(251o) Development of Layered Multi-Scale Porous Thin Films By Tuning Deposition Time and Molecular Weight of Polyelectrolytes

Porous polymeric films consisting of different sized pores in distinct zones are desired for many applications. For example, a well-controlled porous structure (i.e. mesoporous shell and macroporous core) enables a tunable drug release over time. Commercial nanofiltration/reverse osmosis membranes have an asymmetric structure with two distinct zones of micro and nano-sized pores, respectively. Motivated by these prospects, we focused on the design of porous films with well-defined nano and micro sized porous regions. In this work, the porous networks were fabricated by post treatment of layer-by-layer (LbL) assembled poly(allylamine hydrochloride) (PAH)/ poly(acrylic acid) (PAA) multilayers. First, we focused on the precise control of porous structure in micrometer and nanometer scales and the improvement of fabrication efficiency at the same time. In order to overcome the long processing time used in conventional LbL assembly, the dipping time was shortened from 15-20 min to 10 s. The effect of dipping time on the porous morphology was investigated in details. The molecular weight of polyelectrolytes could be one of the critical and intrinsic parameters to tune the porous structure by influencing the reorganization behavior of polymer chains during the post treatment. In this regard, the effect of using polyelectrolytes with widely different molecular weights was also studied in this work. Both nano and micro sized porous structures could be achieved by tuning the above parameters. Further, the layered multi-scale porous thin films were developed through a bottom up approach by combining well-defined micro and nano-sized porous regions.