No abstract

Two azo substituted achiral bent-core mesogens have been synthesized. Optical polarizing microscopy and synchrotron X-ray scattering studies of both compounds reveal the existence of the thermotropic uniaxial and biaxial nematic and three smectic phases at different temperatures in these single component small molecule systems. The transition from the uniaxial to biaxial nematic phase is confirmed to be second order. The transitions from the biaxial nematic to the underlying smectic phase and between the smectic phases have barely discernible heat capacity signatures and thus are also second order.

We present experimental evidence of pattern formation during the liquid expanded-liquid condensed phase transition in 2D monolayers of myristic acid. The shape of the liquid condensed domains changes continuously from self-similar fingering structures to circular platelets over a 5 °C temperature range below the estimated critical temperature Tc = (31 ± 0.5) °C. A qualitative interpretation of the pattern changes is given in terms of a diffusion-driven instability, taking into account the damping effect of line tension, which vanishes at Tc but gets large at lower temperatures. It is further shown that noise-reduced diffusion limited aggregation models can provide a satisfactory simulation of the observed structures.