College of Engineering, College of Family and Consumer Sciences, University of Georgia , Athens, Georgia 30602, United States.
Leibniz-Institut für Polymerforschung Dresden e.V. , Hohe Str. 6, 01069 Dresden, Germany.
ACS Appl Mater Interfaces. 2017 Feb 8;9(5):4873-4881. doi: 10.1021/acsami.6b13084. Epub 2016 Dec 19.
It is commonly assumed that the substantial element of reversibly actuating soft polymeric materials is chemical cross-linking, which is needed to provide elasticity required for the reversible actuation. On the example of melt spun and three-dimensional printed Janus fibers, we demonstrate here for the first time that cross-linking is not an obligatory prerequisite for reversible actuation of solid entangled polymers, since the entanglement network itself can build elasticity during crystallization. Indeed, we show that not-cross-linked polymers, which typically demonstrate plastic deformation in melt, possess enough elastic behavior to actuate reversibly. The Janus polymeric structure bends because of contraction of the polymer and due to entanglements and formation of nanocrystallites upon cooling. Actuation upon melting is simply due to relaxation of the stressed nonfusible component. This approach opens perspectives for design of solid active materials and actuator for robotics, biotechnology, and smart textile applications. The great advantage of our principle is that it allows design of non-cross-linked self-moving materials, which are able to actuate in both water and air, which are not cross-linked. We demonstrate application of actuating fibers for design of walkers, structures with switchable length, width, and thickness, which can be used for smart textile applications.
人们通常认为，可反复驱动的软聚合物材料的主要成分是化学交联，这是提供可反复驱动所需的弹性所必需的。我们以熔融纺丝和三维打印的 Janus 纤维为例，首次证明交联不是固态缠结聚合物可反复驱动的必要前提，因为缠结网络本身可以在结晶过程中形成弹性。事实上，我们表明，通常在熔体中表现出塑性变形的非交联聚合物具有足够的弹性行为，可以进行可反复的驱动。Janus 聚合物结构会弯曲，这是由于聚合物的收缩以及冷却时缠结和纳米晶的形成。在熔融时的驱动仅仅是由于不可熔成分的应力松弛。这种方法为设计用于机器人技术、生物技术和智能纺织品应用的固态活性材料和致动器开辟了前景。我们的原理的一个巨大优势是，它允许设计非交联的自移动材料，这些材料能够在水和空气中进行驱动，而无需交联。我们演示了驱动纤维在设计步行机、长度、宽度和厚度可切换的结构中的应用，这些结构可用于智能纺织品应用。
