Abstract
Abstract Electroactive hydrogels have received increasing attention due to the possibility of being used in biomimetics, such as for soft robotics and artificial muscles. However, the applications are hindered by the poor mechanical properties and slow response time. To address these issues, in this study, supramolecular ionic polymer–carbon nanotube (SIPC) composite hydrogels were fabricated via in situ free radical polymerization. The polymer matrix consisted of carbon nanotubes (CNTs), styrene sulfonic sodium (SSNa), β-cyclodextrin (β-CD)-grafted acrylamide, and ferrocene (Fc)-grafted acrylamide, with the incorporation of SSNa serving as the ionic source. On applying an external voltage, the ions accumulate on one side of the matrix, leading to localized swelling and bending of the structure. Therefore, a controllable and reversible actuation can be achieved by changing the applied voltage. The tensile strength of the SIPC was improved by over 300%, from 12 to 49 kPa, due to the reinforcement effect of the CNTs and the supramolecular host–guest interactions between the β-CD and Fc moieties. The inclusion of CNTs not only improved the tensile properties but also enhanced the ion mobility, which lead to a faster electromechanical response. The presented electro-responsive composite hydrogel shows a high potential for the development of robotic devices and soft smart components for sensing and actuating applications.
Highlights
Hydrogels with smart functionalities, such as self-healing [1] and stimuli-responsive properties [2,3,4], have drawn wide research attention in a variety of applications, including therapeutics [5,6], robotics [7,8], and sensors [9]
Vinyl-functionalized single-wall carbon nanotubes (V-single-walled carbon nanotubes (SWCNTs)) (Figure 1), β-CD-grafted acrylamide (β-CD-AAM), and Fc-grafted acrylamide (FcAAM) were the starting materials for the fabrication of the supramolecular ionic polymer–carbon nanotube (SIPC), which were synthesized according to the literature [43,44]
The SWCNTs are covalently attached to the polymer backbones
Summary
Hydrogels with smart functionalities, such as self-healing [1] and stimuli-responsive properties [2,3,4], have drawn wide research attention in a variety of applications, including therapeutics [5,6], robotics [7,8], and sensors [9]. Reports have indicated that the mechanical strength and electro-response characteristics of EAHs could be improved by adding electro-active components, such as graphene [24] and multi-walled carbon nanotubes (MWCNTs) [25], to the polymer matrix. Some research studies have been carried out to fabricate the actuating materials based on the supramolecular assembly of two individual hydrogels containing a β-cyclodextrin (β-CD) host and ferrocene (Fc) guest moieties [38,39] This bilayer strip has shown a reversible bending behavior in response to a temperature change. The influence of the supramolecular and carbon nanotube concentration on the structure, swelling behavior, thermal degradation, and mechanical properties and electromechanical performance of the composite hydrogels were investigated. The electromechanical response time was reduced with the addition of the CNTs
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