Patent Application
20240093005
The present invention belongs to the field of nano-composite materials, and in particular relates to polymer-coated nanoparticles, a composite nano-emulsion and a macro-emulsion.
An emulsion is a heterogeneous system composed of two or more immiscible phases, with at least one being dispersed in the other continuous phase liquids in the form of liquid droplets. Two liquids, such as oil and water, can either form an oil-in-water (O/W) emulsion, with oil being a dispersed phase, or form a water-in-oil emulsion (W/O), with water being the dispersed phase. By mixing these two liquids, a variety of emulsions can also be formed, including “oil in water in oil (O/W/O)” and “water in oil in water (W/O/W)” emulsions.
Emulsions can be divided into macro-emulsions, nano-emulsions, and micro-emulsions according to particle size and properties. Traditional macro-emulsions are easily formed by adding low concentrations of surfactants or surface-active polymers to reduce the surface tension between the dispersed phase and continuous phase. Surfactants are amphiphilic and are widely used as emulsifiers, which have a strong adsorption effect on the oil-water interface. The hydrophobic groups point to the oil phase, and the hydrophilic groups point to the aqueous phase, which reduces the interfacial energy and hinders the expansion and coalescence of droplets. These surfactants may be nonionic, anionic, cationic or zwitterionic. Likewise, surface-active polymers with amphiphilic properties have also been proven to be effective stabilizers because the chains are amphiphilic and can effectively reduce the oil-water interfacial tension and prevent emulsion instability. For example, in patent US2008/0250701A1, it is described that succinic acid diester polymers can be used to prepare a water-in-oil macro-emulsion. The polymer contains a large hydrocarbon group connected by two ester bonds to two hydrophilic alkyl oxygen chains, and the molecular weight ranges from 500 to 1200.
An alternative method to surfactants and surface-active polymers to form macro-emulsions is to use solid particles to form emulsions, which are known as Pickering emulsions. Compared with traditional emulsions, Pickering emulsions can maintain long-term stability because solid particles can reside at the liquid-liquid interface and form a shell around the droplets, providing a strong mechanical barrier for droplet coalescence. In addition, due to the reduced use of surfactants, Pickering emulsions have lower cytotoxicity and better biocompatibility than conventional emulsions. Therefore, Pickering emulsions are being widely concerned by industries such as petroleum, biomedicine, and food. According to the Pickering emulsion theory, there are two key factors to form a stable emulsion: first, the surface coverage needs to be high enough to stabilize the emulsion over time, which requires that the particles should be close to complete surface coverage on the droplet surface and have a sufficiently dense particle layer. At this stage, the interaction of nanoparticles at the interface is dominated by gravitational forces, resulting in the formation of a coherent monolayer with significant mechanical strength, preventing coalescence between droplets. Although Vignati et al. reported that the particle surface coverage of droplets can be as low as 5% (Vignati et al., 2003), it is generally believed that to obtain a stable emulsion, the particle surface coverage should not be less than 29%, and crosslinking between particles is required to form gel structures (Midmore, 1998). Second, the partial wettability of an emulsifier is another important factor affecting the stability and type of the emulsion. In order to achieve interfacial adsorption, the particle surface must have both hydrophilic and lipophilic groups. In order to control the wettability of the surface of solid particles, various methods have been used to adjust the surface properties of the particles. For example, the surface of rigid particles can be modified by non-covalent adsorption or covalent linkage of surfactants, polymers, and small molecules to selectively alter wettability and monodispersity. Yoon et al. previously synthesized iron oxide nanoparticles by the co-precipitation method of Fe2+ and Fe3+ ions, and then simply mixed the synthesized nanoparticles with a copolymer of sulfonated polystyrene and malonic acid (PSS-alt-MA) polymer. Their study and subsequent studies found that PSS-alt-MA iron oxide nanoparticles synthesized by this simple adsorption method could not stabilize non-covalently adsorbed polymers in high-salt solutions in the presence of divalent metal ions (such as calcium ions), and that noncovalently adsorbed polymers were easily shed from the particle surface. In addition, the PSS-alt-MA iron oxide nanoparticles are highly hydrophilic nanoparticles, which do not have lipophilic and hydrophilic amphiphilic properties, and cannot be directly used as emulsifiers to stabilize emulsions. The emulsions can be stabilized only by linking each copolymer-adsorbed iron oxide nanoparticle with hexamethylene diamine and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride cross-linking agent to enhance its hydrophobicity. And due to weak gelation, PSS-alt-MA iron oxide nanoparticles are not stable in API solution (8 wt % NaCl+2 wt % CaCl) in the presence of divalent metal ions (Yoon et al., 2011; Bargaria et al., 2013). Although Bargaria et al., 2013 found that a polysulfonated copolymer (2-acrylamide-2-methylpropanesulfonic acid and acrylic acid copolymer, 2-methyl-2-acrylamidopropanesulfonate-co-acrylic acid) (AMPS-co-AA) weakly bind calcium ions, which can stabilize iron oxide nanoparticles in high temperature, high sodium and high calcium API saline solution (8 wt % sodium chloride+2 wt % calcium chloride), and can resist extreme dilution and prevent aggregation substances from nanoparticles (Iqbal et al., 2017). But the production of such nanoparticles requires a tedious and expensive process of covalent attachment to encase the entire nanoparticle in a polymer. For example, in order to realize the complete coating of iron oxide nanoparticles by polymers, at least three steps are required: firstly, the iron oxide nanoparticles synthesized by a co-precipitation method were placed in tetraethoxysilane, so that the surface of the nanoparticles is covered by silicon; secondly, the silicon-coated iron oxide nanoparticles were putted into 3-aminopropyltriethoxysilane for surface amination; finally, the aminated and silicon-coated iron oxide nanoparticles were completely encapsulated with 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid copolymer. Obviously, this method of fully encapsulating nanoparticles through covalent linkage requires cumbersome steps and is difficult to apply to a large-scale production process. Therefore, it is urgent to develop a method for conveniently wrapping nanoparticles, so that nanoparticles can resist the environment of high temperature, high pressure and high salt in the ground.
Compared with macro-emulsions and microemulsions, the droplet diameter of nano-emulsions is about 20-500 nanometers, which can be stably dispersed in solutions like nanoparticles, with high specific surface area per unit, optically transparent appearance and a tunable rheology, and therefore the nano-emulsions have a wide range of applications in the fields of drug delivery, food, cosmetics, drugs and material synthesis. Nano-emulsions were first widely used in nanomedicine, but recently the concept of nanomedicine has also been applied to petroleum engineering. Compared to traditional surfactant flooding, the use of surfactant-synthesized nanodroplets can significantly reduce the adsorption of surfactants to rock surfaces and increase tertiary oil recovery by about 8% (Nourafkan et al., 2018). However, nano-emulsions are a thermodynamically extremely unstable system, which is very prone to Ostawald ripening (Ostawald ripening), and the small nanodroplets in the nano-emulsion are prone to aggregation and growth. Traditional nano-emulsions can also be stabilized by surfactants and polymers. For example, the U.S. Pat. No. 835,763B92 describes a method including introducing a nano-emulsion into a wellbore containing a surfactant. However, such oil-surfactant-polymer-stabilized nano-emulsions are prone to surfactant desorption and droplet aggregation growth at high temperature and pressure. Theoretically, if nanoparticles are used to stabilize a liquid-liquid interface, the formed Pickering nano-emulsions have higher stability. However, even with very fine nanoparticles, the synthesis of stable Pickering nanodroplets smaller than 500 nm remains a great challenge. Kang et al. (2018) designed a method for the synthesis of nanoscale Pickering nano-emulsions using water vapor condensation, but this method can only synthesize water-in-oil Pickering nano-emulsions. Saelices and Capron (2018) tried to use dextran nanoparticles to synthesize oil-in-water Pickering nano-emulsions. However, they found that it is difficult to synthesize Pickering nano-emulsions under normal pressure conditions, and the Pickering nano-emulsions of oil-in-water can only be synthesized under high pressure conditions.
Based on difficult synthesis, complicated steps and high cost of the above-mentioned Pickering emulsions, the current synthesis of macro-emulsions often requires high concentrations of surfactants and solid particles to stay on an oil-water interface, and surface tension is reduced to stabilize large oil droplets. It is of great interest to develop a simple, cost-effective method for synthesizing emulsions.
Based on the defects of the above-mentioned synthesis of Pickering emulsions in the prior art, a technical problem to be solved by the present invention is to provide a method for synthesizing emulsions, which method uses polymer-coated nanoparticles or surfactants in combination with metal ions as emulsifiers to stabilize nanodroplets, and then uses nanodroplets as emulsifiers to stabilize the emulsion and expand the surface area of the emulsion, thereby reducing the amount of nanoparticles and surfactants used to stabilize the emulsion, and reducing the production cost of traditional emulsions.
The present invention provides a method for preparing stable nano-emulsion and micro-emulsion with polymer-coated nano particles. The nanodroplets provided by the present invention are much more efficient in stabilizing emulsions than using nanoparticles and surfactants alone. The present invention also develops a method for polymer-encapsulated nanoparticles: nanoparticles, especially iron oxide nanoparticles (5-150 nm), can be synthesized by biomimetic mineralization methods. First, the polymer is assembled to form a cage-shaped structure, and by taking the cage formed by the self-assembly of the polymer as the cage-shaped structure, nanoparticles are formed inside the cage-shaped structure, so that the nanoparticles are completely wrapped by the polymer and are not affected by high salt water, brine, elevated temperature or other harsh conditions, and without the need for expensive and cumbersome chemical covalent linkages to wrap polymer molecules onto the nanoparticle surface. The composition of the polymer can be adjusted according to the conditions of the target application, such as reservoir temperature, pressure and salinity. These coated nanoparticles and surfactants, especially in combination with multivalent metal cations, can form stabilized oil-phase nano-droplets (100 to 600 nm in diameter) in the aqueous phase. Nanodroplets in turn stabilize emulsion systems with larger particle sizes (large oil droplets dispersed in the aqueous phase).
The polymer-coated nanoparticles provided by the present invention and surfactants provide a new and convenient method for preparing stable nanodroplets. Both nanodroplets and nanodroplet-stabilized macro-emulsions have broad applications ranging from drug delivery to enhanced in situ or in vivo imaging to enhanced oil recovery rates and catalysis.
Specifically, in order to solve the above-mentioned technical problems, the present invention provides the following technical solutions:
The first object of the present invention is to provide a polymer-coated nanoparticle, where the polymer self-assembles into a cage-shaped structure and coats the nanoparticle; and the nanoparticles are iron-containing metal oxides.
The polymer contains sulfonic acid groups and carboxyl groups, the sulfonic acid groups and the carboxyl groups can be completely or partially converted into salt forms, and the salts are potassium salts, sodium salts, and ammonium salts.
Further, the polymer is obtained by copolymerization of unsaturated monomers containing the sulfonic acid groups and unsaturated monomers containing the carboxyl groups; the unsaturated monomers containing the sulfonic acid groups include styrene sulfonate, methacryl sulfonate, propenyl sulfonate, vinyl sulfonate, butenyl sulfonate, 2-acrylamide-2-methyl propane sulfonate; and the unsaturated monomers containing the carboxyl groups are selected from maleic acid, acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, 2-pentenoic acid, 4-pentene, 2-octenoic acid, 3-vinylbenzoic acid, 4-vinylbenzoic acid, 10-undecenoic acid, erucic acid, brassenoic acid, palmitoleic acid, oleic acid, nervonic acid, linolenic acid, ricinoleic acid, 4-oxo-4-phenyl-2-butenoic acid, 2-bromoacrylic acid, 2-bromomethyl-acrylic acid, sorbic acid, itaconic acid, citraconic acid, fumaric acid, methylfumaric acid, mesaconic acid, 2-methylsuccinic acid, mucofuric acid.
The molecular weight of the polymer is determined by the size and space of the cage-shaped structure. Generally, the molecular weight of the polymer is 1 million to 3 million, preferably 1.5 million to 2 million; or the number of repeating units of the polymer is 50-200, preferably 90-120.
Preferably, the polymer is a sodium salt of poly(4-styrenesulfonic acid-maleic acid copolymer), with the quantity ratio of the sulfonate and the carboxyl in the polymer being 1:2, and the molecular weight being 1.5-2 million.
The chemical structure of the metal oxide nanoparticles is Fe(3-x)MxO4 (0≤x≤3) or Fe(2-x)MxO3 (0≤x≤2), wherein M is selected from Mn, Cu, Zn, Ni, Gd or Co; and the size of the metal oxide nanoparticles is 5-150 nm, preferably 10-20 nm.
Preferably, the metal oxide nanoparticles are Fe3O4, Fe1.5Co1.5O4.
According to the polymer-coated iron-containing metal oxide nanoparticles provided by the present invention, the polymer can self-assemble to form a cage-shaped structure similar to a sphere, with an inner diameter of about 10-40 nm. The metal oxide nanoparticles are approximately spherical or ellipsoidal, and the ratio of the long axis to the short axis is 1-2. The polymer-coated iron-containing metal oxide nanoparticles can be stabilized in an aqueous solution with a pH of 3-11. The polymer-coated iron-containing metal oxide nanoparticles can withstand a high temperature of at least 90° C.; and the weight ratio of the polymer to iron oxide nanoparticles is 1-4.
A second object of the present invention is to provide a preparation method for the above-mentioned polymer-coated nanoparticles, including the following steps: a) allowing the polymer self-assemble to form a cage-shaped structure; and b) ddding metal salts and oxidants to grow nanoparticle crystals within the cavity of the cage-shaped structure formed by the polymer.
The condition for the self-assembly of the polymer into a cage-shaped structure is a salt concentration of 0.05-1M halide salt, such as NaCl, KCl, preferably 0.1-0.2M, and a pH value of 3-10, preferably 5-8.5, more preferably 7-8.5; the temperature is 45-90° C., preferably 50-60° C., more preferably 50-55° C.; and the concentration of the polymer is 0.25-5 mg/mL, preferably 1-2 mg/mL. By controlling the ionic strength, pH and temperature in the solution, the polymer can form cage-shaped structures of different sizes.
The synthetic nanoparticles are synthesized in the cage formed by the polymer, specifically, the metal salt and the oxidizing agent are slowly added into the system respectively. The amount of metal salt added determines the particle size distribution of nanoparticles. Theoretically, the metal salt is added in an amount such that each polymer cage contains one nanoparticle, and a single nanoparticle in the cage has 1,000-120,000 metal atoms, preferably 5,000-10,000 metal atoms in each polymer cage.
The metal salts include iron salts, and optionally, a metal M salt may also be added, and the metal M is selected from at least one of Mn, Cu, Zn, Ni, Gd, and Co. The anions of the salts are not particularly limited, such as halide salts, sulfates, and nitrates. The iron salts are specifically selected from at least one of ferrous ammonium sulfate, ferrous chloride, ferrous sulfate, and ferrous nitrate, and the salt of the metal M is preferably a halide salt, such as manganese chloride, copper chloride, cobalt chloride.
The oxidizing agent is not particularly limited, as long as it can oxidize low-valent metal salts to high-valent salts, such as hydrogen peroxide.
The metal oxide nanoparticles and the oxidizing agent are fed according to the molar ratio of the metal salt and the oxidizing agent according to 2-3:1.
The metal salt is added at a rate of 10-200 metal ions per polymer per minute in the system, preferably 80-120 metal ions per polymer per minute.
Preferably, after the polymer-coated nanoparticles are obtained, a purification step (c) is also performed: after centrifugation, the synthesized magnetic nanoparticles were concentrated using protein enrichment tubes. Nanoparticles that did not form inside the polymer cages were removed by centrifugation, followed by concentration to obtain high concentrations of polymer-coated nanoparticles.
Further preferably, in order to ensure that each iron oxide nanoparticle is completely wrapped by the polymer cage, centrifugation was performed at a centrifugal force of 5000-20000 g for 10-30 minutes to remove magnetic nanoparticles that are easy to aggregate or difficult to wrap, and the synthesized magnetic nanoparticles were then concentrated to 20-50 mg/mL using a protein enrichment and concentration tube with a molecular weight cut-off of 100-200 KD and stored same for future use. After the polymer forms a cage-shaped structure, the nanoparticles reside in a single, self-assembled polymer cage cavity that protects the nanoparticles from being damaged by high salinity, high temperature, or other harsh conditions.
The third object of the present invention is to provide a composite nano-emulsion, including; a) a continuous phase; b) a discontinuous phase; c) a stabilizer; and d) metal ions, where the stabilizer includes the above-mentioned polymer-coated nanoparticles.
The particle size of the composite nano-emulsion is 20-1000 nm, preferably 100-600 nm.
The continuous phase is a polar solvent such as water, alcohol and nitriles, and the alcohol and nitriles polar solvents are resins in the art, such as methanol, ethanol, isopropanol, butanol, propylene glycol, glycerin, butylene glycol, acetonitrile, propionitrile etc. The polar solvent can be added alone or in the form of a solvent in the stabilizer solution.
The discontinuous phase is oil, such as unsaturated fatty acid, mineral oil, fatty oil, silicone oil, etc., which is incompatible with the continuous phase, with the ratio of discontinuous phase volume to continuous phase volume being from 0.15 to less than 1, preferably 0.18-0.3.
Polymer-coated nanoparticles can be used alone as stabilizers. Preferably, the polymer-coated nanoparticles can be combined with metal ions, which makes it easier to reach the oil-water interface.
The concentration of the polymer-coated nanoparticles in the nano-emulsion is 0.2-2 wt %, preferably 0.8-1.2 wt %.
Metal ions can be monovalent or polyvalent ions, such as at least one of Na+, K+, Ca2+, Co2+, Ni2+, Ba2+, Mg2+, and Cu2+. The concentration of metal ions in the system is 0.1-0.3M, preferably a divalent metal ion, such as at least one of Ca2+, Co2+, Ni2+, Ba2+, and Mg2+.
The polymer-coated nanoparticles can react with oil to form very small oil-phase nanodroplets with a particle size of less than 1000 nm. In this composite nano-emulsion system, polymer-coated nanoparticles, metal ions and nanodroplets all play a role in stabilizing the emulsion.
The fourth object of the present invention is to provide a preparation method for the composite nano-emulsion, including the follow steps:
Nano-emulsions can aggregate at the oil-water interface, and the oil and water content can be quantitatively evaluated by optical or magnetic methods, where the optical method may be a fluorescence or laser method, and the magnetic method may be a magnetic resonance, magnetoacoustic, electromagnetic, magnetic susceptibility or magnetization method.
Further preferably, the stabilizer can also be added with an anionic surfactant and a cationic surfactant, and adsorbed on the nanodroplets so that the nanodroplets can reduce the surface tension of the liquid-liquid interface and oil is more effectively extracted from the reservoir. Metal ions at the interface of polymer-coated nanoparticles and nanodroplets can dynamically react with oil to form nano- or micro-scale emulsions. More efficient recovery of oil from reservoirs is achieved compared to conventional Pickering emulsions.
The fifth object of the present invention is to provide a macro-emulsion, including: a) a continuous phase; b) a discontinuous phase; and c) a stabilizer which includes the above-mentioned composite nano-emulsion. The meaning of the term “macro-emulsion” corresponds to “micro-emulsion” or “nano-emulsion”, indicating that the size of the particles in the emulsion is 10-100 μm, and its oil-water interface covers many composite nano-emulsions and microemulsions (1-10 μm), with a very high specific surface area.
The continuous phase is a polar solvent such as water, alcohol and nitriles, and the alcohol and nitriles polar solvents are resins known in the art, such as methanol, ethanol, isopropanol, butanol, propylene glycol, glycerol, butanediol, acetonitrile, propionitrile, etc. The polar solvent can be added alone or in the form of a solvent in the stabilizer solution.
The discontinuous phase is an oil, such as unsaturated fatty acid, mineral oil, fatty oil, silicone oil, etc., which is incompatible with the continuous phase, with the ratio of discontinuous phase volume to the continuous phase volume being 0.5-3, preferably 1-2.
The role of the polymer-coated nanoparticles provided by the present invention as a stabilizer that can stabilize the emulsion is multifaceted. First, the specific wettability of the polymer-coated nanoparticles themselves makes the nanoparticles adsorbed on the oil/water interface to form a monolayer and/or multilayer film, thereby stabilizing the emulsion. Second, the metal ions can be combined with the functional groups of the polymer and attached to the nanodroplet interface together with the polymer-coated nanoparticles to play a stabilizing role. Third, the polymer-coated nanoparticles combined with metal ions stabilize the oil-water interface and can form very small oil-phase nanodroplets with oil-water, and the nanodroplets can stabilize the oil-water interface with a larger size and further form microndroplets, i.e. macro-emulsions. This one-to-one stabilization mode, that is, the stabilizer provided by the present invention, is a macro-emulsion stabilized by the synergistic effect of the polymer-coated nanoparticles, metal ions and the formed nano/microdroplets, and the concentration of the polymer-coated nanoparticles required is very low. It has been proved through experiments that at a very low concentration of 0.0002 wt %, the polymer-coated nanoparticles provided by the present invention can form a stable macro-emulsion. The concentration is extremely low to have the advantage of low cost. At the same time, the method for stabilizing the emulsion is simple, easy to operate, and has industrial advantages.
The sixth object of the present invention is to provide a preparation method for above-mentioned macro-emulsion, including the following steps:
The prepared composite nano-emulsion was uniformly mixed with a continuous phase and a discontinuous phase to obtain a macro-emulsion.
The seventh object of the present invention is to provide use of the composite nano-emulsion for drug delivery, in situ or in vivo imaging, displacement of residual petroleum or catalysis.
For example, when used to displace residual oil, compared with other oil displacing agents, the Pickering composite nano-emulsion of the present invention can be specifically adsorbed on the oil-water interface of residual oil and react to generate oil-phase nanodroplets with larger particle size and microndroplet displacement, and about 30% of the residual oil at normal temperature and pressure can be displaced out.
Compared with other currently synthesized polymer iron oxide nanoparticles and Pickering emulsions, the technical solution of the present invention has the following advantages:
The polymer-coated nanoparticles of the present invention, as well as the composite nano-emulsion and macro-emulsion formed therefrom will be further explained with specific examples below.
Unless otherwise specified, the reagents used in the examples of the present invention can be purchased commercially.
Sodium salt of 4-styrenesulfonic acid-maleic acid copolymer (the molecular weight is about 20000, and the molar ratio of styrenesulfonic acid and the maleic acid is 1:1) was prepared with 0.1M NaCl to a concentration of 1 mg/mL, the pH of the solution was adjusted to pH3, pH5, pH7, pH8.5, and pH9 with 0.01 M NaOH and hydrochloric acid, and the hydrated particle size of the polymer was measured under the conditions of different pH and different temperatures (25° C., 55° C., 90° C.) using dynamic light scattering. It was found that only at pH5-8.5, the polymer could well maintain the secondary structure, and the volume percent hydrated particle size was about 12 nm at 25° C. (
All solutions were deoxygenated and placed in anaerobic chambers. Solutions of ammonium ferrous sulfate (100 mM) and hydrogen peroxide (33.33 mM) were prepared separately in anaerobic deionized water. In order to obtain self-assembled polymers, 1 g of polystyrene sulfonate sodium-maleic acid copolymer (PSS-co-MA, molecular weight about 20,000) polymer was dissolved in 1 L of 0.1 M NaCl solution until the final concentration is 1 mg/mL, the pH value is adjusted to 8.5 with 0.5M NaOH, and the temperature is controlled at 55° C. for 10 min through an electric heating mantle, so that the polymer begins to self-assemble and form a cage-shaped structure (each cage contains 96 monomers with a molecular weight of about 1,920,000) under the conditions of salt ion concentration, pH and temperature. Based on the number of moles of polymer cages and the molar concentration of ferrous ammonium sulfate, it was calculated to add ferrous ammonium sulfate (100 mM) and hydrogen peroxide (33.34 mM) solutions at a rate of 80 iron atoms per minute per cage, theoretically about 5000, 20000, 60000 and 80000 iron atoms were added to each cage to form iron oxide (magnetite, Fe3O4) nanoparticles with different particle size distribution, respectively PSS-co-MA5000, PSS-co-MA20000, PSS-co-MA60000, PSS-co-MA80000, respectively. In order to ensure that each iron oxide nanoparticle is completely encapsulated by the polymer cage, the magnetic nanoparticles that are easy to assemble or difficult to encapsulate are removed under a centrifugal force of 10,000 g, and the synthesized magnetic nanoparticles were concentrated using a molecular weight 100 kD protein enrichment tube (amicon Ultra-12100kda) to remove free polymer to 30 mg/mL for storage. The iron content and the polymer content in the nanoparticles were determined by inductively coupled plasma mass spectrometry (ICP-MS) and thermogravimetric analysis (TGA).
All solutions were deoxygenated and placed in anaerobic chambers. A mixture of ammonium ferrous sulfate (50 mM) and cobalt chloride (50 mM) was first prepared in anaerobic deionized water, followed by a solution of the oxidant hydrogen peroxide (33.34 mM) in deionized water. To obtain self-assembled polymers, 1 g of polystyrene sulfonate sodium-maleic acid copolymer (PSS-co-MA) polymer was dissolved in 1 L of 0.1 M NaCl solution to a final concentration of 1 mg/mL, the pH value was adjusted to 8.5 with 0.5M NaOH, and the temperature was controlled at 55° C. for 10 min, so that the polymer began to self-assemble to form a cage-shaped structure under the conditions of salt ion concentration, pH value and temperature. Assuming that the cage-shaped structure of the polymer is composed of 96-mers with a molecular weight of about 1920000, a mixture of ammonium ferrous sulfate (50 mM) and cobalt chloride (50 mM) and a solution of hydrogen peroxide (33.34 mM) were then added at a rate of 40 iron and 40 cobalt atoms per minute per cage. Theoretically, 10000 iron atoms and 10000 cobalt atoms were added to each cage respectively. In order to ensure that each cobalt-manganese iron oxide nanoparticle is completely encapsulated by the polymer cage, magnetic nanoparticles that are easy to assemble or difficult to encapsulate were removed under a centrifugal force of 10,000 g, and a protein enrichment tube with a molecular weight of 100 kD (amicon Ultra-12100kda) to concentrate the synthesized magnetic nanoparticles and remove the free polymer to 30 mg/mL for storage. The incorporation of cobalt into iron oxide nanoparticles was analyzed by energy dispersive spectroscopy.
CaCl2·2H2O was first dissolved in a separate vessel at a concentration of 5 M. A 20 ml glass vial was used to add 16.2 ml of 1.23 wt % PSS-co-MA5000 iron oxide nanoparticles prepared in Example 1, 0.8 ml of 5 M CaCl solution and 3 ml of octadecene were added. The vial was held in a 400 milliliter beaker with a foam holder, cooled in an ice bath, and sonicated for a total time of 10 minutes at a 30 second/30 second 50% amplitude setting. The solution was further centrifuged at 3000 rpm to three layers. The middle layer was taken to obtain a stable nano-emulsion, the upper and lower layers were discarded, and the free oil and free nanoparticles were removed respectively.
Firstly, a high-concentration mixed solution containing different metal ions was prepared, 3.68 g CaCl2·2H2O, 3.64 g Co(NO3)2·6H2O and 2.97 g NiCl2·2H2O were weighed and dissolved in 10 mL of water to prepare a final concentration of 2.5 M CaCl2·2H2O, 1.25 M Co(NO3)2·6H2O and 1.25 M NiCl2·2H2O. In another separate glass bottle, 15.4 mL of PSS-co-MA5000 iron oxide nanoparticles prepared in Example 1 with a concentration of 1.3 wt %, 1.6 mL of metal ion mixture, and 3 mL of octadecene were added, and the vials were fixed in a 400 ml beaker in an ice bath and sonicated with an ultrasonic wave at 30 s/30 s 50% amplitude for 10 min. To prepare composite nano-emulsions with other single oil components, other oils such as dodecane, mineral oil, and silicone oil can be used instead of octadecene. The solution was further separated into three layers by centrifugation at 3000 rpm. The middle layer was extracted to obtain a stable nano-emulsion, the upper and lower layers were discarded, and the free oil and free nanoparticles were removed, respectively.
Firstly, a high-concentration mixed solution containing different metal ions was prepared, 3.68 g CaCl2·2H2O, 3.64 g Co(NO3)2·6H2O and 2.97 g NiCl2·2H2O were weighed and dissolved in 10 mL of water to prepare a final concentration of 2.5 M CaCl2·2H2O, 1.25 M Co(NO3)2·6H2O and 1.25 M NiCl2·2H2O. In another separate glass bottle, 15.4 mL of PSS-co-MA5000 iron oxide nanoparticles with a concentration of 1.3 wt % prepared in Example 1, 1.6 mL of metal ion mixture, 1 mL of octadecene, 1 mL of mineral oil and 1 mL of silicone oil were added, the vials were fixed with a foam holder in a 400 ml beaker in an ice bath and sonicated with an ultrasonic wave at 30 s/30 s 50% amplitude for 10 minutes. The solution was further separated into three layers by centrifugation at 3000 rpm. The middle layer was taken to obtain a stable nano-emulsion, the upper and lower layers were discarded, and the free oil and free nanoparticles were removed, respectively.
Firstly, the cationic surfactant dodecyltrimethylammonium bromide (DTAB) was dissolved in a separate container at a concentration of 10 mg/mL. Then another container was used to configure a high-concentration mixed solution containing different metal ions, 3.68 g CaCl2·2H2O, 3.64 g Co(NO3)2·6H2O and 2.97 g NiCl2·2H2O were weighed and dissolved in 10 mL of water to configure a final concentration of 2.5 M CaCl2·2H2O, 1.25 M Co(NO3)2·6H2O and 1.25 M NiCl2·2H2O. In a separate glass bottle, 15.2 mL of PSS-co-MA5000 iron oxide nanoparticles prepared in Example 1 with a concentration of 1.3 wt %, 0.2 mL of DTAB solution (10 mg/mL), 1.6 mL of metal ion mixture, 1 mL octadecene, 1 mL mineral oil and 1 mL silicone oil were added, the vials were fixed with a foam holder in a 400 mL beaker in an ice bath and sonicated with an ultrasonic wave at 30 s/30 s 50% amplitude for 10 min. The solution was further separated into three layers by centrifugation at 3000 rpm. The middle layer was extracted to obtain a stable nano-emulsion, discard the upper and lower layers were discarded, and the free oil and free nanoparticles were removed, respectively.
Firstly, the anionic surfactant sodium dodecyl sulfate (SDS) was dissolved in a separate container at a concentration of 10 mg/mL. Then another container was used to configure a high-concentration mixed solution containing different metal ions, 3.68 g CaCl2·2H2O, 3.64 g Co(NO3)2·6H2O and 2.97 g NiCl2·2H2O were weighed and dissolved in 10 mL of water to configure a final concentration of 2.5 M CaCl2·2H2O, 1.25 M Co(NO3)2·6H2O and 1.25 M NiCl2·2H2O. In a separate glass bottle, 15.2 mL of PSS-co-MA5000 iron oxide nanoparticles prepared in Example 1 with a concentration of 1.3 wt %, 0.2 mL of DTAB solution (10 mg/mL), 1.6 mL of metal ion mixture, 1 mL octadecene, 1 mL mineral oil and 1 mL silicone oil were added, the vials were fixed with a foam holder in a 400 mL beaker in an ice bath and sonicated with an ultrasonic wave at 30 s/30 s 50% amplitude for 10 min. The solution was further separated into three layers by centrifugation at 3000 rpm. The middle layer was extracted to obtain a stable nano-emulsion, the upper and lower layers were discard, and the free oil and free nanoparticles were removed, respectively.
In order to prepare nanodroplet stabilized macro-emulsions and compare same with nanoparticle stabilized emulsions, 10 mL of stabilizers and 10 mL of octadecene were respectively added to the vials, and the stabilizers were respectively a combination of the PSS-co-MA coated iron oxide nanoparticles prepared in Example 2, the polymer PSS-co-MA coated iron oxide nanoparticles prepared in Example 2 and a solution of CaCl2) (the concentration of CaCl2) after combination was 0.2 M), a nano-emulsion prepared in Example 4, and a combination of the nano-emulsion prepared in Example 4 and CaCl2) (the concentration of CaCl2) after combination was 0.2 M). The oil, water, and nano-emulsion in the vial were then homogenized using a medium intensity homogenizer for 2 minutes to obtain a macro-emulsion. The amounts of PSS-co-MA coated iron oxide nanoparticles and nano-emulsion were adjusted, so that the concentration of polymer PSS-co-MA-coated iron oxide nanoparticles in the finally macro-emulsion is 0.001-0.01 wt %. The obtained macro-emulsion was allowed to stand on a table at normal temperature and observed continuously for 58 days to see whether there was demulsification. In order to further compare the difference between polymer-coated nanoparticles and nano-emulsion stabilized macro-emulsions, the macro-emulsions prepared above were stored at room temperature, and the hydrated particle size distributions were measured using a dynamic light scattering instrument for 56 hours and 6 days, respectively, and after 7 days storage the dynamic rheological data of each emulsion was further measured using a rheometer under fixed frequency conditions. Alternatively, a stable oil-in-water nano-emulsion can be synthesized using a co-surfactant and a metal ion to prepare a macro-emulsion, similar to the procedure described above.
A macro-emulsion was prepared according to the same operation and conditions as in Example 9, with the complexation of the nano-emulsion prepared in Example 4 and CaCl2) (the concentration of CaCl2) after complexation was 0.2M) as the stabilizer, except that the solution of 0.2M CaCl2) was replaced by 0.2M NaCl, 1M NaCl, 0.2M NiCl2, 0.2M FeCl3, respectively.
When a macro-emulsion is prepared according to the same operation and condition of Example 9, the difference is that the oil-in-water composite nano-emulsion containing single oil component and multiple metal ions prepared in Example 5 and CaCl2) compounding (CaCl2) concentration after compounding was 0.2 M) are used as stabilizers, and the concentration ratio of polymer PSS-co-MA coated iron oxide nanoparticles in the composite nano-emulsion is 0.0002 wt %, 0.0003 wt %, 0.0004 wt %, 0.0005 wt %.
300 ml of MiliQ water was poured into a 400 ml clean beaker and 12 g of PSS-co-MA polymer was dissolved in the water. Concentrated hydrochloric acid was added to adjust the pH of the polymer solution to 5. Stir with an appropriately sized stir bar for 10 minutes. Then 3 g of Fe3O4 particles (Research Nanomaterials, 20-30 nm) were added to the solution and sonicated for 60 min in an ice bath at the 50% amplitude setting. To remove aggregated nanoparticles, the sonicated solution was centrifuged at 4000 g for 20 min. Finally, the supernatant was concentrated and free aggregate was removed to 30 mg/mL for storage using a 100 kD protein enrichment tube (amicon Ultra-12,100 kDa). The iron content and polymer content in the nanoparticles were determined by inductively coupled plasma mass spectrometry (ICP-MS) and thermogravimetric analysis (TGA).
In order to observe the dynamic interaction between the nano-emulsion and oil without adding metal ions, the glass micromodel was first saturated with water using a syringe pump at an injection rate of 15 uL/min. Then 1-octadecene was injected into the micromodel at an injection rate of 5 ul/min until oil saturation was reached. The first water displacement was performed by injecting water at a rate of 5 microliters per minute until no more oil was produced in the effluent. A nano-emulsion with a single pore volume (concentration 0.01 wt %) was injected into the micromodel, and real-time imaging was performed with a laser confocal microscope to study the interaction between the nano-emulsion and residual oil and the oil recovery rate to evaluate the displacement effect of residual oil.
To observe the interaction of nano-emulsions with oil in a salt solution containing metal ions, the glass micromodel was first saturated with 0.2 M calcium chloride solution using a syringe pump at an injection rate of 15 μL/min. Then 1-octadecene was injected into the micromodel at an injection rate of 5 μL/min until synaptic water saturation conditions are reached. 0.2 M CaCl2) solution was injected at a rate of 5 μl per min until no more oil is produced in the effluent. Nano-oil droplets at concentrations of 0.01 wt % and 0.2 m CaCl2) were injected into the micro-model and the interaction and displacement effect of the nano-emulsion with residual oil was studied using confocal microscopy imaging.
The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the disclosed content of the present invention and all belong to the protection scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110167224.1 | Feb 2021 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2022/071489 | 1/12/2022 | WO |
