Bioengineering Department, The University of Texas at Dallas, 800 W Campbell Rd, Richardson, TX 75080, USA.
Soft Matter. 2017 Jun 21;13(24):4349-4356. doi: 10.1039/c7sm00541e.
Materials that change shape are attractive candidates to replace traditional actuators for applications with power or size restrictions. In this work, we design a polymeric bilayer that changes shape in response to both heat and water by the incorporation of a water-responsive hydrophilic polymer with a heat-responsive liquid crystal elastomer. The distinct shape changes based on stimulus are controlled by the molecular order, and consequently the anisotropic modulus, of a liquid crystal elastomer. In response to water, the hydrophilic polymer layer expands, bending the bilayer along the path dictated by the anisotropic modulus of the liquid crystal elastomer layer, which is approximately 5 times higher along the molecular orientation than in perpendicular directions. We demonstrate that by varying the direction of this stiffer axis in LCE films, helical pitch of the swollen bilayer can be controlled from 0.1 to 20 mm. By spatially patterning the stiffer axis with a resolution of 900 μm, we demonstrate bilayers that fold and bend based on the pattern within the LCE. In response to heat, the liquid crystal elastomer contracts along the direction of molecular order, and when this actuation is constrained by the hydrophilic polymer, this contraction results in a 3D shape that is distinct from the shape seen in water. Furthermore, by using the vitrification of the dry hydrophilic polymer this 3D shape can be retained in the bilayer after cooling. By utilizing sequential exposure to heat and water, we can drive the initially flat bilayer to reversibly shift between 3D shapes.
具有形状变化能力的材料是替代传统执行器的有吸引力的候选材料，适用于受功率或尺寸限制的应用。在这项工作中，我们设计了一种聚合物双层结构，通过将对水响应的亲水性聚合物与对热响应的液晶弹性体结合，使其能够响应热和水来改变形状。基于刺激的独特形状变化由液晶弹性体的分子有序性控制，进而控制各向异性模量。响应水时，亲水性聚合物层膨胀，使双层沿液晶弹性体层各向异性模量决定的路径弯曲，该模量沿分子取向的方向大约是垂直方向的 5 倍。我们证明，通过改变 LCE 薄膜中这种更硬轴的方向，可以控制膨胀双层的螺旋节距从 0.1 到 20mm。通过以 900μm 的分辨率对更硬轴进行空间图案化，我们展示了基于 LCE 内图案进行折叠和弯曲的双层。响应热时，液晶弹性体沿分子有序方向收缩，当这种致动受到亲水性聚合物的限制时，这种收缩导致与在水中看到的形状不同的 3D 形状。此外，通过利用干燥亲水性聚合物的玻璃化转变，可以在冷却后将这种 3D 形状保留在双层中。通过利用热和水的顺序暴露，可以使最初平坦的双层在 3D 形状之间可逆地切换。
