Effect of stretching angle on the stress plateau behavior of main-chain liquid crystal elastomers

The equilibrium nonlinear stress-stretch relationships for a monodomain main-chain nematic elastomer (MNE) are investigated by varying the angle between the stretching and initial director axes (theta (0)). Angle theta (0) has pronounced effects on the ultimate elongation as well as on the width of the low stress plateau regime (Lambda (p)) during director rotation, whereas theta (0) has no appreciable effect on the plateau stress (sigma (p)). In the stretching normal to the initial director (theta (0) = 90 degrees), the plateau end exceeds 200% strain. At oblique angles of 90 degrees > theta (0) >= 35 degrees, Lambda (p) decreases with decreasing theta (0), whereas the definite plateau regime vanishes at theta (0) < 24. Wide-angle X-ray scattering and polarized optical microscopy measurements reveal that the director rotates uniformly in the biased direction for the MNE of theta (0)degrees << 90 degrees, whereas directors rotating clockwise and counterclockwise are coexistent for theta (0) = 90 degrees. Over the entire plateau regime, the MNEs exhibit pure shear deformation characterized by a Poisson's ratio of zero in the direction of the rotation axis. The Lambda (p) for the corresponding polydomain NE (PNE) undergoing a transition to the monodomain alignment is smaller than that of the MNE of theta (0) = 90 degrees, while the sigma (p) values for both NEs are almost similar. The semi-soft elasticity concept satisfactorily explains the effects of theta (0) on Lambda (p), and the Lambda (p) value of the PNE, using a single anisotropy parameter which is evaluated from the degree of thermally induced deformation of MNEs.

Automated summary

The study investigates the effects of angle theta (0) on the stress-stretch relationships of a monodomain main-chain nematic elastomer (MNE). The results show that theta (0) significantly impacts the ultimate elongation and width of the low stress plateau regime, while having minimal effect on the plateau stress. Additionally, the rotation behavior of the director in MNE varies with theta (0), with different deformation characteristics observed at different angles.