Morphology Of Polymer Dispersed Liquid Crystal Research Articles

The regulation of electro-optical properties and polymer morphology of polymer-dispersed liquid crystal containing POSS microstructure by click chemistry and UV intensity

In this work, the thiol‐ene click reaction was used to prepare polymer-dispersed liquid crystal films by a photo-initiated polymerization reaction. Different content of DET was introduced into the polymer matrix to enhance the electro-optical performance of PDLC. Our results showed that the introducing of DET significantly improved the electro-optical properties of PDLC. The SEM results showed that larger and uniform pores were observed with increasing DET content. And it was found that an increase in UV intensity resulted in a continuous decrease in Toff and an increase in CR for weakening the anchoring effect of the polymer matrix.

Effect of the magnetic nanoparticle concentration on the electro-optical properties of the polymer-dispersed liquid crystals

ABSTRACT In this paper, we investigated the electro-optical properties of the dilute magnetic polymer dispersed liquid crystals (PDLCs) prepared with the liquid crystal colloids containing low concentrations of γ-Fe2O3 nanoparticles. The doped nanoparticles have hardly changed the morphology of PDLCs, but they have significantly changed the threshold voltage, saturation voltage, and contrast ratio of PDLCs. Such changes result from ionic adsorption in competition with the concentration of the nanoparticles. When the concentration of the nanoparticles was below the critical concentration, the adsorption of free ions was dominant, and the contrast ratio increased while the saturation voltage decreased. However, when the concentration of the nanoparticles was above the critical concentration, the intrinsic electro-optical effect of the nanoparticles was dominant, and the contrast ratio decreased while the saturation voltage increased.

Effect of preparation conditions on the electro-optical performance and the polymer morphology of polymer-dispersed liquid crystals with polyhedral oligomeric silsesquioxane (POSS) microstructure

In this work, the effects of the preparation conditions on the electro-optical performance and the polymer morphology of the polymer dispersed liquid crystal (PDLC) samples in which the polymer matrix contained polyhedral oligomeric silsesquioxane (POSS) microstructure were studied. The results confirmed the dramatic improvement effect of POSS microstructure for the electro-optical properties of PDLC. Moreover, the electro-optical performance and the polymer morphology of the PDLC samples with POSS microstructure can be regulated successfully by the preparation conditions, such as UV light intensity and polymerization temperatures. This work can provide a way for regulating methods for PDLC films.

Pinning effect on the phase separation dynamics of thin polymer-dispersed liquid crystals

The surface pining effects on phase separation dynamics of polymer-dispersed liquid crystals (PDLCs) with thin cell gaps are demonstrated. Comparing various boundary conditions, the inner surfaces of the substrates with or without polyimide layers [but no rubbing] cannot provide enough anchoring force, so in either case the liquid crystal (LC) droplets flow and coalesce to form larger and less uniform droplets. However, if the inner surfaces of the substrates are coated with rubbed polyimide layers with anchoring energy >1x10-4 J/m2, almost all the nucleated LC droplets grow at a fixed position during phase separation. The appearance of the coalescence is not obvious and the formed LC droplets are relatively uniform. The surface anchoring has a significant effect on the morphology of PDLCs.

Cell dynamics model of droplet formation in polymer-dispersed liquid crystals.

We present a model for the dynamics of formation and morphology of polymer-dispersed liquid crystals (PDLCs). This incorporates, in a simplified manner, all the key physical ingredients of the actual fabrication process, viz. polymerization and gelation, phase separation, and growth and stabilization of a spatially inhomogeneous structure. We model phase separation of the initial pre-PDLC mixture into monomer- and liquid-crystal-rich phases by the cell dynamics systems (CDS) method of Oono and Puri [Phys. Rev. Lett. 58, 836 (1987); Phys. Rev. A 38, 434 (1988); 38, 1542 (1988)]. Gelation at the expense of monomers is described by an auxiliary field (the phase field), which also obeys a CDS equation for the conserved-order-parameter case. Growth is assumed to occur at the gel surface. Finally, structure stabilization is achieved by the inclusion of a nonlocal term that mimics the effect of the long-range interaction responsible for gel cohesion. We have performed detailed numerical calculations on a two-dimensional system for an initial composition of 30% LC plus 70% monomer. A pattern of LC-rich droplets is found to develop that is stable as t\ensuremath{\rightarrow}\ensuremath{\infty}, where t is time. Moreover, the droplet size distribution exhibits a very sharp peak, in agreement with observations on real PDLCs. \textcopyright{} 1996 The American Physical Society.