Chemical Engineering Department, University of Pittsburgh, Pittsburgh, PA 15261, USA.
Department of Materials Science and Engineering, Clemson University, Clemson, SC 29634, USA.
Soft Matter. 2016 Nov 16;12(45):9170-9184. doi: 10.1039/c6sm02006b.
Using computational modeling, we design a composite that encompasses a thermo-responsive gel and photo-responsive fibers that extend from the surface of the gel. By simulating the effect of light and heat on the sample, we isolate scenarios where cooperative interactions within the system allow the gel to actuate the "finger-like" motion of the embedded fibers. To achieve this distinctive behavior, we consider a gel formed from poly(N-isopropylacrylamide) (PNIPAAm), which shrinks when heated above the lower critical solution temperature (LCST). The fibers are functionalized with spirobenzopyran (SP) chromophores that extend a finite region into the polymer network. The application of heat causes the entire gel to shrink, while the application of light causes the regions around the functionalized fibers to collapse. With the fibers arranged in a square or circular pattern in the center of the gel, heating the non-illuminated samples drives the fibers to move apart as they bend outward (away from the center). With the application of light, the tips of fibers come together as the fibers bend inward. In this configuration, the fibers could act as grippers that bind objects in the presence of light. With the illumination turned off, the grippers could controllably release the objects. By placing the fibers closer to the edge of the sample, the combination of heat and light could be harnessed to bind and release larger objects. We also show that by illuminating the fibers separately, we can manipulate the motion of the individual finger-like objects, and thus, potentially expand the utility of the system. Overall, our findings provide guidelines for controllably reconfiguring the shape of soft materials and thus, tailoring the material to display different functionalities in different environments.
通过计算建模，我们设计了一种复合材料，其中包含一个热敏凝胶和从凝胶表面延伸出来的光响应纤维。通过模拟光和热对样品的影响，我们分离出系统内部协同作用允许凝胶驱动嵌入纤维的“指状”运动的情况。为了实现这种独特的行为，我们考虑了由聚 N-异丙基丙烯酰胺（PNIPAAm）形成的凝胶，当加热到低于临界溶液温度（LCST）以上时，凝胶会收缩。纤维用螺苯并吡喃（SP）发色团官能化，发色团将有限的区域延伸到聚合物网络中。加热会导致整个凝胶收缩，而光照会导致功能化纤维周围的区域坍塌。当纤维以正方形或圆形图案排列在凝胶中心时，加热未被照亮的样品会导致纤维在向外弯曲（远离中心）时彼此分开。当应用光时，纤维的尖端会在纤维向内弯曲时聚集在一起。在这种配置中，纤维可以作为在光存在下固定物体的夹具。当关闭照明时，夹具可以控制地释放物体。通过将纤维放置在样品边缘附近，可以利用热和光的组合来固定和释放更大的物体。我们还表明，通过分别照亮纤维，我们可以操纵单个指状物体的运动，从而有可能扩展系统的用途。总的来说，我们的研究结果为可控地重新配置软材料的形状提供了指导，从而使材料能够在不同环境中显示不同的功能。
