Dual effects of fullerene doped to holographic polymer dispersed liquid crystals

Doping of conductive fullerene particles to the formulation of conventional holographic polymer dispersed liquid crystal‐induced dual effects of reducing both droplet coalescence and operating voltage. Fullerene induced an induction period which otherwise does not exist, followed by a gradual increase of diffraction efficiency to a saturation value being increased with increasing fullerene content. The increased diffraction efficiency was caused by the decreased droplet coalescence which was due to the hindered migration of LC by the fullerene particles. On the other hand, doped fullerene particles augmented the conductivity of polymer phase and hence the local electrical field imposed on LC droplet, which overcome the threshold for driving and reduced operating voltage and response times. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5590–5596, 2007     

Effects of surfactant and molecular weight of polyol on grating formation and switching of holographic PDLC

The interposition of surfactants between polymer and liquid crystal (LC) droplets was theoretically predicted by the positive spreading coefficient (0 < λ₃₁) and utilized to interpret the morphology, grating formation kinetics, diffraction efficiency, and switching of the holographic polymer dispersed liquid crystal (HPDLC), prepared from various types (octanoic acid, poly oxyethylene octyl phenyl ether, and perfluoro‐1‐butanesulfonyl fluoride) and amounts (0–9 wt%) of surfactant and molecular weights of polyol (PPG). Regardless of the surfactant type, diffraction efficiency increased with the addition and increasing amount of surfactant, a tendency consistent with increasing value of spreading coefficient, which is determined by the formulations of grating formation. In contrast, diffraction efficiency showed a maximum with the polypropylene glycol (PPG) molecular weight. Surfactant effectively reduced the anchoring energy and electrically drove the film which otherwise was not driven. Overall, surfactant with greater λ₃₁ gave smaller droplet, greater diffraction efficiency, driving voltage, contrast ratio, and smaller response time. Copyright © 2008 John Wiley & Sons, Ltd.     

High‐performance holographic polymer‐dispersed liquid crystals by incorporating hyperbranched polymers

A minute amount (0.01–0.3 wt %) of ally isocyanate functionalized hyperbranched 2,2‐bis (hydroxymethyl) propionic acid (bis‐MPA) polyester‐16‐hydroxyl (HBP) was incorporated covalently into polyurethane acrylate‐based holographic polymer dispersed liquid crystals (HPDLCs), and its effects on the compound viscosity, grating kinetics, morphology, diffraction efficiency (DE), and electro‐optical properties of the HPDLC films were examined. HBP at low concentrations (0.01–0.05%) reduced the compound viscosity and domain size of liquid crystal (LC) significantly and augmented the cure rate and saturation DE by up to threefold compared to the HBP‐free compound. At high concentrations (0.10 and 0.30%), HBP increased the compound viscosity and decreased the rate of grating formation, giving rise to distorted LC‐polymer interfaces, which caused a significant decrease in the threshold and operating voltages. The rise and decay time showed a minimum and maximum, respectively, when the compound viscosity was a minimum at 0.03% HBP. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Biodegradable Holographic Polymer-Dispersed Liquid Crystal

The a-D-glucose was chemically modified with an allyl isocyanate (MG) and introduced into the polymer matrix for holographic polymer-dispersed liquid crystal (HPDLC), and the effects were studied in terms of morphology, grating formulation dynamics and electro-optical and biodegradable properties. Phase separation and diffraction efficiency increased at low content of (MG ≤ 4 wt%), while a rapid increase in crosslink density entrapped the LC droplets within the polymer to give poor phase separation, small droplet size, and low diffraction efficiency at high content. The HPDLC film was driven only with the addition of MG due to the increased droplet size with a minimum driving voltage of 18 V at 6.0 wt% MG. With the addition and an increasing amount of MG, the biodegradation of the composite film in a buffer solution was significantly increased in proportion to its amount.     

Holographic polymer dispersed liquid crystals using vinyltrimethoxysilane

Various amounts of vinyltrimethoxysilane (VTMOS) have been added to the conventional grating formulation of transmission holographic polymer dispersed liquid crystal (HPDLC) based polyurethane acrylate (PUA). With the addition and increasing amount of VTMOS, contact angle of the film with LC and droplet size of LC monotonically increased, implying that VTMOS segments of the polymers are preferentially exposed to the surfaces and provided greater immiscibility with LC molecules giving rise to an increase in droplet size of LC. However, with VTMOS content over 6 wt%, droplets were coalesced to sizes for random scatterings to lower the off state diffraction efficiency below that of virgin PUA. VTMOS was essential to drive the film by lowering the anchoring strength. The operating voltage monotonically decreased with increasing VTMOS content with a minimum switching voltage of about 15 V with response time of about 8 ms.     

Nanosized‐Silica‐Reinforced Holographic Polymer‐Dispersed Liquid Crystals

Summary: Nanosized silicas added to holographic polymer‐dispersed liquid crystals (HPDLC) provide the resin phase with increased elasticity, dimensional stability, and the high diffraction efficiency of the gratings. On the other hand, nucleation and growth of periodic modulation are delayed, especially with small‐sized silica because of the increased viscosity of the resin mixture. Effects of the LC/resin composition and cell gap on the diffraction efficiency have also been studied.

AFM image of silica added HPDLC.     

表面垂直取向对HPDLC光栅特性的影响

为了提高聚合物/液晶（HPDLC）光栅的衍射效率并改善光栅的表面形貌,研究了表面垂直取向处理对HPDLC光栅的影响。首先,研究了表面垂直处理对液晶分子的取向作用,发现垂直取向层对液晶的锚定作用随着盒厚的增加而逐渐减弱,取向层的作用范围大概在3 m ~5 m之间;其次,对相分离程度进行了实验表征,结果表明,随着液晶盒厚度的增加,相分离开始的时间越来越快,并且分离程度也越来越彻底。最后,讨论了表面垂直取向对HPDLC光栅衍射效率的影响,随着盒厚的增加,相分离出来的液晶微滴形成连续的区域,光栅的衍射效率逐渐升高,当盒厚增加到一定程度,其衍射效率和无取向处理的光栅接近。当盒厚过大时,垂直取向处理对HPDLC光栅散射损失并没有太大的改善,只有当盒厚适中（12 m）时,光栅的衍射效率最高,散射损失最小。     

Effect of graphene doping of holographic polymer‐dispersed liquid crystals

Doping a polymer matrix with a minute amount of graphene (0.05–0.25%) had significant effects on the grating formation kinetics and electro‐optical performance of a holographic polymer‐dispersed liquid crystal. Low graphene contents (≤0.1%) reduced the viscosity and induced rapid diffusion, curing, grating formation, and high diffraction efficiency with a diffraction overshoot of 0.05%. Conversely, high graphene contents increased the compound viscosity, and the entire process proceeded slowly. Graphene increased the polymer conductivity and local electric field, reduced the operating voltage from 65 to 25–50 V, and increased the contrast ratio from 7 to 8–23 with a concomitant decrease in rise time. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

适用于高空间频率透射式全息聚合物分散液晶光栅的材料研究

提出了适用于空间频率为3000 lp/mm的透射式全息聚合物分散液晶(HF-THPDLC)光栅的材料体系,并在反应动力学方面进行了深入的分析.为了能够得到高衍射效率并具有良好表面形貌的HF-THPDLC 光栅,首先确定了体系的平均官能度,使得预聚单体和液晶的扩散时间、液晶的成核时间以及于聚合物的凝胶时间达到最佳匹配状态...