INVESTIGADORES
GALANTE Maria Jose
artículos
Título:
Polymer-Dispersed Liquid Crystals Based on Polystyrene and EBBA: Analysis of Phase Diagrams and Morphologies Generated
Autor/es:
C. E. HOPPE; M.J. GALANTE; P.A. OYANGUREN; R.J.J. WILLIAMS
Revista:
MACROMOLECULAR CHEMISTRY AND PHYSICS
Editorial:
WILEY-V C H VERLAG GMBH
Referencias:
Lugar: Weinheim; Año: 2003 vol. 204 p. 928 - 935
ISSN:
1022-1352
Resumen:
As an example of thermoplastic/liquid crystal
blends that do not exhibit a liquid-liquid immiscibility region
in their phase diagrams, a polystyrene (PS)/N-4-ethoxybenzylidene-
40-butylaniline (EBBA) blend was analyzed. The
complete phase diagram was built up using thermal transitions
determined by differential scanning calorimetry (DSC)
and polarized optical microscopy (POM). The boundary of
the nematicþisotropic region was fitted with the Flory-
Huggins-Maier-Saupe model, extended to consider the
polydispersity of PS. Main factors controlling the morphologies
generated by thermal-induced phase separation (TIPS)
were the initial EBBA concentration in the blend and the
cooling rate. Cooling at a fast rate led to small nematic domains
with a narrow size distribution. Slow cooling rates led
to the coexistence of very large and small dispersed domains.
This was because of the large extent of coalescence of the
droplets first generated associated with the continuation of
the nucleation/growth process in a medium of increasing
viscosity. The use of fast cooling rates might be important for
the generation of a narrow size-distribution of nematic droplets
by TIPS in polymer-dispersed liquid crystals (PDLC)
used in electrooptical devices.