Swelling and electroresponsive characteristics of gelatin immobilized onto multi-walled carbon nanotubes

We prepared multi-walled carbon nanotube (MWNT)/gelatin composites by dispersion of MWNT through ultrasonication in an aqueous medium with anionic surfactant sodium dodecyl sulfate (SDS). The swelling behavior and the bending mechanism of the composite and pure gelatin films were studied in order to clarify the potential use of MWNT in the gelatin actuator. The response of the composite and pure hydrogel to the applied electrical field in the NaCl aqueous solution was investigated. Both the composite and pure hydrogel showed a two-stage bending phenomenon, an early bending towards the anode and a later bending towards the cathode. We investigated the mechanism of this bending phenomenon based on osmotic pressure difference at the inter-phase between the hydrogel film and salt solution. The swelling behavior of the composite was studied by immersion of the vacuum-dried samples into a 0.1 M NaCl aqueous solution at room temperature. The incorporation of MWNT gradually decreased the swelling of the hydrogel and exerted no effect on the swelling mechanism, which followed the second order kinetic. Both the bound and unbound water contents (measured from DSC) decreased with the addition of MWNT. This phenomenon might be due to the hydrophobic effect of the MWNT and increase in crosslinking density between the MWNTs and gelatin by increasing the MWNT concentration.