CN114149550A - Method for preparing diluted magnetic polymer dispersed liquid crystal by photo-initiation free radical series reaction and product thereof - Google Patents
Method for preparing diluted magnetic polymer dispersed liquid crystal by photo-initiation free radical series reaction and product thereof Download PDFInfo
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- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
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Abstract
The invention relates to a method for preparing diluted magnetic polymer dispersed liquid crystal by photo-initiation free radical series reaction and a product thereof, belonging to the technical field of dispersed liquid crystal preparation. The invention uses gamma-Fe2O3Oleic acid-coated gamma-Fe formed by magnetic nanoparticles and oleic acid2O3Dispersing magnetic nano-particle powder in n-hexane to form n-hexane intermediate colloid, and dispersing and mixing the n-hexane intermediate colloid with liquid crystal to form gamma-Fe2O3And (3) carrying out ultraviolet irradiation polymerization reaction on the base liquid crystal magnetic colloid, a photoinitiator and a polymer monomer in a sample box to obtain the diluted magnetic polymer dispersed liquid crystal. The method adopts oleic acid coated gamma-Fe2O3Magnetic nano particles optimize the electromagnetic property of liquid crystal, and finally prepare the obtained polymer dispersion liquidCrystalline, liquid crystal droplet morphology, size and distribution can remain unchanged due to negligible scattering and absorption effects of nanoparticles, but the electro-optic properties of polymer dispersed liquid crystals can be followed by incorporation of γ -Fe2O3The concentration of the magnetic nanoparticles changes.
Description
Technical Field
The invention belongs to the technical field and relates to a method for preparing diluted magnetic polymer dispersed liquid crystal by photo-initiation free radical series reaction and a product thereof.
Background
Liquid crystals are liquid crystal materials having an orientation order and no position order formed by molecular interaction, and are widely researched and applied due to their special physical and chemical properties. The polymer dispersed liquid crystal composite material with micron-sized liquid crystal microdroplets dispersed in a polymer matrix can be prepared by mixing liquid crystal with a polymer precursor (comprising a photoinitiator and a polymer monomer) and carrying out a polymerization reaction. The polymer dispersed liquid crystal is called PDLC for short, and has an electro-optic effect based on light scattering characteristics, namely, under the control of applied voltage, the light intensity of the Polymer Dispersed Liquid Crystal (PDLC) film changes along with the change of the voltage, so the polymer dispersed liquid crystal can be used as a novel display device, an optical shutter, an intelligent window and the like. Compared with the common liquid crystal electro-optical device, the Polymer Dispersed Liquid Crystal (PDLC) device has the advantages of no need of a polarizer, low electric power consumption and the like.
The nanoparticles are generally particles having a size of 1 to 100 nm. Nanoparticles with dimensions much smaller than the wavelength of light have negligible scattering effects. The liquid crystal colloid formed by doping the liquid crystal with the low-concentration nano particles does not destroy the orientation sequence of the liquid crystal, has negligible absorption effect, but can modulate the physical properties of the liquid crystal. Existing studies have shown that: the Polymer Dispersed Liquid Crystal (PDLC) doped with nanoparticles, whose microstructure including the morphology, size and distribution of the liquid crystal droplets will vary with the concentration and size of the doped nanoparticles, so that its electro-optic effect will also vary. However, doping nanoparticles may affect the microstructure of Polymer Dispersed Liquid Crystal (PDLC) in a number of ways, and it is therefore difficult to determine how much the properties of nanoparticle-doped Polymer Dispersed Liquid Crystal (PDLC) may change relative to undoped nanoparticle-doped Polymer Dispersed Liquid Crystal (PDLC).
Since free ions are generated during the synthesis of the liquid crystal, the quality of the synthesized liquid crystal is affected. By adopting the nano-particle adsorption technology, the negative effect caused by free ions can be reduced, and the performance of practical liquid crystal is improved. The liquid crystal is diamagnetic organic molecules, and the magnetization intensity of the liquid crystal is negative; the magnetization intensity can be increased by adding a small amount of ferromagnetic ferrite nanoparticles with high dielectric constant into the liquid crystal colloid formed by liquid crystal, and the dielectric constant is basically unchanged as shown in the formulas (1) and (2):
(1) magnetization M of ferrite nanoparticle-doped liquid crystal colloidLCcCan be expressed as:
MLCc＝φMNP MMNP+(1-φMNP)MLC (1)
in the formula (1), phiMNPIs the volume fraction of the magnetic nanoparticles in the liquid crystal colloid; mMNP(> 0) is the magnetization of the nanoparticles; mLC(< 0) is the magnetization of the liquid crystal, where MMNP＞＞|MLC|. are provided. From the above formula, it can be seen that: with ferrite nanoparticles phiMNPIncrease of (2), MLCcAnd (4) increasing.
(2) Dielectric constant epsilon of ferrite nanoparticle-doped liquid crystal colloidLCcCan be expressed as:
εLCc＝εLC[1+3φMNP(εMNP-εLC)/(εMNP+2εLC)] (2)
in the formula (2), phiMNPThe definition is as defined in formula (1); epsilonMNPIs the dielectric constant of the ferrite nanoparticles; epsilonLCIs the dielectric constant of the liquid crystal. Because of eMNP＞εLCSo that in general eLCc＞εLC. For diluted magnetic liquid crystal, due to phiMNP< 0.1%, therefore, ∈LCc≈εLC。
The ferrite nanoparticles commonly used are Fe3O4And gamma-Fe2o3Nanoparticles. Fe3O4Has a magnetization higher than gamma-Fe2O3But gamma-Fe2O3Chemical property ratio of (1) Fe3O4And (4) stabilizing.
Therefore, it is necessary to use gamma-Fe2O3The process for preparing the polymer dispersed liquid crystal and the properties of the prepared product are further researched and applied.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a method for preparing diluted magnetic polymer dispersed liquid crystal by photo-induced radical tandem reaction; the other purpose of the invention is to provide a diluted magnetic polymer dispersed liquid crystal prepared by photo-initiated free radical series reaction; the invention also aims to provide application of the diluted magnetic polymer dispersed liquid crystal prepared by the photo-initiated free radical series reaction in preparation of an electro-optic display device, intelligent glass or an optical modulator.
In order to achieve the purpose, the invention provides the following technical scheme:
1. a method for preparing diluted magnetic polymer dispersed liquid crystal by photoinitiated free radical series reaction, which comprises the following steps:
(1) preparation of oleic acid-coated gamma-Fe2O3Magnetic nanoparticle powder: mixing gamma-Fe2O3Mixing the magnetic nanoparticles with water, heating to 65-75 ℃, adding Oleic Acid (OA) preheated to 30-60 ℃, preserving heat for 30-70 min, naturally cooling to room temperature, cleaning, drying, grinding and dispersing to obtain oleic acid-coated gamma-Fe2O3A magnetic nanoparticle powder;
(2) preparing diluted magnetic liquid crystal colloid: gamma-Fe encapsulating said oleic acid2O3Dispersing magnetic nano particle powder in n-hexane to form n-hexane intermediate colloid, adding liquid crystal, stirring until the n-hexane is uniformly dispersed, heating to 40-60 ℃ to volatilize the n-hexane, and obtaining gamma-Fe2O3A liquid crystal based magnetic colloid;
(3) preparing diluted magnetic polymer dispersed liquid crystal: firstly, mixing a photoinitiator and a polymer monomer to form a polymer precursor, heating to 65-100 ℃, and then mixing with gamma-Fe at 65-100 DEG C2O3And mixing the base liquid crystal magnetic colloid to form a mixed solution, injecting the mixed solution into a sample box by a capillary method, and irradiating the sample box by ultraviolet rays to perform polymerization reaction to obtain the diluted magnetic polymer dispersed liquid crystal.
Preferably, the gamma-Fe in step (1)2O3The magnetic nanoparticles were prepared as follows:
a. preparation of FeOOH @ Mg (OH)2Precursor: addition of alkaline Medium to FeCl3With Mg (NO)3)2Heating and boiling the mixed aqueous solution for 3-5 min, cooling to room temperature, and generating FeOOH @ Mg (OH) by a chemical precipitation method2With dilute HNO3Cleaning the aqueous solution until the pH value is 7-8, and performing centrifugal separation, dehydration, drying and grinding to obtain FeOOH @ Mg (OH)2A precursor;
b. preparation of gamma-Fe2O3Magnetic nanoparticles: reacting the FeOOH @ Mg (OH)2Adding FeCl into the precursor at the temperature of 40-90 DEG C2Preserving the heat of the treatment liquid for 20-60 min, naturally cooling to room temperature, centrifugally separating, dehydrating, drying and grinding to obtain spheroidal gamma-Fe with the average particle size of 9.5-12.5 nm2O3Magnetic nanoparticles.
Further preferably, the FeCl in step a3With Mg (NO)3)2In a molar ratio of 2: 1; the alkaline medium is a sodium hydroxide aqueous solution with the concentration of 0.5-1.0 mol/L, and sodium hydroxide and FeCl in the sodium hydroxide aqueous solution3The molar ratio of the sodium hydroxide aqueous solution to the mixed aqueous solution is 3: 2-2: 1, and the volume ratio of the sodium hydroxide aqueous solution to the mixed aqueous solution is 8: 1-12: 1; the dilute HNO3The concentration of the aqueous solution is 0.005-0.02 mol/L;
the FeOOH @ Mg (OH) in step b2Precursor and FeCl2The mass-to-volume ratio of the treatment liquid is 1: 60-1: 100, g: mL, and the FeCl is2The treating fluid is FeCl with the concentration of 0.03-0.22 mol/L2An aqueous solution.
Preferably, the gamma-Fe in step (1)2O3The mass-to-volume ratio of the magnetic nanoparticles to water is 1: 20-1: 80, and g: ml;
the gamma-Fe2O3The mass-to-volume ratio of the magnetic nanoparticles to the oleic acid is 1: 0.1-1: 1, and g: ml;
the cleaning and drying specifically comprises the following steps: firstly, carrying out magnetic separation to obtain particle precipitates, repeatedly cleaning the precipitates with acetone, carrying out vacuum filtration to obtain a solid, and naturally drying the solid.
Preferably, the oleic acid-coated γ -Fe in step (2)2O3The mass ratio of the magnetic nano-particle powder to n-hexane is 1: 79-1: 119;
the oleic acid-coated gamma-Fe2O3The mass ratio of the magnetic nanoparticle powder to the liquid crystal is less than 3: 20;
the liquid crystal is E7 type liquid crystal.
Preferably, γ -Fe is contained in the mixed solution in the step (3)2O3The mass ratio of the base liquid crystal magnetic colloid, the photoinitiator and the polymer monomer is 50:1: 49.
Preferably, the photoinitiator is 2-Methyl-1- (4-methylthiophenyl) -2-morpholinyl-1-propanone (2-Methyl-1- [4- (methylithio) phenyl ] -2-morpholino-1-propanone);
the polymer monomer is Nolan ultraviolet curing Adhesive NOA65 shadowless Adhesive (Norland Optical Adhesive 65, NOA 65).
Preferably, the ultraviolet radiation is specifically: irradiating for 5-20 min under an ultraviolet lamp with the power of 80-120 mW.
2. A diluted magnetic polymer dispersed liquid crystal prepared according to the above method for preparing a diluted magnetic polymer dispersed liquid crystal.
3. The diluted magnetic polymer dispersed liquid crystal is applied to the preparation of an electro-optical display device, intelligent glass or an optical modulator.
The invention has the beneficial effects that:
1. the invention discloses a method for preparing diluted magnetic polymer dispersed liquid crystal by photo-initiation free radical series reaction, which mainly uses gamma-Fe2O3Oleic acid-coated gamma-Fe formed by magnetic nanoparticles and oleic acid2O3Dispersing magnetic nano-particle powder in n-hexane to form n-hexane intermediate colloid, and dispersing and mixing the n-hexane intermediate colloid with liquid crystal to form gamma-Fe2O3And finally, carrying out polymerization reaction on the base liquid crystal magnetic colloid, the photoinitiator and the polymer monomer in a sample box through ultraviolet irradiation to obtain the diluted magnetic polymer dispersed liquid crystal. The preparation method adopts oleic acid coated gamma-Fe2O3Magnetic nano-meterThe particles optimize the electromagnetic performance of the liquid crystal, and the finally prepared Polymer Dispersed Liquid Crystal (PDLC) has negligible scattering and absorption effects due to the nanoparticles, the shape, size and distribution of liquid crystal droplets can be kept unchanged, but the electro-optic property of the Polymer Dispersed Liquid Crystal (PDLC) can be changed along with the doping of gamma-Fe2O3The concentration of the magnetic nanoparticles changes.
2. The invention also discloses a diluted magnetic polymer dispersed liquid crystal prepared by the photo-initiated free radical series reaction, which has the advantages of high contrast, low threshold voltage, low saturation voltage and the like, and has the advantages of improving the contrast, reducing the acting voltage, saving the power consumption and the like when being used for preparing an electro-optical display device, intelligent glass or an optical modulator.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.
Drawings
For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a specific magnetization curve in which γ -Fe2O3gamma-Fe encapsulated in oleic acid2O3Magnetic nanoparticles, a is the diluted magnetic liquid crystal colloid prepared in example 1, b is the diluted magnetic liquid crystal colloid prepared in example 2, and c is E7 type liquid crystal;
FIG. 2 shows oleic acid-encapsulated γ -Fe prepared in example 12O3Transmission electron microscopy of magnetic nanoparticles;
FIG. 3 is a scanning electron microscope photograph of a diluted magnetic polymer-dispersed liquid crystal prepared by the photo-initiated radical tandem reaction in example 1;
FIG. 4 is a scanning electron microscope photograph of a diluted magnetic polymer-dispersed liquid crystal prepared by the photo-initiated radical tandem reaction in example 2;
FIG. 5 shows the preparation of gamma-Fe undoped by photoinitiated radical tandem reaction in comparative example 12O3Scanning electron micrographs of polymer dispersed liquid crystals of magnetic nanoparticle single liquid crystals;
FIG. 6 is a scanning electron microscope image of a diluted magnetic polymer dispersed liquid crystal prepared by the photo-induced radical tandem reaction in example 3;
FIG. 7 is a scanning electron microscope photograph of a diluted magnetic polymer dispersed liquid crystal prepared by the photo-induced radical tandem reaction in example 4.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.
Example 1
A method for preparing diluted magnetic polymer dispersed liquid crystal by photo-initiation free radical series reaction is specifically as follows:
1. preparation of gamma-Fe2O3Magnetic nanoparticles: (1) preparation of FeOOH @ Mg (OH)2Precursor: an alkaline medium (0.7 mol/L aqueous sodium hydroxide solution) was added to FeCl in a volume ratio of 10:13With Mg (NO)3)2Mixed aqueous solution (FeCl in the mixed aqueous solution)3With Mg (NO)3)2In the molar ratio of 2:1), boiling for 5min, cooling to room temperature, and generating FeOOH @ Mg (OH) by a chemical precipitation method2With dilute HNO equivalent to 5 times the volume of the precipitate3Washing with water solution (concentration of 0.01mol/L) until pH of the washing solution is 8, centrifuging (washing and separating can be repeated), dehydrating, drying, and grinding to obtain FeOOH @ Mg (O)H)2A precursor; (2) preparation of gamma-Fe2O3Magnetic nanoparticles: FeOOH @ Mg (OH) to be prepared in a mass-to-volume ratio of 1:80, g: mL2Adding FeCl into the precursor at the temperature of 60 DEG C2Treatment solution (FeCl with concentration of 0.06mol/L2Aqueous solution), preserving heat for 40min, naturally cooling to room temperature, centrifugally separating, dehydrating, drying and grinding to obtain spheroidal gamma-Fe with the average grain diameter of 10nm2O3Magnetic nanoparticles.
2. Preparation of oleic acid-coated gamma-Fe2O3Magnetic nanoparticle powder: according to the mass-volume ratio of 1:50, g: mL, mixing gamma-Fe2O3Mixing magnetic nanoparticles with water, heating to 70 deg.C, adding Oleic Acid (OA) (gamma-Fe) preheated to 40 deg.C2O3The mass-volume ratio of the magnetic nanoparticles to the oleic acid is 1:0.4, g: mL), the mixture is kept warm for 50min, then is naturally cooled to room temperature, is washed and dried (firstly, magnetic separation is used for obtaining particle precipitate, the particle precipitate is washed twice by acetone and then is filtered in vacuum to obtain solid, and then natural drying is carried out), and then is ground and dispersed for 8min to obtain the oleic acid-coated gamma-Fe2O3Magnetic nanoparticle powder (average density of 2.92 g/cm)3)。
3. Preparing diluted magnetic liquid crystal colloid: gamma-Fe coated with oleic acid according to the mass ratio of 1:992O3Dispersing magnetic nanometer particle powder in n-hexane to form n-hexane intermediate colloid with particle mass fraction of 1%, and adding E7 type liquid crystal (composed of 5CB (51%), 7CB (25%), 8OCB (16%), 5CT (8%)) (oleic acid coated gamma-Fe)2O3The mass ratio of the magnetic nano particle powder to the liquid crystal is 0.11:99.89) is stirred until the magnetic nano particle powder and the liquid crystal are uniformly dispersed, and the mixture is heated to 50 ℃ to volatilize normal hexane, so that gamma-Fe is obtained2O3A base liquid crystal magnetic colloid.
4. Preparing diluted magnetic polymer dispersed liquid crystal: firstly, 2-Methyl-1- (4-methylthiophenyl) -2-morpholinyl-1-acetone (2-Methyl-1- [4- (meththio) phenyl) as a photoinitiator]-2-morpholino-1-propanone) and polymer monomer (Nolan ultraviolet curing Adhesive NOA65 shadowless Adhesive (Norland Optical Adhesive 65, NOA65) to form a polymer precursor (mass ratio of photoinitiator to polymer monomer is 1:49), and then addingHeating to 85 deg.C, and reacting with 85 deg.C gamma-Fe2O3Mixing the basic liquid crystal magnetic colloid to form mixed solution (gamma-Fe)2O3The mass ratio of the liquid crystal magnetic colloid to the polymer precursor is 1:1), cooling to room temperature, storing for 24h, heating to 85 ℃, injecting the mixed solution into a sample box by a capillary method, cooling to room temperature, and irradiating by ultraviolet rays (irradiating for 10min under an ultraviolet lamp of 100 mW) to generate polymerization reaction to obtain the diluted magnetic polymer dispersed liquid crystal.
In the preparation process, gamma-Fe is used in the preparation method of diluted magnetic liquid crystal colloid2O3Volume fraction (. phi.) of base liquid crystal magnetic colloidp) With mass fraction (phi)m) The relationship of (1):
where rhopgamma-Fe encapsulated in oleic acid2O3Average density (p) of magnetic nanoparticle powderp＝2.92g/cm3)，ρLCDensity (rho) of E7 type liquid crystalLC＝1.06g/ml)。
Synthesis of gamma-Fe2O3Magnetic nanoparticles having a mass fraction of phimTotal mass of mLg liquid crystal magnetic colloid, wherein n-hexane intermediate colloid with mass fraction of 1% is mh g
Let phip0.04%, and mixing m with a mass fraction of 1% according to formulas (3) and (4)hg n-hexane intermediate colloid and mLg of E7 liquid crystal, heating to 55 ℃, preserving heat for 120min, and obtaining gamma-Fe after n-hexane is completely volatilized2O3The volume fraction of the magnetic nanoparticles is 0.04 percent of liquid crystal magnetic colloid.
Example 2
0.04% of gamma-Fe in example 12O3Magnetic nanoparticle volume fractionThe number was changed to 0.06%, and the same conditions as in example 1 were otherwise applied to the same extent to obtain an intermediate liquid crystal colloid (the specific magnetization curve of which is shown by b in FIG. 1) and a final product diluted magnetic polymer dispersed liquid crystal (the scanning electron microscope image of which is shown in FIG. 4).
Example 3
A method for preparing diluted magnetic polymer dispersed liquid crystal by photo-initiation free radical series reaction is specifically as follows:
1. preparation of gamma-Fe2O3Magnetic nanoparticles: (1) preparation of FeOOH @ Mg (OH)2Precursor: an alkaline medium (0.5 mol/L aqueous sodium hydroxide solution) was added to FeCl in a volume ratio of 8:13With Mg (NO)3)2Mixed aqueous solution (FeCl in the mixed aqueous solution)3With Mg (NO)3)2In the molar ratio of 2:1), boiling for 3min, cooling to room temperature, and generating FeOOH @ Mg (OH) by a chemical precipitation method2With 10 volumes of dilute HNO equivalent to precipitation3Washing with water solution (concentration of 0.005mol/L) until the pH value of the washing liquid is 8, centrifuging (washing and separating can be repeated), dehydrating, drying and grinding to obtain FeOOH @ Mg (OH)2A precursor; (2) preparation of gamma-Fe2O3Magnetic nanoparticles: FeOOH @ Mg (OH) to be prepared in a mass-to-volume ratio of 1:60, g: mL2Adding FeCl into the precursor at the temperature of 60 DEG C2Treatment solution (FeCl with concentration of 0.03mol/L2Aqueous solution), preserving the heat for 20min, naturally cooling to room temperature, centrifugally separating, dehydrating, drying and grinding to obtain spheroidal gamma-Fe with the average grain diameter of 10nm2O3Magnetic nanoparticles.
2. Preparation of oleic acid-coated gamma-Fe2O3Magnetic nanoparticle powder: according to the mass-volume ratio of 1:20, g: mL, mixing gamma-Fe2O3Mixing magnetic nanoparticles with water, heating to 70 deg.C, adding Oleic Acid (OA) (gamma-Fe) preheated to 30 deg.C2O3The mass-volume ratio of the magnetic nanoparticles to the oleic acid is 1:0.1, g: mL), the temperature is kept for 70min, the mixture is naturally cooled to room temperature, washed and dried (firstly, magnetic separation is used to obtain particle precipitate, the particle precipitate is washed twice by acetone and then vacuum filtration is used to obtain solid,then naturally drying) and grinding and dispersing for 5min to obtain oleic acid coated gamma-Fe2O3Magnetic nanoparticle powder.
3. Preparing diluted magnetic liquid crystal colloid: gamma-Fe coated with oleic acid according to the mass ratio of 1:792O3Dispersing magnetic nanometer particle powder in n-hexane to form n-hexane intermediate colloid with particle mass fraction of 1.25%, and adding E7 type liquid crystal (composed of 5CB (51%), 7CB (25%), 8OCB (16%), 5CT (8%)) (oleic acid coated gamma-Fe)2O3The mass ratio of the magnetic nano particle powder to the liquid crystal is 3:20) is stirred until the magnetic nano particle powder and the liquid crystal are uniformly dispersed, and the mixture is heated to 50 ℃ to volatilize normal hexane, so that gamma-Fe is obtained2O3A base liquid crystal magnetic colloid.
4. Preparing diluted magnetic polymer dispersed liquid crystal: firstly, 2-Methyl-1- (4-methylthiophenyl) -2-morpholinyl-1-acetone (2-Methyl-1- [4- (meththio) phenyl) as a photoinitiator]Mixing-2-morpholino-1-propanone) and polymer monomer (Nolan ultraviolet curing Adhesive NOA65 shadowless Adhesive (Norland Optical Adhesive 65, NOA65) to form polymer precursor (mass ratio of photoinitiator to polymer monomer is 1:49), heating to 65 ℃, and mixing with gamma-Fe at 65 ℃2O3Mixing the basic liquid crystal magnetic colloid to form mixed solution (gamma-Fe)2O3The mass ratio of the liquid crystal magnetic colloid to the polymer precursor is 1:1), cooling to room temperature, storing for 24h, heating to 65 ℃, injecting the mixed solution into a sample box by a capillary method, cooling to room temperature, and irradiating by ultraviolet rays (irradiating for 20min under an ultraviolet lamp of 80 mW) to generate polymerization reaction to obtain the diluted magnetic polymer dispersed liquid crystal.
Example 4
A method for preparing diluted magnetic polymer dispersed liquid crystal by photo-initiation free radical series reaction is specifically as follows:
1. preparation of gamma-Fe2O3Magnetic nanoparticles: (1) preparation of FeOOH @ Mg (OH)2Precursor: an alkaline medium (aqueous sodium hydroxide solution with a concentration of 1.0 mol/L) was added to FeCl in a volume ratio of 12:13With Mg (NO)3)2Mixed aqueous solution (FeCl in the mixed aqueous solution)3With Mg (NO)3)2In the molar ratio of 2:1), boiling for 4min, cooling to room temperature, and generating FeOOH @ Mg (OH) by a chemical precipitation method2With dilute HNO equivalent to 5 times the volume of the precipitate3Washing with water solution (concentration of 0.02mol/L) until the pH value of the washing liquid is 8, centrifuging (washing and separating can be repeated), dehydrating, drying and grinding to obtain FeOOH @ Mg (OH)2A precursor; (2) preparation of gamma-Fe2O3Magnetic nanoparticles: FeOOH @ Mg (OH) to be prepared in a mass-to-volume ratio of 1:100, g: mL2Adding FeCl into the precursor at the temperature of 90 DEG C2Treatment solution (FeCl with concentration of 0.22mol/L2Aqueous solution), keeping the temperature for 60min, naturally cooling to room temperature, centrifugally separating, dehydrating, drying and grinding to obtain spheroidal gamma-Fe with the average grain diameter of 10nm2O3Magnetic nanoparticles.
2. Preparation of oleic acid-coated gamma-Fe2O3Magnetic nanoparticle powder: according to the mass-volume ratio of 1:80, g: mL, mixing gamma-Fe2O3Mixing magnetic nanoparticles with water, heating to 75 deg.C, adding Oleic Acid (OA) (gamma-Fe) preheated to 60 deg.C2O3The mass-volume ratio of the magnetic nanoparticles to the oleic acid is 1:1, g: mL), the mixture is kept warm for 70min, then is naturally cooled to room temperature, is washed and dried (firstly, magnetic separation is used for obtaining particle precipitate, acetone is used for washing twice, vacuum filtration is used for obtaining solid, then natural drying is carried out), and then is ground and dispersed for 10min to obtain oleic acid coated gamma-Fe2O3Magnetic nanoparticle powder.
3. Preparing diluted magnetic liquid crystal colloid: gamma-Fe coated with oleic acid according to the mass ratio of 1:1192O3Dispersing magnetic nanometer particle powder in n-hexane to form n-hexane intermediate colloid with particle mass fraction of 0.83%, and adding E7 type liquid crystal (composed of 5CB (51%), 7CB (25%), 8OCB (16%), 5CT (8%)) (oleic acid coated gamma-Fe)2O3The mass ratio of the magnetic nano particle powder to the liquid crystal is 1:20) is stirred until the magnetic nano particle powder and the liquid crystal are uniformly dispersed, and the mixture is heated to 60 ℃ to volatilize normal hexane, so that gamma-Fe is obtained2O3A base liquid crystal magnetic colloid.
4. Preparing diluted magnetic polymer dispersed liquid crystal: firstly, 2-methyl as a photoinitiator-1- (4-methylthiophenyl) -2-morpholinyl-1-propanone (2-Methyl-1- [4- (methylthio) phenyl)]Mixing-2-morpholino-1-propanone) and polymer monomer (Nolan ultraviolet curing Adhesive NOA65 shadowless Adhesive (Norland Optical Adhesive 65, NOA65) to form polymer precursor (mass ratio of photoinitiator to polymer monomer is 1:49), heating to 85 ℃, and mixing with gamma-Fe at 85 ℃2O3Mixing the basic liquid crystal magnetic colloid to form mixed solution (gamma-Fe)2O3The mass ratio of the liquid crystal magnetic colloid to the polymer precursor is 1:1), cooling to room temperature, storing for 24h, heating to 85 ℃, injecting the mixed solution into a sample box by a capillary method, cooling to room temperature, and irradiating by ultraviolet rays (irradiating for 5min under an ultraviolet lamp of 120 mW) to generate polymerization reaction to obtain the diluted magnetic polymer dispersed liquid crystal.
Comparative example 1
Preparation of undoped gamma-Fe2O3The preparation method of the polymer dispersed liquid crystal of the magnetic nano-particle single liquid crystal comprises the following steps:
mixing photoinitiator 2-Methyl-1- (4-methylthiophenyl) -2-morpholino-1-acetone (2-Methyl-1- [4- (methylthio) phenyl ] -2-morpholino-1-propanone) and polymer monomer (Nolan ultraviolet curing Adhesive NOA65 shadowless Adhesive (NOA 65) to form a polymer precursor (mass ratio of photoinitiator to polymer monomer is 1:49), heating to 85 deg.C, mixing with 85 deg.C E7 liquid crystal (the ratio magnetization curve is shown as c in FIG. 1) to form a mixture, cooling to room temperature, storing for 24h, heating to 85 deg.C, injecting the mixture into a sample box by capillary method, cooling to room temperature, irradiating with ultraviolet (10 min under 100mW ultraviolet lamp) to polymerize to obtain diluted magnetic polymer dispersed liquid crystal (the scanning electron microscope is shown in FIG. 5) Shown).
From the specific magnetization curve of FIG. 1 (where. gamma. -Fe2O3gamma-Fe encapsulated in oleic acid2O3Magnetic nanoparticles, a is the diluted magnetic liquid crystal colloid prepared in example 1, b is the diluted magnetic liquid crystal colloid prepared in example 2, and c is E7 type liquid crystal), and doped with gamma-Fe2O3Liquid crystal magnetic colloid with improved magnetic nano-particle contentMagnetic properties of (1); FIG. 2 shows oleic acid-encapsulated γ -Fe prepared in example 12O3Typical TEM image of magnetic nanoparticles, synthesized gamma-Fe can be seen from FIG. 22O3The particle size of the magnetic nanometer particles is about 10 nanometers; FIG. 3 is a scanning electron microscope photograph of a diluted magnetic polymer-dispersed liquid crystal prepared by a photo-induced radical tandem reaction in example 1, FIG. 4 is a scanning electron microscope photograph of a diluted magnetic polymer-dispersed liquid crystal prepared by a photo-induced radical tandem reaction in example 2, and FIG. 5 is a scanning electron microscope photograph of an undoped gamma-Fe prepared by a photo-induced radical tandem reaction in comparative example 12O3Scanning electron micrographs of Polymer dispersed liquid crystals of magnetic nanoparticle Single liquid Crystal, as can be seen in FIGS. 3-5, doped with a small amount of gamma-Fe2O3The microstructures of the diluted magnetic polymer dispersed liquid crystal film prepared by the magnetic nano particles are basically the same, namely gamma-Fe2O3The incorporation of magnetic nanoparticles does not alter the microstructure of the polymer dispersed liquid crystal.
Scanning electron microscope observations of the diluted magnetic polymer dispersed liquid crystals prepared by the photo-initiated radical series reaction in example 3 and example 4 were also carried out, and the results are shown in FIG. 6 (scanning electron microscope of the diluted magnetic polymer dispersed liquid crystal prepared by the photo-initiated radical series reaction in example 3) and FIG. 7 (scanning electron microscope of the diluted magnetic polymer dispersed liquid crystal prepared by the photo-initiated radical series reaction in example 4), respectively.
The diluted magnetic polymer dispersed liquid crystals prepared in the examples were subjected to the performance test, and the results thereof are shown in table 1.
TABLE 1 Dilute magnetic polymer dispersed liquid crystal prepared in example was subjected to performance test
| Concentration of fine particles | Comparative example 1 | Example 1 | Example 2 | Example 3 | Example 4 |
| Contrast ratio | 27.80 | 44.16 | 30.30 | 39.30 | 42.61 |
| Threshold voltage | 8.59 | 7.48 | 6.03 | 7.36 | 7.50 |
| Saturation voltage | 29.52 | 22.56 | 25.30 | 21.96 | 22.86 |
Therefore, the diluted magnetic polymer dispersed liquid crystal with the advantages of high contrast, low threshold voltage, low saturation voltage and the like is used for preparing an electro-optical display device, intelligent glass or an optical modulator, and has the advantages of improving the contrast, reducing the applied voltage and saving the power consumption.
In summary, the present invention discloses a photo-initiated self-assemblyA process for preparing the diluted magnetic polymer dispersed liquid crystal by the radical series reaction features that the gamma-Fe is used2O3Oleic acid-coated gamma-Fe formed by magnetic nanoparticles and oleic acid2O3Dispersing magnetic nano-particle powder in n-hexane to form n-hexane intermediate colloid, and dispersing and mixing the n-hexane intermediate colloid with liquid crystal to form gamma-Fe2O3And finally, carrying out polymerization reaction on the base liquid crystal magnetic colloid, the photoinitiator and the polymer monomer in a sample box through ultraviolet irradiation to obtain the diluted magnetic polymer dispersed liquid crystal. The preparation method of the invention adopts gamma-Fe2O3The magnetic nanoparticles optimize the electromagnetic performance of the liquid crystal, and the finally prepared Polymer Dispersed Liquid Crystal (PDLC) has negligible scattering and absorption effects, so that the form, size and distribution of liquid crystal microdroplets can be kept unchanged, but the electro-optic property of the Polymer Dispersed Liquid Crystal (PDLC) can be changed along with the doping of gamma-Fe2O3The concentration of the magnetic nanoparticles changes. The invention also discloses a diluted magnetic polymer dispersed liquid crystal prepared by the photo-initiated free radical series reaction, which has the advantages of high contrast, low threshold voltage, low saturation voltage and the like, and has the advantages of improving the contrast, reducing the action voltage and saving the power consumption when being used for preparing an electro-optical display device, intelligent glass or an optical modulator.
Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.
Claims (10)
1. A method for preparing diluted magnetic polymer dispersed liquid crystal by photoinitiated free radical series reaction is characterized by comprising the following steps:
(1) preparation of oleic acid-coated gamma-Fe2O3Magnetic nanoparticle powder: mixing gamma-Fe2O3Mixing the magnetic nanoparticles with water, heating to 65-75 ℃, adding the mixture to preheat to 30 ℃Preserving the temperature of the oleic acid at 60 ℃ for 30-70 min, naturally cooling to room temperature, cleaning, drying, grinding and dispersing to obtain oleic acid coated gamma-Fe2O3A magnetic nanoparticle powder;
(2) preparing diluted magnetic liquid crystal colloid: gamma-Fe encapsulating said oleic acid2O3Dispersing magnetic nano particle powder in n-hexane to form n-hexane intermediate colloid, adding liquid crystal, stirring until the n-hexane is uniformly dispersed, heating to 40-60 ℃ to volatilize the n-hexane, and obtaining gamma-Fe2O3A liquid crystal based magnetic colloid;
(3) preparing diluted magnetic polymer dispersed liquid crystal: firstly, mixing a photoinitiator and a polymer monomer to form a polymer precursor, heating to 65-100 ℃, and then mixing with gamma-Fe at 65-100 DEG C2O3And mixing the base liquid crystal magnetic colloid to form a mixed solution, injecting the mixed solution into a sample box by a capillary method, and irradiating the sample box by ultraviolet rays to perform polymerization reaction to obtain the diluted magnetic polymer dispersed liquid crystal.
2. The method for preparing diluted magnetic polymer dispersed liquid crystal according to claim 1, wherein the γ -Fe in step (1)2O3The magnetic nanoparticles were prepared as follows:
(1) preparation of FeOOH @ Mg (OH)2Precursor: addition of alkaline Medium to FeCl3With Mg (NO)3)2Heating and boiling the mixed aqueous solution for 3-5 min, cooling to room temperature, and generating FeOOH @ Mg (OH) by a chemical precipitation method2With dilute HNO3Cleaning the aqueous solution until the pH value is 7-8, and performing centrifugal separation, dehydration, drying and grinding to obtain FeOOH @ Mg (OH)2A precursor;
(2) preparation of gamma-Fe2O3Magnetic nanoparticles: reacting the FeOOH @ Mg (OH)2Adding FeCl into the precursor at the temperature of 40-90 DEG C2Preserving the heat of the treatment liquid for 20-60 min, naturally cooling to room temperature, centrifugally separating, dehydrating, drying and grinding to obtain spheroidal gamma-Fe with the average particle size of 9.5-12.5 nm2O3Magnetic nanoparticles.
3. According toThe method for preparing diluted magnetic polymer dispersed liquid crystal according to claim 2, wherein the FeCl is used in the step (1)3With Mg (NO)3)2In a molar ratio of 2: 1; the alkaline medium is a sodium hydroxide aqueous solution with the concentration of 0.5-1.0 mol/L, and sodium hydroxide and FeCl in the sodium hydroxide aqueous solution3The molar ratio of the sodium hydroxide aqueous solution to the mixed aqueous solution is 3: 2-2: 1, and the volume ratio of the sodium hydroxide aqueous solution to the mixed aqueous solution is 8: 1-12: 1; the dilute HNO3The concentration of the aqueous solution is 0.005-0.02 mol/L;
the FeOOH @ Mg (OH) in the step (2)2Precursor and FeCl2The mass-to-volume ratio of the treatment liquid is 1: 60-1: 100, g: mL, and the FeCl is2The treating fluid is FeCl with the concentration of 0.03-0.22 mol/L2An aqueous solution.
4. The method for preparing diluted magnetic polymer dispersed liquid crystal according to claim 1, wherein the γ -Fe in step (1)2O3The mass-to-volume ratio of the magnetic nanoparticles to water is 1: 20-1: 80, and g: ml;
the gamma-Fe2O3The mass-to-volume ratio of the magnetic nanoparticles to the oleic acid is 1: 0.1-1: 1, and g: ml;
the cleaning and drying specifically comprises the following steps: firstly, carrying out magnetic separation to obtain particle precipitates, repeatedly cleaning the precipitates with acetone, carrying out vacuum filtration to obtain a solid, and naturally drying the solid.
5. The method for preparing diluted magnetic polymer dispersed liquid crystal according to claim 1, wherein the oleic acid-coated γ -Fe in the step (2)2O3The mass ratio of the magnetic nano-particle powder to n-hexane is 1: 79-1: 119;
the oleic acid-coated gamma-Fe2O3The mass ratio of the magnetic nanoparticle powder to the liquid crystal is less than 3: 20;
the liquid crystal is E7 type liquid crystal.
6. The method of claim 1, wherein the mixed solution in step (3) contains gamma-Fe2O3The mass ratio of the base liquid crystal magnetic colloid, the photoinitiator and the polymer monomer is 50:1: 49.
7. The method of claim 6, wherein the photoinitiator is 2-methyl-1- (4-methylthiophenyl) -2-morpholino-1-propanone;
the polymer monomer is NOLAN ultraviolet curing adhesive NOA65 shadowless adhesive.
8. The method for preparing diluted magnetic polymer dispersed liquid crystal according to claim 1, wherein the ultraviolet irradiation is specifically: irradiating for 5-20 min under an ultraviolet lamp with the power of 80-120 mW.
9. A diluted magnetic polymer dispersed liquid crystal prepared by the method for preparing a diluted magnetic polymer dispersed liquid crystal according to any one of claims 1 to 8.
10. Use of the diluted magnetic polymer dispersed liquid crystal of claim 9 in the preparation of an electro-optic display device, smart glass, or optical modulator.
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