We report on a comprehensive study of the unique adhesive properties of mats of polymethylmethacrylate (PMMA) nanofibers produced by electrospinning. Fibers are deposited on glass, varying the diameter and the relative orientation of the polymer fila
ments (random vs aligned configuration). While no significant variation is observed in the static contact angle (about 130{deg}) of deposited water drops upon changing the average fiber diameter up to the micrometer scale, fibers are found to exhibit unequalled water adhesion. Placed vertically, they can hold up water drops as large as 60 microL, more than twice the values typically obtained with hairy surfaces prepared by different methods. For aligned fibers with anisotropic wetting behavior, the maximum volume measured in the direction perpendicular to the fibers goes up to 90 {mu}L. This work suggests new routes to tailor the wetting behavior on extended areas by nanofiber coatings, with possible applications in adsorbing and catalytic surfaces, microfluidic devices, and filtration technologies.
The nanofriction of Xe monolayers deposited on graphene was explored with a quartz crystal microbalance (QCM) at temperatures between 25 and 50 K. Graphene was grown by chemical vapor deposition and transferred to the QCM electrodes with a polymer st
amp. At low temperatures, the Xe monolayers are fully pinned to the graphene surface. Above 30 K, the Xe film slides and the depinning onset coverage beyond which the film starts sliding decreases with temperature. Similar measurements repeated on bare gold show an enhanced slippage of the Xe films and a decrease of the depinning temperature below 25 K. Nanofriction measurements of krypton and nitrogen confirm this scenario.This thermolubric behavior is explained in terms of a recent theory of the size dependence of static friction between adsorbed islands and crystalline substrates.
G. Brambilla et al. Reply to a Comment by J. Reinhardt et al. questioning the existence of equilibrium dynamics above the critical volume fraction of colloidal hard spheres predicted by mode coupling theory.
The phase behavior of membrane proteins stems from a complex synergy with the amphiphilic molecules required for their solubilization. We show that ionization of a pH-sensitive surfactant, LDAO, bound to a bacterial photosynthetic protein, the Reacti
on Center (RC), leads in a narrow pH range to protein liquid-liquid phase separation in surprisingly stable `droplets, forerunning reversible aggregation at lower pH. Phase segregation is promoted by increasing temperature and hindered by adding salt. RC light-absorption and photoinduced electron cycle are moreover strongly affected by phase segregation.
