Fabrication of highly ordered microporous thin films by PS-b-PAA self-assembly and investigation of their tunable surface properties

A facile approach is presented to fabricate three-dimensional ordered microporous thin films by self-assembly via an amphiphilic block polymer, polystryene-b-polyacrylic acid (PS-b-PAA). The highly ordered microporous thin films were formed by casting a PS-b-PAA tetrahydrofuran (THF) solution onto a glass slide under high humidity conditions. The condensed water droplets act as sacrificial templates on the air - polymer solution interface based on thermocapillary convection. Some critical influencing factors, such as the concentration of the block polymer solution, the relative humidity of the atmosphere, the properties of the solvent, the spreading volume and the substrates, were investigated to control micropore size and tune film surface properties. The surface composition and wettability of the film were found to be dramatically changed in aqueous solution, and the contact angle of the film surface was interestingly reduced from nearly hydrophobic to super-hydrophilic, which was shown by optical contact angle measurements. The influence of porosity and the ionization degree of PAA on the above properties was investigated. Micropore diameters of the films determine the initial contact angle, while the PAA ionization degree determines the transformation time of the wettability behavior and the final contact angle. The microporous thin films, as potential functional materials, are expected to play an important role in future applications.