We have developed a new experimental methodology to investigate the adhesive properties of hydrogels on solid surfaces under fully immersed conditions. The method, based on contact mechanics, provides time-resolved reproducible and quantitative data on the work of adhesion between a hydrogel at swelling equilibrium and a planar surface grafted with responsive brushes. We used poly(N,Ndimethylacrylamide) (PDMA) and polyacrylamide (PAM) as model gels and poly(acrylic acid) (PAA) as pH dependent polymer brush. The effect of pH, contact time and debonding velocity on adhesive interactions was specifically investigated. As expected from molecular interactions, we found that adhesion increased as the pH decreased and this was attributed to the formation of hydrogen bonds at the interface. Surprisingly, however, the buildup of adhesion increased slowly with the time of contact up to one hour and depended markedly on debonding velocity despite the very elastic nature of the hydrogels. Furthermore, the maximum pH where adhesion was observed was significantly higher for the couple PAM-PAA than for the couple PDMA-PAA, in contrast with the onset of molecular interactions in dilute solutions.

We report on an experimental and theoretical study of the high-frequency mixing properties of ion-irradiated YBa 2 Cu 3 O 7 Josephson junctions embedded in THz antennas. We investigated the influence of the local oscillator power and frequency on the device performances. The experimental data are compared with theoretical predictions of the general three-port model for mixers in which the junction is described by the resistively shunted junction model. A good agreement is obtained for the conversion efficiency in different frequency ranges, spanning above and below the characteristic frequencies f c of the junctions. V C 2014 AIP Publishing LLC.