<title>Video-microscopy of NCAP films: the observation of LC droplets in real time</title>

Abstract

We have used video-microscopy to observe the behavior of liquid crystal (LC) droplets within nematic droplet-polymer films (NCAP) as the droplets respond to an applied electric field. The textures observed at intermediate fields yielded information about the process of liquid crystal orientation dynamics within droplets.The nematic droplet-polymer films had low LC content (less than 1 percent) to allow the observation of individual droplets in a 2-6Rm size range. The aqueous emulsification technique was used to prepare the films as it allows the straightforward preparation of low LC content films with a controlled droplet size range. Standard electro-optical (E-O) tests were also performed on the films, allowing us to correlate single droplet behavior with that of the film as a whole. Hysteresis measured in E-O tests was visually confirmed by droplet orientation dynamics; a film which had high hysteresis in E-O tests exhibited distinctly different LC orientations within the droplet when ramped up in voltage than when ramped down in voltage.Ramping the applied voltage to well above saturation resulted in some droplets becoming "stuck" in a new droplet structure which can be made to revert back to bipolar with high voltage pulses or with heat.

Electrooptic studies on polymer‐dispersed liquid‐crystal composite films. III. Poly(methyl methacrylate‐co‐butyl acrylate)/E7 and poly(methyl methacrylate‐co‐butyl acrylate)/E8 composites

“…The response of the LC no longer followed the change in the electric polarity 36, 42, 45–48. For a series‐connected dielectric composite model that is quite analogous to the present polymer/LC composite films, the applied electric field is not totally imposed on the LC phase but depends on the magnitude of the dielectric constants and the conductivity of the matrix polymer and LC 17, 37, 38. This partition of the external electric field to LC is given by eq.…”

“…The degree of the hysteresis was apparent in all cases of switching frequency from 50 HZ to 1 kHz. The basic reason for hysteresis in PDLC films has been the topic of several discussions 35–37. However, the phenomenon may be related to the mechanism of orientation of the LC droplet director,38 which may depend on the LC/polymer compatibility‐induced interfacial polarization process, which ultimately influences the distribution of the relaxation time 30.…”

Effect of temperature on the optical and electro‐optical properties of poly(methyl methacrylate)/E7 polymer‐dispersed liquid crystal composites

“…It has been suggested that hysteresis might be due to the possible defect movement in a droplet. 2,38 Reamy et al 38 observed that hysteresis may be related to the mechanism of orientation of the droplet director, which ultimately may depend on the polymer/LC compatibility induced interfacial polymerization. We observed that DV 50 became less significant as the E7 content in PMMA increased.…”

An Overview of Polymer-Dispersed Liquid Crystals Composite Films and Their Applications

“…The sources which give rise to hysteresis phenomenon have been studied by various researchers [117,135,138,140,141]. Hysteresis depends on the rate at which fields are applied and removed.…”