Double-layer hydrogel with photoresponsive shape memory features for controllable catalysis
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Double-layer hydrogel with photoresponsive shape memory features for controllable catalysis Jinghang Leng1, Shujing Li2,a), Mingxin Yang1, Jie Hu1,b) 1
School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, People’s Republic of China Key Laboratory of Cosmetic, China National Light Industry, Beijing Technology and Business University, Beijing 100048, People’s Republic of China a) Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] 2
Received: 28 October 2018; accepted: 2 April 2019
A photoresponsive double-layer hydrogel has been developed, in which light-sensitive cinnamic moieties are grafted onto a polyacrylamide network to produce a photoresponsive layer and pure polyacrylamide formed the supporting layer. Ag nanoparticles were dispersed using in situ reduction on the photoresponsive layer to act as the catalyst. The as-fabricated hydrogel exhibits a shape memory effect and controllable catalytic behavior under an external light stimulus. When exposed to ultraviolet (UV) light at k > 260 nm, the resulting cycloaddition of cinnamic moieties not only fix the hydrogel’s temporary shape, but also greatly slow down the catalytic reaction rate. After irradiated with UV light at k < 260 nm, however, the newly formed crosslinking points are reversibly cleaved. This results in the shape recovery of the hydrogel to its permanent shape. At the same time, the catalytic reaction was greatly accelerated because of the facile diffusion of the reactants into the hydrogel.
Introduction As a class of smart materials, shape memory polymers (SMPs) are able to adopt a temporary shape and recover their “remembered” permanent shape when exposed to an external stimulus [1, 2]. Thermoresponsive SMPs have been extensively investigated over the last few decades [3]. In those materials, thermal transitions such as glass transition or melting of the polymer upon direct or indirect heating are generally responsible for their shape memory effect. Owing to their large deformability, excellent strain fixity and recovery, and versatile shape configuration, these materials have been applied or are finding applications in many fields, such as biomedicine, electronic devices, and robotics [4, 5]. Chemoresponsive SMPs, in particular, water-responsive SMPs, have also been intensively studied in recent years [6]. This type of SMP is particularly valuable in biomedical applications. In recent years, because of urgent requirements of many special applications under ambient conditions, a lot of attention has been paid to develop novel SMPs triggered by stimuli other than temperature [7, 8]. In various stimulus signals, light is particularly appealing because it allows remote and noncontact irradiation at ambient temperature, which can be
ª Materials Research Society 2019
delivered instantaneously to the stimulus-responsive system without any diffusion limitations. In addition, environmental safety and operational convenience enormously improves its potential in practic
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