Strain-induced reorientation and mobility in nematic liquid-crystalline elastomers as studied by time-resolved FTIR spectroscopy

Abstract

Polarized Fourier transform infrared (FTIR) spectroscopy is employed to study the segmental orientation and mobility of liquid-crystalline elastomers (LCEs) with a monodomain structure in response to external mechanical fields parallel and perpendicular to the initial nematic director. The mean orientation and the molecular order parameter of the different molecular moieties referring to the mesogen, the spacer and the network are analyzed in detail. Parallel stretch leaves the mean orientation of the different molecular moieties and its molecular order parameter nearly uninfluenced. Perpendicular stretch results in a threshold-like dependence: for elongation ratios lambda < or = lambda(c) = 1.3 (10 mol% crosslinker density), respectively lambda < or = lambda(c) = 1.6 (5 mol% crosslinker density) no change of the mean orientation and the molecular order parameters is observed, while for lambda > or = lambda(c) all molecular units reorient and their molecular order parameters are strongly decreased. The present studies give no indications that the reorientational dynamics of the network and the mesogens differ as long as the elongation ratio is smaller than lambda(c).

Effect of the degree of soft and hard segment ordering on the morphology and mechanical behavior of semicrystalline segmented polyurethanes

“…Even relatively low strains would be expected to induce straininduced soft segment crystallization, but the low melt temperature also implies relatively high mobility of the soft segment chains, thus crystallites may be formed and deformed simultaneously throughout the deformation process. This form of transient, reformable order may play a role in toughening of the polymer matrix, much as is observed in a number of naturally occurring materials and as liquid crystalline order might be observed to do in other systems [54]. In fact, PU-2-41 displays superior ultimate mechanical properties compared to the PEO-PPO-PEO systems.…”

Development of bio-based thermoplastic polyurethanes formulations using corn-derived chain extender for reactive rotational molding

“…Even relatively low strains would be expected to induce strain-induced SS crystallization, but the low melting temperature also implies relatively high mobility of the SS chains, thus crystallites may be formed and deformed simultaneously throughout the deformation process. This form of transient, reformable order may play a role in toughening of the polymer matrix, much as observed in a number of naturally occurring materials [25]. The properties of the prepared TPU samples are comparatively lower to those of PUs obtained from prepolymer-based polymerization in solution, which make 'one-shot' technique applicability limited [24].…”

FTIR spectroscopy of smectic elastomer films under lateral strain

“…Liquid crystal elastomers (LCEs) have become an important object of experimental and theoretical investigations due to their unusual physical properties [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. This class of material combines the rubber elasticity of polymers with the anisotropic properties of liquid crystals.…”

“…It allows the study of the molecular structure of soft materials in response to external forces such as electromagnetic field [14,15,19,20] and mechanical strain [16,21]. The main goal of this article is to explain the molecular mechanisms of the strain-induced compression of smectic layers in oriented smectic LCE samples by polarized FTIR spectroscopy.…”