Supramolecular Interaction Controlled Diffusion Mechanism and Improved Mechanical Behavior of Hybrid Hydrogel Systems of Zwitterions and CNT

Hybrid hydrogels of poly(N-isopropylacrylamide) (pNIPAM) containing carboxylate carbon nanotubes (CNTs) and/or zwitterions are synthesized by free radical polymerization. The supramolecular interactions among zwitterionic monomers and CNTs influence the mechanical properties and diffusion mechanism in hybrid hydrogel systems. These supramolecular interactions and response behavior of hybrid hydrogels were tested mechanically and with respect to their swelling characteristics. Hybrid hydrogels of pNIPAM and CNT or pNIPAM, zwitterions, and CNT follow a Fickian diffusion behavior, while adding zwitterions leads to an anomalous triple-stage swelling behavior and stiffening of the gel due to the interactions of the zwitterions with each other, which significantly increase the viscous dissipation and change the microscopic structure. While CNT itself stiffens the gel and slightly increases the diffusion speed, it complexes zwitterions, which leads to a novel property profile that is both potentially antibiotic and electrically conductive. CNT affords a relaxation process at long relaxation times, while zwitterion attachment and detachment lead to dissipation predominantly at high frequencies. Dynamic rheological measurements were performed during swelling of these complex materials.