CN114854431B - A kind of intelligent Pickering emulsion based on dynamic covalent bond and preparation method thereof - Google Patents

Abstract

The invention discloses an intelligent Pickering emulsion based on dynamic covalent bonds and a preparation method thereof, belonging to the field of colloid and interface chemistry. The invention utilizes a surfactant system (H) ⁺ AA and FA) and oppositely charged SiO ₂ The particles act to form surface active particles with pH as a trigger mechanism, and the Pickering emulsion is synergistically stabilized; bola compounds which are "strongly polar" under alkaline conditions, which compounds do not possess surface activity and cannot synergistically act on SiO ₂ The granules stabilize Pickering emulsions; the intelligent conversion of the compound from 'amphiphilicity', 'strong polarity' and the conversion of the emulsion from 'milk formation' to 'non-milk formation' are realized, and the circulation times are six times; meanwhile, the surfactant does not remain in the oil phase, so that the recovery and the reutilization of the surfactant are realized, and the surfactant has important roles in the fields of oil transportation, emulsion polymerization, nano material synthesis, heterogeneous catalysis, oil exploitation, cosmetics, food science and the like.

Description

Intelligent Pickering emulsion based on dynamic covalent bond and preparation method thereof

Technical Field

The invention belongs to the field of colloid and interface chemistry, and specifically relates to an intelligent Pickering emulsion based on dynamic covalent bonds and a preparation method thereof.

Background Art

In recent years, with the rapid development of nanotechnology, Pickering emulsions stabilized by colloidal particles or surfactant particles have attracted widespread attention. Colloidal particles can be tightly arranged at the oil-water interface, making Pickering emulsions extremely stable. However, when it is applied to oil transportation, emulsion polymerization, nanomaterial synthesis, and heterogeneous catalysis, this super stability brings great challenges to its demulsification, which has spawned a Pickering emulsion with stimulus-responsive properties.

The formation of stimulus-responsive Pickering emulsions often relies on surfactants with stimulus-responsiveness. The stimulus methods reported so far include pH, redox, CO ₂ /N ₂ , temperature, ion pairs, magnetism and light, and the main control method is to convert polar groups into non-polar groups or weak polar groups. However, in the emulsion system, this type of control method will cause the surfactant to transfer to the oil phase after inactivation, which will not only pollute the oil phase, but also be unfavorable for the recovery and reuse of the surfactant. Surfactants that can be intelligently converted between "amphiphilic" and "strong polarity" have been reported. The main control method is to convert weak polar groups into polar groups, so that the surfactant is too hydrophilic and dissolves in water after losing its surface activity, thus realizing the recovery and reuse of the surfactant. However, the synthesis process of this type of surfactant is relatively complicated. Not only is the conversion rate extremely low (about 15.16%), but it also involves the use of many organic solvents. The synthesis process is not "green" enough, which greatly limits its application in fields such as oil extraction, cosmetics and food science.

Therefore, it is very important to develop an "environmentally friendly" and "recyclable" emulsifier process.

Summary of the invention

Technical issues

Generally, stimulus-responsive surfactants switch between "surfactant" and "non-surfactant" by regulating their polar groups. However, this regulation method often causes the surfactant to dissolve in the oil phase after deactivation, which not only affects the quality of the oil phase, but also is not conducive to the recovery and reuse of the surfactant. Existing surfactants that can be recycled and reused have problems such as complex synthesis process, high synthesis cost, low conversion rate, "ungreen" synthesis process, and limited application fields. In addition, emulsions stabilized by conventional surfactants have disadvantages such as poor stability and excessively high concentrations.

Therefore, the present invention attempts to provide a smart Pickering emulsion based on dynamic covalent bonds to solve the above problems. The Pickering emulsion is synergistically stabilized by a cationic surfactant H ⁺ AA (which can be converted between "amphiphilicity" and "strong polarity") and _SiO2 particles with opposite charges, which integrates many advantages such as simple synthesis, low synthesis cost, green synthesis process, good emulsion stability, low concentration, and recyclable use. Among them, the introduction of dynamic covalent bonds enables the surfactant to be intelligently converted between "amphiphilicity" and "strong polarity". Under acidic conditions, the surfactant (H ⁺ AA) retains amphiphilicity and has surface activity; under alkaline conditions, the surfactant and another substance form a Bola compound (FA-AA), which exhibits "strong polarity", loses surface activity, and dissolves in water. The whole process can be cycled multiple times to achieve intelligent conversion of "amphiphilicity" and "strong polarity", and the surfactant is always in an aqueous solution, which is convenient for recycling and reuse.

Technical Solution

The present invention utilizes a surfactant system (H ⁺ AA and FA) based on dynamic covalent bonds. The surfactant system has "amphiphilicity" and can react with _SiO2 particles with opposite charges to form surfactant particles with pH as the trigger mechanism. Select n-decane as the oil phase and homogenize at a speed of 11000r/min for 2min to prepare a stable Pickering emulsion. Then, acid and alkali are added alternately to convert the structure of the surfactant in the solution to form a "strong polarity" Bola compound FA-AA, which cannot stabilize the emulsion with _SiO2 particles due to its strong hydrophilicity; the surfactant particles can be converted between "amphiphilicity" and "strong polarity", that is, "surface active" and "non-surface active". Add an appropriate amount of acid to the system, and the dynamic covalent bonds in FA-AA will break, generating "amphiphilic" cationic surfactants H ⁺ AA and FA, thereby realizing circulation. It is worth noting that FA plays a considerable role in this circulation process, not only giving the surfactant stimulus response performance, but also being the key to the circulation of the system. At the same time, after the emulsion is broken, the fresh oil phase is replaced to verify whether the surfactant is dissolved in the oil phase and taken away by the n-decane after the emulsion is broken.

The first object of the present invention is to provide a smart Pickering emulsion based on dynamic covalent bonds, wherein the preparation method of the smart Pickering emulsion is to mix and homogenize a water phase, hydrophilic _SiO2 particles, a surfactant system and an oil phase;

The surfactant system is composed of components H ⁺ AA, FA:

Wherein, n=7-9, and X is Cl or Br.

In one embodiment of the present invention, the molar ratio of the two components is 1:1.

In one embodiment of the present invention, a method for preparing a surfactant system is as follows:

Aminoalkyl acid AA and FA react under alkaline conditions at room temperature to form a covalent bond to obtain FA-AA; then FA-AA obtains a surfactant system under the action of acid HX; the surfactant system can be restored again under the action of alkalinity to obtain FA-AA, thereby realizing the reuse of the surfactant system.

In one embodiment of the present invention, the AA in the method is a compound containing a primary amine, which can form a dynamic covalent bond with an aldehyde group at room temperature and has a negative charge under alkaline conditions.

In one embodiment of the present invention, the FA in the method is a compound containing a benzene ring, which can form a dynamic covalent bond with a primary amine at room temperature and has a negative charge under alkaline conditions.

In one embodiment of the present invention, the alkaline pH value in the method is 10-13, preferably 11-12.

In one embodiment of the present invention, the reaction temperature in the method is room temperature.

In one embodiment of the present invention, the reaction time in the method is ≥30 min to ensure sufficient reaction.

In one embodiment of the present invention, the reaction condition in the method is stirring.

In one embodiment of the present invention, the FA-AA in the method has strong hydrophilicity.

In one embodiment of the present invention, the acidic pH value in the method is 3-5.

In one embodiment of the present invention, the H ⁺ AA in the method is a surfactant.

In one embodiment of the present invention, the surfactant system achieves intelligent response through the following process:

In one embodiment of the present invention, the pH value of the base is 10-13, preferably 11-12; the pH value of the acid is 3-5.

In one embodiment of the present invention, the mass concentration of the hydrophilic _SiO2 particles relative to the aqueous phase is 0.001% to 3%.

In one embodiment of the present invention, the concentration of the surfactant system, calculated as FA, relative to the aqueous phase is 0.01 to 10 mmol/L.

In one embodiment of the present invention, the oil phase comprises any one or more of the following: n-decane, toluene, and tricaprylin.

Another object of the present invention is to apply the above-mentioned intelligent Pickering emulsion based on dynamic covalent bonds to the fields of oil transportation, emulsion polymerization, nanomaterial synthesis, heterogeneous catalysis, oil extraction, cosmetics and food science.

Beneficial Effects

The present invention utilizes a surfactant system (H ⁺ AA and FA), which has "amphiphilicity" and can react with _SiO2 particles with opposite charges to form surfactant particles with pH as the trigger mechanism, and cooperate with _SiO2 particles to stabilize Pickering emulsions; Bola compounds that are "strongly polar" under alkaline conditions do not have surface activity and cannot cooperate with _SiO2 particles to stabilize Pickering emulsions. The intelligent conversion of compounds from "amphiphilicity" to "strong polarity" and the conversion of emulsions from "emulsification" to "non-emulsification" are realized, and this conversion can be recycled up to six times. At the same time, by detecting the ultraviolet absorbance of the oil phase after demulsification, it is proved that the surfactant does not remain in the oil phase, and the recovery and reuse of the surfactant is realized. This characteristic plays an important role in the fields of oil transportation, emulsion polymerization, nanomaterial synthesis, heterogeneous catalysis, oil extraction, cosmetics, and food science.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is the ESI-MS spectrum of Bola compound FA-AA.

FIG2 is the ¹ H NMR spectrum of Bola compound FA-AA (60 mM, pH=12.00, D ₂ O).

FIG3 is a comparison of ¹ H NMR spectra of (A) FA-AA, (B) AA, and (C) FA (60 mM, pH=12.00, D ₂ O).

FIG4 is a comparison of FT-IR spectra of (A) FA-AA, (B) AA and (C) FA (pH = 12.00).

FIG5 is the ¹ H NMR spectrum of the surfactant H ⁺ AA (60 mM, pH=4.00, DMSO).

FIG. 6 shows (a) SEM and (b) TEM of nano-SiO ₂ particles and (c) Zeta potential as a function of pH value.

FIG. 7 is a photograph showing the appearance of a n-decane/water (3 mL/3 mL) emulsion stabilized by nano-SiO ₂ particles alone (0.1 wt.%, relative to the aqueous phase).

Figure 8 shows (A and B) appearance photos and (C) microphotographs of n-decane/water Pickering emulsions stabilized with 0.1wt.% nano- _SiO2 particles and different concentrations of H ⁺ AA, where A was taken immediately after emulsification, and (B and C) were taken after the emulsions were stabilized for 24 hours.

Figure 9 shows (A) appearance photos and (B) microscopic photos of n-decane/water Pickering emulsions stabilized with 0.1 wt.% nano-SiO ₂ particles and different concentrations of H ⁺ AA. Both A and B were taken after stabilization for one month.

Figure 10 shows the emulsion stimulus response process. Switching by adding HCl and NaOH: (a) initial solution, (b) adding n-decane and homogenizing for 2 min, (c) separating the upper oil phase and adding HCl for acidification, (d) adding fresh n-decane and homogenizing for 2 min.

Figure 11 shows (A) appearance photos and (B) micrographs of Pickering emulsions stabilized with 0.1 wt.% nano-SiO ₂ particles and 0.6 mM H ⁺ AA. On or off cycles were performed by adding HCl and NaOH.

Figure 12 is a mechanism diagram of nano- _SiO2 particles and surfactant H ⁺ AA stabilizing smart Pickering emulsion.

Figure 13 is (a) the absorbance-wavelength scanning curve of FA-AA aqueous solution with different concentrations (pH = 12.00); (b) the absorbance-concentration standard curve of FA-AA aqueous solution with different concentrations at a wavelength of 296 nm (pH = 12.00).

DETAILED DESCRIPTION

The emulsion appearance photos are taken with a digital camera or mobile phone; the emulsion micrographs are taken with a super-depth-of-field three-dimensional microscope of Keyence (Hong Kong) Co., Ltd., with a lower light source, a magnification of 250 to 2500 times, and a test temperature of 25°C.

Embodiment 1:

The synthetic route of Bola compound FA-AA is as follows:

Equimolar amounts of FA and AA and 2 times the molar amount of NaOH were added to a 100 mL volumetric flask and fixed to volume with ultrapure water. The pH of the solution was then adjusted to 12.00, a magnetic particle was added, and stirred for half an hour to ensure that the reaction was complete. Finally, an aqueous solution of FA-AA constructed by dynamic covalent bonds was obtained. The ESI-MS, ¹ H NMR and FT-IR spectra of FA-AA are shown in Figures 1-4.

Similarly, by replacing 11-aminoundecanoic acid with 10-aminodecanoic acid and 12-aminododecanoic acid, the corresponding Bola compounds 10-FA-AA and 12-FA-AA can be obtained.

Example 2: Preparation of surfactant system

10 mmol of 11-aminoundecanoic acid was added to a 100 mL volumetric flask and made up to volume with ultrapure water. Then, a 2 M hydrochloric acid solution was used to adjust the system pH to 4.00, a magnetic particle was added, and stirred for half an hour to ensure complete protonation. Finally, an aqueous solution of surfactant 11-H ⁺ AA was obtained. The ¹ H NMR of the surfactant is shown in Figure 5.

Similarly, by replacing 11-aminoundecanoic acid with 10-aminononanoic acid and 12-aminododecanoic acid, the corresponding surfactants 10-H ⁺ AA and 12-H ⁺ AA can be obtained.

10-H ⁺ AA, 11-H ⁺ AA and 12-H ⁺ AA were respectively compounded with equimolar FA to obtain a surfactant system.

Example 3: Surface activity test of nano- _SiO2 particles

In a 10mL glass bottle, 0.003g of commercial nano- _SiO2 particles (primary particle size of about 20nm, specific surface area S _BET of about 200± ^20m2 /g, SEM and TEM see Figure 6) were weighed, 3mL of ultrapure water was added, and then the particles were evenly dispersed (0.1wt.%) using an ultrasonic disperser. 3mL of n-decane was added to the glass bottle, and then a high shear homogenizer was used for homogenization and emulsification at a speed of 11000r/min for 2min. As shown in Figure 7, no stable emulsion could be obtained, indicating that the commercial nano- _SiO2 particles used were not surface active.

Example 4: Preparation of Pickering emulsion

0.003 g of nano-SiO ₂ particles were ultrasonically dispersed in 3 mL of surfactant systems with different concentrations (in terms of FA, the concentrations relative to the aqueous phase were 0.01 mM, 0.03 mM, 0.06 mM, 0.1 mM, 0.3 mM, 0.6 mM, 1.0 mM, 3.0 mM, and 6.0 mM, respectively), and 3 mL of n-decane was added. After homogenization and emulsification with a high shear homogenizer for 2 minutes, a stable O/W Pickering emulsion was obtained, as shown in Figure 8. After the emulsion was placed for one month, no emulsion or demulsification occurred, indicating that the obtained Pickering emulsion had very good stability, as shown in Figure 9.

Example 5: pH stimulus-response properties of Pickering emulsions

In order to facilitate the experiment, the test was performed according to the process in Figure 10.

The study was conducted based on 0.1wt.% nano-SiO ₂ particles and 0.6mM FA-AA. Weigh 0.003g of nano-SiO ₂ particles and ultrasonically disperse them in 0.6mM FA-AA solution (pH=12.00), add 7mL of n-decane, and homogenize with a high shear homogenizer for 2min. No stable Pickering emulsion can be formed. The oil phase precipitated from the upper layer is separated, and then 50μL of 20mM HCl solution is added to the aqueous phase of the lower layer, and then 3mL of fresh n-decane is added. After homogenizing with a high shear homogenizer for 2min, a stable O/W type Pickering emulsion is formed. The emulsion is placed in a 25℃ thermostat and left to stand for 24h to investigate its stability. Alternating the addition of NaOH and HCl can achieve at least 6 cycles, as shown in Figure 11. The mechanism diagram is shown in Figure 12.

Example 6: Emulsification properties of different surfactants

Referring to Example 3, 0.003 g of nano-SiO ₂ particles were weighed and ultrasonically dispersed in 3 mL of 0.6 mM surfactant system, 3 mL of n-decane was added, and the mixture was homogenized and emulsified with a high shear homogenizer for 2 min to obtain a stable O/W Pickering emulsion.

Only the surfactants were replaced with 10-H ⁺ AA (n=7) and 12-H ⁺ AA (n=9), and other conditions remained unchanged, and the corresponding Pickering emulsions were obtained. The obtained emulsions were placed at room temperature to determine their stability.

The pH response performance was tested by adjusting the pH with reference to Example 4. The performance results of the obtained emulsion are shown in Table 1.

Table 1 Emulsification performance results of different surfactants

Example 7: Detection of residual surfactant in oil phase

The UV spectrophotometer was used for detection. As shown in FIG13 , the maximum absorption wavelength and the absorbance at the maximum absorption wavelength of FA-AA of different concentrations were detected. As can be seen from FIG13 (a), FA-AA has two maximum absorption wavelengths. Considering that the absorption intensity of the E1 band is relatively large, it is not easy to control the absorbance within 1. Therefore, the maximum absorption wavelength under the E2 absorption band (λ _max = 296nm) was selected as the experimental basis. Then, the absorbance-concentration standard curve was drawn according to the absorbance of FA-AA of different concentrations at this absorption wavelength ( FIG13 (b) ). The equation of the fitting curve is y = 1.7333x, and the variance r ² = 0.9995.

The oil phase separated in each cycle was collected, its UV absorbance was detected, and the interfacial tension between it and ultrapure water was measured. The test results are shown in Table 2.

Table 2 UV absorbance of fresh n-decane and n-decane separated after each demulsification

The total absorbance of the separated oil phase was 0.098, which means that 9.4% of FA was lost after six cycles, which would affect the recovery and reuse of H ⁺ AA to a certain extent. This may be the reason why it can only be cycled six times. Of course, in addition to this, it will also be affected by the dilution effect and accumulated NaCl.

Claims (9)

1. A method for preparing intelligent Pickering emulsion based on dynamic covalent bonds is characterized in that aqueous phase and hydrophilic SiO ₂ Mixing the particles, the surface active system and the oil phase, and homogenizing to obtain the product;

the saidThe surface active system is composed of a component H ⁺ AA. FA composition:

wherein n=7 to 9, and x is Cl or Br;

dynamic covalent bonding refers to:

intelligence refers to intelligent switching between amphiphilicity and strong polarity.

2. The method of claim 1, wherein the hydrophilic SiO ₂ The mass concentration of the particles relative to the water phase is 0.001-3%.

3. The process according to claim 1, wherein the concentration of the surface-active system, calculated as FA, relative to the aqueous phase is from 0.01 to 10mmol/L.

4. The method of claim 1, wherein the oil phase comprises any one or more of: n-decane, toluene, glyceryl tricaprylate.

5. The method according to claim 1, wherein the molar ratio of the two components in the surface-active system is 1:1.

6. the method according to claim 1, characterized in that the method for preparing the surface-active system is as follows:

reacting amino alkyl acid AA and FA under alkaline condition at normal temperature to form covalent bond to obtain FA-AA; then FA-AA is subjected to the action of acid HX to obtain a surfactant system; the surface active system can be recovered again under the alkaline action to obtain FA-AA for repeated use.

7. An intelligent Pickering emulsion prepared by the method of any one of claims 1-6; wherein the surfactant system achieves intelligent response by:

8. the intelligent Pickering emulsion of claim 7, wherein the pH of the base is 10 to 13; the pH value of the acid is 3-5.

9. Use of the intelligent Pickering emulsion of claim 7 in the fields of oil transportation, emulsion polymerization, nanomaterial synthesis, heterogeneous catalysis, oil exploitation, cosmetics, food science, and the like.

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