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Multiplicity of shape selection in functionally graded liquid crystalline polymers

机译：功能梯度液晶聚合物中形状选择的多样性

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The synergy of through-thickness gradation in the orientation of the molecular director and the extent of polymerization is shown to offer a framework for controlling shape selection in integral polymer films. Native curvatures are realized under ambient conditions in splayed liquid crystalline polymers that are photopolymerized on anchoring surfaces, while being exposed to the atmosphere. Residual multiaxial polymerization strains drive the spontaneous assembly of a range of geometries (tape springs, helical coils and arches) in strips that are excised from the as-prepared films. Gradients in the director orientation and the cross linking through the thickness enable a temperature dependent structural evolution. Following a moderate temperature rise (<70 °C), the samples are found to intensify their native shapes. However, further temperature rise leads to a relaxation of the strains followed by an eversion of the geometry (>100 °C), which generates curvature orthogonal to that in the native state. This multiplicity in shape selection, which spontaneously emerges without requiring any mechanical training offers a useful framework for actuation and morphing. In a prototypical demonstration, a suitably excised sample is shown to spontaneously jump when placed on a hot-plate as a result of the eversion. Also, when confined in ring-like geometries, hinge-like structures are generated due to the interplay of the imposed bending strains with that existing in the native state. The evolution of the curvatures as a function of temperature offers control over the active hinge/fold and expands the multiplicity of shapes that can be realized.
机译：分子导向器方向上的全厚度渐变与聚合程度的协同作用显示出可为控制整体聚合物薄膜中的形状选择提供框架。在环境条件下，张开的液晶聚合物在暴露于大气的同时在锚定表面上进行光聚合，从而实现了自然曲率。残留的多轴聚合应变会驱动从准备好的薄膜上切下的条带中的各种几何形状（卷带弹簧，螺旋线圈和拱形）自发组装。指向矢方向上的渐变和穿过厚度的交联使温度取决于结构。在温和升高（<70°C）之后，发现样品会增强其原始形状。但是，进一步的温度升高会导致应变松弛，进而导致几何形状外翻（> 100°C），从而产生与原始状态下正交的曲率。这种形状选择的多样性，不需要任何机械训练就可以自发出现，为操纵和变形提供了有用的框架。在一个原型演示中，显示了适当切除的样本在外翻时放在加热板上会自发跳跃。而且，当限制在环形几何形状中时，由于施加的弯曲应变与原始状态下存在的弯曲应变之间的相互作用而产生铰链状结构。曲率作为温度的函数的演变提供了对活动铰链/折叠的控制，并扩展了可以实现的多种形状。

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