RESUMO
Two classes of laterally azo-bridged H-shaped ferroelectric liquid crystals (FLCs), incorporating azobenzene and disperse red 1 (DR-1) chromophores along the FLC polar axes, were synthesized and characterized by polarized light microscopy, differential scanning calorimetry, 2D X-ray diffraction analysis, and electro-optical investigations. They represent the first H-shaped FLC materials exhibiting the ground-state, thermodynamically stable enantiotropic SmC* phase, i.e., ground-state ferroelectricity. Second harmonic generation measurements of one compound incorporating a DR-1 chromophore at the incident wavelength of 1064 nm give a nonlinear coefficient of d(22) = 17 pm/V, the largest nonlinear optics coefficient reported to date for calamitic FLCs. This value enables viable applications of FLCs in nonlinear optics.
RESUMO
Individual fatty acid molecules adsorbed at the interface between hexadecane and fused silica have been tracked using total internal reflection fluorescence microscopy. Two cooperative diffusive mechanisms are observed: continuous small-scale Brownian motion and occasional large "jumps." The continuous diffusion exhibits evidence of confinement. The effective interfacial diffusion coefficients for each mechanism increase systematically with temperature; an Arrhenius analysis gives an activation barrier of approximately 50 kJ/mol for "jumping" and an upper limit of approximately 10 kJ/mol for confined diffusion.