Direct synchrotron x-ray scattering measurements of the orientational order parameter, S, corresponding to the siloxane and hydrocarbon parts of the molecule, smectic layer spacing, and director tilt angle with respect to the smectic-C (SmC) layer normal in the de Vries smectics-A (SmA) and SmC phases of two organosiloxane mesogens are reported. The results reveal that (i) the SmC (tilt) order parameter exponent β = 0.26 ± 0.01 for 2nd order SmA-SmC transition in excellent agreement with the tricritical behavior, (ii) the siloxane and hydrocarbon parts of the molecules are segregated and oriented parallel to the director with different degree of orientational order, and (iii) thermal evolution of the effective molecular length is different in the two phases contrary to the conventional wisdom.
The process of phase separation leads to several well known display technologies such as Polymer Dispersed liquid crystals and Polymer Stabilized cholesteric and ferroelectric devices. Several new limits of the general phenomena of phase separation have been discovered in recent years. In one of the limits, a very simple and powerful process known as the phase separated composite structures method permits the construction of conventional devices; such as, TN, STN, and FLC devices with great ease and with flexible substrates. It has also been employed in the fabrication of one- and two-dimensional optical gratings and fly's eye lenses (micro-lens array) with electrically controllable focal length. In the second limit, one obtains microscopic polymer columns perpendicular to the substrates. These structures have been used to fabricate large area homeotropic nematic devices having very high-contrast.