A micro-nano calcium carbonate stabilized pH-responsive pickering emulsion

Abstract

This invention discloses a pH-responsive Pickerling emulsion stabilized by micro / nano-sized calcium carbonate. The emulsion is obtained by emulsifying calcium chloride solution with aliphatic hydrocarbon solvent oil under the stabilizing effect of fatty acid-modified hydrophobic calcium carbonate particles. Through the interaction between calcium ions and fatty acid groups modified on the calcium carbonate surface at different pH levels, the hydrophilicity / hydrophobicity of the calcium carbonate surface changes at different pH values, resulting in an effect where the emulsion phase type changes according to pH variations. The obtained pH-responsive Pickerling emulsion can be widely used in coatings, fluid transportation, food, and cosmetics.

Description

Technical Field

[0001] This invention relates to the field of Pickering emulsions, specifically a micro / nano-sized calcium carbonate-stabilized pH-responsive Pickering emulsion. The pH responsiveness of the emulsion is achieved through the interaction between calcium ions in the aqueous phase and fatty acid ions on the surface of hydrophobically modified calcium carbonate, allowing the emulsion type to be changed from water-in-oil (O / W) to oil-in-water (W / O) or vice versa. The preparation and application of this emulsion involve colloidal dispersions, coatings, fluid transport, food, and cosmetics. Background Technology

[0002] Pickering emulsions are emulsions obtained using ultrafine solid particles as emulsifiers. This means that stable emulsions can be prepared directly by dispersing colloidal microparticles within the colloidal size range into the emulsion, eliminating the need for amphiphilic surfactants to reduce interfacial tension. Compared to emulsions stabilized by traditional surfactants, Pickering emulsions offer several significant advantages: they significantly reduce the amount of emulsifier used, are far less toxic to humans than surfactants, and are environmentally friendly. Therefore, Pickering emulsions have important applications in the food, cosmetics, and pharmaceutical industries. The type of Pickering emulsion mainly depends on the hydrophilicity or hydrophobicity of the solid particles used. Hydrophilic solid particles easily form oil-in-water emulsions; conversely, hydrophobic solid particles easily form water-in-oil reverse emulsions. Many types of solid particles have been successfully used in the preparation of Pickering emulsions, such as titanium dioxide, silica, diatomaceous earth, and calcium carbonate.

[0003] In industrial applications, particle stabilizers need to be inexpensive, readily available, environmentally friendly, and biocompatible, all of which calcium carbonate (CaCO3) meets. Calcium carbonate is a very common inorganic compound with significant advantages such as wide availability of raw materials, low price, non-toxicity, environmental friendliness, and good stability. Furthermore, the preparation process of calcium carbonate is easy to control, facilitating industrial production. This has led to a rapid increase in demand for calcium carbonate, which is now widely used in industries such as plastics, rubber, papermaking, and coatings to reduce costs and improve product performance. It can also be used as a stabilizer in the preparation of Pickering emulsions. Changing the type of calcium carbonate-stabilized emulsions through environmental stimuli such as pH and temperature has broad application prospects in the architectural coatings, fluid transportation, food, and cosmetics industries. Existing literature (CN202110355038.0) describes polymerizing pH-responsive functional groups onto the surface of calcium carbonate particles. Changing the pH alters the hydrophilicity or hydrophobicity of these groups, thus changing the emulsion type. However, polymerizing or incorporating pH- or temperature-responsive groups onto the particle surface is complex and increases costs. Currently, there is a lack of a simple and effective method to achieve the pH response of calcium carbonate-stabilized Pickering emulsions, so that changes in pH result in changes in phase type. Summary of the Invention

[0004] Therefore, in order to overcome the above-mentioned shortcomings, the present invention provides a pH-responsive Pickering emulsion with micro / nano calcium carbonate stability. Through the different interactions between calcium ions and fatty acid ions modified on the surface of calcium carbonate at different pH levels, the hydrophilicity and hydrophobicity of the calcium carbonate surface are changed, thereby bringing about a change in the emulsion phase type. The change in pH can transform the emulsion into a water-in-oil or oil-in-water type.

[0005] This invention is achieved by constructing a micro / nano-sized calcium carbonate-stabilized pH-responsive Pickering emulsion, the preparation and emulsion phase type transformation steps of which include:

[0006] (1) Prepare a calcium chloride solution with a concentration of 80-1000 mmol / L using deionized water and anhydrous calcium chloride, and further adjust the pH of the solution to 2-4 with hydrochloric acid to obtain an aqueous phase;

[0007] (2) Weigh a certain mass of hydrophobic micro-nano calcium carbonate particles whose surface has been modified by long-chain fatty acids, add them to a certain volume of aliphatic hydrocarbon solvent oil, and stir to disperse the calcium carbonate particles into the aliphatic hydrocarbon solvent oil to form a uniform suspension oil.

[0008] (3) Under the action of emulsification shear, the aqueous phase is gradually added dropwise to the suspended oil. After all the dropwise phase is added, emulsification is continued for 1-3 minutes to obtain a water-in-oil Pickering emulsion.

[0009] (4) Phase transformation of emulsion: Sodium hydroxide solution is added dropwise to the prepared water-in-oil emulsion to make the pH of the emulsion reach 9-13, and emulsification is carried out for 1-3 minutes. The emulsion can be transformed into an oil-in-water type. Hydrochloric acid solution is added dropwise to the oil-in-water type emulsion to make the pH of the emulsion reach 2-4, and emulsification is carried out for 1-3 minutes. The emulsion can be transformed into a water-in-oil type. This process is repeated.

[0010] Preferably, the micro / nano calcium carbonate water-modified calcium carbonate has a contact angle of 110-140°, an amount of 2-6 wt% of the aqueous phase, and a particle size of 30 nm-10 μm.

[0011] Preferably, the volume ratio of the calcium carbonate suspension oil to the aqueous phase is 1:2-2:1;

[0012] Preferably, the emulsification conditions are 1000-5000 rpm for 1-3 minutes.

[0013] Preferably, the concentrations of the sodium hydroxide solution and hydrochloric acid solution used for the phase transition of the emulsion are 0.01-0.3%;

[0014] Acidic and alkaline solutions will dilute the concentration of calcium ions in the aqueous phase. The number of phase transitions varies from 1 to 10 depending on the concentration of the calcium chloride solution and the acid or alkaline solution.

[0015] This invention has the following advantages: This invention relates to a micro / nano calcium carbonate-stabilized pH-responsive Pickering emulsion, which has the following beneficial effects compared to the prior art:

[0016] This invention uses a calcium ion solution as the aqueous phase. Through the interaction between calcium ions and fatty acid ions modified on the calcium carbonate surface at different pH levels, the hydrophilicity / hydrophobicity of the calcium carbonate surface changes, leading to a change in the emulsion phase type. The pH change can transform the emulsion into a water-in-oil or oil-in-water type. At around pH 7, the fatty acid-modified calcium carbonate surface is hydrophobic, and the resulting stable Pickering emulsion is water-in-oil. When more than 80 mmol of calcium chloride is present in the aqueous phase, calcium ions compete for fatty acid ions on the calcium carbonate surface, forming free calcium fatty acids that enter the oil phase, causing the calcium carbonate surface to change from hydrophobic to hydrophilic. The resulting Pickering emulsion is oil-in-water. Adding hydrochloric acid to the calcium chloride solution causes the hydrochloric acid to react with the calcium fatty acids, producing fatty acid ions and calcium chloride. The fatty acid ions can adsorb onto the calcium carbonate surface, making the calcium carbonate surface hydrophobic, resulting in a water-in-oil emulsion. Adding sodium hydroxide to the system further causes a neutralization reaction between sodium hydroxide and fatty acid ions on the particle surface to form sodium fatty acid. At this point, the fatty acid ions can react with calcium ions to form calcium fatty acid. This process causes calcium carbonate to lose its fatty acid surface modification and become hydrophilic, and the corresponding emulsion becomes an oil-in-water emulsion. This process is repeated.

[0017] This invention uses inexpensive and widely commercialized fatty acid hydrophobically modified calcium carbonate particles as a stabilizer for Pickering emulsions. The pH response of the Pickering emulsion is achieved through simple ion interactions. By changing the pH, the emulsion can be converted from a water-in-oil emulsion to a water-in-oil emulsion or vice versa, without the need to modify the calcium carbonate surface with pH-responsive groups, significantly simplifying the emulsion preparation process. The resulting pH-responsive Pickering emulsion can be widely used in coatings, fluid transport, food, and cosmetics. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation and phase transition of pH-responsive Pickering emulsions stabilized by micro / nano calcium carbonate. Detailed Implementation

[0019] The following will be combined with the appendix Figure 1 This invention will be described in detail, and the technical solutions in the embodiments of this invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] This invention provides a micro / nano calcium carbonate-stabilized pH-responsive Pickering emulsion. The following detailed description, in conjunction with embodiments, enables those skilled in the art to implement the invention based on the description.

[0021] Example 1:

[0022] (1) Prepare a calcium chloride solution with a concentration of 80 mmol / L using deionized water and anhydrous calcium chloride, and further adjust the pH of the solution to 2 with hydrochloric acid to obtain an aqueous phase;

[0023] (2) Weigh 6g of hydrophobic micro-nano calcium carbonate particles with a contact angle of 140° and an average particle size of 30nm, which have been modified by stearic acid hydrophobicity, and add them to 100mL of aliphatic hydrocarbon solvent oil. Stir to disperse the calcium carbonate particles into the aliphatic hydrocarbon solvent oil to form a uniform suspension oil.

[0024] (3) Under the emulsification shearing action of 1000 rpm, 100 mL of aqueous phase was gradually added dropwise to 100 mL of suspended oil. After all the phase was added, emulsification was continued for 1 min to obtain water-in-oil Pickering emulsion.

[0025] (4) Phase transformation of emulsion: Add 0.3% sodium hydroxide solution to the prepared water-in-oil emulsion to make the pH of the emulsion reach 13, continue emulsification for 1 min, and the emulsion can be transformed into an oil-in-water type. Add 0.3% hydrochloric acid solution to the oil-in-water type emulsion again to make the pH of the emulsion reach 2, continue emulsification for 1 min, and the emulsion can be transformed into a water-in-oil type. This process can be repeated once.

[0026] Example 2:

[0027] (1) Prepare a calcium chloride solution with a concentration of 1000 mmol / L using deionized water and anhydrous calcium chloride, and further adjust the pH of the solution to 4 with hydrochloric acid to obtain an aqueous phase;

[0028] (2) Weigh 2g of hydrophobic micro-nano calcium carbonate particles with a contact angle of 110° and an average particle size of 10μm, which have been modified by hexadecanoic acid hydrophobicity, and add them to 200mL of aliphatic hydrocarbon solvent oil. Stir to disperse the calcium carbonate particles into the aliphatic hydrocarbon solvent oil to form a uniform suspension oil.

[0029] (3) Under the emulsification shearing action of 5000rpm, 100mL of aqueous phase was gradually added dropwise to 200mL of suspension oil. After all the phase was added, emulsification was continued for 3min to obtain water-in-oil Pickering emulsion.

[0030] (4) Phase transformation of emulsion: Add 0.01% sodium hydroxide solution to the prepared water-in-oil emulsion to make the pH of the emulsion reach 9, and continue emulsification for 3 minutes to transform the emulsion into an oil-in-water type. Add 0.01% hydrochloric acid solution to the oil-in-water type emulsion again to make the pH of the emulsion reach 4, and continue emulsification for 3 minutes to transform the emulsion into a water-in-oil type. This process can be repeated about 10 times.

[0031] Example 3:

[0032] (1) Prepare a calcium chloride solution with a concentration of 200 mmol / L using deionized water and anhydrous calcium chloride, and further adjust the pH of the solution to 3 with hydrochloric acid to obtain an aqueous phase;

[0033] (2) Weigh 10g of hydrophobic micro-nano calcium carbonate particles with a contact angle of 130° and an average particle size of 500nm, which have been modified by stearic acid hydrophobicity, and add them to 100mL of dearomatic solvent oil D110. Stir to disperse the calcium carbonate particles into D110 and form a uniform suspension oil.

[0034] (3) Under the emulsification shearing action of 3000 rpm, 200 mL of aqueous phase was gradually added dropwise to 100 mL of suspension oil. After all the phase was added, emulsification was continued for 1 min to obtain water-in-oil Pickering emulsion.

[0035] (4) Phase transformation of emulsion: Add 0.1% sodium hydroxide solution to the prepared water-in-oil emulsion to make the pH of the emulsion reach 10, continue emulsification for 1 min, and the emulsion can be transformed into an oil-in-water type. Add 0.1% hydrochloric acid solution to the oil-in-water type emulsion again to make the pH of the emulsion reach 3, continue emulsification for 1 min, and the emulsion can be transformed into a water-in-oil type. This process can be repeated about 8 times.

[0036] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A micro- and nano- calcium carbonate stabilized pH-responsive Pickering emulsion characterized in that Its preparation and emulsion phase type transformation steps include: (1) Prepare a calcium chloride solution with a concentration of 80-1000 mmol / L using deionized water and anhydrous calcium chloride, and further adjust the pH of the solution to 2-4 with hydrochloric acid to obtain an aqueous phase; (2) Weigh a certain mass of hydrophobic micro-nano calcium carbonate particles whose surface has been modified by long-chain fatty acids, add them to a certain volume of aliphatic hydrocarbon solvent oil, and stir to disperse the calcium carbonate particles into the aliphatic hydrocarbon solvent oil to form a uniform suspension oil. (3) Under the action of emulsification shear, the aqueous phase is gradually added dropwise to the suspended oil. After all the dropwise phase is added, emulsification is continued for 1-3 minutes to obtain a water-in-oil Pickering emulsion. (4) Phase transformation of emulsion: Sodium hydroxide solution is added dropwise to the prepared water-in-oil emulsion to make the pH of the emulsion reach 9-13. After emulsification for 1-3 minutes, the emulsion can be transformed into an oil-in-water type. Hydrochloric acid solution is added dropwise to the oil-in-water emulsion to make the pH of the emulsion reach 2-4. After emulsification for 1-3 minutes, the emulsion can be transformed into a water-in-oil type. This process is repeated.

2. The micro-nano calcium carbonate stabilized pH-responsive Pickering emulsion according to claim 1, characterized in that, The hydrophobic micro-nano calcium carbonate particles mentioned in step (2) have a contact angle of 110-140°, a dosage of 2-6 wt% of the aqueous phase, and a particle size of 30 nm-10 μm.

3. The micro-nano calcium carbonate stabilized pH-responsive Pickering emulsion according to claim 1, characterized in that, The volume ratio of the suspended oil and water phase in step (3) is 1:2-2:

1.

4. The micro-nano calcium carbonate stabilized pH-responsive Pickering emulsion according to claim 1, characterized in that, The emulsification conditions are 1000-5000 rpm for 1-3 minutes.

5. The micro-nano calcium carbonate stabilized pH-responsive Pickering emulsion according to claim 1, characterized in that, The concentrations of sodium hydroxide and hydrochloric acid solutions used for the phase transition of the emulsion are 0.01-0.3%.

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