Polarization field effects at liquid-crystal-droplet-polymer interfaces.
The influence of confinement (droplet size) and liquid crystal orientational order (smectic-A and nematic) on the interfacial polarization field effects [Maxwell-Wagner-Sillars (MWS) effect] existing in liquid-crystal-droplets-polymer systems is investigated by broadband dielectric spectroscopy and a forward transmittance measurement technique. A relaxation process observed in the low frequency domain of the dielectric spectrum has been associated with a MWS effect for both micron-size and submicron-size droplets. Using electro-optical measurements and numerical simulations of the field inside droplets, it is shown that a depolarization field takes place in the same frequency range as that determined by dielectric spectroscopy. Differential scanning calorimetry measurements allowed to estimate the phase-separated liquid crystal [4,4'-octylcyanobiphenyl (8CB)] fraction, which was found in the range of 55% for both micron-size and submicron-size droplets. X-ray diffraction experiments showed that smectic 8CB confined to micron-size cavities adopt bulklike properties, i.e., a partial bilayer structure, whereas in submicron-size droplets the layer spacing of the smectic phase is increased due to the strong bending deformations induced by the high curvature of the cavity walls.
Boussoualem
Mourad
M
Laboratoire de Thermophysique de la Matière Condensée, UMR CNRS 8024, MREI, Université du Littoral-Côte d'Opale, 59140 Dunkerque, France.
Ismaili
Mimoun
M
Lamonier
Jean-François
JF
Buisine
Jean-Marc
JM
Roussel
Frédérick
F