CN111909560A - Color-changeable reflective coating and preparation method and application thereof - Google Patents
Color-changeable reflective coating and preparation method and application thereof Download PDFInfo
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- CN111909560A CN111909560A CN202010672654.4A CN202010672654A CN111909560A CN 111909560 A CN111909560 A CN 111909560A CN 202010672654 A CN202010672654 A CN 202010672654A CN 111909560 A CN111909560 A CN 111909560A
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/26—Thermosensitive paints
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D163/00—Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins
- C09D163/10—Epoxy resins modified by unsaturated compounds
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/004—Reflecting paints; Signal paints
Abstract
The invention discloses a color-changeable reflective coating and a preparation method and application thereof, wherein the color-changeable reflective coating comprises a liquid crystal microcapsule and an adhesive, wherein the liquid crystal microcapsule comprises a core material and a shell material coated on the surface of the core material, the core material is a liquid crystal microdroplet formed by wrapping cholesteric liquid crystal with cellulose nanocrystals, the shell material is melamine resin, and the refractive index of the adhesive is matched with that of the liquid crystal microcapsule. Through the mode, the cholesterol phase in the color-changeable reflective coating is stable in structure, the reflection wave band can be adjusted through temperature response, the liquid crystal orientation in the liquid crystal microcapsule is centrosymmetric, and the reflection wavelength is irrelevant to the angle, so that the coating can change along with the change of the ambient temperature, the color-changeable adjustment through temperature response is realized, the color change range can be in a near infrared wave band region and a visible light wave band region, and the color-changeable reflective coating is suitable for the fields of walls, intelligent windows, furniture, ornaments, automobiles and the like.
Description
Technical Field
The invention relates to the technical field of liquid crystal reflective coatings, in particular to a color-changeable reflective coating and a preparation method and application thereof.
Background
The cholesteric liquid crystal material has the characteristic of selective Bragg reflection due to the special spiral structure, and the cholesteric liquid crystal is widely applied to the fields of sensors, liquid crystal displays, intelligent infrared reflectors and the like due to the special optical property.
The non-polymer cholesteric liquid crystal material in the cholesteric liquid crystal material is usually prepared from a nematic liquid crystal composition and a chiral dopant, and the chiral dopant is added to enable the structure of the nematic liquid crystal to be twisted and rotated, so that the cholesteric liquid crystal is obtained.
In a single domain, cholesteric liquid crystal molecules are arranged perpendicular to a spiral axis, and in a plane perpendicular to the spiral axis, the cholesteric liquid crystal molecules can be regarded as nematic liquid crystal; the director of the cholesteric liquid crystal molecules changes in a direction along the helical axis, and the length of the helical axis through which they rotate 360 ° is called the pitch (P). The reflection wavelength lambda of the cholesteric liquid crystal with a single pitch is equal to P x n (the average optical refractive index is n); and the liquid crystal reflection spectral bandwidth delta lambda is (n)e-no)*P＝Δn*P(Δn＝ne-noIs birefringence); it can be seen from the above formula that when the P value is constant, the Δ n of the cholesteric liquid crystal material is increased under the premise that the Δ λ value is constant, which is beneficial to improving the reflection effect of the liquid crystal. When the cholesteric liquid crystal material is constant in delta n, the pitch P value is changed through temperature change, and the reflection waveband delta lambda can also be changed; thereby enabling temperature responsive adjustment of the reflected light.
The coating on the market at present is mainly a liquid or solid material which is coated on the surface of a substrate to form a film under certain conditions to play a role in protecting devices or other special functions (such as insulation, rust prevention, mildew prevention, heat resistance and the like), and the temperature response type color-variable reflective coating is not available on the market temporarily. If the non-polymerized cholesteric liquid crystal material can be used for developing a temperature response type color-changeable reflective coating, the surface of a sample can be protected, the decoration is attractive, and if the temperature response type color-changeable reflective coating is applied to the field of buildings, the color-changeable reflective coating in visible light and near infrared wave band areas can regulate and control heat to enter indoors, so that the building energy consumption is reduced, and the life quality of people is improved. However, due to the difficulty in maintaining the cholesteric structure of the non-polymeric cholesteric liquid crystal system, non-polymeric cholesteric liquid crystal materials are generally not suitable for direct coating on a substrate surface, thereby limiting their application to reflective coatings.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a color-changeable reflective coating and a preparation method and application thereof.
The technical scheme adopted by the invention is as follows:
in a first aspect of the present invention, there is provided a color-changeable reflective paint, which comprises raw materials including liquid crystal microcapsules and a binder; the liquid crystal microcapsule comprises a core material and a shell material coated on the surface of the core material, wherein the core material is a liquid crystal microdroplet formed by wrapping cholesteric liquid crystal with cellulose nanocrystals, and the shell material is melamine resin; the refractive index of the binder is matched to the refractive index of the liquid crystal microcapsule.
If the refractive index of the adopted adhesive is not matched with or is far away from that of the liquid crystal microcapsule, the color change of the coating can be influenced, and the scattering is serious, so that the refractive index of the adhesive needs to be matched with that of the liquid crystal microcapsule. In particular, if n is1Denotes the refractive index of the adhesive, n2N is a general requirement that the refractive index of the liquid crystal microcapsule is expressed and the refractive index of the binder is matched with that of the liquid crystal microcapsule1＝n20.2. The refractive index of the liquid crystal microcapsule is generally 1.4 to 1.6. In addition, the liquid crystal microcapsule is spherical and has a diameter of 5 to 50 μmAnd (3) removing the solvent. The liquid crystal in the liquid crystal microcapsule core material liquid crystal microdroplet is in a cholesteric spiral structure, and the Maltese crossing phenomenon can be seen under a polarizing microscope.
According to some embodiments of the invention, the liquid crystal microdroplets are prepared by mixing cholesteric liquid crystal and a cellulose nanocrystal solution, adjusting the pH value to 4-5, and performing ultrasonic emulsification. Wherein, the pH value is adjusted before the ultrasonic emulsification, so that a great amount of agglomeration generated in the coating process of the prepolymer can be avoided.
According to some embodiments of the invention, the cholesteric liquid crystal is formed by self-assembly of a mixture of preparation raw materials comprising nematic liquid crystal and chiral dopant.
According to some embodiments of the invention, the raw material for preparing the cholesteric liquid crystal comprises: 75 to 97.55 weight percent of nematic liquid crystal and 2.45 to 25 weight percent of chiral dopant.
According to some embodiments of the invention, the chiral dopant is selected from at least one of S5011, S811, R5011, R811.
According to some embodiments of the present invention, the cellulose nanocrystal solution is prepared by mixing 0.01 wt% to 0.1 wt% of cellulose nanocrystals, 0.01 wt% to 0.1 wt% of sodium salt, and 99.8 wt% to 99.98 wt% of deionized water and then subjecting the mixture to ultrasonic treatment. Sodium salt is specifically and generally sodium chloride.
According to some embodiments of the invention, the mass ratio of the cholesteric liquid crystal to the cellulose nanocrystal solution is (3-5): (5-7).
According to some embodiments of the invention, the mass ratio of the liquid crystal microcapsule to the binder is (3-6): (4-7). The adhesive can be at least one of UV curable adhesive, PVA adhesive and varnish, and specifically AgiSyn 2871(CAS number: 72009-86-0) from Dismann NewLeimei.
When the color-changeable reflective coating is used, the raw materials can be uniformly mixed so as to uniformly disperse the liquid crystal microcapsules in the adhesive, and then the mixed coating is coated on the surface of a substrate and cured to form a coating.
In a second aspect of the present invention, there is provided a method for preparing any one of the color-changeable reflective paints provided in the first aspect of the present invention, comprising the steps of:
s1, preparing a cholesteric liquid crystal and a cellulose nanocrystal solution; mixing cholesteric liquid crystal and cellulose nanocrystal solution, adjusting the pH value to 4-5, and performing ultrasonic emulsification to obtain Pickering emulsion with liquid crystal microdroplets; mixing formaldehyde and melamine to form melamine resin prepolymer;
s2, dripping the melamine resin prepolymer into the Pickering emulsion to perform in-situ polymerization reaction on the surface of a liquid crystal microdroplet in the Pickering emulsion to generate melamine resin to wrap the surface of the liquid crystal microdroplet to form a liquid crystal microcapsule;
s3, mixing the liquid crystal microcapsule with a binder.
In a third aspect of the invention, the application of any one of the color-changeable reflective coatings provided by the first aspect of the invention in building walls, intelligent windows, furniture, ornaments and automobiles is provided.
The embodiment of the invention has the beneficial effects that:
the embodiment of the invention provides a color-changeable reflective coating, which comprises a liquid crystal microcapsule and an adhesive matched with the refractive index of the liquid crystal microcapsule, wherein the liquid crystal microcapsule takes liquid crystal microdroplets formed by wrapping temperature-responsive cholesteric liquid crystals with cellulose nanocrystals as a core material, and a layer of melamine resin shell material is coated on the outer surface of the core material, so that the liquid crystal microcapsule has a hard shell to protect the structure of the cholesteric liquid crystals, the cholesteric liquid crystals cannot be easily damaged, and the service life can be prolonged. In addition, the cellulose nanocrystals in the core material wrap the cholesteric liquid crystal, and the liquid crystal molecules in contact with the cellulose nanocrystals are arranged in the direction of the cellulose nanocrystals due to the oriented arrangement of the cellulose nanocrystals, so that the oriented effect similar to that of an oriented layer is generated, and the maintenance of a cholesteric structure is ensured. Through the mode, the liquid crystal microcapsule of the reflective coating contains temperature response type cholesteric liquid crystal, the reflective wave band can change along with the temperature, and particularly when the temperature is reduced, the cholesteric liquid crystal is uncoiled, the thread pitch is increased, and the reflective wave band is red-shifted; when the temperature rises, the pitch of the cholesteric liquid crystal is reduced, and the reflection wave band is blue-shifted; and because the orientation of the liquid crystal in the liquid crystal microcapsule is centrosymmetric, the reflected wavelength is irrelevant to the angle, so when the ambient temperature changes, the coating can change color along with the change, the color change range can be in a near infrared band region and a visible light band region, and the color-changeable reflective coating can be applied to walls, intelligent windows, furniture, ornaments, automobiles and the like, not only can protect the surface of a sample and beautify the decoration, but also can regulate and control the heat of the visible light and the near infrared band region to enter the room, thereby reducing the building energy consumption.
Drawings
FIG. 1 is a graph showing the reflection curves of cholesteric liquid crystals prepared in example 1 at different temperatures;
FIG. 2 is a schematic view showing the structure of a liquid crystal microcapsule prepared in example 1;
FIG. 3 is a photograph of a polarizing microscope after diluting a color changeable reflective paint prepared in example 1 by 10 times;
FIG. 4 is a photograph of FIG. 3 taken without the polarizer;
FIG. 5 is a magnified polarization microscope photograph of FIG. 3;
FIG. 6 is a schematic representation of the reflection of the color-changeable reflective coating prepared in example 1 applied to architectural glass at elevated temperatures in the near infrared band;
FIG. 7 is a schematic representation of the reflection of the color-changeable reflective coating prepared in example 1 applied to architectural glass at a reduced temperature in the near infrared band;
FIG. 8 is a schematic reflection diagram of the color-changeable reflective coating prepared in example 2 applied to a building wall at an elevated temperature in a visible light band region;
FIG. 9 is a schematic view showing the reflection of the color-changeable reflective coating prepared in example 2 applied to a building wall when the temperature of the building wall is reduced in the visible light band region;
FIG. 10 is a polarizing microscope photograph of the coating prepared in comparative example 1;
FIG. 11 is a polarizing microscope photograph of the coating prepared in comparative example 2;
FIG. 12 is a polarization microscope photograph of the coating prepared in comparative example 3.
Detailed Description
The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.
Details of the chemical reagents used in the examples of the present invention are as follows:
nematic liquid crystal-mixed liquid crystal E7 (Technology Co., Ltd., Mitsu mu Run Co., Ltd.);
chiral dopant-S811 (south beijing mu run new materials science and technology ltd);
chiral dopant-S5011 (nanjing mu run new materials science and technology ltd);
cellulose nanocrystals (Shanghai Aladdin Biotechnology Ltd.);
formaldehyde (shanghai alatin biochemical science and technology, ltd);
melamine (Shanghai Aladdin Biotechnology Ltd.).
Example 1
The preparation method of the color-changeable reflective coating comprises the following steps:
s1, preparing cholesteric liquid crystal
Taking the following raw materials in proportion: the preparation method comprises the following steps of (1) dissolving 79 wt% of nematic liquid crystal (mixed liquid crystal E7) and 21 wt% of chiral dopant (S811) in solvent dichloromethane under the condition of yellow light, stirring at 50 ℃ until the solvent is completely volatilized, and slowly cooling to room temperature to obtain cholesteric liquid crystal. The reflection characteristics of the cholesteric liquid crystal are studied, and the reflection curve of the cholesteric liquid crystal at different temperatures is shown in figure 1, and the reflection wave band of the cholesteric liquid crystal can be changed along with the change of the temperature as can be seen from figure 1.
S2, preparing a cellulose nanocrystal solution
Weighing the following raw materials in proportion: 0.05 wt% of cellulose nanocrystal, 0.05 wt% of sodium chloride and 99.9 wt% of deionized water, and the cellulose nanocrystal solution is prepared by mixing and then carrying out ultrasonic treatment by using a cell crusher until no precipitate exists.
S3 preparation of Pickering emulsion
The mass ratio is 3: and 7, weighing the cholesteric liquid crystal prepared in the step S1 and the cellulose nanocrystalline solution prepared in the step S2, mixing, adjusting the pH value to 4-5, and performing ultrasonic emulsification to prepare pickering emulsion, wherein the pickering emulsion contains liquid crystal microdrops formed by wrapping the cholesteric liquid crystal with the cellulose nanocrystals.
S4 preparation of melamine resin prepolymer
Formaldehyde and melamine were mixed as 3: 1, adjusting the pH value to 8-9, and stirring for 30min at the temperature of 65-75 ℃ to form a melamine resin prepolymer.
S5 preparation of liquid crystal microcapsule
Putting the Pickering emulsion prepared in the step S3 into a shaking table to shake, slowly dropwise adding the melamine resin prepolymer prepared in the step S4 into the Pickering emulsion, shaking for 3 hours at 70 ℃, finally slowly cooling to room temperature, carrying out in-situ polymerization reaction on the surface of liquid crystal microdrops in the Pickering emulsion to wrap a layer of melamine resin, and then carrying out drying treatment to form a liquid crystal microcapsule, wherein the schematic diagram is shown in figure 2, the liquid crystal microcapsule comprises a core material and a shell material melamine resin 13 wrapping the surface of the core material, and the core material comprises cholesteric liquid crystal 11 and cellulose nanocrystal 12 wrapping the cholesteric liquid crystal 11; the refractive index was 1.5 as measured by Abbe refractometer.
S6 preparation of color-changeable reflective paint
And (4) mixing the liquid crystal microcapsule prepared in the step (S5) with a binder with a matched refractive index according to the mass ratio of 2:3, and performing ultrasonic treatment to uniformly mix and disperse the mixture to obtain the color-changeable reflective coating. The adhesive used is a UV curing agent with a refractive index of 1.5, specifically Bisphenol A ethoxylate diacrylate (Bisphenol A epoxy acrylate) available from Sigma, USA.
The color-changeable reflective coating prepared above was diluted 10 times with deionized water and observed by a polarizing microscope, that is, photographed and observed in a reflection mode of the polarizing microscope, and the obtained photograph is shown in fig. 3. The observation showed that the cholesteric structure in each liquid crystal microcapsule was intact and had a distinct color (green).
The observation was carried out without using the polarizing plate on the basis of FIG. 3, i.e., the observation was taken in the transmission mode of the polarization microscope, and the photograph obtained was as shown in FIG. 4. Observation results show that the cholesteric liquid crystal microcapsule is small balls, the particle size of the small balls is uniform, the small balls coated with melamine resin are very hard and are not easy to break, and the structure of cholesteric liquid crystal can be well maintained.
Further, the results of the enlarged observation in addition to fig. 3 are shown in fig. 5. As can be clearly seen from fig. 5, the structure of the liquid crystal microcapsule exhibits a martel crossing phenomenon, and the liquid crystal microcapsule is spherical, so that the angle-independent reflection occurs.
The color-changeable reflective coating prepared above is applied to the surface of transparent architectural glass 21 to form a reflective coating layer comprising liquid crystal microcapsules 22 and a binder 23, whose reflection patterns at the temperature increase and decrease in the near infrared band region are shown in fig. 6 and 7, respectively. As shown in fig. 6, when the temperature rises, the pitch of the cholesteric liquid crystal in the liquid crystal microcapsule is reduced, the reflection waveband is blue-shifted, and the near infrared light is reflected out, so that the heat can be reduced to enter the room through the glass, and the building energy consumption is reduced. As shown in fig. 7, when the temperature is reduced, the cholesteric liquid crystal in the liquid crystal microcapsule is uncoiled, the pitch is increased, the reflection waveband is red-shifted, and near infrared light can penetrate through the liquid crystal microcapsule, so that heat can enter the room, and the indoor temperature is increased.
Example 2
The preparation method of the color-changeable reflective coating comprises the following steps:
s1, preparing cholesteric liquid crystal
Taking the following raw materials in proportion: the method comprises the steps of dissolving 79 wt% of nematic liquid crystal (mixed liquid crystal E7), 20 wt% of chiral dopant (S811) and 1 wt% of chiral dopant (S5011) in solvent dichloromethane under the condition of yellow light, stirring at 50 ℃ until the solvent is completely volatilized, and slowly cooling to room temperature to obtain the cholesteric liquid crystal.
S2, preparing a cellulose nanocrystal solution
Weighing the following raw materials in proportion: 0.05 wt% of cellulose nanocrystal, 0.05 wt% of sodium chloride and 99.9 wt% of deionized water, and the cellulose nanocrystal solution is prepared by mixing and then carrying out ultrasonic treatment by using a cell crusher until no precipitate exists.
S3 preparation of Pickering emulsion
The mass ratio is 3: and 7, weighing the cholesteric liquid crystal prepared in the step S1 and the cellulose nanocrystalline solution prepared in the step S2, mixing, adjusting the pH value to 4-5, and performing ultrasonic emulsification to prepare pickering emulsion, wherein the pickering emulsion contains liquid crystal microdrops formed by wrapping the cholesteric liquid crystal with the cellulose nanocrystals.
S4 preparation of melamine resin prepolymer
Formaldehyde and melamine were mixed as 3: 1, adjusting the pH value to 8-9, and stirring for 30min at the temperature of 65-75 ℃ to form a melamine resin prepolymer.
S5 preparation of liquid crystal microcapsule
Putting the Pickering emulsion prepared in the step S3 into a shaking table to shake, slowly dropwise adding the melamine resin prepolymer prepared in the step S4 into the Pickering emulsion, shaking for 3 hours at 70 ℃, finally slowly cooling to room temperature, carrying out in-situ polymerization reaction on the surface of liquid crystal microdroplets in the Pickering emulsion to wrap a layer of melamine resin, and drying to form a liquid crystal microcapsule; the refractive index was measured to be 1.598 using an Abbe refractometer.
S6 preparation of color-changeable reflective paint
And (4) mixing the liquid crystal microcapsule prepared in the step (S5) with an ultraviolet curing agent with the refractive index of 1.5 according to the mass ratio of 2:3, and performing ultrasonic treatment to uniformly mix and disperse the mixture to obtain the color-changeable reflective coating.
The above color-changeable reflective paint is applied to the surface of the building wall 31 to form a reflective coating layer comprising liquid crystal microcapsules 32 and a binder 33, whose reflection patterns at the time of temperature increase and decrease in the visible light band region are shown in fig. 8 and 9, respectively. As shown in fig. 8, the pitch of the cholesteric liquid crystal decreases and the reflection band shifts blue as the temperature increases, for example, at a temperature of about 30 ℃, the reflective coating reflects green light and is an angle-independent reflection, green from either side, independent of the angle of incidence. As shown in fig. 9, when the temperature is lowered, the cholesteric liquid crystal is uncoiled, the pitch is increased, and the reflection band is red shifted, for example, when the temperature is around 36 ℃, the reflective coating reflects red light and is an angle-independent reflection, red from either side, and is independent of the incident angle.
Comparative example 1
A paint prepared in substantially the same manner as the color-changeable paint of example 1, except that: no cellulose nanocrystals were added. Specifically, first, cholesteric liquid crystal was prepared according to step S1 in example 1; the operation of step S2 in embodiment 1 is cancelled; step S3, mixing the cholesteric liquid crystal prepared in the step S1 with deionized water according to a ratio of 3:7 to obtain a liquid crystal solution; then preparing a melamine resin prepolymer according to the operation of step S4 in example 1; step S5, putting the liquid crystal solution prepared in the step S3 into a shaking table for shaking, slowly dripping melamine resin prepolymer into the liquid crystal solution, shaking for 3 hours at 70 ℃, finally slowly cooling to room temperature, and then drying; finally, the product obtained after drying was used in place of the liquid crystal microcapsule of step S6 in example 1 to prepare a coating material.
The coating material prepared in this comparative example was observed by a polarizing microscope, and the photograph thereof is shown in FIG. 10. The observation results showed that the structure of the cholesteric liquid crystal was destroyed and the arrangement of the liquid crystal molecules was disordered in this comparative example. The performance test of the glass substrate surface applied with the glass substrate surface shows that no method is available for realizing temperature response, and the scattering is serious.
Comparative example 2
A paint prepared in substantially the same manner as the color-changeable paint of example 1, except that: urea-formaldehyde resin was used instead of the melamine resin prepolymer prepared in step S4 in example 1.
The coating material prepared in this comparative example was observed by a polarizing microscope, and the photograph thereof is shown in FIG. 11. As can be seen from fig. 11, the structure of the liquid crystal microcapsule in this comparative example was broken.
Comparative example 3
A paint prepared in substantially the same manner as the color-changeable paint of example 1, except that: in step S2, sodium chloride is not added in the preparation of the cellulose nanocrystal solution.
The coating material prepared in this comparative example was observed by a polarizing microscope, and the photograph thereof is shown in FIG. 12. The result shows that the cellulose nanocrystalline solution is not added with sodium chloride, so that the cellulose nanocrystalline clusters together, the liquid crystal microcapsule becomes very small, even the clustering of some cellulose nanocrystalline can influence the subsequent in-situ polymerization and wrapping of melamine resin, so that the melamine resin aggregates, the color of cholesteric liquid crystal is finally influenced, the pitch of cholesteric liquid crystal molecules in the formed microcapsule is also very small, and the color change is basically avoided.
Therefore, in the above embodiments of the present invention, a protective layer may be formed at an oil-water interface by utilizing the amphiphilicity of the cellulose nanocrystals, so as to form an oil-in-water emulsion, the cellulose nanocrystals are equivalent to a surfactant and attached to and wrapped on the surface of liquid crystal droplets in the pickering emulsion, and the orientation arrangement of the cellulose nanocrystals enables liquid crystal molecules in contact with the cellulose nanocrystals to be arranged in the direction of the cellulose nanocrystals, thereby generating an orientation effect similar to that of an orientation layer, and ensuring the maintenance of a cholesteric phase structure. In addition, because the cellulose nanocrystals are negatively charged, the addition of sodium chloride in the cellulose nanocrystal solution can reduce the zeta potential of the cellulose nanocrystals by Na ions, and further reduce the repulsive force between the cellulose nanocrystals and cholesteric liquid crystals, so as to form more stable emulsion. In addition, because the liquid crystal microdroplets formed by the cellulose nanocrystals and the cholesteric liquid crystal are fragile, the cellulose nanocrystals are attached to the surfaces of the liquid crystal microdroplets and can be broken by applying a small force, for this reason, the above embodiment adopts an in-situ polymerization method, a layer of melamine resin is wrapped on the surfaces of the core material liquid crystal microdroplets without damaging a liquid crystal microdroplet disassembly structure, and the color of the cholesteric liquid crystal cannot be influenced because the melamine resin is transparent, and the melamine resin is hard and is not easy to damage, and the core material is protected by wrapping the core material liquid crystal microdroplets by taking the melamine resin as a shell material, so that the core material cannot be easily damaged, and the service life can be prolonged; and the in-situ polymerization condition of the melamine resin is not harsh, and the preparation operation is simple and convenient. Through the mode, the liquid crystal microcapsule of the prepared reflective coating contains temperature response type cholesteric liquid crystals, the reflection wave band can change along with the temperature, and particularly when the temperature is reduced, the cholesteric liquid crystals are uncoiled, the thread pitch is increased, and the reflection wave band is red-shifted; when the temperature rises, the pitch of the cholesteric liquid crystal is reduced, and the reflection wave band is blue-shifted; and because the orientation of the liquid crystal in the liquid crystal microcapsule is centrosymmetric, the reflected wavelength is irrelevant to the angle, so when the ambient temperature changes, the coating can change color along with the change, the color change range can be in a near infrared band region and a visible light band region, and further the color-changeable reflective coating can be applied to walls, intelligent windows, furniture, ornaments, automobiles and the like, not only can protect the surface of a sample and beautify the decoration, but also can regulate and control the heat of the visible light and the near infrared band region to enter the room, thereby reducing the building energy consumption.
Claims (10)
1. The color-changeable reflective paint is characterized in that the raw materials comprise liquid crystal microcapsules and a binder; the liquid crystal microcapsule comprises a core material and a shell material coated on the surface of the core material, wherein the core material is a liquid crystal microdroplet formed by wrapping cholesteric liquid crystal with cellulose nanocrystals, and the shell material is melamine resin; the refractive index of the binder is matched to the refractive index of the liquid crystal microcapsule.
2. The color-changeable reflective coating according to claim 1, wherein the liquid crystal droplets are prepared by mixing cholesteric liquid crystal and cellulose nanocrystal solution, adjusting the pH value to 4-5, and performing ultrasonic emulsification.
3. The color-changeable reflective paint according to claim 2, wherein said cholesteric liquid crystal is formed by self-assembly of a mixture of preparation raw materials comprising nematic liquid crystal and chiral dopant.
4. The color-changeable reflective paint according to claim 3, wherein the cholesteric liquid crystal is prepared from the following raw materials: 75 to 97.55 weight percent of nematic liquid crystal and 2.45 to 25 weight percent of chiral dopant.
5. A variable color reflective coating according to claim 4, wherein said chiral dopant is selected from at least one of S5011, S811, R5011, R811.
6. The color-changeable reflective coating according to claim 2, wherein the cellulose nanocrystal solution is prepared by mixing 0.01 to 0.1 weight percent of cellulose nanocrystals, 0.01 to 0.1 weight percent of sodium salt, and 99.8 to 99.98 percent of deionized water and then subjecting the mixture to ultrasonic treatment.
7. The color-changeable reflective coating according to claim 6, wherein the mass ratio of the cholesteric liquid crystal to the cellulose nanocrystal solution is (3-5): (5-7).
8. A color-changeable reflective coating according to any one of claims 1 to 7, wherein the mass ratio of said liquid crystal microcapsule to said binder is (3-6): (4-7).
9. A method of preparing a color variable reflective coating according to any of claims 1 to 8, comprising the steps of:
s1, preparing a cholesteric liquid crystal and a cellulose nanocrystal solution; mixing cholesteric liquid crystal and cellulose nanocrystal solution, adjusting the pH value to 4-5, and performing ultrasonic emulsification to obtain Pickering emulsion with liquid crystal microdroplets; mixing formaldehyde and melamine to prepare melamine resin prepolymer;
s2, dripping the melamine resin prepolymer into the Pickering emulsion to perform in-situ polymerization reaction on the surface of a liquid crystal microdroplet in the Pickering emulsion to generate melamine resin to wrap the surface of the liquid crystal microdroplet to form a liquid crystal microcapsule;
s3, mixing the liquid crystal microcapsule with a binder.
10. Use of the color-changeable reflective coating of any one of claims 1 to 8 in architectural walls, smart windows, furniture, ornaments, automobiles.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010672654.4A CN111909560B (en) | 2020-07-14 | 2020-07-14 | Color-changeable reflective coating and preparation method and application thereof |
| PCT/CN2021/096280 WO2022012181A1 (en) | 2020-07-14 | 2021-05-27 | Color-changeable reflective paint, preparation method therefor, and application thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010672654.4A CN111909560B (en) | 2020-07-14 | 2020-07-14 | Color-changeable reflective coating and preparation method and application thereof |
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| Publication Number | Publication Date |
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| CN111909560A true CN111909560A (en) | 2020-11-10 |
| CN111909560B CN111909560B (en) | 2022-01-14 |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113072963A (en) * | 2021-04-01 | 2021-07-06 | 江苏集萃智能液晶科技有限公司 | Monochromatic liquid crystal composition, liquid crystal microcapsule, coating and preparation method thereof |
| CN113641015A (en) * | 2021-07-30 | 2021-11-12 | 华南师范大学 | Infrared reflector and preparation method and application thereof |
| WO2022012181A1 (en) * | 2020-07-14 | 2022-01-20 | 华南师范大学 | Color-changeable reflective paint, preparation method therefor, and application thereof |
| CN113980558A (en) * | 2021-12-06 | 2022-01-28 | 江苏集萃智能液晶科技有限公司 | Coating and coating suitable for PVC (polyvinyl chloride) product and preparation method thereof |
Families Citing this family (2)
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| CN115093588B (en) * | 2022-07-14 | 2023-11-03 | 华南师范大学 | Cellulose nanocrystalline film and preparation method and application thereof |
| CN116736565A (en) * | 2023-06-19 | 2023-09-12 | 珠海兴业新材料科技有限公司 | Shading type heat-insulation double-control dimming film and preparation method thereof |
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| US6242139B1 (en) * | 1998-07-24 | 2001-06-05 | International Business Machines Corporation | Color filter for TFT displays |
| CN109925985A (en) * | 2019-03-15 | 2019-06-25 | 湖州闪思新材料科技有限公司 | A kind of methods and applications of phase-change material micro-capsule cladding |
| CN111158179A (en) * | 2019-12-30 | 2020-05-15 | 浙江大学 | Temperature control light modulation film based on ellipsoidal cholesteric liquid crystal micro-droplets and state transition method thereof |
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| CN109337489B (en) * | 2018-09-06 | 2021-09-24 | 华南师范大学 | Infrared reflection coating and preparation method and application thereof |
| CN111909560B (en) * | 2020-07-14 | 2022-01-14 | 华南师范大学 | Color-changeable reflective coating and preparation method and application thereof |
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| US6242139B1 (en) * | 1998-07-24 | 2001-06-05 | International Business Machines Corporation | Color filter for TFT displays |
| CN109925985A (en) * | 2019-03-15 | 2019-06-25 | 湖州闪思新材料科技有限公司 | A kind of methods and applications of phase-change material micro-capsule cladding |
| CN111158179A (en) * | 2019-12-30 | 2020-05-15 | 浙江大学 | Temperature control light modulation film based on ellipsoidal cholesteric liquid crystal micro-droplets and state transition method thereof |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2022012181A1 (en) * | 2020-07-14 | 2022-01-20 | 华南师范大学 | Color-changeable reflective paint, preparation method therefor, and application thereof |
| CN113072963A (en) * | 2021-04-01 | 2021-07-06 | 江苏集萃智能液晶科技有限公司 | Monochromatic liquid crystal composition, liquid crystal microcapsule, coating and preparation method thereof |
| CN113641015A (en) * | 2021-07-30 | 2021-11-12 | 华南师范大学 | Infrared reflector and preparation method and application thereof |
| CN113980558A (en) * | 2021-12-06 | 2022-01-28 | 江苏集萃智能液晶科技有限公司 | Coating and coating suitable for PVC (polyvinyl chloride) product and preparation method thereof |
| CN113980558B (en) * | 2021-12-06 | 2022-08-26 | 江苏集萃智能液晶科技有限公司 | Coating and coating suitable for PVC (polyvinyl chloride) product and preparation method thereof |
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| WO2022012181A1 (en) | 2022-01-20 |
| CN111909560B (en) | 2022-01-14 |
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