Temperature difference between bulk and surface transition in freely suspended smectic films

We report an ellipsometric study of freely suspended films of a chiral liquid-crystal compound possessing the phase sequence smectic-C–smectic-A–isotropic with a very broad (67 K) smectic-A phase range. We observe a smectic-C–smectic-A surface transition which is situated more than 60 K above the bulk smectic-C–smectic-A transition temperature. Possible reasons for this unusually large temperature shift are discussed

Effect of co-monomers' relative concentration on self-assembling behaviour of side-chain liquid crystalline elastomers

This work deals with the design and characterization of a new series of liquid crystalline elastomers in the form of monodomain films, showing self-assembling behaviour, namely the nematic and the orthogonal smectic A phases. The procedure for the design and preparation of monodomain and polydomain polysiloxane-based side-chain liquid crystalline elastomers containing different concentrations of two mesogenic monomers and a constant density (about 15 mol%) of the crosslinker is reported. The phase diagram and mesomorphic behaviour of the new resulting liquid crystalline elastomers were determined by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and especially X-ray diffraction studies, which helped to clearly identify the smectic A phase. Among new liquid crystalline elastomer films, a specific concentration of co-mesogens gives an unconventional and fascinating system with a direct transition from the isotropic to smectic A phase. Results of the thermo-mechanic studies confirmed the shape-memory properties of these films, which have elastic properties optimal for applications as thermo-mechanic actuators