Abstract
Conductive hydrogels with stretchable, flexible and wearable properties have made significant contributions in the area of modern electronics. The polyacrylamide/alginate hydrogels are one of the potential emerging materials for application in a diverse range of fields because of their high stretch and toughness. However, most researchers focus on the investigation of their mechanical and swelling behaviors, and the adhesion and effects of the ionic liquids on the conductivities of polyacrylamide/alginate hydrogels are much less explored. Herein, methacrylated lysine and different alkyl chain substituted imidazole-based monomers (IMCx, x = 2, 4, 6 and 8) were introduced to prepare a series of novel pAMAL-IMCx-Ca hydrogels. We systematically investigated their macroscopic and microscopic properties through tensile tests, electrochemical impedance spectra and scanning electron microscopy, as well as Fourier transform infrared spectroscopy, and demonstrated that an alkyl chain length of the IMCx plays an important role in the designing of hydrogel strain sensors. The experiment result shows that the hexyl chains of IMC6 can effectively entangle with LysMA through hydrophobic and electrostatic interactions, which significantly enhance the mechanical strength of the hydrogels. Furthermore, the different strain rates and the durability of the pAMAL-IMC6-Ca hydrogel were investigated and the relative resistance responses remain almost the same in both conditions, making it a potential candidate for wearable strain sensors.
Highlights
Stretchable, flexible, wearable and environmentally friendly electronic devices are of great significance to meet the increasing demands for versatility and complexity of modern electronics [1,2,3,4,5,6,7,8]
From the electron microscopic study, Fourier transform infrared spectroscopy (FTIR), mechanical and electrochemical investigations of pAMAL-IMCxCa hydrogels, we demonstrated that pAMAL-IMC6-Ca displayed the optimal performance, which could be attributed to the balance between electrostatic interaction, metal-ligand coordination and hydrogen bonding interaction, as well as hydrophobic interaction
We found that the pAMAL-IMC6-Ca hydrogel displayed lower swelling ratio than that of the pAMAL-Ca (51% and 364%, respectively), while the other 4 hydrogels collapsed after being soaked in water for 5 days
Summary
Stretchable, flexible, wearable and environmentally friendly electronic devices are of great significance to meet the increasing demands for versatility and complexity of modern electronics [1,2,3,4,5,6,7,8]. A hydrogel strain sensor provides a feasible solution for wearable devices, because of its super extensibility and high flexibility, and because of its good biocompatibility [25,26,27,28]. The polyacrylamide/alginate-based hydrogels have been studied by many researchers because of their tunable mechanical properties and biocompatibility [29,30,31,32,33]. Suo and co-workers established the first example of double-network hydrogel with high stretch and toughness based on polyacrylamide/Ca-alginate, opening new application areas for this class of materials [29]. Suo and Vlassak combined short- and long-chain alginates to reduce the viscosity of pregel solutions and successfully demonstrated that polyacrylamide/alginate hydrogels can simultaneously have high stiffness and toughness [32]. Many research efforts are focused on the investigation of the mechanical behaviors and/or the swelling characteristics, the adhesion properties [34,35], and the effects of the ionic liquids on the conductivities of polyacrylamide/alginate-based hydrogels are much less explored
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