We report on the formation of hydrogel layers on conducting substrates via a simple electrochemical route. Free-radical polymerization is initiated by an electron transfer from the substrate to a redox-active initiator. Gels of the thermally responsive material poly-N-isopropylacrylamide (p-NIPAM) with a thickness between 25 and 250 nm were produced and characterized. The gels adhere well to the substrate. They show the characteristic swelling transition at 32 degrees C. Although the films appear homogeneous in optical microscopy, AFM images reveal a slightly heterogeneous, globular structure. The gels are permeable to small ions as evidenced by electrochemical experiments with gel-covered electrodes.

Quartz-crystal resonators were coated with a layer of alumina nanopores in order to allow for simultaneous measurement of density and viscosity of a liquid. Whereas the motion of the liquid contained in the pores is locked to the movement of the crystal, the liquid located above the surface experiences internal shear. The latter portion of the liquid dissipates energy, thereby increasing the bandwidth of the resonance. Based on the increase in bandwidth, viscous loading and mass loading can be distinguished, allowing for an independent determination of the density and the viscosity of Newtonian liquids.