WO2012158610A1

WO2012158610A1 - Temperature-assisted migration of amphiphilic nanoparticles through liquid interfaces

Info

Publication number: WO2012158610A1
Application number: PCT/US2012/037768
Authority: WO
Inventors: James M. Tour; Wei Lu
Original assignee: William Marsh Rice University
Priority date: 2011-05-13
Filing date: 2012-05-14
Publication date: 2012-11-22

Abstract

This invention discloses nanomaterial; hydrophilic moieties associated with the nanomaterial; and hydrophobic moieties associated with the nanomaterial. In some embodiments, the hydrophilic moieties and the hydrophobic moieties are associated with the nanomaterial in substantially equimolar amounts or in substantially equal weight percentages. Additional embodiments of the present invention pertain to methods of reversibly transferring the aforementioned amphiphilic nanoparticles between an aqueous phase and an organic phase of a solution in a temperature dependent manner.

Description

TITLE

TEMPERATURE-ASSISTED MIGRATION OF AMPHIPHILIC NANOPARTICLES

THROUGH LIQUID INTERFACES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 61/485,923, filed on May 13, 2011. The entirety of the aforementioned application is incorporated herein by reference.

BACKGROUND

[0002] Current methods to transport nanoparticles at or across a liquid/liquid interface have numerous limitations in terms of efficiency, reversibility and temperature sensitivity. Therefore, a need exists for new methods and compositions for the transport of nanoparticles through various liquid interfaces.

BRIEF SUMMARY

[0003] In some embodiments, the present disclosure pertains to amphiphilic nanoparticles that generally comprise: a nanomaterial; hydrophilic moieties associated with the nanomaterial; and hydrophobic moieties associated with the nanomaterial. In some embodiments, the hydrophilic moieties and hydrophobic moieties are associated with the nanomaterial in substantially equimolar amounts, or in substantially equal weight percentages.

[0004] In some embodiments, the amphiphilic nanoparticles of the present disclosure are capable of reversibly transferring between aqueous and organic phases of a solution in a temperature dependent manner. For instance, in some embodiments, the amphiphilic nanoparticles reversibly migrate to the organic phase of the solution at or above a first temperature, and to the aqueous phase of the solution at or below a second temperature. In some embodiments, the first temperature is equal to or higher than the second temperature. In some embodiments, the first temperature is at or above the melting point of the hydrophobic moieties. In some embodiments, the second temperature is at or below the melting point of the hydrophobic moieties.

[0005] In some embodiments, the nanomaterials of the amphiphilic nanoparticles include at least one of silica-based nanomaterials, magnetic nanoparticles, carbon nanomaterials, single-walled nanotubes, double-walled nanotubes, triple-walled nanotubes, multi-walled nanotubes, ultrashort nanotubes, graphene, graphene nanoribbons, graphite, graphite oxide nanoribbons, carbon carbon black, oxidized carbon black, hydrophilic carbon clusters, derivatives thereof, and combinations thereof. In some embodiments, the nanomaterial is oxidized carbon black.

[0006] In some embodiments, the hydrophilic moieties of the amphiphilic nanoparticles include at least one of alkylane glycols, alcohols, fatty acids, lactones, polyols, polyamines, saccharides, acrylonitriles, esters, polymers thereof, and combinations thereof. In some embodiments, the hydrophilic moieties comprise polyethylene glycols. In some embodiments, the hydrophilic moieties comprise poly(vinyl alcohol).

[0007] In some embodiments, the hydrophobic moieties of the amphiphilic nanoparticles include at least one of alkyl groups, phenyl groups, styrenes, ethylenes, propylenes, acrylates, polymers thereof, and combinations thereof. In some embodiments, the hydrophobic moieties of the amphiphilic nanoparticles comprise polyethylenes.

[0008] In some embodiments, the hydrophilic moieties and hydrophobic moieties of the amphiphilic nanoparticles are part of the same molecule, such as a copolymer. In some embodiments, the molecule is a copolymer of polyethylene and polyethylene glycol. In some embodiments, the hydrophilic moieties and hydrophobic moieties of the amphiphilic nanoparticles are part of separate molecules, such as separate polymers.

[0009] Additional embodiments of the present disclosure pertain to methods of transferring the aforementioned amphiphilic nanoparticles between an aqueous phase and an organic phase of a solution in a temperature dependent manner. In some embodiments, such methods generally include associating the above-mentioned amphiphilic nanoparticles with the solution to result in a migration of the amphiphilic nanoparticles to a different phase of the solution. [0010] In some embodiments, the amphiphilic nanoparticles of the present disclosure reduce the interfacial tension between the aqueous phase and the organic phase of the solution. In some embodiments, the amphiphilic nanoparticles reduce the interfacial tension between the aqueous phase and the organic phase of the solution by at least about ten fold (e.g., twenty five fold). In some embodiments, the amphiphilic nanoparticles reduce the interfacial tension between the aqueous phase and the organic phase of the solution to lower than about 0.1 dynes/cm (e.g., 0.002 dynes/cm).

[0011] The methods and particles of the present disclosure can provide numerous applications. For instance, in various embodiments, the amphiphilic nanoparticles of the present disclosure could be used in enhanced oil recovery, phase transfer catalysis, fuel cells, and the solubilization of asphaltenes.

BRIEF DESCRIPTION OF THE FIGURES

[0012] FIGURE 1 depicts structures and schemes related to various amphiphilic nanoparticles. FIG. 1A shows the chemical structure of oxidized carbon black (OCB) covalently coupled to diblock copolymers of polyethylene-polyethylene glycol (PE-b-PEG-OCB). FIG. IB shows a schematic illustration of reversible phase transfer of PE-b-PEG-OCBs across the water/oil interface based on the temperature-dependent solubility of the hydrophobic block of the diblock copolymer. FIG. 1C shows the corresponding structures of the PE-b-PEG-OCBs in the aqueous and oil phases at different temperatures. FIG. ID provides a scheme for the preparation of PE-b- PEG-OCBs. FIG. IE shows the phase distribution of amphiphilic nanoparticles that are covalently linked to both hydrophobic and hydrophilic polymers rather than using block polymer systems as in FIG. 1A.

[0013] FIGURE 2 shows photographs of a two-phase mixture of sea brine and isooctane that contain PE-b-PEG-OCBs (the concentration of the PE-b-PEG-OCB in sea brine was 50 mg/L, 1400 Mn PE-b-PEG). FIGS. 2A-B show pictures of the mixture before (FIG. 2A) and after (FIG. 2B) phase transfer caused by heating at 110 °C for 20 min. FIG. 2C shows a picture of the mixture after stirring at room temperature for 1 h upon cooling. FIGS. 2D-2E show transmission electron microscopy (TEM) images of PE-b-PEG-OCBs in sea brine (FIG. 2D) and isooctane (FIG. 2E). The scale bars are 10 nm.

[0014] FIGURE 3 shows photographs of PE-b-PEG-OCBs in sea brine solution at 105 °C (FIG. 3A) and at 25 °C (FIG. 3B). FIG. 3C shows a differential scanning calorimetry (DSC) curve of 1400 Mn PE-b-PEG. The concentration of PE-b-PEG-OCBs was -50 mg/L.

[0015] FIGURE 4 shows sequential photographs of reversible transfer of PE-b-PEG-OCBs through a water/oil interface containing deionized (DI) water and isooctane. Photographs of the solution are shown before heating (FIG. 4A), after 1 hour of heating at 110 °C (FIG. 4B), after 6 hours of heating at 110 °C (FIG. 4C), after 26 hours of heating at 110 °C (FIG. 4D), and after cooling down to room temperature (FIG. 4E).

[0016] FIGURE 5 shows optical micrograph of emulsified isooctane droplets in water stabilized by 1400 Mn PE-b-PEG coated OCB. The scale bar is 50 μιη.

[0017] FIGURE 6 shows a photograph of a sealed ampoule loaded with PE-b-PEG-OCB and equal volumes of DI water and isooctane.

[0018] FIGURE 7 shows a TEM image of OCB. The fingerprint-like structure in the image is the OCB with a diameter between 30-40 nm.

[0019] FIGURE 8 shows UV-vis spectra of PE-b-PEG-OCBs (NP) in sea brine solution before (black solid line) and after phase transfer (red solid line) to isooctane. The characteristic adsorption peak of PE-b-PEG-OCB solution is around 280 nm. Based on Lambert-Beer's law, only 6% of PE-b-PEG-OCB is left in the sea brine solution after phase transfer.

[0020] FIGURE 9 shows photographs of a two-phase mixture of sea brine and isooctane that contain PE-b-PEG-OCBs (the concentration of OCB in sea brine was 50 mg/L, 1400 Mn PE-b- PEG). Photographs of the solution are shown before heating and phase transfer (FIG. 9A), after phase transfer caused by heating at 90 °C for one week (FIG. 9B), and after cooling for 1 hour (FIG. 9C). [0021] FIGURE 10 shows a DSC curve of a 920 Mn PE-b-PEG. The peak at 85.9 °-C is attributed to the main crystalline phase of the PE block, while the one at 47 ^QC is associated with the PEG block.

[0022] FIGURE 11 shows photographs of a two-phase mixture of sea brine and isooctane that contain 920 Mn PE-b-PEG-OCBs (the concentration of OCB in sea brine was -50 mg/L, 920 Mn PE-b-PEG). Photographs of the solution are shown before heating and phase transfer (FIG. 11A), after phase transfer caused by heating at 110 °C for 20 minutes (FIG. 11B), and after cooling to room temperature (FIG. 11C).

[0023] FIGURE 12 shows photographs of a two-phase mixture of sea brine and isooctane that contain 2250 Mn PE-b-PEG-OCBs (the concentration of OCB in sea brine was -50 mg/L, 2250 Mn PE-b-PEG). Photographs of the solution are shown before heating and phase transfer (FIG. 12A), after phase transfer caused by heating at 110 °C for 1 hour (FIG. 12B), and after being stirred at room temperature for 1 hour (FIG. 12C). FIG. 12D shows a photograph of 2250 Mn PE-b-PEG in isooctane (100 mg/12 mL isooctane) that is being heated at 110 °C for 20 min and shaken. Emulsion was formed due to the lower solubility of 2250 Mn PE-b-PEG in the isooctane.

DETAILED DESCRIPTION

[0024] It is to be understood that both the foregoing general description and the following detailed description are illustrative and explanatory, and are not restrictive of the subject matter, as claimed. In this application, the use of the singular includes the plural, the word "a" or "an" means "at least one", and the use of "or" means "and/or", unless specifically stated otherwise. Furthermore, the use of the term "including", as well as other forms, such as "includes" and "included", is not limiting. Also, terms such as "element" or "component" encompass both elements or components comprising one unit and elements or components that comprise more than one unit unless specifically stated otherwise.

[0025] The section headings used herein are for organizational purposes and are not to be construed as limiting the subject matter described. All documents, or portions of documents, cited in this application, including, but not limited to, patents, patent applications, articles, books, and treatises, are hereby expressly incorporated herein by reference in their entirety for any purpose. In the event that one or more of the incorporated literature and similar materials defines a term in a manner that contradicts the definition of that term in this application, this application controls.

[0026] A fundamental understanding of the physical and chemical properties of the water/oil interface is an important aspect of environmental and energy-related research, owing to its applicability to a variety of biologically relevant systems and phenomena. Recently, nanoparticles (NPs) at/across the liquid/liquid interface, especially the water-oil interface, have been investigated for potential applications in phase transfer catalysis, fuel cells and enhanced oil recovery (EOR).

[0027] Generally, it is desirable for NPs to be rendered amphiphilic in order for them to become soluble in both aqueous and organic phases before and after transport. The initial development of phase-transfer NPs utilized metal NPs to transfer water-soluble metal salts from the aqueous phase to the organic phase in the presence of a phase-transfer reagent and a reducing reagent. Then, phase-transfer NPs were made by ligand exchange followed by electrostatic interaction, lipid-based amphiphilic surface coating, and bilayer stabilization. However, transfers from the aqueous phase to the organic phase (or vice versa) are generally irreversible using those aforementioned methods.

[0028] Thus, much effort has been devoted to exploring the reversible transfer of NPs through the interface triggered by an external stimulus. Reversibly moving surfactant- stabilized metal NPs across water/oil interface can be achieved by tuning the pH-induced acid-base interactions of the surfactants, which requires addition of acid or base during phase transfer, or using the temperature-driven hydrophobic effect of small organic molecules, which lacks versatility.

[0029] The first example of using intrinsically temperature-responsive polymer brush for reversible transport of NPs through the water/ethyl acetate interface was reported by Zhao et al., who exploited the thermally induced hydration/dehydration effect of poly(methoxytri(ethylene glycol) methacrylate). Langmuir 2007, 23, 2208-17. Similarly, Edwards et al. developed branched water-soluble copolymers based on 2-(2-methoxyethoxy) ethyl methacrylate and oligo (ethylene glycol) methacrylate for initiating the reversible transfer across a liquid interface by the "salting out" of oligo (ethylene glycol) at low to elevated temperatures. Angew. Chem. Int. Ed. 2008, 120, 326-329.

[0030] However, the correlation between the interface transfer of NPs and the physical characteristics of the polymer coatings, such as molecular weight, melting temperature and the weight percent of the hydrophilic block, has not yet been fully investigated or developed. Furthermore, a need exists for the development of more effective methods of transferring nanoparticles through liquid interfaces. The present invention addresses this need.

[0031] In some embodiments, the present disclosure provides methods of reversibly transferring amphiphilic nanoparticles between an aqueous phase and an organic phase of a solution in a temperature dependent manner. See, e.g., FIGS. IB and IE. Additional embodiments of the present disclosure pertain to the amphiphilic nanoparticles that are used in the methods of the present disclosure. [0032] Amphiphilic Nanoparticles

[0033] Amphiphilic nanoparticles of the present disclosure generally refer to nanomaterials that are associated with hydrophilic moieties and hydrophobic moieties. See, e.g., FIG. 1. As set forth in more detail below, the amphiphilic nanoparticles of the present disclosure may include various nanomaterials that may be associated with various hydrophobic and hydrophilic moieties in various manners.

[0034] Nanomaterials

[0035] In some embodiments, nanomaterials associated with the amphiphilic nanoparticles of the present disclosure may include, without limitation, silica-based nanomaterials, magnetic nanoparticles, carbon nanomaterials, single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs), triple-walled nanotubes (TWNTs), multi-walled nanotubes (MWNTs), ultra-short nanotubes (USNTs), graphenes, graphene nanoribbons (GNRs), graphite, graphite oxide nanoribbons, carbon black, oxidized carbon black, hydrophilic carbon clusters (HCCs), derivatives thereof, and combinations thereof. In some embodiments, the nanomaterial is oxidized carbon black.

[0036] In more specific embodiments, the nanomaterials may include HCCs. HCCs are also referred to as ultra-short SWNTs (US-SWNTs). Therefore, for the purposes of the present disclosure, US-SWNTs are synonymous with HCCs. In some embodiments, HCCs can include oxidized carbon nanoparticles that are about 30 nm to about 40 nm long, and approximately 1-2 nm wide. In some embodiments, US-SWNTs (i.e., HCCs) may be produced by reacting SWNTs in fuming sulfuric acid with nitric acid to produce a shortened carbon nanotube characterized by opening of the nanotube ends. Such methods are disclosed in Applicants' co-pending U.S. Pat. App. No. 12/280,523, entitled "Short Functionalized, Soluble Carbon Nanotubes, Methods of Making Same, and Polymer Composites Made Therefrom." This may be followed by the functionalization of the plurality of carboxylic acid groups. In some embodiments, the HCC may be an oxidized graphene. [0037] The nanomaterials of the present disclosure may be modified in various ways. For instance, in some embodiments, the nanomaterials of the present disclosure may be oxidized. In some embodiments, the nanomaterials of the present disclosure may be functionalized with one or more hydrophilic and hydrophobic moieties.

[0038] Hydrophilic Moieties

[0039] Hydrophilic moieties generally refer to molecules, polymers, chemical groups, solubilizing groups, domains within molecules or polymers, and functional groups that have hydrophilic properties. In some embodiments, hydrophilic moieties may include, without limitation, at least one of alkylane glycols, alcohols, fatty acids, lactones, polyols, polyamines, saccharides, acrylonitriles, esters, polymers of such molecules, and combinations of such molecules. In more specific embodiments, the hydrophilic moieties may include polyethylene glycols (PEGs). More specific examples of hydrophilic moieties include, without limitation, polypropylene glycol (PPG), poly(p-phenylene oxide) (PPOs), poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), poly(vinyl amine), sorbitols, polyvinylpyrrolidiones, polyacrylonitriles, tetradecanols, polyesters, poly(dimethylamino)ethyl methacrylates (PDMA), poly(ethylene imine) and combinations thereof.

[0040] The hydrophilic moieties of the present disclosure may also be associated with nanomaterials in various manners. For instance, in some embodiments, the hydrophilic moieties may be non-covalently associated with nanomaterials, such as through sequestration, adsorption, ionic bonding, dipole-dipole interactions, hydrogen bonding, Van der Waals interactions, and other types of non-covalent associations.

[0041] In some embodiments, the hydrophilic moieties of the present disclosure may be covalently associated with nanomaterials. For instance, in some embodiments, the hydrophilic moieties of the present disclosure may be covalently associated with a nanomaterial through a linker molecule, through a chemical moiety, or through a direct chemical bond between the hydrophilic moieties and the nanomaterial. In some embodiments, the hydrophilic moieties may be covalently associated with the nanomaterial through a cleavable moiety, such as an ester bond or an amide bond. In some embodiments, the cleavable moiety may be a photo-cleavable moiety or a pH sensitive cleavable moiety. Additional modes by which hydrophilic moieties may be covalently or non-covalently associated with nanomaterials can also be envisioned.

[0042] Hydrophobic Moieties

[0043] Hydrophobic moieties generally refer to molecules, polymers, chemical groups, domains within molecules or polymers, and functional groups that have hydrophobic properties. In some embodiments, hydrophobic moieties may include, without limitation, at least one of alkyl groups, phenyl groups, styrenes, ethylenes, propylenes, acrylates, polymers of such molecules, and combinations of such molecules. In more specific embodiments, the hydrophobic moieties may include, without limitation, polyvinyl chloride (PVC), polystyrene (PS), high impact polystyrene (HIPS), polypropylene (PP), polymethyl methacrylate (PMMA) and combinations thereof. In further embodiments, the hydrophobic moieties may include polyethylenes (PE).

[0044] The hydrophobic moieties of the present disclosure may also be associated with nanomaterials in various manners. For instance, in some embodiments, the hydrophobic moieties may be non-covalently associated with nanomaterials, such as through sequestration, adsorption, ionic bonding, dipole-dipole interactions, hydrogen bonding, Van der Waals interactions, and other types of non-covalent associations.

[0045] In some embodiments, the hydrophobic moieties of the present disclosure may be covalently associated with nanomaterials. For instance, in some embodiments, the hydrophobic moieties of the present disclosure may be covalently associated with a nanomaterial through a linker molecule, through a chemical moiety, or through a direct chemical bond between the hydrophobic moieties and the nanomaterial. In some embodiments, the hydrophobic moieties may be covalently associated with the nanomaterial through a cleavable moiety, such as an ester bond or amide bond. In some embodiments, the cleavable moiety may be a photo-cleavable moiety or a pH sensitive cleavable moiety. Additional modes by which hydrophobic moieties may be covalently or non-covalently associated with nanomaterials can also be envisioned. [0046] Variations and Properties

[0047] The association of hydrophilic and hydrophobic moieties with nanomaterials may have additional variations. For instance, in some embodiments, the nanomaterials may be associated with equimolar amounts or substantially equimolar amounts of hydrophilic moieties and hydrophobic moieties. In some embodiments, nanomaterials may have equal weight percentages or substantially equal weight percentages of hydrophilic moieties and hydrophobic moieties. In some embodiments, the hydrophilic moieties and hydrophobic moieties may be part of the same molecule. In some embodiments, the molecule that contains the hydrophilic and hydrophobic moieties may be a copolymer, such as diblock or triblock copolymers with various hydrophilic and hydrophobic domains. In some embodiments, the copolymer may have an equal weight percentage or equimolar amounts of hydrophobic moieties and hydrophilic moieties. In some embodiments, the molecule that contains the hydrophilic and hydrophobic moieties may be a triblock copolymer system with various hydrophilic and hydrophobic domains. In some embodiments, the nanomaterials may be associated with non-equimolar amounts or un-equal weight percentages of hydrophilic moieties and hydrophobic moieties.

[0048] In more specific embodiments, the hydrophobic moieties and hydrophilic moieties may be a copolymer of polyethylene and polyethylene glycol (e.g., PE-b-PEG, as shown in FIG. 1). In further embodiments, the hydrophobic moieties and hydrophilic moieties may be a poly[2- (dimethylamino)ethyl methacrylate -block-methyl methacrylate] (PDMA-PMMA) diblock copolymer.

[0049] In further embodiments, the hydrophobic moieties and hydrophilic moieties may be separate molecules or polymers. For instance, in some embodiments, hydrophobic moieties associated with nanomaterials may include a hydrophobic polymer, such as PMMA, PE or combinations of such polymers. Likewise, hydrophilic moieties associated with nanomaterials may include a hydrophilic polymer, such as PDMA , PEG, or combinations of such polymers.

[0050] In further embodiments, more than two polymer types could be appended to nanomaterials. In some embodiments, the different polymer types may uncoil at various temperatures, and in various environments. In some embodiments, one type of polymer could have two types of hydrophobic moieties and one type of hydrophilic moiety. In further embodiments, a polymer may include a hydrophobic moiety, a hydrophilic moiety, and a pH sensitive moiety, for example. In some embodiments, the nanomaterials of the present disclosure may be associated with a Brij polymer, such as a block polymer containing short chain alkyl groups and PEGs.

[0051] The amphiphilic nanoparticles of the present disclosure can have numerous properties. In some embodiments, the amphiphilic nanoparticles are capable of reversibly transferring between organic and aqueous phases of a solution in a temperature dependent manner. For instance, in some embodiments, the amphiphilic nanoparticles reversibly migrate to the organic phase of the solution at or above a first temperature, and to the aqueous phase of the solution at or below a second temperature. In some embodiments, the first temperature is equal to or higher than the second temperature. In some embodiments, the first temperature is at or above the melting point of the hydrophobic moieties. In some embodiments, the second temperature is at or below the melting point of the hydrophobic moieties. Hence, in some embodiments, the migration temperature of the amphiphilic nanoparticles to another phase of a solution can be tuned by changing the length of the hydrophobic moiety, or by selecting hydrophobic moieties with particular melting points.

[0052] In more specific embodiments, amphiphilic nanoparticles containing diblock copolymers with hydrophobic and hydrophilic moieties can transfer through a water/oil interphase at specific temperatures that correspond to the melting point of the hydrophobic block of the diblock copolymer. In such embodiments, the phase inversion temperature could be adjusted by changing the molecular weight of the hydrophobic block.

[0053] Methods of Transferring Amphiphilic Nanoparticles Through Solution Interfaces

[0054] Additional embodiments of the present disclosure pertain to methods of transferring the aforementioned amphiphilic nanoparticles between an aqueous phase and an organic phase of a solution in a temperature dependent manner. See, e.g., FIGS. IB and IE. In some embodiments, the methods of the present disclosure may involve associating one or more of the aforementioned amphiphilic nanoparticles with a desired solution, such as a mixture of oil and water in an oil well. In some embodiments, the associating can occur by adding the amphiphilic nanoparticles to the solution.

[0055] In some embodiments, the methods of the present disclosure may also involve a step of adjusting the temperature of the solution to result in the migration of the amphiphilic nanoparticles to a different phase of the solution. For instance, in some embodiments, the adjusting may include increasing the temperature of the solution to or above a first temperature to result in the reversible migration of the amphiphilic nanoparticles to the organic phase of the solution. In some embodiments, the adjusting may include decreasing the temperature of the solution to or below a second temperature to result in the reversible migration of the amphiphilic nanoparticles to the aqueous phase of the solution.

[0056] In more specific embodiments, the adjusting may include increasing the temperature of the solution above the melting point of the hydrophobic moieties of the amphiphilic nanoparticles. This in turn can result in the migration of the amphiphilic nanoparticles to the organic phase of the solution. In some embodiments, the adjusting may include decreasing the temperature of the solution below the melting point of the hydrophobic moieties. This in turn can result in the migration of the amphiphilic nanoparticles to the aqueous phase of the solution. In some embodiments, the adjusting of the temperature occurs automatically, or in response to the environment, such as in response to a change in the temperature of an oil well between the surface and subsurface temperatures. For instance, the amphiphilic particles could be injected into the well in the water phase, and then at the subsurface elevated temperature, the nanoparticles could transfer to the oil phase or reside at the surface of the oil-water phase, thereby lowering the interfacial tension and freeing the oil droplet to create a microemulsion of the oil in the water phase. Once the microemulsion approaches or reaches the lower surface temperature at the exit of the oil well, the amphiphilic nanoparticle could migrate back into the aqueous phase. This simple migration between the two phases would ease the laborious separation that is often required of surfactants in enhanced oil recovery (EOR) processes.

[0057] In some embodiments, the migration of the amphiphilic nanoparticles between the organic phase and the aqueous phase of a solution can be reversible. For instance, in some embodiments, an increase in the temperature of the solution to or above a first temperature (e.g., the melting point of the hydrophobic moieties of the amphiphilic nanoparticles, in some embodiments) can result in the migration of the amphiphilic nanoparticles from the aqueous phase to the organic phase of the solution. A subsequent decrease in the temperature of the solution to or below a second temperature (e.g., the melting point of the hydrophobic moieties of the amphiphilic nanoparticles, in some embodiments) can then result in the migration of the amphiphilic nanoparticles back to the aqueous phase. See, e.g., FIG. 2.

[0058] Without being bound by theory or mechanism, it is envisioned that the temperature- dependent transfer of amphiphilic nanoparticles between organic and aqueous phases of a solution can occur due to structural changes within the hydrophobic and hydrophilic moieties. See, e.g., FIGS. 1C and IE. For instance, at temperatures at or below a second temperature (e.g., temperatures at or below the melting point of the hydrophobic moieties), the hydrophobic moieties may be in a collapsed state, and the hydrophilic moieties may be in an expanded state. This can in turn result in the solubility of the amphiphilic nanoparticles in the aqueous phase of a solution. In contrast, at temperatures at or above a first temperature (e.g., temperatures at or above the melting point of the hydrophobic moieties), the hydrophobic moieties may be in an expanded state, and the hydrophilic moieties may be in a collapsed state. This can in turn result in the solubility of the amphiphilic nanoparticles in the organic phase of the solution.

[0059] The melting point of hydrophobic moieties of amphiphilic nanoparticles can be determined by various methods. In some embodiments, differential scanning calorimetry (DSC) or dynamic mechanical analysis (DMA) may be used to determine the melting point of the hydrophobic moieties associated with a carbon nanomaterial. See, e.g., FIGS. 3 and 10. Additional methods of determining the melting point of hydrophobic moieties of amphiphilic nanoparticles may also be envisioned.

[0060] Solutions

[0061] The amphiphilic naoparticles of the present disclosure may be applied to various solutions. In some embodiments, the solutions may be mixtures of organic solvents and aqueous solvents. In some embodiments, the organic solvents may include, without limitation, diesel, kerosene, oil, crude oil, pentane, cyclopentane, hexane, cyclohexane, dimethyl formamide (DMF), chloroform, isooctane, tetradhydrofuran, benzene, toluene, 1,4-dioxane, diethyl ether, and combinations thereof. In some embodiments, the aqueous solvents may include, without limitation, water, brine, calcium salts, sodium salts, potassium salts, magnesium salts, barium salts, barite, seawater, synthetic seawater, API brine, acetic acid, ethanol, methanol, n-propanol, isopropanol, n-butanol, formic acid, and combinations thereof.

[0062] In some embodiments, the solutions may be mixtures of oil and water. In such instances, the water would correspond to the aqueous phase of the solution, and the oil would correspond to the organic phase of the solution.

[0063] Temperature Adjustment

[0064] Various methods may be used to adjust the temperature of solutions in order to initiate the transfer of amphiphilic nanoparticles between aqueous and organic phases of a solution. For instance, in some embodiments, the temperature of the solution may be adjusted by associating the solution with heating devices or cooling devices until a desired temperature is reached. In some embodiments, the temperature of the solution may be adjusted by placing the solution in an environment that is at a desired temperature. For instance, in some embodiments, the solution containing the amphiphilic nanoparticles may be placed in an incubator or an oven until a desired temperature is reached.

[0065] In some embodiments, the temperature of solutions is adjusted automatically by equilibration to the surface and subsurface of a well, such as an oil well. For instance, in some embodiments, as the NPs are injected downhole with an aqueous phase, they warm due to thermal equilibration from the well at the depth temperature, whereupon they move to the organic phase. Upon reaching the surface at the production site, they cool back to atmospheric temperature and transfer back to the aqueous phase upon equilibration with the surface atmosphere temperature. In some embodiments, temperature adjustment may include cooling upon reaching the ocean water temperature of the pipe. [0066] In further embodiments, the temperature of a solution may be adjusted by the addition of various substances to the solution, such as liquids at desired temperatures, ice cubes, and the like. Additional modes of adjusting the temperature of a solution can also be envisioned.

[0067] In some embodiments, the methods and amphiphilic nanoparticles of the present disclosure can reduce the interfacial tension between the aqueous phase and the organic phase of a solution. In some embodiments, the amphiphilic nanoparticles reduce the interfacial tension between the aqueous phase and the organic phase of the solution by at least about ten fold (e.g., twenty five fold). In some embodiments, the amphiphilic nanoparticles can reduce the interfacial tension between the aqueous phase and the organic phase of the solution to lower than about 1 dynes/cm (e.g., 0.002 dynes/cm). In some embodiments, the amphiphilic nanoparticles can reduce the interfacial tension between the aqueous phase and the organic phase of the solution to lower than about 0.1 dynes/cm (e.g., about 0.002 dynes/cm to about 0.001 dynes/cm). In more specific embodiments, the amphiphilic nanoparticles of the present disclosure can reduce the interfacial tension between the aqueous phase and the organic phase of the solution from about 50 dynes/cm to about 0.001 dynes/cm.

[0068] Methods of Making Amphiphilic Nanoparticles

[0069] Various methods may be used to make the amphiphilic nanoparticles of the present disclosure. In some embodiments, the methods may involve associating a nanomaterial with hydrophobic and hydrophilic moieties, as previously described. In some embodiments, various coupling reagents may be utilized to covalently couple the hydrophobic and hydrophilic moieties to the nanomaterials. In further embodiments, radical transfer reactions may be utilized to couple hydrophilic and hydrophobic moieties to nanomaterials.

[0070] FIG. ID depicts a specific method of making amphiphilic nanoparticles. In this embodiment, amphiphilic oxidized carbon black (OCB) was prepared by coating oxidized carbon black with hydroxy-terminated diblock copolymers of PE-b-PEG via a DCC (Ν,Ν'- dicyclohexylcarbodiimide) coupling reaction between the end hydroxyl group of PE-b-PEG and carboxylic groups on OCB. [0071] Applications

[0072] The methods and particles of the present disclosure can provide numerous applications. For instance, in some embodiments, the methods and amphiphilic nanoparticles of the present disclosure can be used for enhanced oil recovery. In more specific embodiments, the methods and amphiphilic nanoparticles of the present disclosure could be used to modify the interfacial tension between the oil and water phases for enhanced oil recovery. In such embodiments, the methods and amphiphilic nanoparticles of the present disclosure could help move entrapped oil particles, residual oil particles or otherwise slower to migrate oil particles into the aqueous phase.

[0073] Unlike typical surfactants, the amphiphilic nanoparticles of the present disclosure can phase separate back to the aqueous phase when they approach or reach surface temperatures. Thus, the amphiphilic nanoparticles of the present disclosure could facilitate oil recovery and be recycled for reinjection. Furthermore, the amphiphilic nanoparticles of the present disclosure can help avoid laborious protocols for separating enhanced oil recovery surfactants from organic phases of crude mixtures before re-injection.

[0074] In further embodiments, the methods and amphiphilic nanoparticles of the present disclosure can be used for phase transfer catalysis. For instance, the methods and amphiphilic nanoparticles of the present disclosure can be used as smart carriers for facilitating the migration of a reactant from one phase into another phase in heterogeneous catalytic reactions. In some embodiments, the amphiphilic nanoparticles of the present disclosure can be used to reduce the water/oil interfacial tension. In some embodiments, the amphiphilic nanoparticles of the present disclosure can be used to solubilize various compositions, such as asphaltenes.

[0075] Additional Embodiments

[0076] Reference will now be made to more specific embodiments of the present disclosure and experimental results that provide support for such embodiments. However, Applicants note that the disclosure below is for illustrative purposes and is not intended to limit the scope of the claimed subject matter in any way. [0077] The Examples below pertain to temperature-driven reversible migration of amphiphilic nanoparticles through the water/oil interface. In particular, the Examples below pertain to the preparation of amphiphilic carbon nanoparticles capable of reversibly transferring through the water/oil interface. In these Examples, nanosized carbon black was oxidized and then functionalized with amphiphilic diblock polyethylene-b-polyethylene glycol (PE-b-PEG) copolymers that were water-soluble at low-to-moderate temperatures but oil- soluble at high temperatures. The correlation between the phase transfer temperature and the melting temperature of the hydrophobic block of the copolymers and weight percent of hydrophilic block was investigated. The amphiphilic nanoparticles were used to stabilize oil droplets for demonstrating potential applications in reducing the water/oil interfacial tension.

[0078] In particular, Applicants demonstrate the rational design and synthesis of temperature- responsive nanoparticles (NPs) that are capable of reversibly migrating across the water/oil interface by choosing amphiphilic diblock copolymers with the appropriate content of the hydrophilic block and molecular weight. Also demonstrated is a new type of stimuli-responsive amphiphilic diblock copolymers with aqueous solubility at low-to-moderate temperatures and oil solubility at high temperatures for the reversible phase transfer, in combination with the known decrease in hydrophilic block water- solubility via dehydration.

[0079] Amphiphilic carbon-based NPs that could migrate to the oil phase at the temperature corresponding to the melting temperature of the hydrophobic block of the diblock copolymers were prepared. The inexpensive and non-toxic oxidized carbon black (OCB) was used as the core and polyethylene-polyethylene glycol (PE-b-PEG) diblock copolymers were used as the shell. Those diblock copolymers are composed of hydrophilic blocks that form ester linkages with the OCB (i.e., PEGs), and hydrophobic blocks that are oil-soluble at high temperatures (i.e., PEs). In particular, and without being bound by theory, PE blocks collapse in the aqueous phase but straighten in the oil phase due to their oil solubility at high temperature, while PEG blocks collapse in the oil phase but strengthen in the aqueous phase. See, e.g., FIGS. IB and 1C. [0080] Example 1. Phase Transfer of PE-fr-PEG-OCBs

[0081] It was observed that, upon heating at 110 °C, PE-b-PEG-OCBs in a sea brine/isooctane solution could migrate from the aqueous phase (sea brine) to the oil/organic phase (isooctane) overnight. See FIG. 2B. In addition, it was observed that the phase transfer could be completed in 20 min by vigorous stirring. Without being bound by theory, it is envisioned that this facile phase transfer could be due to the increased interfacial area induced by strong agitation.

[0082] PE-b-PEG-OCBs migrated back to the aqueous phase upon cooling, as illustrated in FIG. 2C. In addition, the phase-transfer process was accompanied by a change in the color of the mixtures. In particular, the aqueous phase in FIG. 2 was black before phase transfer and became colorless after phase transfer. On the other hand, the oil phase was colorless before phase transfer and became black after phase transfer.

[0083] Transmission electron microscope (TEM) was used to examine the size of PE-b-PEG- OCBs in the aqueous and oil phases. FIGS. 2D-E show the TEM images of the NPs before and after phase transfer, respectively. The spots highlighted in red are black carbon cores and the amorphous materials surrounding those black cores may be the diblock copolymers. No observable aggregation or size change could be identified, compared to the OCB. See FIG. 7.

[0084] Applicants also investigated the transfer efficiency of PE-b-PEG-OCBs through the interface by calculating the amount of nanoparticles in the sea brine after phase transfer. See FIG. 8. It was found that only 6% of the nanoparticles remained in the aqueous phase.

[0085] Example 2. Temperature-dependent Solubility of PE-6-PEG-OCBs

[0086] Since no phase transfer was observed at low-to-moderate temperatures, Applicants studied the temperature-dependent solubility of PE-b-PEG-OCBs in isooctane at high temperatures. As shown in FIGS. 3A-B, PE-b-PEG-OCBs were well dispersed in isooctane at high temperatures but precipitated as soon as the oil bath was removed, implying a temperature- dependent solubility in the oil phase. As shown in FIG. 3C, the differential scanning calorimetry (DSC) measurement of 1400 Mn was observed for PE-b-PEG. The characteristic melting peak at 105 °C is apparent, corresponding to the main crystalline phase of the PE block. The shoulder peak at 94 °C corresponds to a secondary, less ordered crystalline phase associated with the PE block.

[0087] Example 3. Temperature-dependent Phase Transfer of PE-6-PEG-OCBs

[0088] As illustrated in FIG. 9, phase transfer of PE-b-PEG-OCBs across the sea brine/isooctane phase also occurred at a lower temperature (90 °C). However, the phase transfer took about one week to complete. Without being bound by theory, such results indicate that transportation across the aqueous/organic interface is dependent on the kinetics of the PE-b-PEG dissolution in the isooctane phase.

[0089] To determine if the phase transfer could be solely driven by temperature, Applicants mixed PE-b-PEG-OCB/deionized water (DI water) solution with an equal volume of isooctane in a sealed ampoule to prevent solvent loss. See FIG. 6. Upon heating at 110 °C, PE-b-PEG-OCBs transferred from the DI water into the organic phase without the presence of salt ions. See FIG. 4. Such results were contrary to the previous work in which salt ions were required to lower the solubility of the oligo (ethylene glycol) methacrylate block and thus drive the nanoparticles into the oil phase. The sequential photographs indicate that the formation of isooctane droplets (FIG. 4B) at the interface was the first step for phase transfer: oil-in-water droplets were formed (FIG. 4B) and gradually dissolved in the oil layer (FIGS. 4C-D, respectively) as a result of the increased oil-solubility of PE blocks at high temperature. This further confirms that the solubility-dependent phase-transfer process is controlled by temperature. However, it is envisioned that the introduction of salt could speed up the phase transportation process.

[0090] Example 4. Role of PE-6-PEGs on PE-6-PEG-OCB Phase Transfer

[0091] Although the reversible phase transfer of polymer-coated nanoparticles across the liquid/liquid interface has been demonstrated based on the temperature-driven hydration/dehydration of the surfactant coatings, the important link between the intrinsic properties of the polymer coating and the corresponding phase transfer have not been explored. Here, Applicants demonstrate the first correlation between the characteristic properties of polymer coatings and the temperature-driven phase transfer process. Due to the dependency of melting temperature on the molecular weight, PE-b-PEG diblock copolymers with Mn around 2250, 920, and 575 were also used for tuning the phase transfer temperature. Only 920 Mn PE- b-PEG coated OCB reversibly moved across the water/oil interface at a relatively low temperature (90 °C) in 20 min. However, 575 Mn PE-b-PEG coated OCBs was not water- soluble. In addition, 2250 Mn PE-b-PEG coated OCBs did not move into the isooctane phase even when heated at 110 °C for 1 h. See FIG. 12.

[0092] Next, Applicants aimed to identify the common feature of the diblock copolymers that do transfer across the water/oil interface. Applicants observed that all of those copolymers have an equal wt of hydrophobic and hydrophilic blocks: 575 Mn PE-b-PEG only has 20 wt ethylene oxide in the backbone and the corresponding PE-b-PEG-OCB was insoluble in water; 2250 Mn PE-b-PEG only has 20 wt ethylene in the backbone and therefore the corresponding PE-b- PEG-OCB did not move into the isooctane phase even at 110 °C, because of the insufficient PE block content. Hence, and without being bound by theory, it is envisioned that reversible phase transportation can be triggered in some embodiments by diblock copolymers with equal wt of hydrophobic and hydrophilic blocks. Furthermore, it is envisioned that, in some embodiments, as the molecular weight of the copolymer increases, the temperature that is required for faster phase transfer also increases.

[0093] Due to its amphiphilicity, PE-b-PEG-OCBs were used to stabilize oil droplets for potential applications in reducing water/oil interfacial tension. Equal volumes of PE-b-PEG- OCB solutions and isooctane were mixed and magnetically stirred overnight. Successful emulsification was obtained with the 920 Mn and 1400 Mn PE-b-PEG copolymer-coated NPs. Stable oil-in-water emulsions were verified by optical microscopy and a bimodal distribution of stable oil-in-water emulsion droplets was observed in the image. Most droplets were 30-60 μιη in diameter, but smaller droplets with diameters ranging from 1 to 10 μιη were also present. Without being bound by theory, those amphiphilic nanoparticles could potentially reduce the interfacial tension of the water-oil interfacial tension due to emulsification caused by increased oil solubility at high temperature. [0094] In conclusion, Applicants have shown that diblock copolymer-coated carbon black nanoparticles (NPs) can reversibly transfer across the water/oil interface in a process solely driven by temperature. Introducing salt ions could accelerate the phase-transfer process due to the lower solubility of the copolymers in water (i.e., the "salting out" effect). Also shown here is that, contrary to hydration/dehydration-induced phase transfer because of temperature, the solubility of the hydrophobic blocks increases as the temperature increases, favoring the transportation of OCB into the isooctane phase. More importantly, a correlation between the phase-transfer behavior and the intrinsic properties of the copolymers is described. Through emulsification of oil droplets with amphiphilic NPs, Applicants have demonstrated the potential applications of those polymer-coated NPs for reducing interfacial tension owing to the increased oil-solubility. The flexibility of choosing diblock copolymers with different molecular weight enables systematic variations in temperatures at which phase transfer occurs to engineer the stabilization of oil droplets for potential applications in EOR. Taking advantage of temperature- dependent solubility, the present approach could also open new directions for designing temperature-responsive polymers in the applications of phase-transfer catalysts. This can facilitate the simple recovery and reuse of the NPs relative to the conventional surfactants, the latter requiring more extensive separation from the oil phase upon reaching the recovery hole.

[0095] Example 5. Materials and Characterizations

[0096] Unless specified, all chemicals were purchased from Sigma- Aldrich and used without further purification unless otherwise stated. CaCl₂-2H₂0, MgCl₂-6H₂0, NaCl, KC1, NaHC0₃, and Na₂SC"4 were purchased from Fisher Scientific (USA). Carbon black (Vulcan 9A32) was donated by Cabot. Dialysis bags (MWCO 5,000) were purchased from CelluSep HI. The nanoparticle solution was placed onto a carbon-coated copper grid, dried at 60 ^QC overnight and imaged by a JEOL 2100 field emission gun transmission electron microscope (TEM) with an accelerating voltage of 200 kV. DSC measurements were performed on a TA instrument (DSC, Q10). The sample was capped in aluminum pan, heated to 160 ^QC at a rate of 5 ^QC/min, cooled to room temperature and then heated to 160 ^QC under the same conditions. The second heating curve was recorded and given in this study. Isooctane was magnetically stirred with amphiphilic OCB overnight and the oil droplets at the interface were imaged by optical microscopy (Olympus 1X71).

[0097] Synthesis of OCB

[0098] The OCB used in this study were from the same batch reported earlier. Energy &

Environmental Science 2011, 4, 505.

[0099] Synthesis of PE-b-PEG-OCB

[00100] DMF (50 mL) and OCB (50 mg) were added into a 50 mL round-bottom flask equipped with a stir bar. The mixture was sonicated by a bath sonicator until the OCB was completely dispersed in DMF. Then N, N'-dicyclohexylcarbodiimide (465 mg) and PE-b-PEG (5 g) were added, followed by 4-dimethylaminopyridine (10 flakes). The reaction was stirred at room temperature overnight, transferred to a dialysis bag and dialyzed in standing DMF for 2 days then in running DI water for 7 days to remove the unbounded diblock copolymers. 145 mL of PE-b-PEG-OCB in DI water was collected.

[00101] Phase Transfer of PE-b-PEG-OCB in vials

[00102] The phase transfer of NPs was carried out by vigorously stirring or gently shaking the mixtures of 8 mL of amphiphilc OCB in sea brine and equal volume of isooctane (Sigma- Aldrich) at high temperatures. The typical concentration of nanoparticles in sea brine was 50 mg/L. After phase transfer, the top isooctane layer became black and the suspension was used for TEM imaging; while the bottom aqueous layer was collected and examined by a UV-vis spectrometer (Shimadzu UV-3101PC) for determining how much of NPs was left in the aqueous phase.

[00103] Phase Transfer of PE-b-PEG-OCB in a sealed ampoule

[00104] 8 mL of amphiphilic OCB in DI water and 8 mL of isooctane were loaded into an ampoule and it was sealed under atmosphere. Then, it was heated at 110 ^QC in an oven and gently shaken for improving the phase transfer process. The photograph of a sealed ampoule loaded with equal volume of PE-b-PEG-OCB in DI water and isooctane is shown in FIG. 6.

[00105] Composition of the sea brine

[00106] Sea brine components include the following (g/L): CaCl₂ (0.386), MgCl₂ (0.523), KC1 (1.478), NaCl (28.311), Na₂S0₄ (0.072), and NaHC0₃ (0.181).

[00107] Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present disclosure to its fullest extent. The embodiments described herein are to be construed as illustrative and not as constraining the remainder of the disclosure in any way whatsoever. While the embodiments have been shown and described, many variations and modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims, including all equivalents of the subject matter of the claims. The disclosures of all patents, patent applications and publications cited herein are hereby incorporated herein by reference, to the extent that they provide procedural or other details consistent with and supplementary to those set forth herein.

Claims

WHAT IS CLAIMED IS:

1. A method of transferring an amphiphilic nanoparticle between an aqueous phase and an organic phase of a solution in a temperature dependent manner, wherein the method comprises: associating the amphiphilic nanoparticle with the solution, wherein the amphiphilic nanoparticle comprises:

a nanomaterial,

hydrophilic moieties associated with the nanomaterial, and

hydrophobic moieties associated with the nanomaterial,

wherein the amphiphilic nanoparticles reversibly migrate to the organic phase of the solution at or above a first temperature,

wherein the amphiphilic nanoparticles reversibly migrate to the aqueous phase of the solution at or below a second temperature, and

wherein the first temperature is equal to or higher than the second temperature.

2. The method of claim 1, wherein the first temperature is at or above the melting point of the hydrophobic moieties.

3. The method of claim 1, wherein the second temperature is at or below the melting point of the hydrophobic moieties.

4. The method of claim 1, wherein the aqueous phase comprises water, and wherein the organic phase comprises oil.

5. The method of claim 1, wherein the nanomaterial is selected from the group consisting of silica-based nanomaterials, magnetic nanoparticles, carbon nanomaterials, single-walled nanotubes, double-walled nanotubes, triple-walled nanotubes, multi-walled nanotubes, ultra- short nanotubes, graphene, graphene nanoribbons, graphite, graphite oxide nanoribbons, carbon black, oxidized carbon black, hydrophilic carbon clusters, derivatives thereof, and combinations thereof.

6. The method of claim 1 , wherein the nanomaterial is oxidized carbon black.

7. The method of claim 1, wherein the hydrophilic moieties are selected from the group consisting of alkylane glycols, alcohols, fatty acids, lactones, polyols, poly amines, saccharides, acrylonitriles, esters, polymers thereof, and combinations thereof.

8. The method of claim 1, wherein the hydrophilic moieties comprise polyethylene glycols.

9. The method of claim 1, wherein the hydrophilic moieties comprise poly (vinyl alcohol).

10. The method of claim 1, wherein the hydrophobic moieties are selected from the group consisting of alkyl groups, phenyl groups, polystyrenes, polyethylenes, polypropylenes, acrylates, polymers thereof, and combinations thereof.

11. The method of claim 1, wherein the hydrophobic moieties comprise polyethylenes.

12. The method of claim 1, wherein the hydrophobic moieties and the hydrophilic moieties are covalently associated with the nanomaterial.

13. The method of claim 1, wherein the hydrophilic moieties and hydrophobic moieties are part of the same molecule.

14. The method of claim 13, wherein the molecule is a copolymer, and wherein the copolymer has a substantially equal weight percentage or a substantially equimolar amount of hydrophobic moieties and hydrophilic moieties.

15. The method of claim 13, wherein the molecule is a copolymer, and wherein the copolymer has an unequal weight percentage or a non-equimolar amount of hydrophobic moieties and hydrophilic moieties.

16. The method of claim 13, wherein the molecule is a copolymer of polyethylene and polyethylene glycol.

17. The method of claim 1, wherein the hydrophilic moieties and hydrophobic moieties are associated with the nanomaterial in substantially equimolar amounts or in substantially equal weight percentages.

18. The method of claim 1, wherein the hydrophilic moieties and hydrophobic moieties are part of separate molecules.

19. The method of claim 1, wherein the hydrophilic moieties and hydrophobic moieties are associated with the nanomaterial in non-equimolar amounts or in unequal weight percentages.

20. The method of claim 1, wherein the amphiphilic nanoparticles reduce the interfacial tension between the aqueous phase and the organic phase of the solution.

21. The method of claim 20, wherein the amphiphilic nanoparticles reduce the interfacial tension between the aqueous phase and the organic phase of the solution by at least about ten fold.

22. The method of claim 20, wherein the amphiphilic nanoparticles reduce the interfacial tension between the aqueous phase and the organic phase of the solution to lower than about 0.1 dynes/cm.

23. The method of claim 1, wherein the method is used for enhanced oil recovery.

24. An amphiphilic nanoparticle, comprising: a nanomaterial;

hydrophilic moieties associated with the nanomaterial; and

hydrophobic moieties associated with the nanomaterial.

25. The amphiphilic nanoparticle of claim 24, wherein the hydrophilic moieties and hydrophobic moieties are associated with the nanomaterial in substantially equimolar amounts or in substantially equal weight percentages.

26. The amphiphilic nanoparticle of claim 24, wherein the hydrophilic moieties and hydrophobic moieties are associated with the nanomaterial in non-equimolar amounts or unequal weight percentages.

27. The amphiphilic nanoparticle of claim 24, wherein the amphiphilic nanoparticles are capable of reversibly transferring between aqueous and organic phases of a solution in a temperature dependent manner,

28. The amphiphilic nanoparticle of claim 27, wherein the first temperature is at or above the melting point of the hydrophobic moieties.

29. The amphiphilic nanoparticle of claim 27, wherein the second temperature is at or below the melting point of the hydrophobic moieties.

30. The amphiphilic nanoparticle of claim 24, wherein the nanomaterial is selected from the group consisting of silica-based nanomaterials, magnetic nanoparticles, carbon nanomaterials, single-walled nanotubes, double-walled nanotubes, triple-walled nanotubes, multi-walled nanotubes, ultra-short nanotubes, graphene, graphene nanoribbons, graphite, graphite oxide nanoribbons, carbon black, oxidized carbon black, hydrophilic carbon clusters, derivatives thereof, and combinations thereof.

31. The amphiphilic nanoparticle of claim 24, wherein the nanomaterial is oxidized carbon black.

32. The amphiphilic nanoparticle of claim 24, wherein the hydrophilic moieties are selected from the group consisting of alkylane glycols, alcohols, fatty acids, lactones, polyols, polyamines, saccharides, acrylonitriles, esters, polymers thereof, and combinations thereof.

33. The amphiphilic nanoparticle of claim 24, wherein the hydrophilic moieties comprise polyethylene glycols.

34. The amphiphilic nanoparticle of claim 24, wherein the hydrophilic moieties comprise poly( vinyl alcohol).

35. The amphiphilic nanoparticle of claim 24, wherein the hydrophobic moieties are selected from the group consisting of alkyl groups, phenyl groups, polystyrenes, poly ethylenes, polypropylenes, acrylates, polymers thereof, and combinations thereof.

36. The amphiphilic nanoparticle of claim 24, wherein the hydrophobic moieties comprise polyethylenes.

37. The amphiphilic nanoparticle of claim 24, wherein the hydrophobic moieties and hydrophilic moieties are covalently associated with the nanomaterial.

38. The amphiphilic nanoparticle of claim 24, wherein the hydrophilic moieties and hydrophobic moieties are part of the same molecule.

39. The amphiphilic nanoparticle of claim 38, wherein the molecule is a copolymer.

40. The amphiphilic nanoparticle of claim 38, wherein the molecule is a copolymer of polyethylene and polyethylene glycol.

41. The amphiphilic nanoparticle of claim 24, wherein the hydrophilic moieties and hydrophobic moieties are part of separate molecules.