A preparation method of a CS-g-PNVCL microgel and a stable pickering emulsion thereof

Abstract

The application discloses a kind of CS-g-PNVCL microgel and its stable Pickering emulsion preparation method, it is related to material technical field, the present application will chitosan and N-vinyl-caprolactam as raw material, preparation obtains flexible microgel particle, the whole CS-g-PNVCL microgel particle preparation process is simple, raw material is less, raw material cost is low;Toxicity polymerization does not appear the case of increase, the CS-g-PNVCL microgel particle obtained has good biocompatibility, effectively avoids the shortcoming of inorganic particles and biological macromolecule, applicability is better in food science, drug controlled release and interface catalysis etc.Field.By the preparation method of the CS-g-PNVCL microgel particle of the application, the CS-g-PNVCL microgel particle obtained can be prepared to obtain stable Pickering emulsion by the method provided by the application, and the preparation process does not need to add additional stabilizer, just join the prepared material can be mixed into Pickering emulsion with water and oil phase, and can stably exist more than 60 days.

Description

Technical Field

[0001] This invention relates to the field of materials technology, specifically to a method for preparing a CS-g-PNVCL microgel and its stabilized Pickering emulsion. Background Technology

[0002] Pickering emulsions are emulsion systems that use solid particles instead of traditional molecular surfactants as stabilizers. They can be oil-in-water (w / o), water-in-oil (o / w), or have multiple structures. Pickering emulsions possess almost all the basic properties of traditional emulsions while overcoming their drawbacks such as poor stability, toxicity, and difficulty in separating emulsifiers. Therefore, the preparation of multifunctional materials such as microcapsules, Janus particles, and porous materials using Pickering emulsions has attracted increasing attention from researchers. Pickering emulsions offer significant advantages in many fields and are currently widely used in food, pharmaceuticals, cosmetics, and petrochemicals.

[0003] Chitosan (CS) is a natural high-molecular-weight organic compound with excellent biocompatibility. It is a pH-sensitive, tissue-compatible, and blood-compatible biomaterial that is safe, non-toxic, and biodegradable, and has been widely used in medicine, food, chemical, biochemical, and water treatment fields. N-vinylcaprolactam (NVCL) is temperature-sensitive, with its low critical phase transition temperature (lcst) close to human body temperature. The preparation of microgel particles and Pickering emulsions using these two materials can aid research in medicine, food, and other fields.

[0004] The existing technology CN115536863A discloses a method for grafting chitosan onto inorganic materials, but this method requires the use of crosslinking agents, surfactants, etc., making the preparation complex and the process cumbersome. Furthermore, the raw materials used have different properties from PNVCL, making it difficult to directly apply them in the preparation of CS-g-PNVCL microgels.

[0005] Existing technology CN110507664A discloses the RAFT polymerization method for grafting chitosan onto PNVCL. RAFT polymerization is applicable to a wide range of monomers and can prepare CS-g-PNVCL. However, the dithioester derivatives used in RAFT polymerization may increase the polymer's toxicity, and the preparation process of dithioesters is relatively complex. It may also impart color and odor to the polymer. Like NMP, it requires an initiator, and initiating free radicals can easily lead to chain termination. The preparation process is difficult, and the yield is unstable. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, this invention provides a green, stable, and efficient method for preparing CS-g-PNVCL microgels and their stable Pickering emulsions.

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

[0008] A method for preparing CS-g-PNVCL microgels is provided, comprising the following steps:

[0009] S1: Add chitosan and glacial acetic acid to ultrapure water; stir continuously for 12-24 hours to obtain a chitosan solution; the volume ratio of glacial acetic acid to ultrapure water is 1%;

[0010] S2: Add N-vinylcaprolactam and NN-methylenebisacrylamide to the chitosan solution, and use ultrasound to uniformly disperse N-vinylcaprolactam and NN-methylenebisacrylamide in the chitosan solution to obtain a mixture;

[0011] S3: Add the mixture to a sealed container, evacuate the inside of the sealed container, and purge it with nitrogen for 0.5-1 hours to create an inert atmosphere; stir the mixture continuously during the nitrogen purging process.

[0012] S4: While maintaining an inert atmosphere, add ammonium persulfate solution to the mixture, and heat the sealed container to 65-75℃, keep the reaction at this temperature for 5-7 hours, and stir continuously during the heat preservation process;

[0013] S5: After the reaction is complete, the reaction solution is dialyzed, frozen and dried in sequence to obtain CS-g-PNVCL microgel particles.

[0014] Furthermore, the mass ratio of chitosan to N-vinylcaprolactam is 20%-100%.

[0015] Furthermore, the mass ratio of chitosan to N-vinylcaprolactam is 60%.

[0016] Furthermore, the mass ratio of N-methylenebisacrylamide to N-vinylcaprolactam is 4%-7.5%.

[0017] Furthermore, the mass ratio of ammonium persulfate to N-vinylcaprolactam is 1.2%–3.5%.

[0018] Furthermore, in step S1, when preparing the chitosan solution, the stirring speed is 500-1000 rpm / min.

[0019] Furthermore, in step S3, when continuously stirring the mixture, the stirring speed is 100-500 rpm / min.

[0020] Furthermore, during the heat preservation process in step S4, the stirring speed is 500-1500 rpm / min.

[0021] Furthermore, the specific steps of dialysis, freezing, and drying in step S5 include:

[0022] Transfer the reaction solution to a dialysis bag and place it in ultrapure water for continuous dialysis for one week, changing the ultrapure water every 18-24 hours during dialysis.

[0023] After dialysis, the liquid in the dialysis bag is frozen into a solid and then dried in a vacuum freeze dryer for 24-48 hours to obtain CS-g-PNVCL microgel particles.

[0024] A method for preparing a stable Pickering emulsion of CS-g-PNVCL microgel includes the following steps:

[0025] A1: Disperse the prepared CS-g-PNVCL microgel particles in ultrapure water and add oil phase to obtain a solid-oil-water mixture; the volume ratio of oil to water in the solid-oil-water mixture is 0.25-4.

[0026] A2: Use a homogenizer to homogenize the solid-oil-water mixture at a homogenization speed of 8000-13000 rpm / min for 1-6 min to obtain a Pickering emulsion of CS-g-PNVCL microgel.

[0027] The beneficial effects of this invention are as follows:

[0028] This invention uses chitosan and N-vinyl-caprolactam as raw materials to prepare flexible microgel particles. The entire preparation process of CS-g-PNVCL microgel particles is simple, requires few raw materials, and has low raw material costs. It does not lead to an increase in toxic polymerization. The obtained CS-g-PNVCL microgel particles have good biocompatibility and effectively avoid the disadvantages of inorganic particles and biomacromolecules. They are more suitable for applications in food science, drug controlled release, and interfacial catalysis.

[0029] The CS-g-PNVCL microgel particles prepared by the method of this invention can be used to prepare stable Pickering emulsions. The preparation process requires no additional stabilizers; only the prepared material is added to mix the water and oil phases into a Pickering emulsion, which remains stable for over 60 days. This excellent stability provides a new approach to obtaining a greener, more environmentally friendly Pickering emulsion, and has new development potential in food science, controlled drug release, and interfacial catalysis. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the preparation process of CS-g-PNVCL microgels;

[0031] Figure 2 A schematic diagram of the preparation process of a stable Pickering emulsion for CS-g-PNVCL microgels;

[0032] Figure 3 SEM image of CS-g-PNVCL microgel particles prepared in Example 1;

[0033] Figure 4 The contact angle diagram is shown for the CS-g-PNVCL microgel particles prepared in Example 1.

[0034] Figure 5 A macroscopic photograph of the Pickering emulsion prepared in Example 6;

[0035] Figure 6 An optical microscope image of the Pickering emulsion prepared in Example 6;

[0036] Figure 7 This is a particle size distribution diagram of the CS-g-PNVCL microgel particles prepared in Example 2;

[0037] Figure 8 This is a particle size distribution diagram of the CS-g-PNVCL microgel particles prepared in Example 3. Detailed Implementation

[0038] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0039] like Figure 1 As shown, a method for preparing CS-g-PNVCL microgels includes the following steps:

[0040] S1: Add chitosan and glacial acetic acid to ultrapure water; stir continuously at 500 rpm / min for 12 hours. The stirring time can also be 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours. The stirring speed can also be 600 rpm / min, 700 rpm / min, 800 rpm / min, 900 rpm / min, or 1000 rpm / min to obtain a chitosan solution. The volume ratio of glacial acetic acid to ultrapure water is 1%.

[0041] S2: Add N-vinylcaprolactam and NN-methylenebisacrylamide to the chitosan solution. The mass ratio of chitosan to N-vinylcaprolactam is 20%, and the mass ratio can also be 40%, 60%, 80%, or 100%. The mass ratio of NN-methylenebisacrylamide to N-vinylcaprolactam is 4%, and the mass ratio can also be 5%, 6%, 7%, or 7.5%. Use ultrasound to uniformly disperse N-vinylcaprolactam and NN-methylenebisacrylamide in the chitosan solution to obtain a mixture. Use ultrasound to work the chitosan solution mixed with N-vinylcaprolactam and NN-methylenebisacrylamide for 5 minutes. The working time of ultrasound can also be 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes.

[0042] S3: Add the mixture to a sealed container, evacuate the inside of the sealed container, and purge it with nitrogen for 0.5 hours to create an inert atmosphere; the nitrogen purging time can also be 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, or 1.0 hours; throughout the nitrogen purging process, the mixture is continuously stirred at a stirring speed of 100 rpm / min, and the stirring speed can also be 200, 300, 400, or 500 rpm / min;

[0043] S4: While maintaining an inert atmosphere, add ammonium persulfate solution to the mixture and heat the sealed container to 65°C. The temperature can also be 68°C, 70°C, 72°C, or 75°C. Maintain the reaction at this temperature for 5 hours. The holding time can also be 5.5 hours, 6 hours, 6.5 hours, or 7 hours. During the holding process, continuously stir at a stirring speed of 500 rpm / min. The stirring speed can also be 700 rpm / min, 900 rpm / min, 1100 rpm / min, 1300 rpm / min, or 1500 rpm / min.

[0044] S5: After the reaction is complete, the reaction solution is transferred to a dialysis bag and placed in ultrapure water for continuous dialysis for one week. The ultrapure water is replaced every 18 hours during dialysis, and the interval can also be 20 hours, 22 hours or 24 hours. After dialysis, the liquid in the dialysis bag is frozen into a solid and dried in a vacuum freeze dryer for 24 hours to obtain CS-g-PNVCL microgel particles. The freeze drying time can also be 28 hours, 32 hours, 36 hours, 40 hours, 44 hours or 48 hours.

[0045] Example 1

[0046] CS-g-PNVCL microgel particles were prepared with a chitosan to N-vinyl-caprolactam mass ratio of 20%.

[0047] Take 0.05g of chitosan and put it into a round-bottom flask. Add 12.87ml of ultrapure water and 0.13ml of glacial acetic acid. Stir continuously at 1000rpm / min for 18h at room temperature to obtain a chitosan solution. Then add 0.25g of N-vinylcaprolactam and 10mg of N-N-methylenebisacrylamide to the chitosan solution. Use an ultrasonic cleaner to uniformly disperse the solution in the round-bottom flask in a water bath to obtain a mixed solution. The ultrasonic cleaner is operated for 5min.

[0048] The mixture was placed into a round-bottom flask, a stir bar was added, and the flask was sealed with a plug. The plug was equipped with an interface for connecting to a vacuum machine, a nitrogen purging port, and a feeding port. The round-bottom flask was evacuated using the vacuum machine, and nitrogen was then purged into the flask. During this process, the feeding port was sealed. The nitrogen purging time lasted for 0.5 hours, and the mixture was stirred with a magnetic stirrer at a stirring speed of 100 rpm / min during the nitrogen purging process.

[0049] Next, maintaining an inert atmosphere inside the round-bottom flask, heat it to 65°C using a water bath with a constant temperature heater; open the feeding port and quickly add 2 ml of a 2.57 mg / ml ammonium persulfate aqueous solution, then close the feeding port. The mixture and the ammonium persulfate aqueous solution continue to react in the round-bottom flask. During the reaction, the solution in the round-bottom flask is continuously stirred with a magnetic stirrer at a stirring speed of 500 rpm / min for 6 hours; and the temperature is maintained at 65°C during stirring.

[0050] After the reaction was complete, the solution in the round-bottom flask was transferred to a 14000 Da dialysis bag for dialysis. The dialysis bag was placed in 1.5 L of ultrapure water, and the water was changed every 12 hours. The liquid was then frozen into a solid using liquid nitrogen and freeze-dried in a vacuum freeze dryer for 48 hours to obtain 50.85 mg of CS-g-PNVCL microgel solid particles. The CS-g-PNVCL microgel solid particles were analyzed to obtain the following results: Figure 3 The SEM image is shown; and the three-phase contact angle of the CS-g-PNVCL microgel solid particles was measured as follows. Figure 4 The contact angle diagram shown; by Figure 3 It is evident that the CS-g-PNVCL microgel particles prepared using the method of this invention form uniform and regular spherical shapes; the more closely the material approximates a regular spherical shape, the more beneficial it is to the stability of the Pickering emulsion. From Figure 4 It is known that the CS-g-PNVCL microgel particles prepared by the method provided by the present invention with a mass ratio of chitosan to N-vinyl-caprolactam of 20% have a contact angle of 47°, good wettability, and can help form a stable Pickering emulsion.

[0051] Example 2

[0052] CS-g-PNVCL microgel particles were prepared with a chitosan to N-vinyl-caprolactam mass ratio of 40%.

[0053] 0.084 g of chitosan was placed in a round-bottom flask, 12.87 ml of ultrapure water was added, and then 0.13 ml of glacial acetic acid was added. The mixture was stirred continuously at 900 rpm / min for 16 hours at room temperature to obtain a chitosan solution. Then, 0.21 g of N-vinylcaprolactam and 12 mg of N-N-methylenebisacrylamide were added to the chitosan solution. The solution in the round-bottom flask was uniformly dispersed using an ultrasonic cleaner in a water-separated environment to obtain a mixed solution. The ultrasonic cleaner was run for 5 minutes.

[0054] Place the mixture into a round-bottom flask, add a stir bar, and cover with a sealing plug. The sealing plug is equipped with an interface for connecting to a vacuum machine, a nitrogen filling port, and a feeding port. Use the vacuum machine to evacuate the round-bottom flask and fill it with nitrogen. At this time, the feeding port is sealed and the nitrogen filling time lasts for 0.6 hours. During the nitrogen filling process, use a magnetic stirrer to stir the mixture at a stirring speed of 100 rpm / min.

[0055] Next, maintaining an inert atmosphere inside the round-bottom flask, heat it to 70°C using a water bath with a constant temperature heater; open the feeding port and quickly add 2 ml of a 1.71 mg / ml ammonium persulfate aqueous solution, then close the feeding port. The mixture and the ammonium persulfate aqueous solution continue to react in the round-bottom flask. During the reaction, the solution in the round-bottom flask is continuously stirred with a magnetic stirrer at a stirring speed of 500 rpm / min for 6 hours; and the temperature is maintained at 70°C during stirring.

[0056] After the reaction was completed, the solution in the round-bottom flask was transferred to a 14000 Da dialysis bag for dialysis. The dialysis bag was placed in 1.8 L of ultrapure water, and the water was changed every 12 hours. Then, the liquid inside was frozen into a solid with liquid nitrogen and then placed in a vacuum freeze dryer for 48 hours to obtain 64.71 mg of CS-g-PNVCL microgel solid particles.

[0057] Example 3

[0058] CS-g-PNVCL microgel particles were prepared with a chitosan to N-vinyl-caprolactam mass ratio of 60%.

[0059] 0.12 g of chitosan was placed in a round-bottom flask, 12.87 ml of ultrapure water was added, and then 0.13 ml of glacial acetic acid was added. The mixture was stirred continuously at 600 rpm / min for 18 hours at room temperature to obtain a chitosan solution. Then, 0.20 g of N-vinylcaprolactam and 10 mg of N-N-methylenebisacrylamide were added to the chitosan solution. The solution in the round-bottom flask was uniformly dispersed using an ultrasonic cleaner in a water-separated environment to obtain a mixed solution. The ultrasonic cleaner was operated for 6 minutes.

[0060] The mixture was placed in a round-bottom flask, a stir bar was added, and the flask was sealed with a plug. The plug was equipped with an interface for connecting to a vacuum machine, a nitrogen purging port, and a feeding port. The round-bottom flask was evacuated using the vacuum machine, and nitrogen was then purged into the flask. During this process, the feeding port was sealed. The nitrogen purging time lasted for 0.7 hours, and the mixture was stirred with a magnetic stirrer at a stirring speed of 100 rpm / min during the nitrogen purging process.

[0061] Next, maintaining an inert atmosphere inside the round-bottom flask, heat it to 70°C using a water bath with a constant temperature heater; open the feeding port and quickly add 2 ml of a 3.08 mg / ml ammonium persulfate aqueous solution, then close the feeding port. The mixture and the ammonium persulfate aqueous solution continue to react in the round-bottom flask. During the reaction, the solution in the round-bottom flask is continuously stirred with a magnetic stirrer at a stirring speed of 600 rpm / min for 6 hours; and the temperature is maintained at 70°C during stirring.

[0062] After the reaction was completed, the solution in the round-bottom flask was transferred to a 14000 Da dialysis bag for dialysis. The dialysis bag was placed in 2L of ultrapure water, and the water was changed every 24 hours. Then, the liquid inside was frozen into a solid with liquid nitrogen and then placed in a vacuum freeze dryer for 48 hours to obtain 131.46 mg of CS-g-PNVCL microgel solid particles.

[0063] Example 4

[0064] CS-g-PNVCL microgel particles were prepared with a chitosan to N-vinyl-caprolactam mass ratio of 80%.

[0065] 0.184 g of chitosan was placed in a round-bottom flask, 12.87 ml of ultrapure water was added, and then 0.13 ml of glacial acetic acid was added. The mixture was stirred continuously at 800 rpm / min for 20 h at room temperature to obtain a chitosan solution. Then, 0.23 g of N-vinylcaprolactam and 14 mg of N-N-methylenebisacrylamide were added to the chitosan solution. The solution in the round-bottom flask was uniformly dispersed using an ultrasonic cleaner in a water-separated environment to obtain a mixed solution. The ultrasonic cleaner was operated for 8 min.

[0066] The mixture was placed in a round-bottom flask, a stir bar was added, and the flask was sealed with a plug. The plug was equipped with an interface for connecting to a vacuum machine, a nitrogen purging port, and a feeding port. The round-bottom flask was evacuated using the vacuum machine, and nitrogen was then purged into the flask. During this process, the feeding port was sealed. The nitrogen purging time lasted for 0.8 hours, and the mixture was stirred with a magnetic stirrer at a stirring speed of 100 rpm / min during the nitrogen purging process.

[0067] Next, maintaining an inert atmosphere inside the round-bottom flask, heat it to 70°C using a water bath with a constant temperature heater; open the feeding port and quickly add 2 ml of a 3.42 mg / ml ammonium persulfate aqueous solution, then close the feeding port. The mixture and the ammonium persulfate aqueous solution continue to react in the round-bottom flask. During the reaction, the solution in the round-bottom flask is continuously stirred with a magnetic stirrer at a stirring speed of 800 rpm / min for 6 hours; and the temperature is maintained at 70°C during stirring.

[0068] After the reaction was completed, the solution in the round-bottom flask was transferred to a 14000 Da dialysis bag for dialysis. The dialysis bag was placed in 1.7 L of ultrapure water, and the water was changed every 12 hours. Then the liquid inside was frozen into a solid with liquid nitrogen and then placed in a vacuum freeze dryer for 48 hours to obtain 121.38 mg of CS-g-PNVCL microgel solid particles.

[0069] Example 5

[0070] CS-g-PNVCL microgel particles were prepared with a chitosan to N-vinyl-caprolactam mass ratio of 100%.

[0071] 0.24 g of chitosan was placed in a round-bottom flask, 12.87 ml of ultrapure water was added, and then 0.13 ml of glacial acetic acid was added. The mixture was stirred continuously at 1000 rpm / min for 24 hours at room temperature to obtain a chitosan solution. Then, 0.24 g of N-vinylcaprolactam and 15 mg of N-N-methylenebisacrylamide were added to the chitosan solution. The solution in the round-bottom flask was uniformly dispersed using an ultrasonic cleaner in a water-separated environment to obtain a mixed solution. The ultrasonic cleaner was operated for 10 minutes.

[0072] Place the mixture into a round-bottom flask, add a stir bar, and seal the flask with a plug. The plug has an interface for connecting to a vacuum machine, a nitrogen filling port, and a feeding port. Use the vacuum machine to evacuate the round-bottom flask and fill it with nitrogen. At this time, the feeding port is sealed. The nitrogen filling time lasts for 1 hour, and during the nitrogen filling process, use a magnetic stirrer to stir the mixture at a stirring speed of 500 rpm / min.

[0073] Next, maintaining an inert atmosphere inside the round-bottom flask, heat it to 70°C using a water bath with a constant temperature heater; open the feeding port and quickly add 2 ml of a 2.74 mg / ml ammonium persulfate aqueous solution, then close the feeding port. The mixture and the ammonium persulfate aqueous solution continue to react in the round-bottom flask. During the reaction, the solution in the round-bottom flask is continuously stirred with a magnetic stirrer at a stirring speed of 1000 rpm / min for 6 hours; and the temperature is maintained at 70°C during stirring.

[0074] After the reaction was completed, the solution in the round-bottom flask was transferred to a 14000 Da dialysis bag for dialysis. The dialysis bag was placed in 2L of ultrapure water, and the water was changed every 24 hours. Then, the liquid inside was frozen into a solid with liquid nitrogen and then placed in a vacuum freeze dryer for 48 hours to obtain 191.57 mg of CS-g-PNVCL microgel solid particles.

[0075] like Figure 2 As shown, a method for preparing CS-g-PNVCL microgels includes the following steps:

[0076] A1: Disperse the prepared CS-g-PNVCL microgel particles in ultrapure water and add heptane or other oil phases to obtain a solid-oil-water mixture; the volume ratio of oil to water in the solid-oil-water mixture is 0.25; the volume ratio of oil to water can also be 0.43, 0.67, 1, 1.5, 2.33 or 4, that is, the volume ratio of oil to water is 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 or 8:2.

[0077] A2: Using a homogenizer at a homogenization speed of 8000 rpm / min, the homogenization speed can also be 9000 rpm / min, 10000 rpm / min, 11000 rpm / min, 12000 rpm / min or 13000 rpm / min; the solid-oil-water mixture is homogenized at high speed for 1 min, and the homogenization time can also be 2 min, 3 min, 4 min, 5 min or 6 min to obtain the Pickering emulsion of CS-g-PNVCL microgel.

[0078] Example 6

[0079] 12 mg of the CS-g-PNVCL microgel particles prepared in Example 1 was added to 2 ml of ultrapure water, followed by 2 ml of heptane. The mixture was then homogenized at 8000 rpm for 1.5 min to obtain a Pickering emulsion of the CS-g-PNVCL microgel. The emulsion was then photographed and analyzed to obtain the following results: Figure 5 The macro photos shown and such Figure 6 The image shown is an optical microscope image at 100X optical magnification, created by... Figure 5It can be seen that after homogenization of the oil and water phases, a milky white, homogeneous, and stable emulsion was formed. Figure 6 It is evident that the CS-g-PNVCL microgel particles, water, and heptane formed regularly shaped, spherical droplets. The emulsion diameter was 28.47 ± 5.28 μm. After 60 days of standing, it remained in a Pickering emulsion state. This indicates that the Pickering emulsion prepared by the method provided in this invention, using a chitosan to N-vinylcaprolactam mass ratio of 20%, exhibits excellent stability.

[0080] Example 7

[0081] Take 15 mg of CS-g-PNVCL microgel particles prepared in Example 2, add 2.4 ml of ultrapure water, then add 1.6 ml of heptane, and then homogenize at 9000 rpm / min for 1 min to obtain a Pickering emulsion of CS-g-PNVCL microgel.

[0082] Example 8

[0083] Take 11 mg of CS-g-PNVCL microgel particles prepared in Example 3, add 1.6 ml of ultrapure water, then add 2.4 ml of heptane, and then homogenize at 11000 rpm / min for 3 min to obtain a Pickering emulsion of CS-g-PNVCL microgel.

[0084] Example 9

[0085] Take 18 mg of CS-g-PNVCL microgel particles prepared in Example 4, add 1.2 ml of ultrapure water, then add 2.8 ml of heptane, and then homogenize at 12000 rpm / min for 5 min to obtain a Pickering emulsion of CS-g-PNVCL microgel.

[0086] Example 10

[0087] Take 10 mg of CS-g-PNVCL microgel particles prepared in Example 5, add 2.8 ml of ultrapure water, then add 1.2 ml of heptane, and then homogenize at 13000 rpm / min for 6 min to obtain a Pickering emulsion of CS-g-PNVCL microgel.

[0088] Data Results

[0089] The CS-g-PNVCL microgel particles prepared in Examples 1, 2, 3, 4, and 5 were taken respectively. The average particle size and PDI of each CS-g-PNVCL microgel particle were measured using a Zeta potential analyzer (model ZEV360011000). The particle size comparison table is as follows:

[0090] Table 1

[0091] Example 1 Example 2 Example 3 Example 4 Example 5 Average particle size 1017nm 288.4nm 343.4nm 613.1nm 771.7nm PDI 0.068 0.296 0.337 0.388 0.141

[0092] The smaller the particle size of the solid particles, the more stable the Pickering emulsion prepared using them will be.

[0093] As can be seen from Example 1, which was prepared into Pickering emulsion (Example 6), the Pickering emulsion with the largest particle size in Example 1 can be prepared by the method of the present invention and remain stable for more than 60 days.

[0094] As shown in Table 1, the CS-g-PNVCL microgel particles prepared in Example 3 have a particle size of 343.4 nm and a PDI of 0.337. Clearly, the average particle size of the CS-g-PNVCL microgel particles prepared in Example 3 is smaller than that in Example 1.

[0095] While the average particle size of the CS-g-PNVCL microgel particles prepared in Example 2 was smaller than that in Example 3, the combination with... Figure 7 The particle size distribution diagram of the CS-g-PNVCL microgel particles prepared in Example 2 with a chitosan to N-vinyl-caprolactam mass ratio of 40% shows that the particle size in Example 2 exhibits a bimodal distribution and is not uniform; while... Figure 8 As shown in the particle size distribution diagram of the CS-g-PNVCL microgel particles prepared in Example 3, the average particle size of the CS-g-PNVCL microgel particles with a mass ratio of chitosan to N-vinylcaprolactam of 60% exhibits a unimodal distribution.

[0096] The non-uniform particle size of solid particles is detrimental to maintaining the stability of Pickering emulsions.

[0097] In summary, the Pickering emulsion prepared in Example 3, i.e., when the mass ratio of chitosan to N-vinyl-caprolactam is 60%, is the most stable, as is the Pickering emulsion in Example 8.

[0098] The Pickering emulsions prepared in Examples 6, 7, 8, 9, and 10 all maintained a stable Pickering emulsion state after 60 days of storage. It should be noted that 60 days refers to the experimental period, not the time limit for the Pickering emulsions prepared by this method to maintain a stable state. In practice, the Pickering emulsions prepared in each example can maintain a stable state for far longer than 60 days.

Claims

1. A method for preparing CS-g-PNVCL microgels, characterized in that, Includes the following steps: S1: Add chitosan and glacial acetic acid to ultrapure water; stir continuously for 12-24 hours to obtain a chitosan solution; the volume ratio of glacial acetic acid to ultrapure water is 1%. S2: Add N-vinylcaprolactam and NN-methylenebisacrylamide to the chitosan solution, and use ultrasound to uniformly disperse N-vinylcaprolactam and NN-methylenebisacrylamide in the chitosan solution to obtain a mixture; S3: Add the mixture to a sealed container, evacuate the inside of the sealed container, and purge it with nitrogen for 0.5-1 hours to create an inert atmosphere; stir the mixture continuously during the nitrogen purging process. S4: While maintaining an inert atmosphere, add ammonium persulfate solution to the mixture, and heat the sealed container to 65-75℃, keep the reaction at this temperature for 5-7 hours, and stir continuously during the heat preservation process; S5: After the reaction is complete, the reaction solution is dialyzed, frozen and dried in sequence to obtain CS-g-PNVCL microgel particles; The mass ratio of chitosan to N-vinylcaprolactam is 60%. The mass ratio of N-methylenebisacrylamide to N-vinylcaprolactam is 4%-7.5%; The mass ratio of ammonium persulfate to N-vinylcaprolactam is 1.2%-3.5%.

2. The method for preparing CS-g-PNVCL microgel according to claim 1, characterized in that, In step S1, when preparing the chitosan solution, the stirring speed is 500-1000 rpm.

3. The method for preparing CS-g-PNVCL microgel according to claim 1, characterized in that, In step S3, when the mixture is continuously stirred, the stirring speed is 100-500 rpm.

4. The method for preparing CS-g-PNVCL microgel according to claim 1, characterized in that, During the heat preservation process in step S4, the stirring speed is 500-1500 rpm.

5. The method for preparing CS-g-PNVCL microgel according to claim 1, characterized in that, The specific steps of dialysis, freezing, and drying in step S5 include: Transfer the reaction solution to a dialysis bag and place it in ultrapure water for continuous dialysis for one week, changing the ultrapure water every 18-24 hours during dialysis. After dialysis, the liquid in the dialysis bag is frozen into a solid and then dried in a vacuum freeze dryer for 24-48 hours to obtain CS-g-PNVCL microgel particles.

6. A method for preparing a stable Pickering emulsion of CS-g-PNVCL microgel prepared by any one of the methods described in claims 1-5, characterized in that, Includes the following steps: A1: Disperse the prepared CS-g-PNVCL microgel particles in ultrapure water and add oil phase to obtain a solid-oil-water mixture; the volume ratio of oil to water in the solid-oil-water mixture is 0.25-4. A2: Use a homogenizer to homogenize the solid-oil-water mixture at a speed of 8000-13000 rpm for 1-6 min to obtain a Pickering emulsion of CS-g-PNVCL microgel.

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