English Abstract

In situ Measurements for Understanding Actuation Mechanism of Polymer Fiber Actuators

Graduate School of Science and Technology, Gunma University, Kiryu, Gunma, Japan
Nippon Gomu Kyokaishi,(2023),96(5),119-125 General Review in Japanese

One possible choice for soft actuator is polymeric actuator composed of twisted fishing line. An actuator composed of twisted linear low-density polyethylene (LLDPE) exhibits reversible extension and shrinkage induced by changes in temperature. It has been assumed that the origin of this actuation is attributed to the tie molecules bridging crystalline lamellae. In this study, a combination of in situ X-ray and NMR measurements are adopted for evaluation of the role of tie molecules on stretching and shrinking of drawn LLDPE film. In situ small-angle X-ray scattering (SAXS) measurements indicate that crystalline lamellae stack perpendicular to the stretching direction for the stretched state; however, they tilt for the shrunk state. In situ pulse NMR measurements confirm that the intermediate components attributed to tie molecules bridging crystalline lamellae are mainly stretched and shrunk, reflecting the resultant stress response. Macroscopic strain change of the sample film agrees with microscopic tie-molecular stretching and shrinking, which dominates the actuating behavior of the drawn LLDPE film. Structural changes on heating correspond to those on shrinking, indicating that temperature actuation is also driven by stretching and shrinking of tie molecules. Such obtained results predict the mechanism of actuation of drawn LLDPE.

Keywords: Actuation, Tie Molecules, Linear Low-density Polyethylene (LLDPE), Drawing, Cyclic Stretching/ Shrinking, In situ Measurements, X-ray, NMR