Evidence for the "zigzag" model of the smectic-C phase in the liquid crystal 4(')-butoxyphenylester 4-decyloxybenzoic acid (4OP10OB): A high-resolution x-ray study.

Abstract

We report, for the first time to our knowledge, on high-resolution x-ray scattering measurements of the liquid crystal 4'-butoxyphenylester 4-decyloxybenzoic acid (4OP10OB) with emphasis on the smectic-C phase and the smectic-A to smectic-C phase transition. From angular scans in reciprocal space we found that the smectic-C layer planes undergo a continuous tilt ${\ensuremath{\varphi}}_{p}$ with respect to temperature that can be described either by a Landau-type mean-field theory (which includes a sixth-order term in ${\ensuremath{\varphi}}_{p}$) or by a simple scaling form: ${\ensuremath{\varphi}}_{p}$\ensuremath{\sim}[(${T}_{c}$-T)/${T}_{c}$${]}^{0.44}$, where ${T}_{c}$ is the smectic-A\char21{}smectic-C transition temperature. Simultaneous measurements of the lattice spacing in the smectic-C phase suggest that the molecules do not behave like rigid rods. We found that the diamagnetic part of the molecule strongly couples to the magnetic field and tilts independently of the aliphatic end chains. The end chains are melted and thus maintain an almost-temperature-independent contact angle to the layer planes. Our measurements are consistent with the ``zigzag'' model of Bartolino, Doucet, and Durand.