Time-dependent nonlinear optical properties of pyroelectric liquid crystalline polymers

• Published in: Macromolecular symposia. Vol. 148; no. 1; pp. 179 - 195
• Main Authors: Örtegren, Jonas, Busson, Philippe, Gedde, Ulf W, Hult, Anders, Eriksson, Anders, Lindgren, Mikael, Arntzén, Per-Otto, Hermann, David S, Rudquist, Per, Lagerwall, Sven T
• Format: Journal Article
• Language: English
• Published: Wiley-VCH Verlag GmbH & Co. KGaA 01.12.1999
• ISSN: 1022-1360; 1521-3900
• DOI: 10.1002/masy.19991480115

Highly oriented pyroelectric liquid-crystalline polymers were prepared by photopolymerization under the influence of a static electric field from binary mixtures of two acrylate monomers exhibiting chiral smectic C mesomorphism. Both monomers contained nitro groups to yield second order nonlinear optical properties (second harmonic generation) and one of the monomers had two functional groups to yield a crosslinked polymer. The room temperature second order nonlinear susceptibility of the polymers showed during the first two hours a 10 % decrease after which it remained constant during the next 48 days. At elevated temperatures there was a significant difference in the nonlinear optical properties over time between crosslinked and uncrosslinked polymers. The uncrosslinked polymer showed a pronounced loss of second order nonlinear optical activity with time at ≥38°C. The crosslinked polymer showed a much smaller and basically a temperature independent decrease rate in the second order nonlinear optical properties at all the ageing temperatures (23-130°C). Both the loss in mesogen order parameter, very evident for the uncrosslinked polymer, and conformational changes occurring within the mesogens (β mechanism), may account for the observations made.