FTIR‐Spectroscopy on Segmental Reorientation of a Nematic Elastomer under External Mechanical Fields

Abstract

Summary: Fourier transform infrared (FTIR) spectroscopy with polarized light is employed to study the segmental orientation and the order of a nematic liquid crystalline elastomers (NLCEs) with a monodomain structure in response to an external mechanical field. The reorientation and the order parameter of the different molecular moieties are analyzed in detail, revealing information about angular excursion in the rearrangement of the mesogens, the spacer molecules, and the main‐chain. In case of an elongation of the NLCE films perpendicular to the initial mesogen orientation, no reorientation or change of order is observed for an elongation ratio less than 1.3. At higher strain, a molecular reorientation process is induced on all molecular segments and the order of alignment is decreased. When the NLCE‐films are stretched parallel to the mesogens, no molecular reorientation takes place and the order parameters show no significant change.Angular reorientation of different molecular moieties at mechanical strain perpendicular to the initial mesogen orientation.magnified imageAngular reorientation of different molecular moieties at mechanical strain perpendicular to the initial mesogen orientation.

Photomechanics of Liquid‐Crystalline Elastomers and Other Polymers

“…The advantage of this method is that the induced network anisotropy in the first step is reproducible, so that wellaligned elastomers are obtained. LCEs with various LC phases, such as nematic, [97,98] cholesteric, [99][100][101] smectic, [102][103][104][105][106][107][108][109][110] and discotic, [111] were prepared by polymerization of various LC monomers containing more than one polymerizable group. [96] Broer et al developed the one-step method to prepare highly oriented LC side-chain polymers, namely, the in situ photopolymerization of macroscopically aligned LC monomers.…”

Effect of external electric field on morphologies and properties of the cured epoxy and epoxy/acrylate systems

“…There are many methods to achieve uniform orientation or alignment in polymeric materials, such as mechanical, magnetic, and electric fields. To achieve large‐scale alignment throughout a macroscopically extended bulk sample, most prominently, external mechanical fields have been successfully applied to orient some polymers 6–9. However, these technologies susceptibly lead to an inhomogeneous microstructure observable as a characteristic striped pattern of the direction orientation 10.…”

Effects of structural imperfections on the dynamic mechanical response of main‐chain smectic elastomers

“…LCE therefore exhibit strong deviations from ordinary rubber elasticity, leading to striking physical phenomena such as the polydomain-to-monodomain (P-M) transition [3][4][5][6][7] and the shape changes and director reorientations observed in globally oriented ''monodomain'' samples. [8][9][10][11][12][13][14][15][16][17][18][19][20] The physical factors governing the dynamic mechanical response of LCE are of primary fundamental interest, as it is exceptional mechanical behavior that distinguishes LCE from all other elastomers.…”