INVESTIGADORES
GALANTE Maria Jose
artículos
Título:
Polymer-Dispersed Liquid Crystals with Co-continuous Structures Generated by Polymerization-Induced Phase Separation of EBBA-Epoxy Solutions
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: 2002 vol. 35 p. 6324 - 6331
ISSN:
0024-9297
Resumen:
ABSTRACT: Polymer-dispersed liquid crystals
(PDLCs), consisting of a dispersion of LC-rich domains
in a polymer matrix, are used in different
types of electrooptical devices. Their efficiency can in principle
be increased if the LC domains exhibit a
uniform characteristic size in the range of the wavelength of
visible light. In an attempt to generate
this type of morphology, a model PDLC system based on a 50 wt
% solution of N-4-ethoxybenzylidene-4¢-n-butylaniline
(EBBA) in an epoxy monomer (diglycidyl ether of
bisphenol A, DGEBA) was analyzed. The
polymerization-induced phase separation was performed at 80
°C, using a tertiary amine as initiator
(benzyldimethylamine, BDMA). By selecting an initial concentration
located close to the critical composition to
promote spinodal demixing, co-continuous morphologies were
obtained, which were rapidly fixed by
gelation. The conversion of epoxy groups (p) was followed by
nearinfrared
spectroscopy (NIR). At p ) 0.28, phase
separation took place as revealed by transmission optical
microscopy (TOM) and by the acceleration
observed in the isothermal cure rate. Gelation took place at p
) 0.35, soon after
the cloud point. Although the primary structure was arrested by gelation, the
LC-rich
phase was continuously enriched in pure
EBBA, as revealed by the increase in TNI with
conversion
monitored by differential scanning
calorimetry (DSC). Co-continuous structures remained unmodified
after the storage of PDLCs for several
months. The nematic range of the LC-rich phase at p ) 1 was
comprised between 34 °C (melting point) and TNI ) 68 °C. A 57% of the initial LC was present in
nematic
domains at 40 °C, as determined by the
variation of the FTIR absorbance of a characteristic LC peak
between isotropic and nematic states. Therefore,
a possible route to obtain PDLCs with a uniform
characteristic size of LC domains is to
start with a composition close to the critical one and select conditions
to produce liquid-liquid demixing soon before gelation.