A method for preparing a reversible response pickering emulsion

Abstract

This invention discloses a method for preparing a reversible responsive Pickering emulsion, using Cn-MPA-N as the emulsifier. The structure of Cn-MPA-N is shown below, where n = 10, 12, 14, 16, 18. Upon introducing CO2 into an aqueous solution of Cn-MPA-N, Cn-MPA-N is protonated and converted to a cationic form of Cn-MPA-N. + Then to Cn-MPA-N + N2 is bubbled into an aqueous solution, Cn-MPA-N + The deprotonation process reverts the Cn-MPA-N to its nonionic form, and this process can be repeated. This invention's reversible Pickering emulsion allows emulsification and demulsification to occur at room temperature, eliminating the need for special operating environments and temperatures, thus simplifying operation and reducing costs. Emulsification and demulsification can be repeatedly cycled, and the emulsion particle size and stability remain essentially unchanged after multiple cycles. Furthermore, the emulsifier in this application can be reused, and the collected aqueous phase after demulsification can be used to emulsify a new oil phase with a particle size essentially consistent with the first emulsification. 12 The combined use of MPA-N and nano-alumina can effectively reduce C 12 The amount of -MPA-N used improves the stability of Pickering emulsion; the emulsifier in this application uses natural rosin as raw material, which is in line with the concept of green and sustainable development.

Description

Technical Field

[0001] This invention belongs to the field of green surfactant technology, specifically relating to a method for preparing a reversible responsive Pickering emulsion. Background Technology

[0002] Traditional emulsions are dispersion systems where one liquid is dispersed into another immiscible liquid, stabilized by surfactants; these are thermodynamically unstable systems. Pickering emulsions, on the other hand, are dispersion systems composed of two immiscible liquids stabilized by surface-active solid particles; these are thermodynamically stable systems. In Pickering emulsions, surface-active solid particles adsorb at the oil-water interface and form a dense film, thereby stabilizing the oil-water emulsion. Compared to traditional emulsions stabilized by surfactants, Pickering emulsions exhibit higher stability, a larger oil-water interface, and lower toxicity, thus possessing greater application potential in fields such as petroleum, cosmetics, food, biomedicine, and interfacial catalysis.

[0003] However, in practical applications, people have different requirements for the stability of emulsions. Some fields, such as food and cosmetics, require emulsions with long-term stability, while fields like oil transportation and interfacial reactions often require temporarily stable emulsions. After their functionality is achieved, the emulsion needs to be broken down to achieve our needs, such as product separation. Therefore, in recent years, intelligently responsive or controllable Pickering emulsions have attracted much attention from researchers.

[0004] With the development of smart materials, smart responsive surfactants, which can reversibly switch between surface activity and inactivity in response to external stimuli, have attracted widespread attention. Particles adsorbed by these responsive surfactants can also respond to external stimuli such as pH, gases, light, heat, and magnetic fields. pH responses can lead to salt accumulation in the system, affecting the physicochemical properties of substances and limiting their application in some fields. In contrast, gas-responsive surfactants are widely popular due to their environmental friendliness, non-toxicity, low cost, and ease of removal.

[0005] However, in existing reports, most gas-responsive surfactants use traditional petroleum-based surfactants as raw materials, which not only harms the environment but also greatly limits the types of surfactants available. With increasing environmental awareness, green chemistry is receiving more and more attention, creating an urgent need to develop green and environmentally friendly gas-responsive surfactants that replace petrochemical resources with natural resources. Meanwhile, existing gas-responsive Pickering emulsions require heating to complete demulsification, which is cumbersome, energy-intensive, and in many practical situations where on-site heating is inconvenient, thus hindering widespread adoption. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a reversible responsive Pickering emulsion, which belongs to the category of gas-responsive Pickering emulsions. Under room temperature conditions, it can achieve repeated cycles of emulsification and demulsification in response to gas stimulation without introducing pollution accumulation. Moreover, the particle size of the emulsion remains basically unchanged after multiple cycles. The amount of emulsifier used is small, and the stability is good.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a reversible responsive Pickering emulsion, using Cn-MPA-N as the emulsifier, the structure of which is... Where n = 10, 12, 14, 16, 18; after CO2 is introduced into an aqueous solution of Cn-MPA-N, Cn-MPA-N is protonated and converted into the cationic form of Cn-MPA-N. + Then to Cn-MPA-N + N2 is bubbled into the aqueous solution, Cn-MPA-N + Deprotonation back into the nonionic form of Cn-MPA-N can be repeated repeatedly, as follows:

[0009]

[0010] The aforementioned Cn-MPA-N is made from natural rosin resin, which is abundant, environmentally friendly, inexpensive, and renewable.

[0011] Cn-MPA-N is prepared by reacting maleic amylate imide with oxaloyl chloride at 25–55 °C for 3–6 h, followed by reaction with N,N-dimethylethylenediamine at 0–5 °C for 2–4 h.

[0012] The specific process for preparing Cn-MPA-N is as follows:

[0013] (1) Maleic rosin is prepared by addition reaction of refined rosin and maleic anhydride, and maleic acrid acid is obtained by recrystallization with glacial acetic acid; wherein the molar ratio of refined rosin to maleic anhydride is 1:(1.1-1.5), for example, the ratio can be 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5; glacial acetic acid is used as solvent, and the mass of glacial acetic acid is 3-6g / 10g of refined rosin, for example 3g / 10g, 4g / 10g, 5g / 10g, 6g / 10g; the reaction temperature is 140-150℃, for example 140℃, 145℃, 150℃; the reaction time is 4-6h, for example 4h, 5h, 6h; after the reaction is completed and cooled, glacial acetic acid is added to precipitate crystals, and the solid is obtained by filtration; the obtained solid is recrystallized with glacial acetic acid to obtain maleic acrid acid;

[0014] (2) Maleicopteric acid is reacted with a long-chain alkylamine to prepare maleicopteric acid imide Cn-MPA, wherein the long-chain alkylamine can be any one of n-decylamine, dodecylamine, tetradecylamine, hexadecylamine, or octadecylamine; the chemical formula of Cn-MPA is shown below; wherein the molar ratio of maleicopteric acid to long-chain alkylamine is 1:(1.0~1.2), for example, the ratio can be 1:1.0, 1:1.1, or 1:1.2; anhydrous ethanol is used as solvent, the reaction temperature of imidization is 75~85℃, for example, 75℃, 80℃, or 85℃; the reaction time is 9~11h, for example, 9h, 10h, or 11h;

[0015] (3) Maleic pine acid imide Cn-MPA is first acyl chloride reacted with oxaloyl chloride, and then reacted with N,N-dimethylethylenediamine to prepare rosin-based CO2 / N2 responsive surfactants Cn-MPA-N with different flexible chain lengths; wherein the molar ratio of Cn-MPA to oxaloyl chloride is 1:(1.5~2.0), for example, the ratio can be selected as 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0; dichloromethane is used as solvent, and the reaction temperature is 25°C. The reaction temperature is 25℃, 35℃, 45℃, or 55℃; the reaction time is 3 to 6 hours, for example, 3 hours, 4 hours, 5 hours, or 6 hours; maleic amylinimide chloride is obtained; the molar ratio of maleic amylinimide chloride to N,N-dimethylethylenediamine is 1:(1.0 to 1.2), for example, the ratio can be 1:1.0, 1:1.1, or 1:1.2; dichloromethane is used as the solvent; the reaction temperature is 0 to 5℃, for example, 0℃ or 5℃; the reaction time is 2 to 4 hours, for example, 2 hours, 3 hours, or 4 hours.

[0016] In this application, the emulsifier is further preferred to have n=12. The inventors have discovered that when n=12, when combined with nano-alumina, the amount of emulsifier used can be effectively reduced, thereby improving the stability of the Pickering emulsion.

[0017] The Pickering emulsion was prepared as follows: Cn-MPA-N was dissolved in an aqueous CO2 solution to form a cationic bicarbonate, which was then reacted with charged nanoparticles under high shear conditions via electrostatic interaction to prepare a CO2 / N2-responsive Pickering emulsion. The resulting Pickering emulsion exhibited excellent stability. N2 was introduced into the emulsion at room temperature, causing rapid demulsification. After demulsification, CO2 was introduced again to form a stable emulsion. This demulsification and emulsification process could be repeated. Furthermore, the particle size of the emulsion obtained after demulsification and re-emulsification was essentially the same as that of the initially prepared emulsion.

[0018] The Pickering emulsion prepared in this application is of the O / W type. Under normal conditions, N2 in the air does not affect the stability of the Pickering emulsion; demulsification requires the introduction of additional N2 into the emulsion. CO2 in the air also does not affect demulsification; re-emulsification requires the introduction of additional CO2 into the emulsion.

[0019] The aforementioned charged nanoparticles can be nano-alumina, nano-titanium oxide, nano-ferric oxide, or nano-silicon oxide, etc. Nano-alumina is preferred, and the nano-alumina conforms to the composition of this application (C). 12 -MPA-N, when used in combination, can effectively reduce C 12 The dosage of MPA-N improves the stability of Pickering emulsions.

[0020] Further preferred, the Pickering emulsion is prepared by: C 12 -MPA-N, charged nanoparticles, and water are mixed, and CO2 is introduced to make C 12 -MPA-N protonated to C 12 -MPA-N + Then, the oil phase is added and subjected to high shear at 5000-11000 rpm for 1-2 minutes to obtain a uniformly dispersed Pickering emulsion. N2 is introduced into the emulsion at room temperature, and the Pickering emulsion quickly demulsifies. After demulsification, CO2 is introduced to form a stable emulsion again. The aforementioned demulsification and emulsification can be repeated.

[0021] The preferred inlet rates for both CO2 and N2 are 100-150 mL / min.

[0022] The aqueous phase after demulsification is collected and used to emulsify a new oil phase. The resulting emulsion has a particle size that is basically the same as that of the emulsion obtained in the initial emulsification. Therefore, this responsive surfactant can be reused.

[0023] The oil phase described above is liquid paraffin.

[0024] To improve the homogeneity of the emulsion system, the volume ratio of water to oil phase is 1:(0-4).

[0025] In the above preparation, C 12 The concentration of -MPA-N in water is 0.01–1 mM (millimoles per liter). When the volume ratio of water to oil is 1:1, 0.01 mM... 12 -MPA-N can yield a uniformly dispersed Pickering emulsion. C 12 As the concentration of MPA-N increases, the volume of the emulsifiable oil phase increases; however, when the concentration exceeds 1 mM, the emulsification effect essentially remains unchanged. Unless otherwise specified in this application, C 12 -MPA-N concentration refers to C 12-Concentration of MPA-N in water.

[0026] To ensure the stability of the emulsion system, the mass of the charged nanoparticles used is 0.05–0.15% of the water mass.

[0027] Any techniques not mentioned in this invention are based on existing technologies.

[0028] This invention relates to a reversible, responsive Pickering emulsion where emulsification and demulsification occur at room temperature, requiring no special operating environment or temperature, thus simplifying operation and reducing costs. Emulsification and demulsification can be repeatedly cycled, and the emulsion particle size and stability remain essentially unchanged after multiple cycles. Furthermore, the emulsifier in this application is reusable, and the collected aqueous phase after demulsification can be used to emulsify a new oil phase with a particle size essentially consistent with the first emulsification. 12 - The combination of MPA-N and nano-alumina can effectively reduce C 12 The amount of MPA-N used improves the stability of the Pickering emulsion; the resulting cinnamon oil Pickering emulsion, when applied or sprayed onto fruits or vegetables, forms a protective film, effectively extending shelf life; the emulsifier in this application uses natural rosin as raw material, which is in line with the concept of green and sustainable development. Attached Figure Description

[0029] Figure 1 C 12 -MPA-N NMR spectrum;

[0030] Figure 2 C 12 -MPA-N response appearance diagram with alternating CO2 / N2 inlet;

[0031] Figure 3 C 12 -MPA-N + Cyclic changes in pH and redox potential with alternating CO2 / N2 introduction;

[0032] Figure 4 C 12 -MPA-N + The γ-lgC relationship curve;

[0033] Figure 5 Microscopic images of the resulting Pickering emulsion at room temperature;

[0034] Figure 6 The image shows the microstructure of the Pickering emulsion during three cycles. Detailed Implementation

[0035] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0036] In all cases, the temperature operation was not specifically mentioned and was performed at room temperature, which was 15–25°C.

[0037] Example 1

[0038] The preparation of Cn-MPA-N includes the following steps:

[0039] (1) Weigh 100g (0.33mol) of refined rosin, 35.6g (0.3625mol) of maleic anhydride and 40g of glacial acetic acid into a four-necked flask, stir mechanically, reflux under condensation, slowly heat to 140℃, and continue the reaction for 5 hours. After cooling to room temperature, add 100g of glacial acetic acid to crystallize, filter to obtain maleic rosin, recrystallize 3 times with glacial acetic acid to obtain maleic acridinium (MPA).

[0040] (2) Weigh 10 g (0.025 mol) of maleic acrid acid and 5.1 g (0.0275 mol) of dodecylamine into a three-necked flask, add 60 mL of anhydrous ethanol, stir magnetically, reflux under condensation, and heat to 80 °C for 10 h. After the reaction is complete, a pale yellow liquid is formed. After removing the solvent by rotary evaporation, 50 mL of dichloromethane is added to dissolve the liquid, and the solution is dried over anhydrous sodium sulfate. After silica gel column chromatography (petroleum ether: ethyl acetate = 2:1), a colorless solid, namely maleic acrid acid imide C, is obtained. 12 -MPA.

[0041] (3) Weigh out maleic anhydride imide C 12 -MPA (5.67 g, 0.010 mol) was added to a three-necked flask, along with 25 mL of dichloromethane. The mixture was magnetically stirred, refluxed, and oxalyl chloride (1.91 g, 0.015 mol) was added dropwise at room temperature. After the addition was complete, the temperature was raised to 50 °C and the reaction was allowed to proceed for 5 hours. After the reaction was complete, volatile substances were removed by rotary evaporation, yielding a pale yellow solid, which was maleic anhydride imide chloride. Maleic anhydride imide chloride was dissolved in 20 mL of anhydrous dichloromethane and slowly added dropwise under ice bath conditions to a mixed solution of N,N-dimethylethylenediamine (1.06 g, 0.012 mol), triethylamine (3.10 g, 0.030 mol), and 30 mL of dichloromethane. After the addition was complete, the reaction was allowed to proceed for 4 hours. After the reaction was complete, crystals precipitated on the upper layer, and the solution was pale yellow. Filter the solution, extract the filtrate thoroughly with ultrapure water and saturated sodium bicarbonate solution, dry the organic phase with anhydrous sodium sulfate, and purify by silica gel column chromatography (dichloromethane:methanol = 10:1) to obtain a pale yellow solid, which is product C. 12 -MPA-N, 1 HNMR such as Figure 1 As shown.

[0042] Example 2

[0043] Through C12 The cyclic changes in pH and redox potential (ORP) of the -MPA-N solution were used to determine the C. 12 -MPA-N's responsiveness to CO2 / N2. C 12 The response process of -MPA-N (1mM) to CO2 / N2 is as follows: Figure 2 and Figure 3 As shown. CO2 dissolves in aqueous solution to form H2CO3. The weak acid solution leads to the protonation of the tertiary amine group, generating a charged cationic surfactant C. 12 -MPA-N + This causes the pH and ORP to drop to approximately 4 and 10 mV, respectively. After introducing N2 at room temperature to expel CO2, the weak acidity of the solution disappears, and the charged cationic surfactant deprotonates back to its initial tertiary amine group state, causing the pH and ORP to rise to their initial values. When CO2 is introduced again, the pH and ORP again drop to approximately 4 and 10 mV. This process can be repeated several times to illustrate the effect of C. 12 -MPA-N exhibits excellent responsiveness to CO2 / N2, and the aforementioned process can be repeatedly cyclical. Due to its reversible responsiveness to CO2, it can be used to prepare smart responsive materials and for applications in gas sensing.

[0044] Example 3

[0045] The surface tension method was used to test different concentrations of C. 12 -MPA-N + Critical micelle concentration (cmc) of aqueous solution and surface tension (γ) at the critical micelle concentration. cmc The method is as follows:

[0046] Prepare different concentrations of C 12 -MPA-N + The surfactant was prepared in aqueous solution and equilibrated in an intelligent biochemical incubator for 24 hours (25±0.5℃). The surface tension of the surfactant was then measured using a Sigma 701 surface tension meter via the Du Noüy ring method. Three parallel tests were performed, and the average value was taken. The test temperature was 25±0.5℃, and the water used in the experiment was ultrapure water (18.2 MΩ·cm). (The last sentence appears to be incomplete and possibly refers to a different topic.) 12 -MPA-N + Plot C with the logarithm of the aqueous solution concentration on the x-axis and the surface tension value corresponding to the concentration on the y-axis. 12 -MPA-N + The γ-lgC relationship curve, such as Figure 4 As shown in the figure. The critical micelle concentration (cmc) of the charged cationic surfactant aqueous solution obtained from this curve is 0.05 mM, and the corresponding surface tension (γ) is... cmcThe critical micelle concentration (CMC) is 33.4 mN / m. Compared to commercially available cationic surfactants like CTAB, it has a much lower CMC and can be used in emulsion polymerization, drug release, cosmetics, and template-based preparation of functional materials.

[0047] Example 4

[0048] The preparation of the picking emulsion, the microstructure of the emulsion was photographed using a polarizing microscope, and the stability of the emulsion was observed. The methods are as follows:

[0049] Prepare 7 mL of C at different concentrations 12 -MPA-N aqueous solutions with concentrations of 0, 0.01 mM, 0.02 mM, 0.06 mM, 0.3 mM, 0.6 mM, and 1 mM were prepared. 0.1 wt% nano-alumina was ultrasonically dispersed in 7 mL of C4O4 solutions of different concentrations for 2 minutes. 12 In an aqueous solution of -MPA-N, CO2 (120 mL / min) was bubbled through for 10 minutes to protonate it, yielding C. 12 -MPA-N + In both cases, 7 mL of liquid paraffin was added to the aqueous solution, and the mixture was subjected to high shear at 11000 rpm for 2 minutes to obtain uniformly dispersed Pickering emulsions. Macroscopic photographs of the Pickering emulsions were recorded using a digital camera at 1 day, 7 days, 30 days, and 60 days after preparation, as shown below. Figure 5 As shown, on the 7th day after the Pickering emulsion preparation, the microstructure of the 0.01mM, 0.02mM, 0.06mM, 0.3mM, 0.6mM, and 1mM emulsions was photographed using a polarizing microscope. It is evident that stable emulsions cannot be formed in the presence of nano-alumina alone; however, when the surfactant concentration is only 0.01mM, it can synergistically form a Pickering emulsion with nano-alumina and remain stable at room temperature for more than 60 days. Emulsions with surfactant concentrations of 0.02 and 0.06mM can remain stable at room temperature for more than 60 days; and emulsions with surfactant concentrations of 0.3mM, 0.6mM, and 1mM can remain stable at room temperature for more than 90 days. This significantly reduces the amount of surfactant used, saving costs.

[0050] Comparative Example 1

[0051] Pickering emulsion was prepared using nano-silica instead of nano-alumina, and all other steps were the same as in Example 4. 12 A stable Pickering emulsion could not be obtained when the concentration of the MPA-N aqueous solution was 0.02 mM. When C 12 Pickering emulsions can be obtained when the concentration of 0.06 mM of 0.06 MPA-N aqueous solution is used, and the stability at room temperature is about 30 days.

[0052] Example 5

[0053] The Pickering emulsion prepared by this surfactant in conjunction with nanoparticles exhibits good responsiveness to CO2 / N2. 0.6 mM C was added to a 20 mL glass bottle. 12 7 mL of MPA-N aqueous solution was added, followed by the addition of 0.1 wt% nano-alumina (relative to the aqueous solution) and ultrasonic dispersion for 2 minutes. CO2 was then introduced at 120 mL / min and maintained for 10 minutes. An equal volume of 7 mL liquid paraffin was added, and homogenization was performed at 11000 rpm under high shear for 2 minutes to obtain a Pickering emulsion. N2 was then introduced at room temperature at 120 mL / min and maintained for 10 minutes, resulting in emulsion demulsification and clear oil-water phase separation. CO2 was again introduced at 120 mL / min and maintained for 10 minutes, followed by homogenization at 11000 rpm under high shear for 2 minutes to form another emulsion. The emulsion's stability was greater than 90 days. This process can be repeated, and a stable emulsion can still be obtained after 20 cycles. Figure 6 As shown, the microstructure of the Pickering emulsion obtained after 10 cycles of CO2 / N2 infusion remained essentially unchanged, indicating that the Pickering emulsion prepared by this method exhibits good responsiveness to CO2 / N2. The aqueous phase after the fifth demulsification was collected and emulsified with a new equal volume of liquid paraffin; the particle size and stability were consistent with the initial emulsification, proving that this responsive surfactant can be reused.

[0054] In the experiment, the inventors used C at concentrations of 0.02, 0.06, 0.3, and 1 mM, respectively. 12 The above steps were repeated for -MPA-N, and the results were basically the same as those for 0.6mM, so they will not be repeated here.

[0055] Example 6

[0056] Constructing a cinnamon oil pickering emulsion coating can enhance the preservation effect on fruits and vegetables.

[0057] Add 0.1 mM C to a 20 mL glass bottle. 12A cinnamon oil pickering emulsion was prepared by ultrasonically dispersing 7 mL of MPA-N aqueous solution with 0.1 wt% nano-alumina for 2 minutes, followed by CO2 (120 mL / min) for 10 minutes, and then adding an equal volume of 7 mL cinnamon oil. The mixture was homogenized at 11000 rpm for 2 minutes under high shear pressure. The pickering emulsion was then applied to mangoes to form a protective film. A blank test was performed by mixing 7 mL of ethanol and 7 mL of cinnamon oil and applying an equal amount (equal to the amount of pickering emulsion) to the mangoes. Compared to the blank test, the pickering emulsion extended the water retention and preservation effect on mangoes by more than 15 days, demonstrating that the protective film formed by the pickering emulsion on the fruit can slowly release cinnamon oil and extend the shelf life of the fruit.

Claims

1. A method for preparing a reversible responsive Pickering emulsion, characterized in that: The emulsifier used in the reversible responsive Pickering emulsion is Cn-MPA-N, and the structure of Cn-MPA-N is as follows: Where n = 12, 14, 16, 18; The following process can be repeated by passing CO2 and N2 into an aqueous solution of Cn-MPA-N: ； The preparation method of reversible responsive Pickering emulsion is as follows: C 12 -MPA-N, charged nanoparticles, and water are mixed, and CO2 is introduced to make C 12 -MPA-N protonated to C 12 -MPA-N + Then, add the oil phase and apply high shear at 5000~11000 rpm for 1~2 minutes to obtain a uniformly dispersed Pickering emulsion; Emulsification and demulsification can be repeatedly cycled under the stimulation of gas at room temperature: when N2 is introduced into the emulsion at room temperature, the Pickering emulsion demulsifies, and after demulsification, CO2 is introduced to form a stable emulsion again. The aforementioned emulsification and demulsification can be repeatedly cycled. When the volume ratio of water to oil is 1:1, 0.01 mmol / L 12 -MPA-N can be used to obtain a uniformly dispersed Pickering emulsion; The mass fraction of charged nanoparticles used is 0.05~0.15% of the water mass; The oil phase is cinnamon essential oil. The resulting Pickering emulsion can be applied or sprayed onto fruits or vegetables to form a protective film, slow-release cinnamon essential oil, and extend shelf life.

2. The method for preparing the reversible responsive Pickering emulsion as described in claim 1, characterized in that: n=12。 3. The method for preparing the reversible responsive Pickering emulsion as described in claim 1 or 2, characterized in that: The charged nanoparticles are nano-alumina.

4. The method for preparing the reversible responsive Pickering emulsion as described in claim 1 or 2, characterized in that: The aqueous phase after demulsification is collected and used to emulsify a new oil phase. The resulting emulsion has the same particle size as the emulsion obtained from the initial emulsification.

5. The method for preparing the reversible responsive Pickering emulsion as described in claim 1 or 2, characterized in that: C 12 The concentration of -MPA-N in water is 0.01~0.1 mmol / L.

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