| Liquid crystal/polymer dispersion (LCPD) films are of technological importance for electro-optic applications such as large-area flat-panel displays, light shutters and switchable windows. The reasons for continued interest in this area are manifold, encompassing both economic and technological realms. Conventional flat-panel display materials made from twisted and supertwisted nematic liquid crystals (LCs) remain relatively expensive and are moderately difficult to fabricate. LCPD films are divided into two kinds: polymer dispersed liquid crystal (PDLC) film and polymer stabilized liquid crystal (PSLC) film according to LC content.The operation principle of a switchable LCPD film is the electrically controlled light scattering based on birefringence characteristics and control of refractive index of LC droplets by the use of applied voltage. Reverse mode is the opposite to normal mode LCPD: a clear state is maintained under no applied voltage and an opaque state appeared under applied voltage. It is more economical and convenient for electro-optic devices whose work state is transparent state. Many methods to form reverse mode film have been proposed using a dual frequency addressable LC, cholesteric LC and negative dielectric anisotropy nematic LC. However, few people obtained reverse mode film using normal positive dielectric anisotropy nematic LC which is more economical and available. The purpose of this paper is to propose a new methodology to prepare a new reverse mode system, parallel PSLC, using positive nematic LC.In this parallel PSLC film, when a positive LC is laminated in a parallel aligned cell at a zero field, the LC molecules are in the planar state. In this state, when the plane of polarized light parallels to the molecule orientation, the refractive index of LC molecules assumed similar which resulted in high transmittance. Upon the application of an electric field, LC molecules out of the polymer network changed their orientation which resulted in the mismatch of LC molecules refractive indexes. In this state, the film appeared opaque.Two monomers were synthesized and used in this system: 2-methyl-acrylic acid 4-(4'-cyano-biphenyl-4-yloxy)-butyl ester (M1) containing a flexible chain, and 2-methyl-acrylic acid 4'-cyano-biphenyl-4-yl ester (M2) without a flexible chain. The structures of monomers were confirmed by ~1H NMR. The effect of structure, concentration of monomer, curing temperature and the UV-exposure time on the film properties was investigated by polarizing optical microscope (POM) and UV-Visible spectrometer.Transmittance is a critical parameter of electro-optic film. M1 and M2 were used to prepare PSLC films to investigate the effect of monomer structure on the transmittance of the film without voltage. Although the refractive indexes of polymers were slight different, but transmittance of PSLC film with M1 was much higher than M2 film. Monomer M1 contained a rigid polar group and an alkyl side chain, which was similar with the 5CB. This structure made side chain oriented at the same time with 5CB under the influence of alignment layers in the process of polymerization. For the monomer M2, the scarcity of the flexible chain increased the effect of acrylate main chain on polar group. Random arrangement of the polymer chains made LC oriented irregular, which resulted in low transmittance of the film. To explore the effect of LC content on the electro-optic properties, transmittances dependence on the applied voltage of 17wt.%, 15wt.%, 13wt.% and 11wt.% M1 systems were observed. With the decrease of monomer content, less LC molecules were affected by the polymer network and more LC molecules were easier to orient regularly, which increased the transmittance. Moreover, the lower monomer concentration made the polymer network weaker, which decreased the driving voltage. The extension of the exposure time increased the molecular weight and firmed the polymer network, which increased the driving voltage and decreased the transmittance.
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