Influence of SMA content on the electro-optical properties of polymer-dispersed liquid crystal prepared by monodisperse poly(MMA-co-SMA)/LC microcapsules

Monodisperse poly(methyl methacrylate) (PMMA) particles containing various concentrations of stearyl methacrylate (SMA) were prepared, and a liquid crystal (LC) was swollen into the particles using a solute co-diffusion method (SCM). Phase separation behaviors between the polymer and LC were monitored by utilizing an optical and a polarized microscope (OM/POM). The monodisperse LC microcapsules were then applied to a polymer-dispersed liquid crystal (PDLC), and the electro-optical properties were investigated. As a result, the threshold and driving voltages were improved when the SMA content increased. The long alkyl chains of SMA in the capsules should exist at the interface of the LC and polymer resulting in an enhancement of phase separation between the polymer and LC, which largely influences the electro-optical properties of PDLC.     

Effect of graft polymer prepared by living radical polymerisation on electro-optical properties of polymer dispersed liquid crystal

In this study, a graft polymer matrix prepared by living radical polymerisation had been incorporated into polymer dispersed liquid crystals (PDLCs). The electro-optical properties of the PDLCs were investigated. The results showed that the length and density of graft chain had a great influence on the memory effect of the PDLCs. Low-driving-voltage and weak-memory-effect PDLCs could easily be obtained with a graft polymer matrix.     

Effect of rGO on polymer-dispersed liquid crystal fabricated by RAFT polymerisation

In this study, we demonstrated that doping polymer matrix with a small amount of reduced graphene oxide (rGO) component (0.05–0.2%) had significant influence on the polymerisation kinetics and electro-optical performances of polymer-dispersed liquid crystal films (PDLCs) fabricated with macro reversible addition-fragmentation chain transfer agents. The effects of rGO content were studied in terms of morphology, compound viscosity, polymer conductivity, polymerisation kinetics and driving voltage of PDLCs. The results exhibited that higher rGO content increased the compound viscosity and the entire process proceeded slowly. Furthermore, the addition of rGO increased the polymer conductivity and local electric field, and reduced the saturation voltage as well as the threshold voltage from 27.3 to 19.5 V and 13.2 to 6.41 V, respectively.     

Improvement of permanent memory effect in PDLC films using TX-100 as an additive

A number of polymer dispersed liquid crystal (PDLC) films based on dimethacrylate monomers were synthesised by polymer-induced phase separation (PIPS) using polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (TX-100) as an additive up to total solution weight of 10% aiming to modify the initial anchorage force of the liquid crystal (LC) molecules to the polymeric matrix. The effects of the addition of this additive to the PDLC films were studied resorting to electro-optical studies. Using a fitting model, several parameters were correlated such as the permanent memory effect (PME), the voltage required to achieve 90% of maximum transmittance (E90), the average elastic constant (K) and the rotational viscosity of the director (γ). The use of TX-100 results on an increase on the PME and γ, and decrease on the E90 and K.     

Control of the microstructure of polymer network and effects of the microstructures on light scattering properties of UV‐cured polymer‐dispersed liquid crystal films

Polymer‐dispersed liquid crystals (PDLC) films were prepared from ultraviolet (UV) irradiation‐induced polymerization of the photopolymerizable monomers in photopolymerizable monomers/nematic liquid crystal (LC) mixtures. The effects of the composition of the mixtures, the curing temperature, and the UV light intensity on the microstructure of the polymer network in the PDLC films were investigated. Furthermore, the effects of the microstructures on the light scattering properties of the PDLC films in the wavelength region of 300–2500 nm were studied experimentally and theoretically based on the combination of three kinds of classical light scattering theories: the Rayleigh‐Gans (RG) approach, the anomalous diffraction (AD) approach, and the geometrical optics (GO) approach. It was found that the sizes of LC domain in PDLC films increased with the increase of the LC content as well as the decrease of the UV curing intensity, while increased at first and then decreased with the increase of the curing temperature. Moreover, smaller LC domain sizes could exhibit strong scattering properties in a smaller VIS wavelength region and the transmittance in NIR region (especially in the wavelength range of 1300–2500 nm) obviously decreased with the increasing sizes of LC domain. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2090–2099, 2008     

Morphologies and electro-optic properties of polystyrene/liquid crystal composite films

Morphology and electro-optic properties of composite films composed of polystyrene (PS) and nematic liquid crystal (LC) have been studied for a wide range (30-70 wt% of liquid crystal) of film composition. At two specific levels of LC loadings (50 and 60 wt%), effects of temperature, frequency and voltage of applied ac electric field on the transmittance of the films were intensively measured, and the results were interpreted in terms of aggregation structure of the film, the geometry of LC domains, LC loading, dielectric constant, conductivity, birefringence, and the solubility of LC in polymer. © 1994 John Wiley & Sons, Inc.     

Nematic and Cholesteric PDLC Elaborated under Shear Stress

Abstract

The properties of nematic and cholesteric Polymer Dispersed Liquid Crystal (PDLC) with ellipsoidal droplets are reported. The shape of the droplets are modified by a shear stress during the preparation. Different values of the shear stress were used which permit an ellipticity ratio modification by a factor 10. The electro-optical properties are measured for different types of samples and compared with theoretical previsions: transmission or reflection under voltage, threshold voltage, response times. We also describe the preparation of the sample, the experimental apparatus used for the shear stress, and the expected theoretical quantities like response times. When the liquid crystals are nematics, we obtain an increase of the threshold voltages, as predicted. The relaxation time decreases with increasing deformation but the diminution is not as great as predicted. When the liquid crystals are cholesterics, the high deformations induce polygonal fields, which strongly modify the electro-optical properties of the micro-composite. The threshold voltages and response time at applied voltage decrease whereas the relaxation time is increasing.     

Effects of a chemically modified multiwall carbon nanotubes on electro-optical properties of PDLC films

Polymer dispersed liquid crystal (PDLC) films are fabricated by well-known polymerization-induced phase separation method. In this paper, the dispersion of multi-walled carbon nanotubes (MWCNT) in liquid crystals has been enhanced by chemical modification and we have investigated their effects on the morphology, electro-optical properties and conductivity of the PDLC films. Results indicated that the threshold voltage and the saturation voltage of PDLC films decreased with the increase of the doping concentration of MWCNT or chemically modified MWCNT, because carbon nanotubes can enhance the electric field by reducing the resistivity of the medium and increasing the capacitance of the cells. It can be viewed obviously that the contrast ratio of the PDLC films doped with the chemically modified MWCNT is higher than that of the MWCNT.