Synchronous Generation of Nano- and Microscaled Hierarchical Porous Polyelectrolyte Multilayers for Superwettable Surfaces

We created both a superhydrophilic polymer surface and a superhydrophobic surface by using the poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) multilayers with the synchronously generated hierarchical porous surface structures. The formation of surface and pore structures induced at acidic pH values is subject to the composition, distribution, and molecular weights of polyelectrolytes in the layer-by-layer (LbL) assembled film, leading to a variety of unique surface topographies and porous structures located on different scales. During the porous induction at pH 2.0, both nano- and microscaled features synchronously developed on the surface as a result of the unique combination of high-molecular-weight PAH (900K g/mol) and low molecular weight PAA (151( g/mol), along with a much reduced deposition time of 1 min. Although thermally cross-linked, the porous surface with hierarchical structure could achieve superhydrophilicity due to the remaining free amine and carboxylate groups on the porous structures. A complete switch from the superhydrophilic to the superhydrophobic surface was achieved via a simple chemical vapor deposition of trichloro(1H,1H,2H,2H-perfluoro-octyl)silane. In this work, the effects of molecular weight of polyelectrolytes (15K-900K g/mol), deposition time (10-900 s) during the LbL assembly, and pH (1.8 to 2.4) for the porous induction on the surface topography, pore structures, and wetting behavior were investigated in detail. A variety of unique porous surface structures on different length scales were systematically studied by controlling the above parameters.