Bistable PDLC (Polymer Dispersed Liquid Crystal) dimming film based on high-specific-surface-area porous carbon doped interface modification as well as preparation method and application thereof

Abstract

The invention discloses a bistable PDLC (Polymer Dispersed Liquid Crystal) dimming film based on high-specific-surface-area porous carbon doped interface modification as well as a preparation method and application thereof, and belongs to the technical field of intelligent dimming materials. According to the invention, the problems of expensive preparation raw materials, continuous voltage application in the use process, high energy consumption and the like of the current bistable PDLC dimming film are solved. The preparation method of the bistable PDLC dimming film comprises the following steps: cracking biomass to prepare a porous carbon material, acidifying and ball-milling the porous carbon material, mixing with an ionic liquid to obtain a cracked ionic liquid-carbon composite additive, dispersing the cracked ionic liquid-carbon composite additive into a prepolymer, and carrying out ultraviolet curing to form the PDLC film. By introducing the porous carbon material with high specific surface area to modify the liquid crystal-polymer interface and combining with the ion adsorption-desorption mechanism of the porous carbon material, the preparation of the bistable PDLC dimming film is realized, and the bistable PDLC dimming film has the characteristics of low energy consumption and low cost and has a bistable dimming function.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent dimming materials, and particularly relates to a bistable PDLC dimming film based on the modification of a high specific surface area porous carbon doped interface, and a preparation method and application thereof. Background Art

[0002] Liquid crystal dimming technology has attracted much attention in the fields of intelligent windows, display devices, etc. due to its advantage of dynamically regulating the light transmission characteristics. Traditional polymer dispersed liquid crystal (PDLC) dimming films adjust the light transmittance by changing the orientation of liquid crystal molecules under an applied electric field, but a continuous voltage needs to be applied to maintain the transparent state, resulting in high energy consumption during long-term operation, especially significant energy waste in large-scale applications. In recent years, technologies based on bistable liquid crystals (such as cholesteric systems) have achieved power-off state retention through the memory effect, but the raw materials used in their preparation process are expensive and the process is complex, restricting their application scope. In addition, the response efficiency of existing bistable devices is low and the response time is long, which can no longer meet the higher requirements of the industry development well. Summary of the Invention

[0003] In order to overcome the above problems in the prior art, the present invention provides a bistable PDLC dimming film based on the modification of a high specific surface area porous carbon doped interface, and a preparation method and application thereof.

[0004] To solve the above technical problems, the present invention is achieved through the following technical solutions:

[0005] One object of the present invention is to provide a bistable PDLC dimming film based on the modification of a high specific surface area porous carbon doped interface. The bistable PDLC dimming film includes: a polymer matrix, liquid crystal microdroplets dispersed in the polymer matrix, an ion-carbon composite additive doped in the polymer matrix, and spacers; the ion-carbon composite additive is obtained by acidifying a porous carbon material and pre-adsorbing an ionic liquid.

[0006] Further defined, the polymer matrix is an ultraviolet curable adhesive; the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate, a derivative of 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0007] Further defined, the ionic liquid is an ionic additive that can enhance the polarization electric field of the liquid crystal microdroplets after dissociation and has good compatibility with the liquid crystal.

[0008] Further defined, the particle size of the liquid crystal microdroplets dispersed in the polymer matrix is 3 - 5 μm; the specific surface area of the porous carbon material is ≥ 1000 m 2 / g, the pore diameter is 4 - 12 nm, and the particle size is 200 - 500 nm.

[0009] More specifically defined, the specific surface area of the porous carbon material is 1800 m 2 / g.

[0010] Further limit that the doping amount of the ionic liquid is 0.1-1 wt% of the sum of the polymer matrix, liquid crystal droplets and ion-carbon composite additive.

[0011] Further limit that the liquid used for acidification treatment of the porous carbon material is concentrated sulfuric acid, and the treatment time is 1-3 h.

[0012] The second object of the present invention is to provide a preparation method of the above-mentioned bistable PDLC dimming film based on the modification of the high specific surface area porous carbon doping interface. The method includes: pyrolyzing biomass to prepare a porous carbon material, mixing the porous carbon material with an ionic liquid after acidification and ball milling to obtain an ion-carbon composite additive, dispersing the ion-carbon composite additive into a prepolymer, and forming droplets by a phase separation method, and then curing under ultraviolet light irradiation to form a PDLC film.

[0013] Further limit that the porous carbon material is ball milled to a particle size of 200-500 nm.

[0014] Further limit that the mass ratio of the ionic liquid to the porous carbon material is 1:0.1-1:1.

[0015] Further limit that the prepolymer includes a polymer matrix and liquid crystal.

[0016] Even further limit that the liquid crystal dosage is 50 wt% of the prepolymer, the polymer matrix dosage is 50 wt% of the prepolymer, and the doping amount of the ion-carbon composite additive is 3 wt% of the prepolymer mass.

[0017] Further limit that the ultraviolet light irradiation wavelength is 365 nm, the power density is 10 mW / cm 2 , and curing for 10 min.

[0018] Further limit that the thickness of the PDLC film is 10-40 μm.

[0019] The third object of the present invention is to provide an application of the above-mentioned bistable PDLC dimming film based on the modification of the high specific surface area porous carbon doping interface. Specifically, the bistable PDLC dimming film is used in the fields of smart windows, dimmable partitions, dynamic displays, etc.

[0020] The beneficial effects of the present invention are:

[0021] In the present invention, a high specific surface area porous carbon material is introduced to modify the liquid crystal-polymer interface, and combined with the ion adsorption-desorption mechanism of the porous carbon material, a bistable PDLC dimming film with low energy consumption, low cost and bistable dimming function is prepared. Compared with the prior art, the present invention also has the following advantages:

[0022] (1) In the present invention, a high specific surface area (≥1500 m2 / g) The porous carbon material is incorporated into the polymer matrix. The pore size of the porous carbon material is mainly mesopores (2 - 50 nm), and the particle size is 50 - 500 nm, which can ensure the efficient adsorption of free ions by the porous carbon material and form a stable polarization electric field. In addition, the surface of the porous carbon material in the present invention is acidified to enhance the ion adsorption capacity of surface functional groups (such as carboxyl groups and hydroxyl groups).

[0023] (2) In the present invention, the porous carbon material and the ionic liquid are mixed at a mass ratio of 1:0.1 - 1:1, so that the ionic liquid is uniformly adsorbed in the pores of the porous carbon material, and then dispersed into the polymer matrix, thereby introducing the ionic liquid into the polymer matrix. The compatibility between the ionic liquid and the liquid crystal is ≥5 wt%, and the optimized ion mobility is ≥10 -4 cm 2 / (V·s).

[0024] (3) The PDLC dimming film of the present invention has a bistable driving mechanism. Maintenance of the transparent state: When a positive DC electric field (50 V, 0.1 - 1 s) is applied to the PDLC dimming film, ions migrate into the pores of the porous carbon material to form a polarization electric field. After removing the external field, the polarization electric field continuously drives the liquid crystal molecules to be orderly arranged and uniformly oriented, and the maintenance time of the polarization electric field > 8 h (i.e., the decay time > 8 h); Switching to the scattering state: When a reverse electric field (-50 V, 0.5 - 2 s) is applied, the ions desorb from the carbon pores, the polarization electric field disappears, and the liquid crystal molecules return to disordered scattering. The storage of the polarization electric field is realized by modifying the liquid crystal-polymer interface.

[0025] (4) Through the bistable driving mechanism and composite doping design, the present invention realizes zero-energy consumption maintenance. After the state of the PDLC dimming film is switched, continuous power supply is not required, and the comprehensive energy consumption is reduced by ≥60%; and based on the dynamic regulation mechanism of ion migration and desorption, the light transmission state switching time of the PDLC dimming film of the present invention is 0.5 - 1.5 s, and the scattering state recovery time is 1.0 - 2.0 s, meeting the requirements of high-frequency dimming scenarios. In addition, compared with the traditional cholesteric bistable technology, expensive raw materials such as special chiral dopants are not required, and the material cost is reduced by more than 40% compared with the cholesteric bistable technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of the bistable PDLC dimming film according to the embodiment of the present invention;

[0027] Figure 2 It is a schematic working diagram of the bistable PDLC dimming film according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is made in conjunction with the embodiments of the specification.

[0029] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0030] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation manner of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it an individual or alternative embodiment that is mutually exclusive with other embodiments.

[0031] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used, unless otherwise specified, are all conventional materials, reagents, methods, and instruments in this field, and those skilled in the art can obtain them through commercial channels.

[0032] In the present invention, the refractive index of the ultraviolet curable adhesive after curing should be close to the refractive index of the nematic liquid crystal mixture. The ultraviolet curable adhesive used in the following embodiments is of model NOA65, purchased from Nouryon, and the liquid crystal is of model BHR40300, purchased from Beijing Boyee Optoelectronic Materials Co., Ltd.

[0033] Example 1

[0034] Step 1: Preparation and treatment of porous carbon material: Pyrolyze biomass in a nitrogen atmosphere at 700 °C to obtain a porous carbon material (specific surface area not less than 1000 m 2 / g, average pore diameter 4 - 12 nm). Immerse the porous carbon material in concentrated sulfuric acid (concentration 95%), stir at 80 °C for 2 h, wash until neutral and then dry. Subsequently, ball-mill the porous carbon material to a particle size of 200 - 500 nm, and screen to remove agglomerated particles.

[0035] Step 2: Preparation of ionic liquid-carbon composite additive: Mix the BMIM + BF 4 - ionic liquid and the porous carbon material in a mass ratio of 1:0.5, ultrasonically disperse for 30 min, and let stand for 12 h to allow the ionic liquid to be fully adsorbed into the carbon pores, obtaining the ionic liquid-carbon composite additive;

[0036] Step 3, prepolymer preparation: Mix liquid crystal (model BHR40300), UV curable adhesive (model NOA65) with an appropriate amount of spacers. The amount of liquid crystal is 50 wt% of the prepolymer, and the amount of polymer matrix is 50 wt% of the prepolymer. The prepolymer includes a polymer matrix and liquid crystal, and then a carbon-ion composite additive is incorporated, with a doping amount of 3 wt%. Stir well and defoam to obtain a slurry.

[0037] Step 4, curing and forming: Cure the slurry under UV irradiation (wavelength 365 nm, power density 10 mW / cm 2 ) for 10 min to form a PDLC film with a thickness of 10 - 40 μm.

[0038] The structural schematic diagram and working schematic diagram of the PDLC film in Example 1 of the present invention are respectively as Figure 1 、 2 shown.

[0039] Perform drive control on the PDLC film formed in this example, where the forward DC electric field strength is 30 - 50 V, and the application time is 0.1 - 1 s; the reverse electric field strength is 80% - 120% of the forward electric field, and the application time is 0.5 - 2 s. The specific method is as follows:

[0040] Transparent state activation: Apply a forward DC voltage of 50 V for 1 s. Ionic liquid (BMIM + BF 4 - ) migrates into the pores of the porous carbon material under the action of the electric field to form a stable polarization electric field, driving the liquid crystal molecules to be orderly arranged along the electric field direction, realizing a jump in transmittance, and the transmittance increases from T 0 (10%) to T max (80%)

[0041] Scattering state recovery: Apply a reverse DC voltage of -50 V for 1.5 s, and the electric field direction is opposite to that in the transparent state activation stage. The ionic liquid desorbs from the carbon pores, the polarization electric field disappears, and the liquid crystal molecules return to a disordered orientation due to the entropy elasticity of the polymer network, and the transmittance significantly decreases to T min (15%).

[0042] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A bistable PDLC dimming film based on high specific surface area porous carbon doping interface modification, characterized in that: The bistable PDLC dimming film comprises: a polymer matrix, liquid crystal droplets dispersed in the polymer matrix, and ion-carbon composite additives and spacers doped in the polymer matrix; The ion-carbon composite additive is obtained by acidifying a porous carbon material and pre-adsorbing an ionic liquid.

2. The bistable PDLC dimming film according to claim 1, characterized in that: The polymer matrix is ​​ultraviolet curing glue; the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate and a 1-ethyl-3-methylimidazolium tetrafluoroborate derivative.

3. The bistable PDLC dimming film according to claim 1, characterized in that: Ionic liquids are ionic additives that can enhance the polarization electric field of liquid crystal droplets after dissociation and have good compatibility with liquid crystals.

4. The bistable PDLC dimming film according to claim 1, characterized in that: The particle size of the liquid crystal droplets dispersed in the polymer matrix is ​​3-5 μm; the specific surface area of ​​the porous carbon material is ≥1000 m 2 / g, pore size 4-12nm, particle size 200-500nm.

5. The bistable PDLC dimming film according to claim 1, characterized in that: The doping amount of the ionic liquid is 0.1-1wt% of the sum of the polymer matrix, the liquid crystal droplets and the ion-carbon composite additive; the liquid used for the acidification treatment of the porous carbon material is concentrated sulfuric acid, and the treatment time is 1-3h.

6. The method for preparing the bistable PDLC dimming film according to any one of claims 1 to 5, characterized in that: The method includes: cracking biomass to prepare porous carbon material, acidifying and ball-milling the porous carbon material and mixing it with ionic liquid to obtain an ionic liquid-carbon composite additive, dispersing the ionic liquid-carbon composite additive into a prepolymer and forming droplets through a phase separation method, and then curing under ultraviolet light irradiation to form a PDLC film.

7. The preparation method according to claim 6, characterized in that: The porous carbon material is ball-milled to a particle size of 200-500 nm; the mass ratio of the ionic liquid to the porous carbon material is 1:0.1-1:1; and the prepolymer includes a liquid crystal and a polymer matrix.

8. The preparation method according to claim 6, characterized in that: The UV light wavelength is 365nm and the power density is 10mW / cm 2 , curing for 10 minutes; the PDLC film thickness is 10-40μm.

9. The preparation method according to claim 7, characterized in that: The amount of liquid crystal used is 50wt% of the prepolymer, the amount of polymer matrix used is 50wt% of the prepolymer, and the doping amount of ion-carbon composite additive is 3wt% of the prepolymer.

10. An application of the bistable PDLC dimming film according to any one of claims 1 to 5, characterized in that: Bistable PDLC dimming film is used in smart windows, dimmable partitions, and dynamic display fields.

Images