Wetting of mesoscopic soft cylinders: Structure and layering transitions

The wetting of soft mesoscopic long-chain particles is studied. As a model system, a cylindrical brush with poly(vinyl)pyridine side chains on the wat er surface is characterized by isotherms and x-ray reflectivity. The forces from the two planar interfaces and the intra- and interparticle interactio ns are all of comparable magnitude. Two layering transitions occur, one fro nt the monolayer to the double layer the next to a homogeneous multilayer. The hard wad hom which layering starts is the smooth polymer/air interface. indeed, they particles in the top layer of both the double- and the multil ayer have their cylinder axis parallel to the surface and are laterally com pressed. In contrast, the polymer/water interface is diffuse due to brush s welling. Generally, the long-chain particles adjacent to the respective int erfaces do not maintain their circular diameters. The thickness of the mono layer can be varied by a factor 3.5, up to 53 Angstrom. An additional phase transition occurs within the monolayer, which is attributed to a change of the side chains from a flattened to a compressed state at constant volume. Atmoic force microscope images of the monolayer transferred onto a solid i ndicate local cylinder alignment. [S1063-651X(99)03710-1].