Static and dynamic behaviour of responsive graphene oxide-poly(N-isopropyl acrylamide) composite gels.

Thermoresponsive hydrogels have enormous potential e.g., as sensors, actuators, and pollution control remedies or in drug delivery systems. Nevertheless, their application is often restricted by physical limitations (poor mechanical strength and uncontrolled thermal response). Composite systems may offer a means of overcoming these limitations. This paper presents a systematic study of the structure and dynamics of graphene oxide-poly-(N-isopropylacrylamide) composite systems, and investigates the effect of the nanoparticle filler content on the mechanical and swelling properties of the systems. A combination of macroscopic (swelling and elastic modulus) and microscopic (differential scanning microcalorimetry, small angle neutron scattering and neutron spin-echo spectroscopy) investigations reveals that the architecture of the polymer network is modified by chain nucleation at the surface of the GO platelets, and these form a percolating network inside the gel. Our results show that the elastic modulus of the gels is reinforced by the filler, but the mobility of the polymer chains in the swollen state is practically unaffected. The macroscopic deswelling of the composites, however, is slowed by the kinetics of ordering in the GO network.