Effect of Stretching Angle on Stress Plateau Behavior of Main-Chain Liquid Crystal Elastomers
Effect of Stretching Angle on Stress Plateau Behavior of Main-Chain Liquid Crystal Elastomers
复制标题
拉伸角度对主链液晶弹性体应力平台行为的影响
作者：
Okamoto;S.;Sakurai;S.;Urayama;K.
通过改变拉伸轴与初始指向矢轴之间的夹角θ0，研究了单畴主链双相弹性体（MNE）的平衡非线性应力-拉伸关系。在指向矢旋转过程中，角度θ0对极限延伸率和低应力平台区宽度（Λp）有显著影响，而θ0对平台应力（σp）没有明显影响。在垂直于初始指向矢（θ0 = 90°）的拉伸中，平台端超过200%应变。当倾角为90° > θ0 ≥ 35°时，Λp随θ0的减小而减小，而当θ0 < 24°时，稳定平台区消失。广角X射线散射和偏光显微镜测量表明，当MNE为θ0° <$90 °时，指向矢沿偏置方向均匀旋转，而当θ0 = 90°时，指向矢顺时针和逆时针旋转共存。在整个平台制度，MNE表现出纯剪切变形的特点是泊松比为零的旋转轴的方向。对应的多畴NE（PNE）经历向单畴取向的转变的Λp小于θ0 = 90°的MNE的Λ p，而两个内斯的σp值几乎相似。半软弹性概念满意地解释了θ0对Λp的影响，以及PNE的Λp值，使用单个各向异性参数，该参数由MNE的热致变形程度来评估。
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 (θ0). Angle θ0 has pronounced effects on the ultimate elongation as well as on the width of the low stress plateau regime (Λp) during director rotation, whereas θ0 has no appreciable effect on the plateau stress (σp). In the stretching normal to the initial director (θ0 = 90°), the plateau end exceeds 200% strain. At oblique angles of 90° > θ0 ≥ 35°, Λp decreases with decreasing θ0, whereas the definite plateau regime vanishes at θ0 < 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 θ0° ≪ 90°, whereas directors rotating clockwise and counterclockwise are coexistent for θ0 = 90°. 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 Λp for the corresponding polydomain NE (PNE) undergoing a transition to the monodomain alignment is smaller than that of the MNE of θ0 = 90°, while the σp values for both NEs are almost similar. The semi-soft elasticity concept satisfactorily explains the effects of θ0 on Λp, and the Λp value of the PNE, using a single anisotropy parameter which is evaluated from the degree of thermally induced deformation of MNEs.