Some dynamic features of the preparation of liquid crystalline elastomers

Abstract

Abstract Liquid crystalline elastomers derived from siloxane polymers, PMHS and PEHS, were prepared following a two-stage reaction scheme to investigate the effects of processing conditions and thermal treatment on mesomorphic characteristics. The LC elastomer samples were analysed by FTIR, DSC, stress-strain relationship, polarized optical microscopy, and X-ray diffraction techniques. Key findings include: (1) Chain length of the precursor siloxane polymer is critical to achieving a bulk alignment via stretching during the second-stage reaction; (2) the imposed strain is also critical to achieving a monodomain nematic character, which is completely recoverable upon heating beyond the clearing temperature followed by cooling back to room temperature (i.e. thermal treatment); (3) enthalpy is stored in an elastomer freshly prepared without an imposed strain, but the imposed strain helps to release the stored enthalpy, which can be almost completely released upon thermal treatment; and (4) while the stored enthalpy does not increase order parameter (HOFA), its release through molecular relaxation contributes to an increased HOFA value.