PH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environment

Abstract

The invention discloses a pH and temperature dual-responsive Pickering emulsion resistant to high temperature and an acid-base environment, which is characterized in that N-vinylcaprolactam (VCL) and sodium alginate (SA) are used as raw materials, flexible P (VCL-co-SA) microgel solid particles with pH and temperature dual-responsiveness are synthesized through a precipitation polymerization method, and the flexible P (VCL-co-SA) microgel solid particles are used for stabilizing the pH and temperature dual-responsive Pickering emulsion with water as a continuous phase and the pH and temperature dual-responsive Pickering emulsion. The O / W type Pickering emulsion is an O / W type Pickering emulsion with a water phase and dodecane and the like as a dispersed phase, and the stability of the emulsion is enhanced by adding Ca < 2 + > into the water phase. The Pickering emulsion disclosed by the invention has pH and temperature responsiveness and excellent stability, and can be stable not only at normal temperature but also at high temperature in strong acid (pH = 3) and strong alkali (pH = 9) environments. The preparation method of the emulsion is simple, the reaction condition is mild, the dosage of raw materials for preparing the microgel is small, the cost is low, and the prepared microgel and emulsion have good biocompatibility and have wide application prospects in the fields of food, medicine, cosmetics, petrochemical engineering and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of materials, and in particular relates to a pH and temperature dual-responsive Pickering emulsion that is resistant to high temperatures and acid-base environments. Background Art

[0002] Emulsions are multiphase mixtures composed of thermodynamically incompatible phases. Such mixtures are thermodynamically unstable due to the increase in interfacial energy. Pickering emulsions are emulsions stabilized only by solid particles located at the oil-water interface. Solid particles replace traditional surfactants, making the emulsions more stable against aggregation and obtaining many useful properties. In addition, they are more biocompatible when the solid particles used are relatively safe in vivo. The interfacial activity of colloidal particles can reduce interfacial tension and stabilize emulsion droplets by providing a physical barrier. Microgel particles are stimuli-responsive and deformable, and the emulsions prepared with them as stabilizers have excellent stability.

[0003] Poly(N-vinyl caprolactam) (PNVCL) and poly(N-isopropylacrylamide) (PNIPAM) are both temperature-responsive polymers with an LCST of about 32°C. Since this temperature is close to human body temperature, it has a wide range of application prospects in biomedicine. However, due to the high cytotoxicity and low cell viability of PNIPAM, PNVCL has biocompatibility and hydrolytic stability, making PNVCL superior to PNIPAM in biomedical applications.

[0004] Sodium alginate, as a linear natural carbohydrate polymer, is a copolymer of 1-4 linked guluronic acid (G unit) and C-5 diastereoisomer D-mannuronic acid (M unit) residues. It has good reproducibility, biocompatibility, biodegradability, antibacterial properties, non-immunogenicity, gelling properties and processing properties. It has been widely used and explored in the fields of tissue engineering, drug delivery, wound healing, textiles, cosmetics and food science. 2+ Ion exchange can occur rapidly to form an egg-box network structure gel. Therefore, Ca is usually used in the preparation of sodium alginate-based microgel particles. 2+ However, the obtained microgel particles have the disadvantages of poor monodispersity, easy agglomeration, and large particle size. In addition, the hydrophilicity of alginate limits the interfacial activity of the microgel, making the emulsification performance of sodium alginate microgel weak, which is not conducive to the stability of the emulsion. Recently, researchers have used the emulsion template method and Ca 2+Spherical sodium alginate microgel particles were prepared by cross-linking. The stability of the sodium alginate microgel oil-water emulsion was improved to a certain extent by adding the cationic surfactant cetyltrimethylammonium bromide (CTAB). However, the biocompatibility of CTAB is poor, which limits the application of this type of sodium alginate microgel.

[0005] Prior art CN116212753A discloses a method for preparing CS-g-PNVCL microgel and its Pickering emulsion, but the particle size distribution of the CS-g-PNVCL microgel particles prepared by this method is uneven and easy to agglomerate, which is not conducive to the stability of the emulsion. Similarly, it can be found from the SEM image that the product prepared is not all uniform spherical particles, which means that the method does not prepare all microgel particles, and it is difficult to directly apply it to the preparation of CS-g-PNVCL microgel and the stabilization of its Pickering emulsion.

[0006] Prior art CN117264233A discloses a pH and temperature responsive Pickering emulsion with high temperature stability, which has good stability and biocompatibility, can be stably present at room temperature and 60°C under acidic and neutral conditions, and can be stably stored for more than 60 days, and is environmentally friendly, but cannot be stable under alkaline conditions. Secondly, it uses poly (N-vinyl caprolactam-co-methacrylic acid) (abbreviated as P (VCL-co-MAA)) microgel as a stabilizer, because methacrylic acid is an important organic chemical raw material and polymer intermediate, and its application in the food industry is subject to certain restrictions. Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the present invention provides a pH and temperature dual-responsive Pickering emulsion having excellent stability, good biocompatibility and biodegradability, and resistance to high temperature and acid-base environments.

[0008] The pH and temperature dual-responsive Pickering emulsion provided by the present invention is resistant to high temperature and acid-base environment. It uses poly (N-vinyl caprolactam-co-sodium alginate) (abbreviated as P (VCL-co-SA)) microgel solid particles as a stabilizer, deionized water as a continuous phase, an oil phase as a dispersed phase, and Ca is added to the continuous phase. 2+ The specific preparation method is as follows: P(VCL-co-SA) microgel solid particles are dissolved in deionized water, and Ca is added 2+ After the sources are evenly mixed, the oil phase is added and mixed at high speed using a homogenizer to obtain the Pickering emulsion.

[0009] The oil phase is any one of dodecane, toluene, heptane, n-decane, soybean oil, rapeseed oil, corn oil and the like.

[0010] Furthermore, it is preferred that the volume ratio of the deionized water to the oil phase is 5:5 to 8:2.

[0011] Furthermore, it is preferred that the mass volume ratio of the stabilizer to deionized water is 0.5-7 mg:1 mL.

[0012] The above Ca 2+ The source is calcium chloride, and the added Ca 2+ Source Ca 2+ The concentration in deionized water is 0.3mM~3mM.

[0013] Furthermore, it is preferred that the shearing is performed by using a homogenizer at a homogenization speed of 12000 to 15000 rpm / min to high-speed homogenize the oil-water mixture for 1 to 5 minutes.

[0014] The above Pickering emulsion is an O / W type Pickering emulsion.

[0015] The preparation method of the above-mentioned P(VCL-co-SA)) microgel solid particles comprises the following steps:

[0016] Step 1: Add sodium alginate (SA) into deionized water and heat to 65-85°C under stirring until it is completely dissolved.

[0017] Step 2: Add N-vinylcaprolactam (VCL), N,N-bis(acryloyl)cystamine and sodium dodecyl sulfate into deionized water and disperse them by ultrasonic for 5 to 10 minutes to obtain a colorless transparent solution.

[0018] Step 3: Add the completely dissolved sodium alginate solution in step 1 to the colorless transparent solution in step 2, and heat and stir at 65-85° C. for 30-40 min under a nitrogen atmosphere to obtain a colorless transparent mixed solution. The mass ratio of N-vinyl caprolactam to sodium alginate is 2:1-6:1, and the added amounts of N,N-bis(acryloyl)cystamine and sodium dodecyl sulfate are 3%-5% and 2-3% of the total mass of N-vinyl caprolactam and sodium alginate, respectively.

[0019] Step 4: Add 10-20 mg / mL ammonium persulfate aqueous solution to the colorless transparent mixed solution of step 3, wherein the amount of ammonium persulfate added is 2%-4% of the total mass of N-vinyl caprolactam and sodium alginate, and continue stirring and reacting at 65-85° C. under a nitrogen atmosphere for 4-6 hours.

[0020] Step 5: After the reaction is completed, turn off the nitrogen, stop heating, keep stirring until the reaction solution cools to room temperature, transfer the reaction solution to a dialysis bag and place it in deionized water for continuous dialysis for 7 days, and replace the deionized water every 24 hours; after the dialysis is completed, vacuum freeze-dry the liquid in the dialysis bag to obtain P(VCL-co-SA)) microgel solid particles.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. The present invention uses N-vinyl caprolactam and sodium alginate as raw materials, and synthesizes poly (N-vinyl caprolactam-co-sodium alginate) microgel by precipitation polymerization. The N-vinyl caprolactam segment in the microgel has temperature responsiveness, and the sodium alginate segment has pH responsiveness, so the microgel has both temperature and pH dual responsiveness, and has good biocompatibility, effectively avoiding the shortcomings of surfactants. And the prepared poly (N-vinyl caprolactam-co-sodium alginate) microgel particles have good monodispersity, the particles are not easy to agglomerate, and the particle size is small, which is conducive to the stability of Pickering emulsion; the whole preparation process is simple, the amount of raw materials used is small and the cost is low, and it is widely used in the fields of food science, interfacial catalysis, drug release, etc.

[0023] 2. The present invention only requires dissolving poly(N-vinyl caprolactam-co-sodium alginate) microgel in deionized water and adding a certain concentration of Ca 2+ The source is then mixed with the oil phase to obtain a temperature and pH dual-responsive Pickering emulsion. The emulsion has good stability and biocompatibility and is environmentally friendly, providing a new idea for obtaining a greener and more environmentally friendly Pickering emulsion. Moreover, the emulsion is stable not only at room temperature but also at a high temperature of 55°C in a strong acid (pH=3) and a strong base (pH=9) environment. In addition, the stability of the emulsion can be regulated by adjusting the pH, temperature, and calcium ion content, which has new development potential in drug controlled release, cosmetics, and food processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a SEM image of the poly(N-vinyl caprolactam-co-sodium alginate) microgel solid particles prepared in Example 1.

[0025] Figure 2 This is a graph showing the change in particle size of the poly(N-vinyl caprolactam-co-sodium alginate) microgel solid particles prepared in Example 1 as a function of temperature.

[0026] Figure 3 is a macroscopic photograph of the Pickering emulsion prepared in Example 1 being stable at 25°C and 55°C.

[0027] Figure 4 No Ca added 2+ Macroscopic photographs of the Pickering emulsion prepared from source at pH = 3 at 25°C and 55°C.

[0028] Figure 5 No Ca added 2+ Macroscopic photographs of the Pickering emulsion prepared from the source at pH = 9 at 25°C and 55°C.

[0029] Figure 6 These are macroscopic photographs of the Pickering emulsion prepared in Example 1 at pH = 3 at 25°C and 55°C.

[0030] Figure 7 These are macroscopic photographs of the Pickering emulsion prepared in Example 1 at pH = 9 at 25°C and 55°C.

[0031] Figure 8 It is an optical micrograph of the Pickering emulsion prepared in Example 1 at pH=3 at 25°C and 55°C.

[0032] Fig. 9 is a SEM image of the poly(N-vinyl caprolactam-co-sodium alginate) microgel solid particles prepared in Example 2.

[0033] Fig.10 This is a graph showing the change in particle size of the poly(N-vinyl caprolactam-co-sodium alginate) microgel solid particles prepared in Example 2 as a function of temperature.

[0034] Fig.11 is a macroscopic photograph of the Pickering emulsion prepared in Example 2 at 25°C.

[0035] Fig.12 These are macroscopic photographs of the Pickering emulsion prepared in Example 2 at pH = 3 at 25°C and 55°C.

[0036] Fig.13 These are macroscopic photographs of the Pickering emulsion prepared in Example 2 at pH = 9 at 25°C and 55°C.

[0037] Fig.14 are macroscopic photographs of the Pickering emulsion prepared in Example 3 at 25°C and 55°C.

[0038] Fig.15 These are macroscopic photographs of the Pickering emulsion prepared in Example 4 at pH = 3 at 25°C and 55°C.

[0039] Fig.16These are macroscopic photographs of the Pickering emulsion prepared in Example 4 at pH = 9 at 25°C and 55°C. DETAILED DESCRIPTION

[0040] The present invention is described in detail below through the accompanying drawings and specific examples, but the protection scope of the present invention is not limited to these examples. The experimental methods described in the following examples are conventional methods unless otherwise specified. The reagents and materials described can be obtained from commercial sources unless otherwise specified.

[0041] Example 1

[0042] 1. Preparation of P(VCL-co-SA) microgel solid particles

[0043] Step 1: Add 200 mg of sodium alginate (SA) into 50 mL of deionized water and heat to 70 °C with stirring until it is completely dissolved.

[0044] Step 2: Add 1200 mg of N-vinylcaprolactam (VCL), 50 mg of N,N-bis(acryloyl)cystamine, and 30 mg of sodium dodecyl sulfate into 68 mL of deionized water, and ultrasonically disperse for 5 minutes to obtain a colorless transparent solution.

[0045] Step 3: Add the completely dissolved sodium alginate solution in step 1 to the colorless transparent solution in step 2, heat and stir at 70° C. for 30 min under a nitrogen atmosphere to obtain a colorless transparent mixed solution.

[0046] Step 4: Dissolve 30 mg of ammonium persulfate in 2 mL of deionized water by ultrasonication to obtain a 15 mg / mL aqueous solution of ammonium persulfate. Add the obtained aqueous solution of ammonium persulfate to the colorless transparent mixed solution of step 3, and continue to stir and react at 70°C under a nitrogen atmosphere for 5 h.

[0047] Step 5: After the reaction is completed, turn off the nitrogen, stop heating, keep stirring until the reaction solution cools to room temperature, transfer the reaction solution to a dialysis bag with a molecular weight of 14000Da and continue dialysis in deionized water for 7 days, and replace the deionized water every 24 hours; after the dialysis is completed, the liquid in the dialysis bag is vacuum freeze-dried for 24 hours to obtain P(VCL-co-SA)) microgel solid particles, such as Figure 1 shown. Figure 2 The particle size of P(VCL-co-SA) microgel solid particles changes with temperature, and the particle size and zeta change with pH are shown in Table 1. The results in Table 1 show that P(VCL-co-SA) microgel solid particles are not easy to agglomerate and have uniform particle size distribution. Figure 2 The results collectively indicate that P(VCL-co-SA) microgel solid particles have dual responsiveness to temperature and pH.

[0048] Table 1 Particle size and zeta of P(VCL-co-SA) microgel solid particles change with pH

[0049]

[0050] 2. Preparation of Pickering emulsion

[0051] Calcium chloride was added to deionized water to prepare a 4 mM calcium chloride aqueous solution; 4.2 mg of P (VCL-co-SA) microgel solid particles were weighed and dissolved in 1.1 mL of deionized water, and 0.1 mL of 4 mM calcium chloride aqueous solution was added. After mixing evenly, 0.8 mL of dodecane was added, and a homogenizer was used to high-speed shear mix at a speed of 13000 rpm for 3 minutes to obtain an O / W type Pickering emulsion. The prepared emulsions were placed in ovens at 25°C and 55°C, respectively, to observe their stability. Figure 3 As shown, the prepared Pickering emulsions are stable at both 25°C and 55°C.

[0052] In order to investigate the temperature stability of the Pickering emulsion of this example at different pH values, the following experiment was conducted: 4.2 mg of P(VCL-co-SA) microgel solid particles were weighed and dissolved in 1.1 mL of deionized water, and the pH of the solution was adjusted to 3 and 9 respectively with 1 M HCl aqueous solution and 1 M NaOH aqueous solution, and then 0.1 mL of 4 mM calcium chloride aqueous solution was added, and after mixing evenly, 0.8 mL of dodecane was added, and a homogenizer was used to high-speed shear mix at a speed of 13,000 rpm for 3 minutes to obtain an O / W Pickering emulsion. At the same time, a comparative experiment was conducted with an O / W Pickering emulsion prepared without adding calcium chloride aqueous solution. The prepared emulsions were placed in ovens at 25°C and 55°C, respectively, and their stability was observed. The results are as follows: Figures 4 to 7 shown.

[0053] Figure 4 It shows that in the comparative experiment, no Ca was added 2+ The Pickering emulsion prepared at pH = 3 can remain stable at 25 °C, but begins to demulsify at 55 °C, indicating that the Pickering emulsion has temperature responsiveness. Figure 5 It shows that in the comparative experiment, no Ca was added 2+ The Pickering emulsion prepared at pH = 9 can maintain good stability at 25°C and 55°C. Comparison of the Pickering emulsions at two pH values ​​shows that the stability of the emulsions varies with pH values, indicating that the emulsion prepared with P(VCL-co-SA) microgel as a stabilizer is pH responsive. Figure 6 and Figure 7 It is shown that in this embodiment, Ca is added2+ The Pickering emulsions prepared at pH = 3 and pH = 9 can remain stable at 25°C and 55°C. Figure 8 It can be seen that the droplet size of the prepared Pickering emulsion is uniform, and no obvious aggregation and flocculation occur, indicating that Ca 2+ The addition of the source is beneficial to the stability of the Pickering emulsion.

[0054] Example 2

[0055] 1. Preparation of P(VCL-co-SA) microgel solid particles

[0056] In this embodiment, in step 1 of preparing P(VCL-co-SA) microgel solid particles, 400 mg of sodium alginate was added to 50 mL of deionized water, and heated and stirred at 70° C. in an oil bath until the sodium alginate was completely dissolved. The other steps were the same as in Example 1 to obtain P(VCL-co-SA) microgel solid particles, such as Fig. 9 shown. Fig.10 The particle size of P(VCL-co-SA) microgel solid particles changes with temperature, and the particle size and zeta change with pH are shown in Table 2. The results in Table 2 show that P(VCL-co-SA) microgel solid particles are not easy to agglomerate and have uniform particle size distribution. Fig.10 The results collectively indicate that P(VCL-co-SA) microgel solid particles have dual responsiveness to temperature and pH.

[0057] Table 2 Particle size and zeta of P(VCL-co-SA) microgel solid particles change with pH

[0058] Solution pH 3 6 9 Microgel particle size (nm) 195.4 214.85 217.6 Microgel zeta potential (mV) -23.1 -55.75 -63.5

[0059] 2. Preparation of Pickering emulsion

[0060] Calcium chloride was added to deionized water to prepare a 4 mM calcium chloride aqueous solution; 4.8 mg of P(VCL-co-SA) microgel solid particles were weighed and dissolved in 1.1 mL of deionized water, and 0.1 mL of 4 mM calcium chloride aqueous solution was added. After mixing evenly, 0.8 mL of dodecane was added, and a homogenizer was used to high-speed shear mix at a speed of 13000 rpm for 3 min to obtain an O / W type Pickering emulsion with dual responsiveness to pH and temperature. Its macroscopic photograph at 25 ° C is shown in the figure. Fig.11 shown.

[0061] The temperature stability of the Pickering emulsion prepared in this example was tested at pH = 3 and pH = 9. The results are shown in Fig.12 and Fig.13As can be seen from the figure, the Pickering emulsion prepared in this example can remain stable at pH=3 and pH=9, at 25°C and 55°C.

[0062] Example 3

[0063] The preparation method of P(VCL-co-SA) microgel solid particles in this example is the same as that in Example 1. Calcium chloride is added to deionized water to prepare a 4 mM calcium chloride aqueous solution; 4.2 mg of P(VCL-co-SA) microgel solid particles are weighed and dissolved in 1.1 mL of deionized water, and 0.1 mL of 4 mM calcium chloride aqueous solution is added. After mixing evenly, 0.8 mL of soybean oil is added, and a homogenizer is used to high-speed shear mix at a speed of 13,000 rpm for 3 minutes to obtain an O / W type Pickering emulsion. The prepared emulsions are placed in ovens at 25°C and 55°C, respectively, and their stability is observed. Fig.14 As shown, the prepared Pickering emulsions are stable at both 25°C and 55°C.

[0064] Example 4

[0065] The preparation method of P(VCL-co-SA) microgel solid particles in this embodiment is the same as that in Example 1. Calcium chloride is added to deionized water to prepare a 10 mM calcium chloride aqueous solution; 4.2 mg of P(VCL-co-SA) microgel solid particles are weighed and dissolved in 1.1 mL of deionized water, and then 0.1 mL of 10 mM calcium chloride aqueous solution is added, mixed evenly, and then 0.8 mL of dodecane is added, and a homogenizer is used to high-speed shear mixing at a speed of 13000 rpm for 3 minutes to obtain an O / W type Pickering emulsion.

[0066] The stability of the Pickering emulsion prepared in this example was tested at pH = 3 and pH = 9, and at 25°C and 55°C. The results showed that the Pickering emulsion prepared in this example had good pH and temperature responsiveness, was resistant to acid, alkali and high temperature, and had good temperature and acid-base stability.

Claims

1. A pH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environments, characterized in that: The Pickering emulsion is composed of poly(N-vinyl caprolactam-co-sodium alginate) microgel solid particles as a stabilizer, deionized water as a continuous phase, an oil phase as a dispersed phase, and Ca is added to the continuous phase. 2+ Source, prepared by shear mixing.

2. The pH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environments according to claim 1, characterized in that: The oil phase is any one of dodecane, toluene, heptane, n-decane, soybean oil, rapeseed oil and corn oil.

3. The pH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environments according to claim 1 or 2, characterized in that: The volume ratio of the deionized water to the oil phase is 5:5 to 8:

2.

4. The pH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environments according to claim 1, characterized in that: The mass volume ratio of the stabilizer to deionized water is 0.5-7 mg:1 mL.

5. The pH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environments according to claim 1, characterized in that: The Ca 2+ The source is calcium chloride.

6. The pH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environments according to claim 1 or 5, characterized in that: Added Ca 2+ Source Ca 2+ The concentration in deionized water is 0.3mM~3mM.

7. The pH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environments according to claim 1, characterized in that: The shearing is performed by using a homogenizer at a homogenizing speed of 12000 to 15000 rpm / min to homogenize the oil-water mixture at high speed for 1 to 5 minutes.

8. The pH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environments according to claim 1, characterized in that: The Pickering emulsion is an O / W type Pickering emulsion.

9. The pH and temperature dual-responsive Pickering emulsion resistant to high temperature and acid-base environments according to claim 1, characterized in that: The preparation method of the poly(N-vinyl caprolactam-co-sodium alginate) microgel solid particles comprises the following steps: Step 1: Add sodium alginate to deionized water and heat to 65-85°C under stirring until it is completely dissolved; Step 2: Add N-vinyl caprolactam, N,N-bis(acryloyl)cystamine and sodium dodecyl sulfate into deionized water and disperse them by ultrasonic for 5 to 10 minutes to obtain a colorless transparent solution; Step 3: adding the completely dissolved sodium alginate solution in step 1 to the colorless transparent solution in step 2, heating and stirring at 65-85° C. for 30-40 min under a nitrogen atmosphere to obtain a colorless transparent mixed solution; the mass ratio of N-vinyl caprolactam to sodium alginate is 2:1-6:1, and the added amounts of N,N-bis(acryloyl)cystamine and sodium dodecyl sulfate are 3%-5% and 2-3% of the total mass of N-vinyl caprolactam and sodium alginate, respectively; Step 4: Add 10-20 mg / mL ammonium persulfate aqueous solution to the colorless transparent mixed solution of step 3, wherein the amount of ammonium persulfate added is 2%-4% of the total mass of N-vinyl caprolactam and sodium alginate, and continue stirring and reacting at 65-85° C. under a nitrogen atmosphere for 4-6 hours; Step 5: After the reaction is completed, turn off the nitrogen, stop heating, keep stirring until the reaction solution cools to room temperature, and continue to dialyze the reaction solution in deionized water for 7 days, replacing the deionized water every 24 hours; after the dialysis is completed, vacuum freeze-dry to obtain poly (N-vinyl caprolactam-co-sodium alginate) microgel solid particles.

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