Molecular Orientation in Polymer-Dispersed Liquid Crystals Using Time-Resolved FT-IR

Abstract

Molecular orientation of nematic microdroplets in polymer-dispersed liquid crystal (PDLC) films has been investigated by time-resolved FT-IR (TR/FT-IR) in the presence of an applied electric field. Two kinds (fast and slow) of reorientation processes are found, and these may be attributed to reorientation of liquid crystal molecules at the surface and the central region of droplets. In addition, an induction time has been observed before the onset of the actual reorientation. It is suggested that there are no essential differences between rigid and flexible molecular segments with respect to reorientation dynamics of at least 1 ms time resolution. TR and micro-FT-IR techniques have been combined in order to study the reorientation dynamics of the different regions of droplets.

Probing the Mesoscopic Chemical and Physical Properties of Polymer-Dispersed Liquid Crystals

“…As shown above, fast and slow reorientation processes are observed in the data. Reproduced from [140]. C NMR correlation data depicting the mobility of various functional groups of the liquid crystal in PDLC films containing droplets of different sizes.…”

“…For example, angle-dependent light scattering has been employed to deduce the predominant liquid crystal configuration in PDLC samples. [36,41,43] Other optical methods useful in such determinations include infrared (IR) spectroscopy, [83,140] and FT Raman spectroscopy. [141] Unlike the previously described methods, these two provide chemically specific orientational information.…”

“…Chemically selective methods, however, already exist and have been used extensively for such studies. The methods of choice include Raman scattering, [141] IR absorption spectroscopy, [70,125,126,140,153,159] and NMR spectroscopy. [86,143±145,147,148] In a recent paper, Kohri and co-workers reported the results of FTIR studies of liquid crystal reorientation dynamics in PDLC films.…”

“…[86,143±145,147,148] In a recent paper, Kohri and co-workers reported the results of FTIR studies of liquid crystal reorientation dynamics in PDLC films. [140] They monitored the time evolution of several infrared absorption bands following application of an electric field. The results obtained for seven different bands are plotted in Figure 12.…”

FTIR Microspectroscopy of Polymeric Systems

“…The influence of the matrix material on local order and resulting droplet configuration could also be identified [88]. The time resolved response of microscopic regions in large and small PDLC droplets could also be obtained [89]. Two major fillers used in the rubber industry are silica and carbon black.…”