CN109293826B

CN109293826B - PNIPAm microgel and preparation method of vanadium dioxide/silicon dioxide/PNIPAm composite microgel

Info

Publication number: CN109293826B
Application number: CN201710608931.3A
Authority: CN
Inventors: 高彦峰; 李满秋; 王煜; 陈长; 张凯强
Original assignee: University of Shanghai for Science and Technology
Current assignee: University of Shanghai for Science and Technology
Priority date: 2017-07-25
Filing date: 2017-07-25
Publication date: 2021-03-12
Anticipated expiration: 2037-07-25
Also published as: CN109293826A

Abstract

The invention relates to a preparation method of PNIPAM microgel and vanadium dioxide/silicon dioxide/PNIPAM composite microgel, wherein the preparation method of the PNIPAM microgel comprises the following steps: a micelle formation step: dissolving a nonionic surfactant into water at a concentration of 0.5-4 g/L, and standing for 0.5-6 hours at 20-80 ℃ to form a solution containing stable micelles; and a crosslinking polymerization step: dissolving an isopropyl acrylamide monomer and a cross-linking agent in the solution under the protection of inert atmosphere, wherein the addition amount of the poly-isopropyl acrylamide monomer is 2-3 wt% of the solution, adding an initiator, and keeping the mixture at the temperature of 20-80 ℃ for 12-20 hours to obtain the PNIPAm microgel. The invention has simple process, and the obtained PNIPAm microgel has higher transmittance which can reach as much as 90 percent.

Description

PNIPAm microgel and preparation method of vanadium dioxide/silicon dioxide/PNIPAm composite microgel

Technical Field

The invention belongs to the technical field of energy-saving material manufacturing, particularly relates to a vanadium dioxide surface modification processing technology and a PNIPAM microgel preparation method, and particularly relates to a PNIPAM microgel suspension polymerization preparation method and VO₂/SiO₂A suspension polymerization preparation method of/PNIPAm composite microgel.

Background

In recent years, as the awareness of environmental protection is increased and the country gives considerable attention, the people are in the field of the technologyWith a batch of materials based on environmental protection and energy conservation as main functions, such as thermally induced material VO₂And cesium tungstate, and the like. Wherein the vanadium-based material, especially vanadium dioxide VO₂The phase transition temperature is close to room temperature, and the dimming performance is excellent, so that the material is the most widely researched thermochromic material. What we first thought about in talking about smart windows is VO₂A base thermochromatic material. Satisfy VO₂The oxide of the chemical structural formula has multiple configurations and has two configurations with phase change characteristics, namely VO with stable tetragonal rutile configuration₂(R) phase, and slightly distorted monoclinic rutile phase VO₂(M) phase. At a temperature lower than the phase transition temperature (68 ℃), in a monoclinic rutile phase VO₂The (M) configuration (semiconducting) exists. VO in stable tetragonal rutile configuration at temperatures above 68 DEG C₂The (R) phase (metallic state) exists, the phase change process has a first-level phase change characteristic, adjacent atoms orderly slide in the process without long-range diffusion, the phase change can be completed within 500 femtoseconds, under the condition of hardly changing indoor lighting, the rutile vanadium dioxide has low-temperature high-transmittance and high-temperature low-transmittance to infrared light, and is an ideal material for the thermochromic dimming window.

VO produced by current powder-film technology₂The visible light transmittance of the intelligent window is 45.6%, the dimming efficiency is 23.7%, but the regulation range is after 1500nm wavelength. How to overcome the VO₂People make a lot of attempts because of the defects of small regulation and control range and low dimming efficiency of the basic intelligent window. Among them, the most effective method is to coat the optical transparency material thermochromatic material SiO₂. Moreover, the main dimming interval of PNIPAm (poly isopropyl acrylamide) is 350-1350 nm, which occupies most of solar energy and can be mixed with VO₂The regulation ranges are complementary after 1500nm, so that VO is prepared₂The PNIPAm composite gel is used for improving the solar dimming rate. But the disadvantage is also very obvious because with the hydrogel system, the phase transition rate of PNIPAm is very slow, which is very unfavorable for the application of smart windows, and VO after compounding₂The dispersion in PNIPAm hydrogel is not good.

In 1995, santa america introduced a thermal hydrogel named "Cloud Gel" which meets different requirements for use by changing the hydrogel composition to adjust LCST, and is the first commercial attempt to apply a thermal sensitive polymer to a smart window system. Long Yi et al (non-patent document 1, Zhou Y., Cai Y., Hu X., Long Y. temperature-responsive hydrogel with an upper-large solar modulation and high luminance transmission for "smart window" applications [ J ]. J Mater Chem A2014, 2: 13550-one 13555.) studied the most widely temperature-sensitive polymer PNIPAm hydrogel as a light-modulating material by designing a structure similar to a "sandwich". Wangman et al (non-patent document 2, Wang M., Gao Y., Cao C., Chen K., Wen Y., Fan D., Li L., Guo X. binary Solvent gels of Thermosensitive Poly (N-isoproylacrylamide) Microgel for Smart Windows [ J ]. Industrial & Engineering Chemistry Research 2014,53:18462-18472.) synthesize PNIPAm Thermosensitive microgels in a binary Solvent by introducing glycerol into the hydrogel system. Because the phase change rate of the microgel system is far greater than that of the traditional hydrogel, and the introduction of the glycerol enables the freezing point to be reduced from 18.1 ℃ below zero to 32 ℃ below zero, the defect of the application of the thermochromic hydrogel in an intelligent window is effectively improved.

Disclosure of Invention

In view of the above problems, it is an object of the present invention to provide PNIPAm microgel and VO having excellent thermochromic properties (e.g., excellent visible light transmittance and solar light control rate)₂/SiO₂A/PNIPAm composite microgel and a preparation method thereof.

In a first aspect, the present invention provides a method for preparing a polyisopropylacrylamide microgel (also referred to as PNIPAm microgel), comprising the following steps:

a micelle formation step: dissolving a nonionic surfactant into water at a concentration of 0.5-4 g/L, and standing for 0.5-6 hours at 20-80 ℃ to form a solution containing stable micelles; and

a crosslinking polymerization step: dissolving an isopropyl acrylamide monomer (NIPAm monomer) and a cross-linking agent in the solution under the protection of inert atmosphere, wherein the addition amount of the poly-isopropyl acrylamide monomer is 2-3 wt% of the solution, adding an initiator, and keeping the mixture at the temperature of 20-80 ℃ for 12-20 hours to obtain the poly-isopropyl acrylamide microgel.

According to the invention, firstly, the nonionic surfactant forms a stable micelle, then the isopropyl acrylamide monomer and the cross-linking agent enter a template formed by the nonionic surfactant, and after the initiator is added, the PNIPAm microgel is formed by suspension polymerization. The production process is simple, the operation is easy, and the yield is high. The obtained PNIPAm microgel has the particle size of about 200nm, is monodisperse, has excellent visible light transmittance (for example, the visible light transmittance can reach 67.02 percent) and sunlight dimming efficiency (for example, the sunlight dimming efficiency can reach 65.05 percent (80 ℃)), and can be used as an ideal thermochromic intelligent window material. Compared with the method of directly mixing the nonionic surfactant, the isopropyl acrylamide monomer and the cross-linking agent, the method has the advantages of simple process, high transmittance of the obtained PNIPAm microgel, high transmission rate (up to 90%), and excellent performance.

Preferably, in the micelle formation step, the nonionic surfactant is dissolved in water at a concentration of 0.5 to 1.5g/L, preferably 1 g/L. Therefore, the prepared PNIPAm microgel has more excellent visible light transmittance and sunlight dimming efficiency.

In a second aspect, the present invention provides a VO₂/SiO₂Poly (isopropyl acrylamide) composite microgel (also called VO)₂@SiO₂@ PNIPAm composite microgel), which comprises the following steps:

a mixing and dispersing step: to be coated with SiO₂Coated VO₂Powder (VO)₂@SiO₂Powder) is dispersed in a solution with the content of the nonionic surfactant of 0.5-4 g/L, stirred for 20-30 hours and then kept stand for 0.5-6 hours at 20-80 ℃ to form a sol containing stable micelles;

initiating polymerization: dissolving an isopropyl acrylamide monomer (NIPAm monomer) and a cross-linking agent in the solution under the protection of inert atmosphere, wherein the addition amount of the poly-isopropyl acrylamide monomer is 2-3 wt% of the solution, adding an initiator, and keeping the mixture at the temperature of 20-80 ℃ for 20-30 hours to obtain VO₂/SiO₂Poly (isopropyl acrylamide) composite microgel.

According to the inventionMing, make VO₂@SiO₂Dispersing the powder in a non-ionic surfactant solution, stirring to make the powder be completely adsorbed in VO₂@SiO₂Forming stable micelle on the surface of the powder, adding NIPAm monomer and cross-linking agent, adding initiator to initiate the mixture to form VO through suspension polymerization₂@SiO₂@ PNIPAm composite microgel. The production process is simple, the operation is easy, and the yield is high. Obtained VO₂@SiO₂In the @ PNIPAm composite microgel, VO₂@SiO₂Nearly monodisperse in PNIPAm microgel pellets, each microgel pellet has a diameter of about 200nm and is coated with 4 to 5 VOs₂@SiO₂And particles, and the average visible light transmittance is close to 50%, and the solar light modulation rate is up to 81%.

Preferably, in the mixing and dispersing step, the content of the nonionic surfactant in the solution is 1.5 to 2.5g/L, preferably 2 g/L. Thus, VO to be produced can be obtained₂@SiO₂The @ PNIPAm composite microgel has more excellent visible light transmittance and sunlight dimming efficiency.

Preferably, in the mixing and dispersing step, VO is added in the mixing and dispersing step₂The concentration of the active carbon in the solution is 60-120 mg/L.

Preferably, the nonionic surfactant is at least one selected from alkylolamide polyoxyethylene ether, alkylphenol polyoxyethylene ether and polyvinylpyrrolidone, preferably polyvinylpyrrolidone (PVP), and more preferably polyvinylpyrrolidone with molecular weight of 30000-70000.

Preferably, in the crosslinking polymerization step and/or the initiation polymerization step, the crosslinking agent is N, N-methylenebisacrylamide (Bis for short); preferably, the addition amount of the cross-linking agent is 40-80% of the mass of the isopropyl acrylamide monomer.

Preferably, in the crosslinking polymerization step and/or the initiating polymerization step, the initiator is potassium persulfate (KPS); preferably, the addition amount of the initiator is 0.005-0.02 g/mL.

In a third aspect, the present invention provides a polyisopropylacrylamide microgel prepared by the method for preparing any one of the polyisopropylacrylamide microgels described above.

In a fourth aspect, the present invention provides a VO composed of any one of the above₂/SiO₂VO prepared by preparation method of poly (isopropyl acrylamide) composite microgel₂/SiO₂Poly (isopropyl acrylamide) composite microgel.

Drawings

FIG. 1 is VO₂@SiO₂A synthesis schematic diagram of the @ PNIPAm composite microgel;

FIGS. 2(a) -2 (d) show the solar light transmittance of PNIPAm microgels at different PVP contents/temperatures and T at different temperatures_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)A change curve;

FIG. 3 shows the variation of the solar light transmittance of PNIPAm microgel at 20-80 ℃ under different PVP contents;

FIG. 4 is VO at a PVP content of 2g/L₂@SiO₂HRTEM image of @ PNIPAm composite microgel;

FIG. 5 VO at PVP content 4g/L₂@SiO₂HRTEM image of @ PNIPAm composite microgel;

FIG. 6 is VO₂@SiO₂@ PNIPAm composite microgel (PVP ═ 2g/L) solar light transmittance at different temperatures and T at different temperatures_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)A change curve;

FIG. 7 is VO₂@SiO₂@ PNIPAm composite microgel (PVP ═ 4g/L) solar light transmittance at different temperatures and T at different temperatures_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)A change curve;

FIGS. 8(a) to 8(d) are VO₂@SiO₂@ PNIPAm composite microgel (PVP ═ 3g/L) VO with different temperatures₂Solar light transmittance of content and T at different temperatures_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)A change curve;

FIG. 9 is a test platform for transmission spectroscopy.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

One embodiment of the invention starts with microgel to improve the dispersibility of PNIPAm hydrogel and improve VO₂Dispersibility in PNIPAm.

In one embodiment of the invention, the nonionic surfactant is firstly made into stable micelles, then NIPAm monomers and the cross-linking agent are made to enter the micelles, and then the initiator is added for initiation, and suspension polymerization is carried out to form PNIPAm microgel.

In another embodiment of the present invention, the non-ionic surfactant is first adsorbed on the VO₂@SiO₂Forming stable micelle on the surface of the powder, introducing NIPAm monomer and cross-linking agent into the micelle, adding initiator for initiation, and performing suspension polymerization to form VO₂@SiO₂@ PNIPAm composite microgel.

FIG. 1 shows an exemplary VO₂@SiO₂The synthesis of the @ PNIPAm composite microgel is schematically shown in figure 1, and VO is subjected to₂@SiO₂Dispersing the powder in nonionic surfactant solution (such as PVP solution), stirring to make it be adsorbed on VO₂@SiO₂Forming stable micelle on the surface of the powder, adding NIPAm monomer and corresponding cross-linking agent (such as Bis) under the protection of inert atmosphere (such as nitrogen), randomly adding the NIPAm monomer and the corresponding cross-linking agent into a template formed by surfactant, heating, dropwise adding initiator (such as KPS) for initiation, and finally performing suspension polymerization to form VO after reacting for a period of time₂@SiO₂@ PNIPAm composite microgel.

In one example, the nonionic surfactant is passed through a micelle formation process, and the NIPAm and cross-linker are passed through a cross-linking polymerization process to provide the PNIPAm microgel.

In another example, VO is₂@SiO₂The powder is subjected to a mixing and dispersing process with a nonionic surfactant, and the NIPAm and the cross-linking agent are subjected to an initiated polymerization process to obtain VO₂@SiO₂@ PNIPAm composite microgel.

In the preparation of PNIPAm microgel, the nonionic surfactant can be dissolved in water in the micelle forming process, and the concentration of the nonionic surfactant can be 0.5-4 g/L, preferably 0.5-1.5 g/L, more preferably 1-1.2 g/L, and further preferably 1 g/L. The nonionic surfactant can be PVP, alkylolamide polyoxyethylene ether, alkylphenol polyoxyethylene ether and the like, and is preferably PVP, so that the prepared PNIPAm microgel has better circulation times. The molecular weight of PVP can be 30000-70000, preferably 58000. Such PVP is the most stable. Standing for a period of time until stable micelles form. The temperature of the standing can be 20-80 ℃ (for example, 50 ℃). The standing time may be 0.5 to 6 hours (e.g., 0.5 hour).

In preparing PNIPAm microgel, NIPAm monomer and crosslinker may be added to the solution from the micelle formation process under an inert atmosphere (e.g., nitrogen) during the crosslinking polymerization process. The amount of NIPAm monomer added may be 2-3 wt%, preferably 2.5 wt% of the mass of the solution. The cross-linking agent can be Bis, clay nanoparticles, EGDMA (ethylene glycol dimethacrylate), and the like. The amount of the cross-linking agent added may be 1-2 wt% of the mass of the solution, i.e., 40-80% of the mass of the NIPAm monomer. And after the monomer and the cross-linking agent are completely dissolved, heating to 20-80 ℃ (preferably 50-70 ℃, such as 60 ℃), dripping an initiator, carrying out suspension polymerization to synthesize the PNIPAm microgel, and keeping for 12-20 hours (such as 12 hours) to obtain the PNIPAm microgel. The initiator may be KPS, ammonium persulfate, hydrogen peroxide, etc. The amount of the initiator added to the solution may be 0.005 to 0.02g/mL (e.g., 0.01 g/mL).

The obtained PNIPAm microgel has good thermochromism performance, and the particle size is about 200 nm. At a low temperature of 20 ℃, the visible light transmittance of the PNIPAm microgel can be 17-93%, and the sunlight dimming efficiency can be 15-83% (80 ℃). In particular, when the content of the nonionic surfactant is 0.5 to 1.5g/L (particularly 1g/L) in the micelle formation process, the visible light transmittance of the PNIPAm microgel reaches 67.02% and the solar light modulation efficiency reaches 65.05% (80%) at a low temperature of 20 ℃. In addition, when the nonionic surfactant is 0.5-1.5 g/L (particularly 1g/L), the solar dimming efficiency of the PNIPAm microgel is far higher than that of PNIPAm microgel obtained by other PVP concentrations (such as 2g/L, 3g/L and 4g/L), the solar dimming efficiency is 7 times that of other PNIPAm microgels, and the average visible transmittance is 3 times that of other PNIPAm microgels. When the concentration of PVP is 1g/L, the PNIPAm microgel is an ideal thermochromic intelligent window material.

Preparation of VO₂@SiO₂In the case of @ PNIPAm composite microgel, VO may be mixed and dispersed in the step of mixing and dispersing₂@SiO₂The powder is dispersed in a nonionic surfactant solution (e.g., an aqueous solution). The concentration of the nonionic surfactant in the nonionic surfactant solution can be 0.5-4 g/L, preferably 1.5-2.5 g/L, and more preferably 2 g/L. VO (vacuum vapor volume)₂@SiO₂The addition amount of the powder can be 100-200mg/L, namely VO₂The concentration in the solution can be 60-120 mg/L, for example, making VO₂The concentration of (3) was 80.63 mg/L. Then stirring for a period of time until PVP is completely adsorbed on VO₂@SiO₂And (5) coating the surface of the powder. The stirring time may be 20 to 30 hours (e.g., 24 hours). Then, standing for a period of time until stable micelles form. The standing temperature can be 20-80 ℃ (for example, 50 ℃). The standing time may be 0.5 to 6 hours (e.g., 0.5 hour).

Here, VO₂@SiO₂The powder is SiO₂Coated VO₂And (3) powder. VO (vacuum vapor volume)₂@SiO₂The powder is nano-particles with a core-shell structure, and the particle size of the nano-particles can be 60-100 nm. Wherein, VO₂The particle diameter of (A) can be 50-80 nm, SiO₂The coating thickness of (2) to (5) nm. At VO₂Surface coated with SiO₂First, protection of VO₂Not easy to be oxidized, and the number of surface hydroxyl is much more than VO₂And lays a foundation for subsequent reaction with NIPAm and enhancement of dispersion of inorganic nano particles in aqueous solution. VO (vacuum vapor volume)₂@SiO₂The method of preparing the powder is not limited. In one embodiment of the invention, VO is prepared by the Stober method₂@SiO₂A core-shell structure. VO is introduced into a reactor₂The powder is evenly dispersed in ethanol containing grinding balls and stirred for a period of time. The grinding balls are, for example, zirconia balls, and the diameter of the grinding balls can be 0.4-0.6 mm. VO (vacuum vapor volume)₂The concentration of the powder can be 1-10 g/L. The content of the grinding balls can be 1-5 g/mL. The stirring speed can be 600-1000 rpm. The stirring temperature can be room temperature. The stirring time is based on the dynamic light scattering test hydraulic radius of about 130 nm. For example, the stirring time is 6 to 10 hours, preferably 8 to 10 hours. Then, a silicon source is added to the system and uniformly dispersed (for example, dispersed for 1 to 2 hours). The silicon source is hydrolyzed into SiO₂The substance (2) may be, for example, a silicate ester, preferably Tetraethylorthosilicate (TEOS). The adding amount of the silicon source can be 5 mL-20 mL. Then, slowly dropwise adding an ammonia water ethanol solution in the original system through a peristaltic injection pump, and reacting for 6-8 hours. The concentration of ammonia water in the ammonia water ethanol solution can be 10-20%. The addition amount of the ammonia water ethanol solution can be as follows: for each VO₂60-160 mL of ammonia water ethanol solution is used for the powder. After hydrolysis has been completed, the reaction is stopped, the product is separated off and washed, for example twice with water and with an ethanol solution. In another embodiment, VO is produced by an aqueous alcohol solution process₂@SiO₂A core-shell structure. VO is introduced into a reactor₂Adding the powder into a mortar (such as agate mortar) and adding ethanol for grinding (such as grinding for 2-4 hours), and transferring the powder into an ethanol solution to make VO₂The concentration of the powder is 0.5-2.5 g/L. Adding an alkali into the solution to adjust the pH to 9-10. The base used may be at least one of aqueous ammonia, aqueous ammonium bicarbonate, aqueous sodium hydroxide, aqueous potassium hydroxide, aqueous sodium carbonate, aqueous sodium bicarbonate, aqueous potassium carbonate and aqueous potassium bicarbonate, and is preferably aqueous ammonia. And then, adding a silicon source into the system under the slow pushing of a peristaltic pump, and keeping the temperature of 60-80 ℃ in the process. The adding amount of the silicon source can be 5 mL-20 mL. After reaction for 1 to 7 hours, preferably 3 to 5 hours, the product is separated, for example, centrifuged, washed, for example, washed with water and ethanol solution, and dried to obtain VO₂@SiO₂A core-shell structure. The drying condition is, for example, drying at 60-80 ℃ for 4-6 hours. In one example, VO₂@SiO₂The powder was prepared by the following method: VO is introduced into a reactor₂The powder is dispersed in ethanol, and the concentration of the powder can be 0.5-1 g/L. Adding ammonia water, wherein the volume ratio of the ammonia water to the ethanol can be 1: (25-30). Slowly dropwise adding a silicon source (such as tetraethyl orthosilicate) into the system, wherein the silicon source and the VO are₂The mass ratio of the powder can be 1: (4-5). After 1 to 7 hours of reaction, the product is separated off and washed (for example with water and ethanol solution)Washing, drying (for example, drying at 60-80 ℃ for 4-6 hours) to obtain VO₂@SiO₂And (3) powder.

Preparation of VO₂@SiO₂In the case of @ PNIPAm composite microgel, the NIPAm monomer and the crosslinking agent may be added to the solution obtained in the mixing and dispersing step in the initiation polymerization step under the protection of an inert gas (e.g., nitrogen gas). The amount of NIPAm monomer added may be 2-3 wt%, preferably 2.5 wt% of the mass of the solution. The cross-linking agent can be Bis, EGDMA, clay nano-particles, etc. The amount of the cross-linking agent added may be 1-2 wt% of the mass of the solution, i.e., 40-80% of the mass of the NIPAm monomer. After the NIPAm monomer and the cross-linking agent randomly enter a template formed by the PVP surfactant (for example, 5 to 10 minutes after the NIPAm monomer and the cross-linking agent are added), heating to 20 to 80 ℃ (preferably 50 to 70 ℃, for example, 60 ℃), dripping an initiator, reacting for 20 to 30 hours (for example, 24 hours), and carrying out suspension polymerization to synthesize VO₂@SiO₂@ PNIPAm composite microgel. The initiator may be KPS, ammonium persulfate, hydrogen peroxide, etc. The amount of the initiator added to the solution may be 0.005 to 0.02g/mL (e.g., 0.01 g/mL).

Obtained VO₂@SiO₂The @ PNIPAm composite microgel has good thermochromism performance, and the particle size is about 200 nm. VO inside the microgel₂Good dispersibility, and is coated with 4 to 5 VO₂@SiO₂And (3) granules. VO (vacuum vapor volume)₂@SiO₂The average visible light transmittance of the @ PNIPAm composite microgel is close to 50%, and the solar light regulation rate reaches 81%, so that the composite microgel can be used as an ideal thermochromic intelligent window material.

The preparation method has the advantages of simple production process, easy operation and higher yield; the method synthesizes the monodisperse microgel PNIPAm beads through a suspension polymerization method, the particle size of the microgel PNIPAm beads is about 200nm, the sunlight dimming performance of the microgel beads is researched under different PVP contents, and the microgel particles are found to have great influence on the dimming performance and the response speed, so that the optical performance of the microgel beads is far higher than that of other PVP content samples when the PVP content is 0.5-1.5 g/L (particularly 1 g/L).

VO prepared by the invention₂@SiO₂the/PNIPAm composite microgel simultaneously satisfiesLight transmission and solar modulation. VO was studied at different PVP contents₂The dispersion in the microgel, VO in the microgel is obtained by regulating and controlling PVP content₂Composite microgel with good dispersibility and the dimming performance of the microgel are researched, wherein VO in one embodiment₂@SiO₂The average visible light transmittance of the/PNIPAm composite microgel is 49.8 percent, which is close to the reported work, and the sunlight dimming rate is 81 percent which is three times higher than the reported work.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

Example 1: a preparation method of poly isopropyl acrylamide (PNIPAm) microgel with 1g/L of PVP content comprises the following procedures:

dissolving 0.05g (1g/L) of PVP surfactant with the molecular weight of 58000 into 50ml of aqueous solution, transferring the solution into a 250ml three-necked bottle, preserving the temperature at 50 ℃ for 30 minutes until stable micelles are formed, adding 1.25g (2.5 wt%) of NIPAm monomer and Bis (such as 1 wt% of the mass of the monomer) serving as a cross-linking agent in a corresponding proportion under the protection of nitrogen, heating to 60 ℃ after the monomer and the cross-linking agent are completely dissolved, dropwise adding an initiator KPS (0.01g/ml), and carrying out suspension polymerization to synthesize PNIPAm microgel, and keeping the temperature for 12 hours.

Example 2

A preparation method of poly isopropyl acrylamide (PNIPAm) microgel with high PVP content comprises the following steps:

dissolving 0.1g-0.2g (2-4g/L) (namely 2g/L, 3g/L and 4g/L respectively) of PVP surfactant with the molecular weight of 58000 into 50ml of aqueous solution, transferring the aqueous solution into a 250ml three-neck flask, preserving the temperature for 30 minutes at 50 ℃ until stable micelles are formed, adding 1.25g (2.5 wt%) of NIPAm monomer and Bis (such as 1 wt% of the mass of the monomer) serving as a cross-linking agent under the protection of nitrogen, heating to 60 ℃ after the monomer and the cross-linking agent are completely dissolved, dropwise adding an initiator KPS (0.01g/ml) to carry out suspension polymerization to synthesize PNIPAm microgel, and keeping for 12 hours.

The copper sleeve is heated by utilizing a self-made glass tank and a water bath (see fig. 9, wherein the glass jacket is used for containing a test sample and can be directly nested in a copper net, holes with the diameter of 1 x 1cm are respectively arranged on two sides of the copper net, the transmission of incident light can be allowed, the copper net is of a hollow structure, the side surface of the copper net is provided with a circulating water inlet and outlet, the temperature of the sample can be controlled by adjusting the water temperature), and the high-low temperature transmission spectrum, the change of the transmittance at different temperatures, the change curve of the transmittance with time of specific wavelength in the temperature rising and falling process and the like of the PNIPAm microgel are tested on a UV-vis-NIR spectrophotometer. Solar light transmittance at 20-80 ℃ and T at different temperatures under different PVP contents_lum(visible light transmittance) Δ T_sol(％)(solar light modulation efficiency), Δ T_IR(％)(rate of light modulation by infrared light) and Δ T_lum(％)Specific change curves (luminous efficiency of visible light) are shown in FIGS. 2(a) to 2(d), wherein FIGS. 2(a) to 2(d) show PVP contents of 1g/L, 2g/L, 3g/L and 4g/L in this order. At a PVP concentration of 1g/L, T_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)The trend with temperature is shown in table 1:

TABLE 1 PVP concentration of 1g/L, T_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)Trend of change with temperature

It can be seen from the figure that the transmittance drops sharply due to water absorption at wavelengths of 1430nm and 1930nm, which is a common phenomenon of hydrogel smart windows. When the PVP content is 1g/L and the temperature is low at 20 ℃, the visible light transmittance of the PNIPAm microgel reaches 67.02 percent (Table 1), the solar light dimming efficiency is 65.05 percent (60 ℃), and the PNIPAm microgel is compared with a PNIPAm hydrogel intelligent window system (T) of non-patent document 1_lum＝70.7％，ΔT_sol(％)25.5%), which may beThe visible light transmittance is similar, but the solar dimming rate is far higher than that of published articles. The PNIPAm hydrogel synthesized under the PVP concentration of 1g/L has good thermochromatic performance.

In the test process, in order to prevent the solvent from volatilizing, the glass cell was sealed with a heat conductive tape. And (3) carrying out temperature correction by adopting an AZ8803 thermocouple, so that the error is within +/-1 ℃ for testing the temperature of the microgel in the glass tank. The change in solar transmittance of the PNIPAm microgel was tested using a UV-vis-NIR spectrophotometer. The specific variation is shown in fig. 3.

As can be seen from FIG. 3, the solar dimming efficiency of the PNIPAm microgel is much higher than that of other three PVP concentration samples when the PVP is 1g/L, the solar dimming efficiency is 7 times that of other samples, and the average visible transmittance is 3 times that of other samples. The reason for this is that PVP is a high molecular polymer with a long molecular chain, and the increase of the amount of PVP can make redundant PVP adhere to the surface of hydrogel to limit the change of the form of hydrogel in the swelling-deswelling process, which has a great influence on the optical performance, and PVP which is not adhered to the surface of microgel can act as a physical cross-linking agent to cause the microgel particles to be bonded with each other, thereby affecting the network structure of the microgel particles and further affecting the optical performance. In addition, when PVP is less than 1g/L, the dispersibility is not good, and the prepared sample is liable to coagulation and is unstable.

Example 3: VO with PVP content of 2g/L₂@SiO₂The preparation method of the/PNIPAm composite material comprises the following steps:

VO₂@SiO₂preparation of powder: 0.05g of VO₂The powder (prepared by the hydrothermal reaction method) is uniformly dispersed in a 20ml glass reagent bottle (10ml ethanol, 20g zirconia balls with the diameter of 0.5 mm), and is magnetically stirred for about 8-10 hours at room temperature, and the rotating speed is 600-1000 rpm. Then, 100. mu.l of tetraethyl orthosilicate (TEOS) was added to the system, and the mixture was uniformly dispersed for 1 hour. Slowly dripping 5mL of ammonia water ethanol solution (the concentration of ammonia water is 10% -20%) into the original system through a peristaltic injection pump, reacting for 8 hours, and stopping the reaction after the hydrolysis is finished. Washing the product twice with water and ethanol solution;

VO is introduced into a reactor₂@SiO₂Powder to make VO₂Of (1) containsDispersing in a PVP content (2g/L) solution in an amount of 80.63mg/L, stirring for 24 hours until PVP is completely adsorbed in VO₂@SiO₂Transferring the powder to a 250ml three-necked bottle, keeping the temperature at 50 ℃ for 30 minutes to stabilize micelle formation, adding 1.25g (2.5 wt%) of NIPAm monomer and Bis (such as 1 wt% of monomer mass) serving as a cross-linking agent under the protection of nitrogen, standing for 10 minutes, randomly entering a template formed by PVP surfactant, heating to 60 ℃, dropwise adding an initiator KPS (0.01g/ml) for initiation, reacting for 24 hours, and performing suspension polymerization to form VO₂@SiO₂@ PNIPAm composite microgel.

Example 4: VO with high PVP content₂@SiO₂The preparation method of the/PNIPAm composite material comprises the following steps:

VO is introduced into a reactor₂@SiO₂The powder is dispersed at 100-200mg/L in PVP content of (3-4g/L) (i.e. 3g/L and 4g/L respectively), wherein when the PVP content is 3g/L, VO is used respectively₂The high content and the low content are respectively 64mg/L and 106 mg/L. Stirring the solution for 24 hours until all PVP is adsorbed on VO₂@SiO₂Transferring the powder to a 250ml three-necked bottle, keeping the temperature at 50 ℃ for 30 minutes to stabilize micelle formation, adding 1.25g (2.5 wt%) of NIPAm monomer and Bis (such as 1 wt% of monomer mass) serving as a cross-linking agent under the protection of nitrogen, standing for 10 minutes, randomly entering a template formed by PVP surfactant, heating to 60 ℃, dropwise adding an initiator KPS (0.01g/ml) for initiation, reacting for 24 hours, and performing suspension polymerization to form VO₂@SiO₂@ PNIPAm composite microgel.

Characterization of VO by TEM₂@SiO₂The microscopic morphology of the @ PNIPAm composite microgel. When the content of PVP is 2g/L, VO₂The morphology of the composite microgel at the content of 80.63mg/L is shown in FIG. 4. VO can be seen from (a), (b) and (c) in FIG. 4₂@SiO₂Nearly monodisperse in PNIPAm microgel pellets, each microgel pellet has a diameter of about 200nm and is coated with 4 to 5 VOs₂@SiO₂And (3) granules. By measuring the lattice fringe spacing, it is in contact with VO₂The (R) phase 120 crystal face coincided and SiO was observed₂The silicon layer is coated on the VO₂The surface and shell thickness is 0.59nmShows that the composite system has good dispersibility and synthesized VO₂@SiO₂the/PNIPAm composite microgel is also monodisperse in the solution, and the nearly perfect structure brings improvement to the performance and the response rate of the intelligent window. VO (vacuum vapor volume)₂@SiO₂@ PNIPAm composite microgel (PVP ═ 2g/L) solar light transmittance at different temperatures and T at different temperatures_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)The variation is shown in fig. 6. It can be seen that the solar light modulation rate reaches 81% while the average visible light transmittance is close to 50%.

FIG. 5 shows VO₂@SiO₂TEM morphology of @ PNIPAm composite microgel (PVP ═ 4 g/L). It can be seen from the figure that under the appropriate sample preparation conditions, the composite microgel shows monodispersion trend, VO₂@SiO₂The particles are dispersed on the surface of the microgel and particle agglomeration occurs (see c in fig. 5). Due to the large addition of PVP, d, e and f in the figure 5 are similar to thin films of gel layers after air drying, but the appearance of each PNIPAm microgel is implicitly accompanied by VO₂@SiO₂Around which the particles are located.

FIG. 7 is VO₂@SiO₂@ PNIPAm composite microgel (PVP ═ 4g/L) solar light transmittance at different temperatures and T at different temperatures_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)The change curve shows the trend that the transmittance is continuously reduced along with the increase of the temperature, and the special change is not shown, so that the excessive PVP is coated on the VO due to the increase of the content of the PVP₂@SiO₂And the surface of the microgel, there is no tendency to be characteristic of complex gels. Similarly, when the temperature is raised to 80 ℃, the VO is generated₂Phase change still brings the promotion of sunlight dimming efficiency for the system.

VO was tested on a UV-vis-NIR spectrophotometer by heating the copper jacket using a homemade glass bath and water bath (see FIG. 9)₂@SiO₂The @ PNIPAm composite microgel has the characteristics of high and low temperature transmission spectrum, transmittance change at different temperatures, a change curve of transmittance of specific wavelength along with time in the process of temperature rise and temperature decrease, and the like. VO (vacuum vapor volume)₂(low/high)@SiO₂@ PNIPAm composite microgel (PVP ═ 3g/L) VO with different temperatures₂Solar light transmittance of content and T at different temperatures_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)The change curves are specifically shown in fig. 8(a) to 8 (d). Low here means low VO₂The content (64mg/L) and high mean high VO₂Content (106 mg/L). As shown in FIGS. 8(a) to 8(d), VO was high and low at a PVP concentration of 3g/L₂The relation between the solar light transmittance and the temperature under the content shows a special trend of the composite microgel, and the transmittance does not rise or fall after the temperature is 40 ℃. Since the sample of FIG. 8(c) contains VO, as compared with that of FIG. 8(a)₂High content, so that VO is reached₂After the phase transition temperature, the regulation rate of the infrared part is higher than that of the former, and the infrared light dimming rate of 5.1% is brought (table 2). Compared with pure VO₂22.3% of total solar regulation rate of powder, VO₂The introduction of the compound effectively enhances the sunlight dimming rate of the system;

TABLE 2 PVP concentration 3g/L, VO₂At a high content, T_lum、ΔT_sol(％)、ΔT_IR(％)、ΔT_lum(％)Trend of change with temperature

Although the present invention has been described and illustrated in greater detail by the inventor, it should be understood that modifications and/or changes to the above-described embodiments or equivalent alternatives will be apparent to those skilled in the art in light of the present disclosure without departing from the scope of the invention as defined by the appended claims.

Claims

1. VO (volatile organic compound)₂/SiO₂The preparation method of the poly (isopropylacrylamide) composite microgel is characterized by comprising the following steps of:

a mixing and dispersing step: to be coated with SiO₂Coated VO₂Dispersing the powder in a solution with the content of the nonionic surfactant of 1.5-2.5 g/L, stirring for 20-30 hours, and then standing for 0.5-6 hours at 20-80 ℃ to form a sol containing stable micelles;

initiating polymerization: dissolving an isopropyl acrylamide monomer and a cross-linking agent in the solution under the protection of inert atmosphere, wherein the addition amount of the poly-isopropyl acrylamide monomer is 2-3 wt% of the solution, adding an initiator, and keeping the mixture at the temperature of 20-80 ℃ for 20-30 hours to obtain VO₂/SiO₂Poly (isopropyl acrylamide) composite microgel;

the nonionic surfactant is PVP surfactant with the molecular weight of 58000.

2. The production method according to claim 1, wherein the content of the nonionic surfactant in the solution in the mixing and dispersing step is 2 g/L.

3. The process according to claim 1, wherein VO is produced in the mixing and dispersing step₂The concentration of the active carbon in the solution is 60-120 mg/L.

4. The method according to claim 1, wherein the crosslinking agent in the step of initiating polymerization is N, N-methylenebisacrylamide.

5. The preparation method according to claim 4, wherein the amount of the crosslinking agent added is 40-80% by mass of the isopropyl acrylamide monomer.

6. The method according to claim 1, wherein the initiator used in the step of initiating polymerization is potassium persulfate.

7. The method according to claim 6, wherein the amount of the initiator added is 0.005 to 0.02 g/mL.

8. VO prepared by the method of claim 1₂/SiO₂Poly (isopropyl acrylamide) composite microgel.