogging.

[0119] The present invention is also directed to an apparatus suitable for testing thermal conductivity of nanofluids. In some embodiments, an apparatus of the present invention enables prediction of nanofluid performance based on a nanomaterial and/or bulk material property. For example, the present invention enables the heat transfer and thermal conductivity properties for a nanofluid composition to be predicted based on the shape, surface area, surface area to volume ratio, surface area to mass ratio, composition and/or concentration of a nanomaterial present in a fluid, as well as properties such as the fluid composition, fluid density, fluid viscosity, and the like.

[0120] Having generally described the invention, a further understanding can be obtained by reference to the examples provided herein. These examples are given for purposes of illustration only and are not intended to be limiting.

EXAMPLES Example 1

[0121] FIG. 1A provides a scanning electron microscope ("SEM") image, 100, of a collection of silver nanocubes, 101, and tetragnoal pyramids, 102, suitable for use with the present invention. The silver nanocubes, 101, have a dimension of about 100 nm per side, and the tetragnoal pyramids, 102, have a dimension of about 120 nm per side. FIG. IB provides a SEM image, 110, of a collection of hollow silver-gold alloy nanocages, 111, suitable for use with the present invention. The silver-gold alloy nanocages, 111, have at least one dimension of about 100 nm.

Example 2

[0122J FIG. 1C provides a SEM image, 120, of a collection of silver nanobars, 121 and

122, and nanocubes, 123, suitable for use with the present invention. The silver nanobars, 121 and 122, have dimensions of about 40 nm and about 160 nm, about 50 nm and about 90 nm, respectively. The silver nanocubes, 123, have at least one dimension of about 60 nm.

Example 3

FIG. ID provides a SEM image, 130, of a collection of silver "nanorice" particles, 131, suitable for use with the present invention. The silver "nanorice" particles, 131, have a width of about 60 nm and a length of about 60 nm to about 180 nm.

Example 4

FIG. IE provides a transmission electron microscope ("TEM") image, 140, of palladium nanoplates, 141 and 142, suitable for use with the present invention. Some of the palladium nanoplates, 141, have a trigonal shape and a dimension of about 15 nm to about 50 nm. Other of the palladium nanoplates, 142, have a circular or multifaceted shape and a diameter of about 20 nm to about 50 nm.

[0125] FIG. IF provides a TEM image, 150, of a collection of silver nanoplates, 151, suitable for use with the present invention. The silver nanoplates, 151, have a multifaceted shape with a diameter of about 10 nm to about 40 nm. Example 6

[0126] FIG. 1G provides a SEM image, 160, of a collection of silver right bi-pyramids,

161, suitable for use with the present invention. The silver right bi-pyramids, 161, have a dimension of about 100 nm to about 120 nm.

Comparative Example 7

[0127] A mixture of water (56% by weight) and ethylene glycol (44% by weight) was prepared. The thermal conductivity of the fluid was measured under static conditions using a KD-2 Pro Thermal Property Analyzer (Decagon Devices Inc., Pullman, WA) as 0.40 W/mK.

Example 8

[0128] Alumina particles having an average particle size of 50 nm (20% by weight) were slowly added to the solution of water and ethylene glycol described in Comparative Example 7. The alumina particles were added while constantly stirring the solution with a magnetic stirrer. The thermal conductivity of the resulting mixture was measured at 0.46 W/mK, an improvement of 15% over the solution lacking the alumina particles.

Example 9

[0129] Alumina particles having an average particle size of 50 nm (80% by weight) were slowly added to the solution of water and ethylene glycol described in Comparative Example 7. The alumina particles were added while constantly stirring the solution with a magnetic stirrer. The thermal conductivity of the resulting mixture was measured at 0.56 W/mK, an improvement of 40% over the solution lacking the alumina particles.

Example 10

[0130] Single-walled carbon nanotubes having an average length of about 1 μιη (3% by weight) and polyvinylpyrrolidone having an average molecular weight of 10 kDa to 100 kDa (0.5% by weight) were added slowly added to the solution of water and ethylene glycol described in Comparative Example 7. The resulting mixture was sonicated for about 10 minutes. The thermal conductivity of the resulting mixture was measured at 0.44 W/mK, an improvement of 10% over the solution lacking the carbon nanotubes and polyvinylpyrrolidone.

Prophetic Example A

[0131] The anisotropic nanoparticles of any of Examples 1-6, or a combination thereof, can be mixed with water to provide an aqueous nanofluid.

Prophetic Example B

[0132] The anisotropic nanoparticles of any of Examples 1-6, or a combination thereof, can be mixed with ethylene glycol to provide a non-aqueous nanofluid.

Prophetic Example C

[0133] The anisotropic nanoparticles of any of Examples 1-6, or a combination thereof, can be mixed with a mixture of water and ethylene glycol to provide an aqueous nanofluid.

Prophetic Example D

[0134] The anisotropic nanoparticles of any of Examples 1-6, or a combination thereof, can be mixed with diethylene glycol to provide a non-aqueous nanofluid.

Prophetic Example E

[0135] The anisotropic nanoparticles of any of Examples 1-6, or a combination thereof, can be mixed with propylene glycol to provide a non-aqueous nanofluid.

Prophetic Example F

[0136] The anisotropic nanoparticles of any of Examples 1-6, or a combination thereof, can be mixed with a silicone oil (available from, e.g., Acros Organics N.V., Fair Lawn, NJ) and/or a silicone grease (available from, e.g., Dow Corning, Midland, MI) to provide a non-aqueous nanofluid. Prophetic Example G

A mixture of silver and gold anisotropic nanoplates can be added to a mixture of water and ethylene glycol (50%-90% ethylene glycol in water, v/v) containing a polyvinylpyrrolidone polymer (1% by weight) to provide an aqueous nanofluid. The silver nanoplates and the gold nanoplates can be present in the nanofluid composition in a total concentration of about 0.01% to about 1% by weight.

Example 11

Fibers comprising a zinc salt (zinc nitrate) and a polymer (polyvinylpyrrolidone), 1 : 1 by weight, "Zn(nitrate)-PVP fibers") were electrospun by the following procedure. A first solution comprising zinc nitrate (1.6 M) was prepared by vortex mixing zinc nitrate in deionized water until a clear solution was provided. A second solution comprising polyvinylpyrrolidone was prepared by vortex mixing polyvinylpyrrolidone (about 0.45 g, having an average molecular weight of 1.5 million Da) in ethanol (about 3.8 mL) until a clear solution was provided. The first and second solutions were then vortex mixed with each other to provide a precursor solution. Zn(nitrate)-PVP fibers were prepared by flowing the precursor solution at a flow rate of about 0.1 mL/hr to about 0.3 mL/hr through a 23 gauge needle (a 21 to 29 gauge needle can be used) to which was applied a DC voltage of about 10 kV to about 30 kV. A collector (a metal plate, either grounded or negatively biased with a DC voltage of about -1 kV to about -10 kV) was placed about 100 mm to about 200 mm from the needle tip. Composite Zn(nitrate)-PVP fibers were collected using the collector.

Example 12

The Zn(nitrate)-PVP fibers prepared in Example 11 were converted to metallic zinc fibers by heating the nanowires and substrate to 550° C in a reducing atmosphere (4% H ₂ in N ₂ ), at a ramp rate of about 2° C per minute, holding at 550° C for about 13 hours, and then cooling the fibers to room temperature (about 21° C) over about 4 hours to provide metallic zinc fibers. Subsequent exposure of the zinc metal fibers to air resulted in the formation of a zinc oxide layer on the surface of the metal fibers, thereby providing zinc metal fibers having a zinc oxide surface layer thereon. Prophetic Example H

[0140] The zinc metal fibers of Example Ϊ2 can be broken into smaller pieces having a length of about 1 μτη to about 1 mm, and mixed with propylene glycol (or another solvent listed herein) to provide a non-aqueous fluid composition comprising a metallic fiber.

CONCLUSION

[0141] These examples illustrate possible embodiments of the present invention. While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

[0142] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forth one or more, but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.

[0143] All documents cited herein, including journal articles or abstracts, published or corresponding U.S. or foreign patent applications, issued or foreign patents, or any other documents, are each entirely incorporated by reference herein, including all data, tables, figures, and text presented in the cited documents.