INVESTIGADORES
GALANTE Maria Jose
artículos
Título:
Thermally-Reversible Light Scattering Films Based on Droplets of a Liquid Crystal (EBBA)/ Polystyrene Solution Dispersed in an Epoxy Matrix
Autor/es:
C. E. HOPPE; M.J .GALANTE; P.A.OYANGUREN; R.J.J. WILLIAMS
Revista:
MACROMOLECULES
Editorial:
AMER CHEMICAL SOC
Referencias:
Lugar: Washington; Año: 2004 vol. 37 p. 5352 - 5357
ISSN:
0024-9297
Resumen:
ABSTRACT: Thermally reversible light scattering (TRLS) films were synthesized by the reaction-induced
phase separation of solutions of N-4-ethoxybenzylidene-4¢-n-butylaniline (EBBA; 20-50 wt %) and
polystyrene (PS; 1-5 wt %) in diglycidyl ether of bisphenol A (DGEBA), using benzyldimethylamine
(BDMA) (0.06 mol with respect to epoxy groups), to initiate the polymerization. The material obtained
after complete reaction consisted of a dispersion of EBBA/PS droplets in the epoxy network partially
swollen by EBBA. The fractionation of EBBA between both phases was estimated using a simple
thermodynamic model. Due to the matching of refractive indices of the three components, the multiphasic
material was transparent above the nematic-isotropic transition temperature (TNI) of the EBBA/PS
droplets. Below TNI the material exhibited a sharp transition to an opaque state due to the mismatching
of refractive indices when EBBA was segregated as a nematic phase inside the droplets. The PS addition
produced a significant decrease of the cloud-point conversion with respect to formulations devoid of PS.
This led to relatively large domains that behave efficiently as light scattering centers in the PS-modified
material, enabling high contrast ratios between transparent and opaque states to be obtained. The
morphologies generated, and the corresponding optical properties of the TRLS films, did not change in
the course of successive cooling/heating cycles.