2014/09/18 by Sonal Dey, Dey, Sonal
Engineering · Materials Science · Physics and Astronomy · #Advanced Materials and Mechanics #FOS: Physical sciences #Liquid Crystal Research Advancements #Materials Science (cond-mat.mtrl-sci) #Polymer composites and self-healing #Soft Condensed Matter (cond-mat.soft) #cond-mat.mtrl-sci #cond-mat.soft
paper · pdf · doi:10.48550/arxiv.1409.5190
23 pages, 16 figures
arxiv created 2014/09/18 · openalex publication_date 2014/09/18 · arxiv updated 2014/09/19 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Structural studies by synchrotron x-ray diffraction on two main-chain smectic-C elastomers reveal the presence of two different relaxation mechanisms in these systems at low and high strains. At low strains, the smectic layers are reoriented with layer-normals distributed in a plane perpendicular to the stretch direction. The system relaxes relatively slowly (time-constant ~ 45 minutes) which is attributed to the flow properties of the LC layers embedded in the elastomer network. At high strains, the equilibration time (~ 4 - 8 minutes) conforms to a faster relaxation and appears to have its origin in the polymer components of the system. Due to misaligned microdomains at small strains, the value of global orientational order parameter S for the mesogenic parts is initially small (~ 0.15). With increasing strain, the local domain-directors, the mesogens, and the polymer chains, all tend to align parallel to the stretch direction giving rise to a higher measured value of S ~ 0.83 at a strain of 4.0. The siloxane segments remain less ordered, attaining a value of S ~ 0.4 for a strain of 4.0. The layers gradually become oblique to the stretch direction conforming to the structural property of the smectic-C phase. The system finally assumes a chevron-like optically monodomain structure. Both elastomers are locked-in this state even after removal of the external stress giving rise to strain retention and the shape memory effect. The presence of a transverse component in the main-chain leads to higher strain retention in the second elastomer. A preference for the orientation of the smectic layer-normals toward the stretch direction persists after removal of external stress. Upon thermal annealing, the chevron-like microstructure gradually melts via a different path to the initial polydomain structure.