Surface grafting of thermoresponsive microgel nanoparticles

A monolayer of thermoresponsive microgel nanoparticles, containing poly(N-isopropylacrylamide) (PNIPAM), has been anchored to the surface of silicon wafers, glass slides, polyvinylidene fluoride (PVDF) fibers, and tungsten wires using a grafting to'' approach. The behavior of the synthesized grafted layers is compared with the behavior of the PNIPAM brushes (densely end-grafted layers). The comparison demonstrates that in many aspects the microgel grafted layer is comparable to PNIPAM brushes with respect to its thermoresponsive properties. Indeed, the grafted monolayer swells and collapses reversibly at temperatures below and above the lower critical solution temperature (LCST) of PNIPAM. For the flat silicon substrate, a wettability study of the grafted layer shows an approximately 20 degrees increase in the advancing contact angle of water upon heating above the LCST of PNIPAM. Wettability data obtained for the tungsten wires indicate that the grafted microgel layer retains its ability to undergo morphological changes when exposed to external temperature variations on complex curved surfaces. Therefore, the microgel-grafted layer can be considered as a system capable of competing with the PNIPAM brushes.