Pre-Stretched Double Network Polymer Films Based on Agarose and Polyacrylamide with Sensitive Humidity-Responsive Deformation, Shape Memory, and Self-Healing Properties

A series of pre-stretched double network (DN) polymer films based on agarose and polyacrylamide (Agar/PAM) are prepared. These films show the rapid and large deformation in response to humidity due to the release of contraction stress. The pre-stretched dry film can curl toward the humidity direction into a scroll-like structure in an extremely short time. The deformation direction can be also well controlled by the stretching direction. The released contraction stress increases with the increase of tensile strain. The DN Agar/PAM hydrogel film shows good water-induced shape memory effect. It can be stretched to form various temporary shapes such as circle, square, and spiral. The shape fixing and recovery ratios are both close to 100%. The released large contraction stress accelerates the shape recovery process. The recovery time increases with the increase of film thickness. The DN dry film shows the good water-induced self-healing ability. The healed film maintains about 88% tensile strength (103 MPa) of the original film. Due to these good properties, the pre-stretched DN dry films can be fabricated into a soft robot jack which can easily lift up to approximate to 20 times its own weight within 8 s.