The effect of fluorine-substituted acrylate monomers on the electro-optical and morphological properties of polymer dispersed liquid crystals

The effects of fluorinated acrylate monomers on the electro-optical and morphological properties of polymer dispersed liquid crystal (PDLC) films are reported. The partial fluorination of host polymer matrices resulted in improved optical properties and better defined morphologies. An enhancement in contrast ratio was observed for fluorinated systems containing trifluoroethyl acrylate (TFEA) and hexafluoroisopropyl acrylate (HFIPA). Conversely, the incorporation of methyl acrylate (MA), a chemically similar non-fluorinated acrylate, resulted in no appreciable change in contrast ratio and an increase in relaxation time. Scanning electron microscopy morphological studies were conducted to understand further the influence of fluorinated monomers in PDLC systems.     

Effects of functionality of thiol monomer on electro-optical properties of polymer-dispersed liquid crystal films

In this paper, polymer-dispersed liquid crystal (PDLC) films which based on the acrylate and the thiol monomers were first prepared by ultraviolet-initiated polymerisation. The electro-optical properties and morphologies of the PDLC films were systematically investigated. The functionality of thiol monomers and their feed ratio showed great influence on the properties of the fabricated PDLC films because of the existence of competition between thiol–acrylate reaction and acrylate monomer polymerisation reaction. This made the polymer network and electro-optical properties of the PDLC films easily tunable by the introduction of the thiol monomers. When added four-functional thiol monomer PETMP with appropriate concentration into the PDLC system, lower driven voltage and higher contrast ratio were achieved.     

Preparation and electro‐optical properties of polymer dispersed liquid crystal films with relatively low liquid crystal content

In this paper, polymer dispersed liquid crystals (PDLC) films with LC content as low as 40 wt% were prepared, and the electro‐optical properties were carefully investigated. To accomplish this, different (meth)acrylate copolymerizaiton monomers have been used. The electro‐optical properties and morphologies of the PDLC films were strongly influenced by the chemical structure of copolymerization monomers (hydroxypropyl methacrylate (HPMA), glycidyl methacrylate, hydroxypropyl acrylate) and their feed ratio. Lower driven voltage and higher contrast ratio were achieved when the PDLC films showed a morphology with suitably LC domain size. At high HPMA content, a thin polymer film was formed on the surface of PDLC samples, which is beneficial to decrease the total LC content in PDLC devices. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of monomer structure on the morphology of polymer networks and the electro-optical properties of polymer-dispersed liquid crystal films

Polymer-dispersed liquid crystal (PDLC) films were prepared by photochemical polymerisation with a series of (meth)acrylate monomers. The effects of monomer structure on the morphology of polymer networks in the PDLC films were studied. The acrylate monomers without sidegroup chain formed uniform polymer networks. The methacrylate monomers with methyl as their sidegroup chains formed lace-like networks. The size of the LC droplets increased with increasing the length of the flexible chain of both methacrylate and acrylate monomers. Meanwhile, the effects of the morphology of the polymer network on the electro-optical properties of PDLC films were also investigated.     

Effects of crosslinking agent/diluents/thiol on morphology of the polymer matrix and electro-optical properties of polymer-dispersed liquid crystal

To study effects of the crosslinking agent/diluents/thiol on morphology of the polymer matrix and the electro-optical properties of polymer-dispersed liquid crystal (PDLC) films, samples were prepared by ultraviolet (UV)-initiated polymerisation. Due to the interaction between thiol–acrylate reaction and acrylate monomers polymerisation, the sample compositions were the foremost determinant to the microstructures which in turn played an essential role on the electro-optical properties of the PDLC films. With the increasing content of the crosslinking agent, the LC droplet size decreased, while the thiol had a contrary effect on the LC droplet size. It was demonstrated that the superior properties of the low-driven voltage (37.2 V), the high contrast ratio (148.2), the short response time (14.9 ms) and the high saturation transmittance (86.6%) could benefit from a novel microstructure which had a dense surface and meshes with microspheres attached. It was of great significance for the optimisation and the potential applications of the PDLC films.     

Studies on the electro-optical and the light-scattering properties of PDLC films with the size gradient of the LC droplets

Polymer dispersed liquid crystal (PDLC) films with the size gradient of the LC droplets were prepared based on the epoxy/acrylate hybrid polymer matrix. The ultraviolet (UV) intensity gradient was induced by the UV-absorbing dye over the thickness of the samples. Taking advantage of the difference between the epoxy monomers and acrylate monomers in polymerisation rates and the UV intensity gradient, the gradient distribution of the LC droplet size was formed in PDLC films. The effect of the size gradient of the LC droplets on the electro-optical and the light-scattering properties of PDLC films was investigated. The results showed that due to the size gradient distribution of the LC droplets, PDLC films could exhibit the strong light scattering in the UV-visible-near infrared (VIS-NIR) region. Consequently, it provides a potential approach for modulating NIR light transmittance.     

The physical properties of alkene-terminated liquid crystal molecules/E8 mixture and the electro-optical properties as they doped in polymer-dispersed liquid crystal systems

Effects of the content of fluorinated alkene-terminated liquid crystal (LC) molecules on the physical properties of the fluorinated alkene-terminated LC/E8 mixture were studied. The morphology and electro-optical properties as they doped in polymer-dispersed liquid crystal (PDLC) films were investigated. The detailed discussion of the obtained results is given. As a result, comparing with the physical properties of the series of LC mixtures with the same content of the analogous fully saturated compounds doped with E8, we find that the birefringence is significantly larger for the LC mixture with the alkene-terminated materials. Both fluorinated alkene-terminated LC molecules and the analogous fully saturated compounds doped with E8 reduce the driving voltage of PDLC films. Moreover, PDLC films with the fluorinated alkene-terminated LC molecules possessed higher contrast ratio and faster response time than that of the PDLC films prepared by adding the same mass fraction of the analogous fully saturated compounds. Thus, the ability to manipulate physical properties of LC mixture and electro-optical properties of PDLC films by changing the LC molecular structures may have future relevance for new LC structures design and applications of PDLC films.     

Comparative studies of polymer‐dispersed liquid crystal films via a thiol‐ene click reaction

In this work, the thiol‐ene click reaction is employed to fabricate polymer‐dispersed liquid crystal (PDLC) films by photoinitiated polymerization. The PDLC films are prepared by systematic variation of key conditions: variety and content of ‐ene monomer, liquid crystal (LC) content, curing time, and curing light intensity. We find that both the morphologies and electro‐optic properties of these films are adjustable. When increasing the length of alkyl main chain of ‐ene monomers, the driving voltages reduce, but in turn, the contrast ratio decreases. Increasing ‐ene monomer content raises the driving voltages as well as the response time, and the increase of LC content lowers the driving voltages but has a negative effect on the contrast ratio. The changes to the curing conditions (both curing time and UV light intensity) can be used to modify the driving voltages, response time, and contrast ratios of PDLC films. These comparative studies will elucidate new insights in commercial applications of intelligent PDLC films.     

核壳型含氟丙烯酸酯共聚物的合成及性能

采用饥饿态半连续种子乳液聚合方法, 在十二烷基硫酸钠(SDS)/辛基苯基聚氧乙烯醚(TX-10)复合乳化剂的作用下, 分别选用甲基丙烯酸三氟乙酯(TFEM)、甲基丙烯酸六氟正丁酯(HFBM)和甲基丙烯酸十二氟庚酯(DFHM)为含氟单体, 合成以丙烯酸正丁酯(BA)、甲基丙烯酸甲酯(MMA)和含氟单体为原料的核壳型结构含氟丙烯酸酯共聚物乳液. FTIR, 1H NMR, TEM和DSC分析结果显示, 获得了BA/MMA/含氟单体的共聚物乳液, 且乳液具有明显的核壳结构. DSC, TGA和SEM-EDX的分析显示, 核壳型结构的共聚物具有优异的热力学稳定性能和成膜性能; 长侧链或短侧链含氟单体对共聚物的热稳定性影响不明显, 但侧链较长的含氟单体所获得的聚合物在成膜过程中更易向表面迁移, 更能体现含氟聚合物的优点.     

A study on the polymer structures and electro-optical properties of epoxy-mercaptan-based polymer dispersed liquid crystal films

ABSTRACT

In this paper, polymer dispersed liquid crystal (PDLC) films based on epoxy-mercaptan system were prepared by thermal-initiated polymerization. The effects of the liquid crystal (LC) content, the proportion and the functionality of epoxy monomers on the polymer structures and electro-optical properties of the as-made PDLC films were investigated systematically. It was found that the morphologies of the polymer matrix can be altered from polymer meshes to polymer balls by increasing the LC content as well as the functionality of epoxy monomers. Accordingly, the electro-optical properties could be regulated by the morphologies of polymer networks. Especially, the as-made PDLC films with homogeneous porous structures exhibited the optimal electro-optical properties. Consequently, this work offers a meaningful approach to control the microstructures and optimize the electro-optical properties of PDLC films, which indeed can form a wonderful footstone for the wide application of PDLC.     

Effects of the fluorinated liquid crystal molecules on the electro-optical properties of polymer dispersed liquid crystal films

The different fluorinated liquid crystal (LC) molecules doped to E8 were used as LC component to prepare polymer dispersed liquid crystal (PDLC) films. The mass fraction of the LC mixture is fixed 50.0 wt%. Results indicate that doping 8.0 wt% fluorinated LC molecule ME3CP to E8 significantly reduced the driving voltage of the PDLC films, and the driving voltage reduced with the rise of mass fraction of ME3CP. Besides, the terminal flexible chain length of the fluorinated LC molecule influenced the LC mixture properties based on E8, such as the dielectric anisotropy, birefringence and viscosity of the LC mixture, and the morphology and the electro-optical properties of PDLC films were controlled not only by the physical properties of the LC mixture, but also by the terminal flexible chain length of the fluorinated LC molecule .     

光致变色含氟丙烯酸酯涂层的制备及性能

选取十二烷基硫酸钠(SDS),辛基苯基聚氧乙烯醚(OP-10)为复合乳化剂,过硫酸钾(KPS)为引发剂,将2-(全氟己基)乙基甲基丙烯酸酯(PFM)与丙烯酸酯类单体采用预乳化-半连续种子乳液聚合法进行乳液共聚,再将羟基螺吡喃(SPOH)与乳液进行物理共混,制得光致变色含氟丙烯酸酯乳液。 通过多种表征手段研究丙烯酸正丁酯(n-BA)和甲基丙烯酸甲酯(MMA)软硬单体的质量比,SPOH的用量对聚合反应和乳胶膜性能的影响。 结果表明,加入含氟单体后乳胶膜与水、油的接触角提高,热稳定性提高;加入SPOH的质量分数为1.25%时,乳胶膜具有较好的光致变色性能。     

Improvements in morphological and electro‐optical properties of polymer‐dispersed liquid crystal grating using a highly fluorine‐substituted acrylate monomer

To improve the morphological and electro‐optical properties of a polymer‐dispersed liquid crystal (PDLC) grating, a type of highly fluorine‐substituted acrylate monomer was added to the prepolymer mixture. The morphologies of the PDLC gratings were investigated using atom force microscopy and scanning electron microscopy. The grating had a very clear polymer/LC interface after addition of 3.9 wt % of fluorine‐substituted monomer. The LC droplets in this case were much larger than the sample without fluorinated monomer. This phenomenon indicated that an almost complete phase separation had occurred. However, as the content of fluorine‐substituted monomer increased, the morphologies of gratings became less defined and the volumes of LC droplets were smaller. The diffraction efficiency (DE) decreased with increasing of fluoride content and the V ₉₀ increased simultaneously, which may be ascribed to the blurry interface and the small LC droplets. The highest DE (90%) and lowest V ₉₀ (70 V) were obtained simultaneously under the condition of 3.9 wt % fluoride added in the prepolymer. In addition, it was also found that the fluorine‐substituted monomer may disorder the alignment of LCs in the grating.     

Preparation of polymer-dispersed liquid crystal doped with indium tin oxide nanoparticles

To study polymer-dispersed liquid crystal (PDLC) films doped with indium tin oxide (ITO) nanoparticles (NPs), samples were prepared by ultraviolet-initiated polymerisation based on the thiol–acrylate system. Owing to the interaction between PDLC system and ITO NPs, the content and the size of ITO NPs are the main determinants to the microstructure which plays an essential role on the electro-optical and anti-infrared properties of the PDLC films. In the polymer matrix, a novel microstructure consisting of a dense surface, micron-sized meshes and submicron meshes is found to benefit the better performances of the low driven voltage (20.7 V), the relatively high contrast ratio (8.3) and the lowest transmittance(500–2500 nm) on average at about 3.55% with maximum of merely 7.6%. Thus, it lays a solid foundation for the further investigations on the microstructure and the performance of the PDLC films. Meanwhile, it is proved that the PDLC film, improved performance through doping ITO NPs, is promising to be a superior choice in the field of energy-saving.     

Studies on electro‐optical properties of polymer matrix/LC/ITO nanoparticles composites

In this paper, polymer‐dispersed liquid crystal (PDLC) films consisting of liquid crystal (LC)/monomers/indium tin oxide (ITO) nanoparticles with good near‐infrared absorption property had been fabricated, and the influence of the ITO nanoparticles modified with 3‐methacryloxypropyltrimethoxysilane (KH570) on the PDLC films was systematically studied. First, different liquid crystal content was studied to obtain PDLC films with good electro‐optical properties. And then, various weight ratio of ITO nanoparticles was added to samples. While the content of ITO nanoparticles was increased, the saturation voltage increased and the CR decreased. Though the electro‐optical properties of PDLC samples reduced with the addition ITO nanoparticles, the near‐infrared absorption property of films was enhanced.     

Photopolymerization kinetics and phase behaviour of acrylate based polymer dispersed liquid crystals

Polymer dispersed liquid crystal (PDLC) materials were prepared by a polymerization induced phase separation (PIPS) process using UV radiation. The samples were obtained from the liquid crystalline component E7 and a blend of monofunctional (2-ethylhexyl acrylate) and difunctional (1,6-hexane diol diacrylate) monomers as precursors of the matrix. Polymerization energetics and thermodynamic properties of PDLC materials were studied by differential scanning calorimetry. Photopolymerization kinetics and phase behaviour of the PDLC are presented and discussed as a function of UV polymerization conditions (UV light intensity, UV time exposure and isothermal curing temperature).     

Effects of the structures of polymerizable monomers on the electro‐optical properties of UV cured polymer dispersed liquid crystal films

Polymer dispersed liquid crystal (PDLC) films were prepared by photopolymerization of liquid crystal (LC)/polymerizable monomers/photoinitiator composites. The effects of the structures of the polymerizable monomers on the electro‐optical properties of PDLC films were investigated. It was found that the length of the molecular chain and the rigidity and flexibility of molecules influenced the structure of the polymer network in the PDLC films somewhat, and then affected the electro‐optical properties of the composites accordingly. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1369–1375, 2008     

TSC study and electro‐optical properties of epoxy/acrylic polymer‐dispersed liquid‐crystal film in DICY thermal cure

We report on the structures and electro‐optical properties of epoxy/acrylic polymer‐dispersed liquid‐crystal (PDLC) films. A thermal stimulated current (TSC) analysis was used to investigate the physical structures of PDLC. In the TSC spectrum of PDLC, three relaxation peaks were observed: the glass transition of the liquid crystal, the glass transition of the polymer matrix, and the ρ transition. The ρ transition represents the discharge behavior of space charges, and its intensity increased as the curing time and content of the curing agent dicyandiamide (DICY) increased. The pre‐UV‐cured films with different DICY contents were thermally cured at 130 °C for various periods. The electro‐optical properties of PDLC, such as the contrast ratio and switching voltage, increased as the curing time of DICY, the content of DICY, or both increased. As the ambient temperature increased from 10 to 40 °C, the contrast ratio and switching voltage of PDLC gradually decreased. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 507–514, 2001     

固化条件对聚合物分散液晶膜电光性能的影响

选用聚乙二醇二缩水甘油醚(EGDE)/季戊四醇缩水甘油醚(PERTGE)/1,8-二氨基-3,6-二氧杂辛烷(EDBEA)/向列相液晶(SLC1717)复合体系,在不同的固化条件下,通过热聚合诱导相分离方法制备了一系列电光性能不同的聚合物分散液晶(polymer dispersed liquid crystal,简称PDLC)膜.研究了固化温度和固化时间对制备的PDLC膜中聚合物网络的微观形貌和电光性能的影响.结果表明,随着固化温度的升高以及固化时间的缩短,PDLC膜的对比度、驱动电压和开态响应时间逐渐增大,而关态响应时间逐渐减小.在固化温度为363.2 K,固化时间为7 h时,所制备的PDLC膜具有较佳的电光性能.     

Propriétés optiques et thermophysiques de composites polyméres-cristaux liquides (PDLC)

Polymer dispersed liquid crystal (PDLC) films can be switched electrically from a light scattering off-state to a highly transparent on-state. Thin films were prepared via a polymerization-induced phase separation process using electron beam radiation. The liquid crystal (LC)/polymer materials were obtained from blends of a eutectic nematic mixture E7 and a polyester acrylate based polymer precursor. The optical and electrooptical properties of the obtained PDLC films strongly depend on the LC concentration. The LC solubility limit in the polymer matrix and the fractional amount of LC contained in the droplets were determined by calorimetric measurements.