Facilitated and site-specific assembly of functional polystyrene microspheres on patterned porous films.

Functional patterned materials have received considerable attention because of their potential applications in biochips, sensors, and optical or electronic materials. Here, we report a versatile approach to functional patterned films based on facilitated and site-specific assembly of microspheres. This method includes the hierarchical formation of honeycomb-patterned porous films from amphiphilic block copolymers and the assembly of functional polystyrene microspheres driven by the gravity and the electrostatic interaction. Polystyrene microspheres containing carboxyl groups with a narrow size distribution were synthesized by dispersion polymerization. Honeycomb-patterned porous films were prepared from polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) (PS-b-PDMAEMA) by the breath figure method and then quaternized. We found that direct deposition of the microspheres on the patterned films reaches high filling ratio only when using ethanol dispersions that can wet the film pores. Plasma treatment of the films improves the hydrophilicity and introduces charged species to the external surface as well as the pore surface, leading to nonspecific assembly of microspheres. Negatively charged microspheres dispersed in buffer solution show a facilitated and site-specific assembly on the quaternized film. The electrostatic interaction as well as the gravity facilitates the assembly and the suborder arrangement of the hydrophilic PDMAEMA block around the pores is responsible for the site-specific assembly. In addition, we demonstrate the applicability of this method in preparing photoluminescent patterns by the assembly of porphyrinated microspheres, which is useful in various fields such as intelligent sensing.