MSE Seminar Series: Anselm Griffin
Friday, November 4, 2011
Room 2110 Chemical and Nuclear Engineering Bldg.
301 405 5240
Toward Shape Memory in Liquid Crystalline Elastomers
School of Materials Science & Engineering
Georgia Institute of Technology
As part of an ongoing program aimed at understanding shape and memory in liquid crystalline elastomers (LCEs), we have synthesized and examined a series of SmC main-chain LCEs. Uniaxial stretching of these polydomain films at room temperature produces a monodomain structure that can, upon removal of load, retain a significant level of strain. Although these films show ordinary elastic response at temperatures near the isotropization (clearing) temperature, at room temperature far below the clearing temperature the mechanical response is anelastic. Results from x-ray scattering, stress-strain experiments, and Poissons ratio measurements will be presented along with the temperature profile of the shape recovery process.
A rationale for the observed shape memory behavior is proposed that involves moving of crosslink points in the smectic lamellar arrangement during the stretching event and trapping of these crosslinks in different positions at low temperatures. This trapping is driven by the chemical segregation of the crosslink points from the mesogenic unit which can be thermally overcome at elevated temperatures allowing full elastic recovery.