CN112831066B - Temperature-sensitive photonic crystal gel with wide threshold and high sensitivity and preparation method thereof - Google Patents
Temperature-sensitive photonic crystal gel with wide threshold and high sensitivity and preparation method thereof Download PDFInfo
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- C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
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- C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
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Abstract
本发明提供了一种具有宽阈值和高灵敏的温敏光子晶体凝胶，该温敏光子晶体凝胶由聚(N‑异丙基丙烯酰胺)水凝胶以及分布在该水凝胶的三维高分子网络结构中的超顺磁纳米粒子组成，该水凝胶的三维高分子网络结构是由单体N‑异丙基丙烯酰胺与交联剂四臂聚乙二醇丙烯酰胺经交联聚合形成的均匀交联结构，所述超顺磁纳米粒子在三维高分子网络结构中排布形成了若干条一维取向的链状结构；该温敏光子晶体凝胶能在20～44℃的条件下保持结构色，在温度检测时该温敏光子晶体凝胶的结构色对应的波长变化范围在658～464nm之间。本发明可拓宽现有温敏光子晶体凝胶的响应阈值并提高其响应灵敏度。The present invention provides a temperature-sensitive photonic crystal gel with a wide threshold and high sensitivity. The temperature-sensitive photonic crystal gel is composed of poly(N-isopropylacrylamide) hydrogel and three-dimensional structures distributed in the hydrogel. It is composed of superparamagnetic nanoparticles in the polymer network structure. The three-dimensional polymer network structure of the hydrogel is composed of monomer N-isopropylacrylamide and crosslinking agent four-arm polyethylene glycol acrylamide through cross-linking polymerization A uniform cross-linked structure is formed, and the superparamagnetic nanoparticles are arranged in a three-dimensional polymer network structure to form several one-dimensional oriented chain structures; the temperature-sensitive photonic crystal gel can be in the condition of 20-44 ° C. The structural color is maintained under the temperature detection, and the wavelength change range corresponding to the structural color of the temperature-sensitive photonic crystal gel is between 658 and 464 nm. The invention can widen the response threshold of the existing temperature-sensitive photonic crystal gel and improve its response sensitivity.
Description
Technical Field
The invention relates to the field of photonic crystal materials, in particular to a temperature-sensitive photonic crystal gel with wide threshold and high sensitivity based on a one-dimensional photonic crystal structure and a preparation method thereof.
Background
Temperature is a common and important source of external stimuli. The temperature sensitive photonic crystal gel can directly detect different external temperatures through color changes recognizable by naked eyes, so that the temperature sensitive photonic crystal gel is widely researched. Poly (N-isopropylacrylamide) (PNIPAM) was widely used in temperature-responsive photonic crystal solidification systems as the earliest discovered temperature-responsive polymer. When the PNIPAM photonic crystal gel is exposed to the change of external temperature, the volume of the PNIPAM photonic crystal gel is swelled or shrunk, the internal lattice spacing of the gel is increased or reduced, the position of a photonic band gap in a spectrum is changed, and the responsiveness of the PNIPAM photonic crystal gel can be evaluated by the color change which can be recognized by naked eyes through the displacement of a diffraction peak macroscopically.
The temperature-sensitive PNIPAM photonic crystal gel can be divided into three structures, namely one-dimensional structure, two-dimensional structure and three-dimensional structure, through the spatial dimension of the periodic arrangement of the substances with different refractive indexes in the temperature-sensitive PNIPAM photonic crystal gel. The existing most of two-dimensional and three-dimensional PNIPAM photonic crystal gels have the problems of complex preparation process, long time consumption and poor strength. In recent years, photonic crystal gel with one-dimensional structure based on magnetic colloid nano particles has attracted attention due to the advantages of simple and rapid preparation process, good mechanical strength, bright and uniform structure color, few defects and the like.
However, the highest response temperature of the PNIPAM photonic crystal gel based on magnetic nanoparticles reported at present is about 33 ℃, which means that the temperature range capable of responding is narrow, the color change is orange red to green at most, and the corresponding maximum wavelength migration amount is only 140nm, which indicates that the response degree is not high enough. On the one hand, this is because these gels mostly use N, N' -methylenebisacrylamide (BIS) small molecules as cross-linking agents, and when the temperature is raised to exceed the Volume Phase Transition Temperature (VPTT), the PNIPAM polymer chains in the gel undergo drastic shrinkage and aggregation, and this inhomogeneous shrinkage converts the microstructure of the gel from a homogeneous state at low temperature to a heterogeneous state. Meanwhile, the heterogeneous structure enables refractive indexes of different parts in the gel to be different, light is scattered when penetrating through the gel, interference is caused to Bragg diffraction, and structural color cannot be generated, so that the photonic crystal gel loses color at about 33 ℃. On the other hand, in the existing research, a higher content of a cross-linking agent or a higher strength initial magnetic field is used, so that the lattice spacing of the gel photonic crystal gel in the initial state is smaller, the color change range and the wavelength migration amount are smaller, and the response sensitivity is not high enough. The narrow temperature response range limits the applicable temperature detection field of the photonic crystal gel, and the low sensitivity limits the accuracy of the photonic crystal gel. Therefore, the design of the temperature-sensitive photonic crystal gel with wide threshold and high sensitivity has important significance.
Disclosure of Invention
Aiming at the problems of narrow response threshold and low response sensitivity of the existing poly (N-isopropylacrylamide) temperature-sensitive photonic crystal gel based on the one-dimensional photonic crystal structure of the magnetic nanoparticles, the temperature-sensitive photonic crystal gel with wide threshold and high sensitivity and the preparation method thereof are provided, so that the response threshold of the temperature-sensitive photonic crystal gel is widened and the response sensitivity of the temperature-sensitive photonic crystal gel is improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a temperature-sensitive photonic crystal gel with wide threshold and high sensitivity comprises poly (N-isopropyl acrylamide) hydrogel and superparamagnetic nano particles distributed in a three-dimensional polymer network structure of the hydrogel, wherein the three-dimensional polymer network structure of the hydrogel is a uniform cross-linked structure formed by cross-linking and polymerizing monomer N-isopropyl acrylamide and cross-linking agent four-arm polyethylene glycol acrylamide, and the superparamagnetic nano particles are distributed in the three-dimensional polymer network structure to form a plurality of one-dimensional oriented chain structures; the temperature-sensitive photonic crystal gel can keep structural color at 20-44 ℃, and the wavelength variation range corresponding to the structural color of the temperature-sensitive photonic crystal gel is 658-464 nm during temperature detection.
The temperature-sensitive photonic crystal gel with wide threshold and high sensitivity provided by the invention has the advantages that in the temperature detection process, the structural color of the gel has obvious color change from orange red to blue from low temperature to high temperature (20-44 ℃), the corresponding wavelength migration range almost covers the whole visible light waveband, and the temperature-sensitive photonic crystal gel has a wide temperature detection range and a high color response degree.
Furthermore, the three-dimensional polymer network structure of the temperature-sensitive photonic crystal gel with the wide threshold and the high sensitivity is a uniform cross-linked structure formed by cross-linking and polymerizing monomer N-isopropyl acrylamide and cross-linking agent quadri-arm polyethylene glycol acrylamide according to a molar ratio of (280-320): 1.
Further, in the temperature-sensitive photonic crystal gel with wide threshold and high sensitivity, the mass fraction of the superparamagnetic nanoparticles is 0.6-0.9%. The particle size of the superparamagnetic nanoparticles is preferably 145-165 nm. The superparamagnetic nanoparticle may be a superparamagnetic nanoparticle that is conventional in the prior art, for example, a superparamagnetic nanoparticle coated with a polymer material.
The invention also provides a preparation method of the temperature-sensitive photonic crystal gel with wide threshold and high sensitivity, which comprises the following steps:
(1) dissolving a monomer N-isopropyl acrylamide, a cross-linking agent four-arm polyethylene glycol acrylamide and a photoinitiator in ethylene glycol, then adding superparamagnetic nano particles, and fully dispersing to form a gel pre-polymerization solution; in the gel pre-polymerization liquid, the molar ratio of monomer N-isopropyl acrylamide to cross-linking agent four-arm polyethylene glycol acrylamide is (280-320): 1;
(2) applying an external magnetic field of 67-70 Gs to the gel prepolymerization liquid, applying ultraviolet irradiation to the gel prepolymerization liquid to enable the gel prepolymerization liquid to be crosslinked and polymerized into gel when the gel prepolymerization liquid has a bright structural color, and placing the obtained gel in water to swell and clean to remove unreacted substances to obtain the temperature-sensitive photonic crystal gel.
In the step (1) of the preparation method of the temperature-sensitive photonic crystal gel with the wide threshold and the high sensitivity, the concentration of the superparamagnetic nanoparticles in the gel pre-polymerization solution is preferably 7-10 mg/mL.
In the preparation methods of the temperature-sensitive photonic crystal gel with wide threshold and high sensitivity, one feasible preparation method of the superparamagnetic nanoparticles is as follows:
dissolving glucose and polyvinylpyrrolidone in ethylene glycol at the temperature of 90-120 ℃, cooling to room temperature, then adding ferric chloride hexahydrate and anhydrous sodium acetate, stirring until the ferric chloride hexahydrate and the anhydrous sodium acetate are dissolved to obtain a mixed reaction solution, transferring the mixed reaction solution to a reaction kettle, reacting for 10-12 hours at the temperature of 190-220 ℃, separating out an obtained solid phase, and cleaning to obtain superparamagnetic nanoparticles;
the particle size of the superparamagnetic nanoparticles can be changed by changing the molar ratio of glucose to ferric chloride hexahydrate in the mixed reaction liquid, wherein the molar ratio of the glucose to the ferric chloride hexahydrate in the reaction mixed liquid is preferably (0.52-0.54): 1;
in the mixed reaction liquid, the concentration of polyvinylpyrrolidone is preferably 0.10-0.16 g/mL, the concentration of glucose is preferably 0.04-0.05 mmol/mL, and the concentration of anhydrous sodium acetate is preferably 1.3-1.4 mmol/mL.
In the step (1) of the preparation method of the temperature-sensitive photonic crystal gel with the wide threshold and the high sensitivity, the concentration of the monomer N-isopropylacrylamide in the gel pre-polymerization solution is preferably 3-4 mmol/mL; the photoinitiator in the gel pre-polymerization solution is a substance for initiating monomer cross-linking polymerization under ultraviolet irradiation, for example, the photoinitiator can be 1-hydroxycyclohexyl phenyl ketone (IRG184), and the concentration of the photoinitiator is preferably 4-6 mg/mL.
In the technical scheme of the temperature-sensitive photonic crystal gel with the wide threshold and the high sensitivity, the superparamagnetic nanoparticles are distributed in the three-dimensional polymer network structure to form a plurality of one-dimensional oriented chain structures, which means that the superparamagnetic nanoparticles are distributed in the three-dimensional polymer network structure to form the chain structures oriented along the magnetic induction line direction of an external magnetic field applied during preparation.
The temperature-sensitive photonic crystal gel prepared by the invention has the characteristics of wide threshold and high sensitivity, and the main reasons are as follows:
on one hand, the invention uses the macromolecular cross-linking agent which is the four-arm polyethylene glycol acrylamide, the cross-linking agent is a macromolecule with a regular structure, and compared with the micromolecular cross-linking agent N, N' -methylene bisacrylamide adopted in the prior art, the macromolecular cross-linking agent can form a more uniform and regular three-dimensional gel network structure, and the uniformity of a gel microstructure is improved. Meanwhile, the macromolecular cross-linking agent contains a large number of hydrophilic polyethylene glycol (PEG) chains, so that the PNIPAM long chain in the formed gel network structure is divided by the hydrophilic PEG chain segments, and severe shrinkage and aggregation of the PNIPAM high molecular chain are prevented to a certain extent. Therefore, the distribution of the internal refractive index in the space can be maintained in a relatively uniform state all the time during the gel shrinkage process, the scattering effect of light is small, and the Bragg diffraction generating the structural color is hardly affected, so that the structural color can be maintained at a higher temperature, and a wider threshold value is provided during temperature detection. On the other hand, the low-content macromolecule crosslinking agent is adopted, an external magnetic field (67-70 Gs) with low strength is applied during preparation, and the initial lattice spacing of the gel at low temperature is larger due to the proper matching of the two factors, so that the lattice spacing variation of the gel in the contraction process is improved, namely, the corresponding diffraction wavelength migration amount of the gel in the contraction process is increased, and the detection sensitivity is higher.
Compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:
1. the invention provides a temperature-sensitive photonic crystal gel with a wide threshold and high sensitivity, which consists of poly (N-isopropylacrylamide) hydrogel and superparamagnetic nano-particles distributed in a three-dimensional polymer network structure of the hydrogel, wherein the three-dimensional polymer network structure of the hydrogel is a uniform cross-linked structure formed by cross-linking and polymerizing monomer N-isopropylacrylamide and cross-linking agent four-arm polyethyleneglycol acrylamide, and the superparamagnetic nano-particles are distributed in the three-dimensional polymer network structure to form a plurality of one-dimensional chain structures. Through the design of a gel three-dimensional network structure and the control of the strength of an applied external magnetic field in preparation, the temperature-sensitive photonic crystal gel can keep the structural color at the temperature of 20-44 ℃, the structural color of the temperature-sensitive photonic crystal gel can be changed from orange red to blue in temperature detection, the corresponding wavelength change range is 659-465 nm, and the temperature-sensitive photonic crystal gel almost covers the whole visible light waveband. Compared with the conventional PNIPAM photonic crystal gel, the temperature-sensitive photonic crystal gel provided by the invention has a wider temperature detection range and a higher color response degree.
2. Experiments prove that the photonic crystal gel provided by the invention has better reversibility and repeatability, and shows excellent stability in multiple high-low temperature cycle experiments, so that the photonic crystal gel is beneficial to practical application in the fields of temperature detection and induction.
3. The invention also provides a preparation method of the temperature-sensitive photonic crystal gel with wide threshold and high sensitivity, and the preparation method is simple in preparation process, short in preparation period and easy to realize batch production.
Drawings
FIG. 1 shows the superparamagnetic nanoparticles Fe of two different particle sizes prepared in example 13O4Scanning Electron Micrographs (SEM), Transmission Electron Micrographs (TEM) and particle size distribution plots of @ PVP, wherein the images a and c are SEM and TEM of the first superparamagnetic nanoparticle, respectively, the images b and d are SEM and TEM of the second superparamagnetic nanoparticle, respectively, and the image e is DLS of the two.
FIG. 2 shows the superparamagnetic nanoparticles Fe of two different particle sizes prepared in example 13O4XRD pattern (a pattern), hysteresis loop (b pattern), FTIR spectrum (c pattern) and TG-DSC curve (d pattern) of @ PVP.
FIG. 3 shows the superparamagnetic nanoparticles Fe of two different particle sizes prepared in example 13O4The optical photograph and the reflection spectrogram of @ PVP under different magnetic fields are shown in the figures, wherein a and b represent the first and second superparamagnetic nano-particles respectively, and curves a-e in the figures sequentially represent the reflection spectrograms under the conditions of magnetic field strengths of 161, 149, 136, 111 and 85 Gs.
FIG. 4 is an optical picture at 20 ℃ to 44 ℃ of HB-0 (panel a) and HT-0 gel (panel b) prepared in comparative example 1.
FIG. 5 is a sectional SEM and elemental analysis plots of HT-0(a, b, c plot) prepared in comparative example 1 and PHT-1(d, e, f plot) prepared in example 2.
FIG. 6 is an optical picture (a, b) and reflectance spectra (c, d) of PHT-1 and PHT-2 prepared in example 2 at 20 ℃ to 44 ℃, wherein curves a to h represent reflectance spectra at 20, 28, 30, 32, 34, 36, 40, and 44 ℃ in sequence.
FIG. 7 is an optical picture (a, b) and reflectance spectra (c, d) of PHT-3 and PHT-4 prepared in example 3 at 20 ℃ to 44 ℃, wherein curves a to h represent reflectance spectra at 20, 28, 30, 32, 34, 36, 40, and 44 ℃ in sequence.
FIG. 8 is an optical picture (a, b) and reflectance spectra (c, d) of PHT-5 and PHT-6 prepared in example 4 at 20 ℃ to 44 ℃, wherein curves a to h represent reflectance spectra at 20, 28, 30, 32, 34, 36, 40, and 44 ℃ in sequence.
FIG. 9 is an optical picture (a, b) and reflectance spectra (c, d) of PHT-7 and PHT-8 prepared in example 5 at 20 ℃ to 44 ℃, wherein curves a to h represent reflectance spectra at 20, 28, 30, 32, 34, 36, 40, and 44 ℃ in sequence.
FIG. 10 is the results of the experiment repeated for PHT-1 in example 6.
Detailed Description
The temperature sensitive photonic crystal gel with wide threshold and high sensitivity and the preparation method thereof provided by the present invention are further illustrated by the following examples. It should be noted that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention, and those skilled in the art can make certain insubstantial modifications and adaptations of the present invention based on the above disclosure and still fall within the scope of the present invention.
Example 1
In this example, superparamagnetic nanoparticles Fe of two different particle sizes were prepared3O4@ PVP, the procedure is as follows:
(1) dissolving 0.243g of glucose in 30mL of ethylene glycol at normal temperature, then placing the obtained solution in an oil bath at 100 ℃ for heating, adding 3.33g of polyvinylpyrrolidone (PVP) while stirring, continuously stirring until the solution is clear and transparent, taking out the solution from the oil bath, cooling to room temperature, then adding 0.677g of ground ferric chloride hexahydrate into the solution (namely the molar ratio of the glucose to the ferric chloride hexahydrate is 0.54), vigorously stirring for 30min to completely dissolve the solid, then adding 3.28g of anhydrous sodium acetate into the solution, further vigorously stirring for 40min to completely dissolve the solid, transferring the obtained mixed reaction liquid into a reaction kettle, reacting for 10h at 200 ℃, and finally respectively washing with secondary pure water and anhydrous ethanol to obtain the first superparamagnetic Fe nanoparticle3O4@PVP。
(2) Dissolving 0.27g of glucose in 30mL of ethylene glycol at normal temperature, then placing the obtained solution in an oil bath at 100 ℃ for heating, adding 3.33g of PVP while stirring, continuously stirring until the solution is clear and transparent, taking out the solution from the oil bath, cooling to room temperature, then adding 0.677g of ground ferric chloride hexahydrate into the solution (namely the molar ratio of the glucose to the ferric chloride hexahydrate is 0.60), violently stirring for 30min to completely dissolve the solid, then adding 3.28g of anhydrous sodium acetate into the solution, continuously and violently stirring for 40min to completely dissolve the solid, transferring the obtained mixed reaction liquid into a reaction kettle, reacting for 10h at 200 ℃, and finally respectively cleaning with secondary pure water and anhydrous ethanol to obtain second superparamagnetic nanoparticles Fe3O4@PVP。
Fig. 1 is SEM, TEM and size distribution diagrams of two kinds of superparamagnetic nanoparticles prepared in this example, fig. 1 a and c are SEM and TEM of a first kind of superparamagnetic nanoparticles, fig. 1 b and d are SEM and TEM of a second kind of superparamagnetic nanoparticles, and e is a size distribution diagram of two kinds of superparamagnetic nanoparticles. As can be seen from FIG. 1, both superparamagnetic nanoparticles were spherical particles and had uniform particle sizes, and the average sizes of the first and second superparamagnetic nanoparticles were measured to be 164nm and 198nm, respectively. As can be seen from fig. 1 c and d, the superparamagnetic nanoparticle prepared in this embodiment has a core-shell structure. As can be seen from the e diagram of FIG. 1, both superparamagnetic nanoparticles have a monomodal particle size distribution, and the monodispersion indexes PDI of the first and second superparamagnetic nanoparticles are measured to be 0.067 and 0.058, respectively, indicating that they have better monodispersion.
The hydrated particle size of the superparamagnetic nanoparticles was measured by Dynamic Light Scattering (DLS), and as a result, it was found that the hydrated particle sizes of the first and second superparamagnetic nanoparticles were 192nm and 219nm, respectively, which were larger than the particle size measured based on SEM, because the particle size measured based on SEM was the actual size of the superparamagnetic nanoparticles in the dry state, whereas DLS measured the kinetic diameter in its solution (hydrated state), including the core inside the superparamagnetic nanoparticles and a layer of stretched PVP polymer chains covering the surface thereof, and thus the hydrated diameter was larger than the actual diameter.
Fig. 2 is an XRD image, a hysteresis loop, an FTIR spectrum and a TGA curve of two superparamagnetic nanoparticles prepared in this example. As can be seen from the a diagram of FIG. 2, the two XRD diagrams are relatively similar and both compare with Fe in JCPDS No.19-0629 (JCPDS: Joint Committee for powder diffraction standards) standard3O4The diffraction patterns of the crystals are substantially identical and correspond to Fe respectively3O4The (220), (311), (400), (422), (511), (440) planes of the crystal. As can be seen from the b diagram of 2, the saturation magnetization of the two superparamagnetic nanoparticles is 53.93emu/g and 56.68emu/g respectively, and the coercive force and residual magnetization are zero, which indicates that both superparamagnetic particles have superparamagnetism. In panel c of FIG. 2, the two FTIR spectra exhibited similar characteristic peaks at 568cm-1The absorption peak is the characteristic peak of Fe-O, which indicates that the superparamagnetic nano-particle contains Fe3O4，1651cm-1And 1375cm-1Characteristic peaks of carbonyl and carbon-nitrogen bonds respectively, confirming the existence of PVP in the superparamagnetic nano-particle, 3412cm-1And is 1049cm-1The characteristic peak indicates that the superparamagnetic nanoparticle contains glucose derivatives. As can be seen from the d-plot of FIG. 2, the weight loss of the first and second superparamagnetic nanoparticles during calcination from 200 ℃ to 400 ℃ was 13.9% and 15.1%, respectively, which represents the content of organic components in their composition.
The optical photograph and the reflected light spectrum of the two kinds of superparamagnetic nanoparticles are shown in fig. 3, wherein, the two pictures a and b correspond to the first and the second superparamagnetic nanoparticles respectively. As can be seen from FIG. 3, for the solution containing the first superparamagnetic nanoparticles, when the magnetic field intensity is gradually increased from 85Gs to 161Gs, the color of the solution changes from yellow-green to blue and finally to blue-violet, and the wavelength shifts from 582nm to 470 nm; for the solution containing the second superparamagnetic nano particle, when the magnetic field intensity is gradually increased from 85Gs to 161Gs, the color of the solution is changed from orange red to yellow and finally to green, and the wavelength is shifted from 676nm to 539 nm. It is shown that when the particle size of the superparamagnetic nanoparticles is different, the color variation range is also different.
Comparative example 1
In the comparative example, N' -methylenebisacrylamide (BIS) and four-arm polyethyleneglycol acrylamide are respectively used as cross-linking agents to prepare a N-isopropylacrylamide (PNIPAM) blank gel without superparamagnetic nanoparticles, the gel with BIS as the cross-linking agent is named as HB-0, and the gel with four-arm polyethyleneglycol acrylamide as the cross-linking agent is named as HT-0, and the steps are as follows:
(1) preparing gel pre-polymerization liquid: monomer NIPAM, crosslinking agent BIS or four-arm polyethylene glycol acrylamide, photoinitiator 1-hydroxy cyclohexyl phenyl ketone (IRG184) are dissolved in ethylene glycol.
For the gel pre-polymerization solution of HB-0, the concentration of BIS was 0.024mol/L, the concentration of NIPAM was 3.6mol/L, and the concentration of photoinitiator IRG184 was 5 mg/mL.
For the gel pre-polymerization solution of HT-0, the concentration of the four-arm polyethylene glycol acrylamide is 0.012mol/L, the concentration of NIPAM is 3.6mol/L, and the concentration of the photoinitiator IRG184 is 5 mg/mL.
(2) 100 μ L of HB-0 gel pre-polymerization solution and HT-0 gel pre-polymerization solution were taken by pipette and injected into two molds, each of which was composed of an upper and a lower quartz glass sheet sandwiching a polytetrafluoroethylene sheet having a thickness of 300 μm. And then irradiating the gel prepolymer liquid for 90s by using a 20W ultraviolet lamp respectively to enable the gel prepolymer liquid to be converted into gel through crosslinking polymerization, taking the obtained gel out of the mold respectively, placing the gel into pure water for soaking and washing, and changing water for 4-5 times during soaking to remove unreacted monomers and other substances to obtain the HB-0 gel and the HT-0 gel.
The obtained gel was cut into 1.5cm × 1.5cm squares, placed in water, and the temperature was controlled by a hot stage, and the gel was allowed to equilibrate for 20min each time a temperature point was reached. FIG. 4 is an optical photograph of HB-0 (panel a) and HT-0 (panel b) prepared in this comparative example at 20 deg.C to 44 deg.C. As can be seen from the graph a in FIG. 4, HB-0 is in a transparent state at 20-30 ℃, the transparency decreases when the temperature rises to about 32 ℃, the gel transparency becomes lower with further rise of the temperature, and the gel becomes substantially completely white when the temperature reaches 36 ℃. This is because the intense shrinkage and aggregation of the hydrophobic PNIPAM long chain in HB-0 causes the uneven microstructure in the gel, which causes the large difference of refractive index at different positions, and the light scattering occurs during transmission to whiten the gel. As can be seen from the b diagram of FIG. 4, it is possible for HT-0 to remain transparent throughout the temperature increase. The regular structure of the four-arm polyethylene glycol acrylamide crosslinking agent greatly improves the uniformity of a three-dimensional network structure in HT-0, and after the hydrophilic PEG chain in the crosslinking agent is crosslinked with the PNIPAM chain, the phenomenon of nonuniform microstructure caused by severe shrinkage aggregation of a hydrophobic PNIPAM long chain in the gel shrinkage process is effectively relieved, so that the refractive index of the gel is distributed uniformly in space, and the transparent state can be maintained in the shrinkage process.
Example 2
In this example, photonic crystal gels were prepared using the first and second superparamagnetic nanoparticles prepared in example 1, respectively, and the prepared photonic crystal gels containing Fe having a particle size of 164nm3O4@ PVP photonic crystal gel was named PHT-1, and the prepared photonic crystal gel containing Fe with a particle size of 198nm3O4The photonic crystal gel of @ PVP is named as PHT-2, and the steps are as follows:
(1) dissolving a monomer NIPAM, a cross-linking agent four-arm polyethylene glycol acrylamide and a photoinitiator IRG-184 in ethylene glycol, then adding the first or second superparamagnetic nano-particles, and fully dispersing to form a gel pre-polymerization liquid.
For the gel pre-polymerization liquid of PHT-1, the concentration of the first superparamagnetic nano particle is 8mg/mL, the concentration of the cross-linking agent four-arm polyethylene glycol acrylamide is 0.012mol/L, the concentration of monomer NIPAM is 3.6mol/L, and the concentration of the photoinitiator IRG184 is 5 mg/mL;
for the gel pre-polymerization liquid of PHT-2, the concentration of the second superparamagnetic nano particle is 8mg/mL, the concentration of the cross-linking agent four-arm polyethyleneglycol acrylamide is 0.012mol/L, the concentration of the monomer NIPAM is 3.6mol/L, and the concentration of the photoinitiator IRG184 is 5 mg/mL.
(2) Respectively taking 100 mu L of gel pre-polymerization liquid of PHT-1 and PHT-2 by using a liquid-transferring gun, respectively injecting the gel pre-polymerization liquid into a mold which is the same as the mold in the comparative example 1, applying an external magnetic field of 70Gs to the gel pre-polymerization liquid, enabling the gel pre-polymerization liquid to present a bright structural color within a few seconds, respectively irradiating the gel pre-polymerization liquid for 90s by using an ultraviolet lamp of 20W to enable the gel pre-polymerization liquid to be converted into gel through crosslinking polymerization, respectively taking out the obtained gel from the mold, then placing the gel in pure water for soaking and washing, and changing water for 4-5 times during soaking to remove unreacted monomers and other substances, thus obtaining the PHT-1 and the PHT-2.
FIG. 5 is an SEM and elemental analysis chart of cross-sections of HT-0(a, b, c diagram) prepared in comparative example 1 and PHT-1(d, e, f diagram) prepared in example 2. As can be seen from both graphs a and d of FIG. 5, both HT-0 and PHT-1 exhibit a porous structure. As can be seen from the two diagrams b and e in FIG. 5, a one-dimensional oriented chain-like arrangement structure appears in the PHT-1, which is formed by arranging dozens of superparamagnetic nanoparticles, while a similar structure does not appear in HT-0. This result confirmed Fe inside the photonic crystal gel3O4@ PVP is assembled into a chain-shaped parallel structure under a magnetic field, and the regular chain-shaped structure cannot be damaged in the process of forming gel through free radical polymerization. The two graphs c and f in FIG. 5 show that PHT-1 contains more iron than HT-0, which also indicates that the superparamagnetic nanoparticles are immobilized in the gel matrix during the polymerization to form the photonic crystal gel.
Cutting PHT-1 and PHT-2 gel into 1.5cm × 1.5cm squares, placing in water, and balancing with a heat table for 20min when each temperature point is reached. FIG. 6 shows optical images (a, b) and reflectance spectra (c, d) of the two at 20-44 ℃. As can be seen from fig. 6, when the sizes of the superparamagnetic nanoparticles inside the photonic crystal gel are different, the color change range and the corresponding wavelength shift range of the reflectivity are also different. The color of the photonic crystal gel containing the first superparamagnetic nano particle (164nm) is gradually changed from orange yellow to yellow green, blue and finally to bluish purple when the temperature is changed, and the wavelength change range is 658-464 nm; and the color of the photonic crystal gel containing the second superparamagnetic nano particle (198nm) can be gradually changed from orange red to yellow green when the temperature is changed, and the wavelength change range is 709-538 nm. The photonic crystal gel containing the first superparamagnetic nanoparticle (164nm) changes color more obviously when the temperature changes, namely has a larger color change range.
Example 3
In the embodiment, photonic crystal gels with different superparamagnetic nanoparticle contents are prepared, the photonic crystal gel with the superparamagnetic nanoparticle concentration of 4mg/mL in the gel pre-polymerization solution is named as PHT-3, and the photonic crystal gel with the superparamagnetic nanoparticle concentration of 12mg/mL in the gel pre-polymerization solution is named as PHT-4, and the steps are as follows:
(1) dissolving a monomer NIPAM, a cross-linking agent four-arm polyethylene glycol acrylamide and a photoinitiator IRG-184 in ethylene glycol, then adding the first superparamagnetic nano-particle, and fully dispersing to form a gel pre-polymerization liquid.
For the gel pre-polymerization liquid of PHT-3, the concentration of the first superparamagnetic nano particle is 4mg/mL, the concentration of the cross-linking agent four-arm polyethylene glycol acrylamide is 0.012mol/L, the concentration of monomer NIPAM is 3.6mol/L, and the concentration of the photoinitiator IRG184 is 5 mg/mL;
for PHT-4 gel pre-polymerization solution, the concentration of the first superparamagnetic nano particle is 12mg/mL, the concentration of the cross-linking agent four-arm polyethyleneglycol acrylamide is 0.012mol/L, the concentration of the monomer NIPAM is 3.6mol/L, and the concentration of the photoinitiator IRG184 is 5 mg/mL.
(2) Respectively taking 100 mu L of gel pre-polymerization liquid of PHT-3 and PHT-4 by using a liquid-transferring gun, respectively injecting the gel pre-polymerization liquid into a mold which is the same as the mold in the comparative example 1, applying an external magnetic field of 70Gs to the gel pre-polymerization liquid, enabling the gel pre-polymerization liquid to present a bright structural color within a few seconds, respectively irradiating the gel pre-polymerization liquid for 90s by using an ultraviolet lamp of 20W to enable the gel pre-polymerization liquid to be converted into gel through crosslinking polymerization, respectively taking out the obtained gel from the mold, then placing the gel in pure water for soaking and washing, and changing water for 4-5 times during soaking to remove unreacted monomers and other substances, thus obtaining the PHT-3 and the PHT-4.
Cutting PHT-3 and PHT-4 gel into 1.5cm × 1.5cm squares, placing in water, and balancing with a heat table for 20min when each temperature point is reached. FIG. 7 shows optical images (a, b) and reflectance spectra (c, d) of the two at 20-44 ℃. As can be seen from FIG. 7, the color variation range and brightness of PHT-3 and PHT-4 are not as good as that of PHT-1, which indicates that the response effect is not ideal due to the content of superparamagnetic nanoparticles in the photonic crystal gel being too high or too low.
Example 4
In this embodiment, photonic crystal gel is prepared under different magnetic field strengths, the photonic crystal gel prepared under the external magnetic field strength of 90Gs is named as PHT-5, and the photonic crystal gel prepared under the external magnetic field strength of 110Gs is named as PHT-6, and the steps are as follows:
(1) dissolving a monomer NIPAM, a cross-linking agent four-arm polyethylene glycol acrylamide and a photoinitiator IRG-184 in ethylene glycol, then adding the first superparamagnetic nano-particle, and fully dispersing to form a gel pre-polymerization liquid. In the gel pre-polymerization liquid, the concentration of the first superparamagnetic nano particle is 8mg/mL, the concentration of the cross-linking agent, namely the four-arm polyethyleneglycol acrylamide, is 0.012mol/L, the concentration of the monomer NIPAM is 3.6mol/L, and the concentration of the photoinitiator IRG184 is 5 mg/mL.
(2) Respectively taking 100 mu L of gel pre-polymerization liquid by using a liquid transfer gun, respectively injecting the gel pre-polymerization liquid into a mold, wherein the mold is the same as the mold in the comparative example 1, respectively applying external magnetic fields of 90Gs and 110Gs to the two groups of gel pre-polymerization liquid, enabling the gel pre-polymerization liquid to present a bright structural color within a few seconds, respectively irradiating the gel pre-polymerization liquid for 90s by using a 20W ultraviolet lamp to enable the gel pre-polymerization liquid to be converted into gel through crosslinking polymerization, respectively taking out the obtained gel from the mold, placing the gel in pure water for soaking and washing, and changing water for 4-5 times during soaking to remove unreacted monomers and other substances, thus obtaining PHT-5 and PHT-6.
Cutting PHT-5 and PHT-6 gel into 1.5cm × 1.5cm squares, placing in water, and balancing with a heat table for 20min when each temperature point is reached. FIG. 8 shows optical images (a, b) and reflectance spectra (c, d) of the two at 20-44 ℃. As can be seen from FIG. 8, PHT-5 and PHT-6 both showed significant color change upon temperature change, but the initial color of the gel was more blue-shifted the greater the external magnetic field strength applied during preparation. Example 2 the initial color at low temperature of the PHT-1 photonic crystal gel prepared at a magnetic field strength of 70Gs was orange red, and the initial colors at low temperature of PHT-5 and PHT-6 prepared in example 4 at magnetic field strengths of 90Gs and 110Gs were yellow and yellow green, respectively. This is because when preparing the photonic crystal gel under a strong magnetic field strength, the distance between the superparamagnetic nanoparticles inside the photonic crystal gel needs to be reduced to generate a strong spatial repulsion to balance and offset the external magnetic field, so the initial color of the photonic crystal gel shifts to blue, resulting in a shortened discoloration range of the photonic crystal gel.
Example 5
In this embodiment, different molar ratios of the monomer to the crosslinking agent are adopted to prepare different photonic crystal gels, the photonic crystal gel prepared when the molar ratio of the monomer to the crosslinking agent in the gel prepolymerization solution is 200:1 is named as PHT-7, and the photonic crystal gel prepared when the molar ratio of the monomer to the crosslinking agent in the gel prepolymerization solution is 100:1 is named as PHT-8, and the steps are as follows:
(1) dissolving a monomer NIPAM, a cross-linking agent four-arm polyethylene glycol acrylamide and a photoinitiator IRG-184 in ethylene glycol, then adding the first superparamagnetic nano-particle, and fully dispersing to form a gel pre-polymerization liquid.
For PHT-7 gel pre-polymerization solution, the concentration of the first superparamagnetic nano particle is 8mg/mL, the concentration of cross-linking agent four-arm polyethyleneglycol acrylamide is 0.012mol/L, the concentration of monomer NIPAM is 2.4mol/L, and the concentration of photoinitiator IRG184 is 5 mg/mL;
for PHT-8 gel pre-polymerization solution, the concentration of the first superparamagnetic nano particle is 8mg/mL, the concentration of the cross-linking agent four-arm polyethyleneglycol acrylamide is 0.012mol/L, the concentration of the monomer NIPAM is 1.2mol/L, and the concentration of the photoinitiator IRG184 is 5 mg/mL.
(2) Respectively taking 100 mu L of gel pre-polymerization liquid of PHT-7 and PHT-8 by using a liquid-transferring gun, respectively injecting the gel pre-polymerization liquid into a mold which is the same as the mold in the comparative example 1, applying an external magnetic field of 70Gs to the gel pre-polymerization liquid, enabling the gel pre-polymerization liquid to present a bright structural color within a few seconds, respectively irradiating the gel pre-polymerization liquid for 90s by using an ultraviolet lamp of 20W to enable the gel pre-polymerization liquid to be converted into gel through crosslinking polymerization, respectively taking out the obtained gel from the mold, then placing the gel in pure water for soaking and washing, and changing water for 4-5 times during soaking to remove unreacted monomers and other substances, thus obtaining the PHT-7 and the PHT-8.
Cutting PHT-7 and PHT-8 gel into 1.5cm × 1.5cm squares, placing in water, and balancing with a heat table for 20min when each temperature point is reached. FIG. 9 shows optical images (a, b) and reflectance spectra (c, d) of the two at 20-44 ℃. As can be seen from fig. 9, when the molar ratio of the monomer to the crosslinking agent is different, both the color change range and the reflection wavelength shift range of the photonic crystal gel are different when the temperature is changed. When the molar ratio of the monomer to the cross-linking agent is 200:1, the color change range of PHT-7 is narrower than that of PHT-1, the color gradually changes from orange to blue and finally to purple, and the wavelength migration range is also shortened to a certain extent and ranges from 621 nm to 462 nm; when the molar ratio of the monomer to the cross-linking agent is 100:1, the color change range of the PHT-8 is further narrowed, the color can only start from yellow green to finally change into blue-violet, and the wavelength migration range is 572-462 nm. The reason is that when the molar ratio of the monomer to the crosslinking agent is reduced and the relative content of the crosslinking agent is increased, the crosslinking degree of the gel is improved, the formed three-dimensional network becomes more compact, the hydrosol swelling degree of the gel at low temperature is influenced, the swelling degree of the gel is reduced, so that the distance between the superparamagnetic nano particles in the gel is reduced, and the color appears a blue shift phenomenon. On the other hand, the three-dimensional network of the gel becomes dense to restrict the contractibility of the gel to a certain extent, so that the volume change amount of the gel between two adjacent temperature points is reduced in the contraction process from low temperature to high temperature, and the color change range and the wavelength migration amount are correspondingly reduced.
Example 6
In this example, the photonic crystal gel PHT-1 prepared in example 2 was placed in water and subjected to a repeated cycle of experiments at a high temperature (44 ℃) to a low temperature (20 ℃) with a hot stage, and after each temperature point was equilibrated for 20min, the reflectance spectrum thereof was measured with a fiber optic spectrometer. This process was repeated 10 times.
FIG. 10 shows the results of the repeated experiments in example 6, and it can be seen that the diffraction wavelengths of photonic crystal gel PHT-1 measured ten times in succession are relatively close, indicating that it has good stability and excellent reversibility.
Example 7
In this example, a photonic crystal gel PHT-9 was prepared by the following steps:
(1) dissolving a monomer NIPAM, a cross-linking agent, four-arm polyethylene glycol acrylamide and a photoinitiator IRG-184 in ethylene glycol, adding the first superparamagnetic nano particle prepared in the embodiment 1, and fully dispersing to form a gel pre-polymerization solution;
in the gel pre-polymerization liquid, the concentration of the first superparamagnetic nano particle is 6mg/mL, the concentration of the cross-linking agent four-arm polyethylene glycol acrylamide is 0.011mol/L, the concentration of monomer NIPAM is 3mol/L, and the concentration of the photoinitiator IRG184 is 4 mg/mL.
(2) And (2) taking 100 mu L of gel pre-polymerization liquid by using a liquid transfer gun, injecting the gel pre-polymerization liquid into a mold, wherein the mold is the same as the mold in the comparative example 1, applying an external magnetic field of 67Gs to the gel pre-polymerization liquid, enabling the gel pre-polymerization liquid to present a bright structural color within a few seconds, irradiating the gel pre-polymerization liquid for 90s by using a 20W ultraviolet lamp to enable the gel pre-polymerization liquid to be converted into gel through crosslinking polymerization, taking the obtained gel out of the mold, placing the gel into pure water for soaking and washing, and changing water for 4-5 times during soaking to remove substances such as unreacted monomers, so as to obtain the PHT-9.
Example 8
In this example, a photonic crystal gel PHT-10 was prepared by the following steps:
(1) dissolving a monomer NIPAM, a cross-linking agent four-arm polyethylene glycol acrylamide and a photoinitiator IRG-184 in ethylene glycol, adding the first superparamagnetic nano particle prepared in the embodiment, and fully dispersing to form a gel pre-polymerization solution;
in the gel pre-polymerization liquid, the concentration of the first superparamagnetic nano particle is 10mg/mL, the concentration of the cross-linking agent four-arm polyethyleneglycol acrylamide is 0.0125mol/L, the concentration of the monomer NIPAM is 4mol/L, and the concentration of the photoinitiator IRG184 is 6 mg/mL.
(2) And (2) taking 100 mu L of gel pre-polymerization liquid by using a liquid transfer gun, injecting the gel pre-polymerization liquid into a mold, wherein the mold is the same as the mold in the comparative example 1, applying an external magnetic field of 70Gs to the gel pre-polymerization liquid, enabling the gel pre-polymerization liquid to present a bright structural color within a few seconds, irradiating the gel pre-polymerization liquid for 90s by using a 20W ultraviolet lamp to enable the gel pre-polymerization liquid to be converted into gel through crosslinking polymerization, taking the obtained gel out of the mold, placing the gel into pure water for soaking and washing, and changing water for 4-5 times during soaking to remove substances such as unreacted monomers, so as to obtain the PHT-10.
Claims (7)
1. A temperature-sensitive photonic crystal gel with wide threshold and high sensitivity is characterized in that the temperature-sensitive photonic crystal gel is prepared by poly (A)N-isopropyl acrylamide) The hydrogel comprises a three-dimensional polymer network structure and superparamagnetic nanoparticles distributed in the three-dimensional polymer network structure, wherein the three-dimensional polymer network structure of the hydrogel is formed by monomersNThe cross-linking agent comprises (by weight parts) isopropyl acrylamide, cross-linking agent, four-arm polyethylene glycol acrylamide and superparamagnetic nanoparticles, wherein the isopropyl acrylamide and the cross-linking agent are in a uniform cross-linking structure formed by cross-linking polymerization according to a molar ratio of (280-320): 1, and the superparamagnetic nanoparticles are distributed in a three-dimensional polymer network structure to form a plurality of one-dimensional oriented chain structures; the temperature-sensitive photonic crystal gel can keep structural color at 20-44 ℃, and the wavelength change range corresponding to the structural color of the temperature-sensitive photonic crystal gel is 658-464 nm during temperature detection;
in the temperature-sensitive photonic crystal gel, the mass fraction of superparamagnetic nanoparticles is 0.6-0.9%, the particle size of the superparamagnetic nanoparticles is 145-165 nm, and the superparamagnetic nanoparticles are Fe with a core-shell structure3O4@PVP。
2. The method for preparing a temperature-sensitive photonic crystal gel with a wide threshold and high sensitivity according to claim 1, comprising the steps of:
(1) mixing the monomersNDissolving isopropyl acrylamide, cross-linking agent four-arm polyethylene glycol acrylamide and photoinitiator in ethylene glycol, adding superparamagnetic nano particles, and fully dispersing to form gel pre-polymerization liquid; in the gel pre-polymerization liquid, monomersNThe molar ratio of isopropyl acrylamide to cross-linking agent quadri-arm polyethylene glycol acrylamide is (280-320): 1;
(2) applying an external magnetic field of 67-70 Gs to the gel prepolymerization liquid, applying ultraviolet irradiation to the gel prepolymerization liquid to enable the gel prepolymerization liquid to be crosslinked and polymerized into gel when the gel prepolymerization liquid has a bright structural color, and placing the obtained gel in water to swell and clean to remove unreacted substances to obtain the temperature-sensitive photonic crystal gel.
3. The preparation method of the temperature-sensitive photonic crystal gel with wide threshold and high sensitivity according to claim 2, wherein in the gel pre-polymerization solution in the step (1), the concentration of the superparamagnetic nanoparticles is 7-10 mg/mL.
4. The preparation method of the temperature-sensitive photonic crystal gel with wide threshold and high sensitivity according to claim 2 or 3, wherein the preparation method of the superparamagnetic nanoparticles is as follows:
dissolving glucose and polyvinylpyrrolidone in 90-120 ℃ ethylene glycol, cooling to room temperature, adding ferric chloride hexahydrate and anhydrous sodium acetate, stirring until the ferric chloride hexahydrate and the anhydrous sodium acetate are dissolved to obtain a mixed reaction solution, transferring the mixed reaction solution to a reaction kettle, reacting for 10-12 hours at 190-220 ℃, separating out the obtained solid phase, and cleaning to obtain superparamagnetic nanoparticles; in the mixed reaction solution, the molar ratio of glucose to ferric chloride hexahydrate is (0.52-0.54): 1.
5. The preparation method of the temperature-sensitive photonic crystal gel with the wide threshold and the high sensitivity according to claim 4, wherein the concentration of polyvinylpyrrolidone is 0.10-0.16 g/mL, the concentration of glucose is 0.04-0.05 mmol/mL, and the concentration of anhydrous sodium acetate is 1.3-1.4 mmol/mL.
6. The method for preparing temperature-sensitive photonic crystal gel with wide threshold and high sensitivity according to claim 2 or 3, wherein in the gel pre-polymerization solution of step (1), the monomerNThe concentration of the isopropyl acrylamide is 3-4 mmol/mL.
7. The preparation method of the temperature-sensitive photonic crystal gel with wide threshold and high sensitivity according to claim 2 or 3, wherein the concentration of the photoinitiator in the gel pre-polymerization solution in the step (1) is 4-6 mg/mL.
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