POLYMERIZATION-INDUCED PHASE-SEPARATION .3. MORPHOLOGIES AND CONTRASTRATIOS OF POLYMER-DISPERSED LIQUID-CRYSTALS

Citation
C. Serbutoviez et al., POLYMERIZATION-INDUCED PHASE-SEPARATION .3. MORPHOLOGIES AND CONTRASTRATIOS OF POLYMER-DISPERSED LIQUID-CRYSTALS, Liquid crystals, 22(2), 1997, pp. 145-156
Citations number
21
Categorie Soggetti
Crystallography
Journal title
ISSN journal
02678292
Volume
22
Issue
2
Year of publication
1997
Pages
145 - 156
Database
ISI
SICI code
0267-8292(1997)22:2<145:PP.MAC>2.0.ZU;2-D
Abstract
Polymerization induced phase separation in mixtures of liquid crystals (LCs) and acrylates (Merck TL205/PN393) proceeds by liquid-gel demixi ng, in most cases of practical interest. At high LC content or low tem perature of polymerization liquid-liquid separation cannot be excluded . Depending on the elasticity and homogeneity of the polymer network a t the onset of phase separation, spherical or non-spherical LC domains are observed; non-spherical domains reflect an inhomogeneous gel stru cture. The change from spherical to non-spherical occurs in a very nar row range of LC concentrations and curing temperatures. The transition between these two morphologies can be explained using conversion phas e diagrams obtained from the Flory-Huggins-Dusek theory. The contrast ratio of PDLCs made from the Merck mixture passes through a maximum wh en the droplet shape at the onset of phase separation changes from sph erical to non-spherical. Lowering the LC content or increasing the tem perature leads to smaller LC domains which scatter less efficiently. T he reverse changes lead to early phase separation and large LC domains which also scatter inefficiently. It is speculated that the maximum o f the contrast ratio is related to secondary phase separation, leading to subdomains of an appropriate size.