Web Release Date: February 26,
DNMR Study of Hydrophilic and Hydrophobic Silica Dispersions in EBBA Liquid Crystals
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Centre for Self-Assembled Chemical Structures (CSACS), Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Québec, Canada H3A 2K6, and Department of Chemistry, Dawson College, 3040 Sherbrooke Street West, Westmount, Québec, Canada H3Z 1A4
Received: September 24, 2007
In Final Form: December 12, 2007
Abstract:
Dispersions of hydrophilic (A300) and hydrophobic (R812) silica aerosils in a Schiff-base-type liquid crystal (LC), p-ethoxy(benzylidene)-p-n-butylaniline (2O.4), EBBA, were characterized by deuterium nuclear magnetic resonance (DNMR). The formation and stability of random (RAN) versus anisotropic (AAN) aerosil networks under zero- versus in-field cooling was studied as a function of aerosil density and compared to previous studies of n-alkylcyanobiphenyl (nCB) dispersions. Whereas the LC directors of the hydrophobic R812 dispersions are almost completely annealed after in-field cooling, the hydrophilic A300 silica in EBBA gives rise to a mixture of RAN and AAN. The more complete R812 AAN partially breaks under in-field sample rotation, but the partial AAN formed by the A300 silica is stable. Weakening the aerosil network to compensate for weaker LC surface anchoring results in a complete network, but a strong LC/silica surface interaction must be combined with hydrophilic aerosils to produce AANs which are both complete and stable.
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