Formation of Conductive Polymer Nanoarrays through Block Copolymer Templating and Electroplating

Abstract

Nanostructured materials have drawn extensive attention because of their unique properties resulting from nanoscale features. One of the convenient ways to generate nanostructured materials is to use patterns with nanoscale textures as templates for the reactions carrying out within the templates (i.e., the concept of nanoreactor). In this study, nanopatterns were obtained from the self-assembly of degradable block copolymers, polystyrene-b-poly(L-lactide) (PS-PLLA) with PLLA hexagonal cylinder (HC) morphology, at which the degradable segment can be scarified to form the nanopatterns with cylindrical pores. Large-scale oriented nanopatterns with perpendicular cylindrical nanopores on conductive substrates (i.e., ITO substrates) were obtained by spin coating. Moreover, the hydrolyzed PS-PLLA templates were stabilized by UV-induced PS-crosslinking so as to enhance the adhesion with substrates and mechanical property for the following electroplating process. For the establishment of conductive polymer nanoarrays, electroplating was then conducted within the cylindrical nanopores of the nanopatterns prepared. To achieve the high efficiency of electroplating, the pore filling of electrolytes is necessary so that appropriate wetting capability should be fulfilled in order to lead the capillary force-driven process. An appropriate co-solvent, tert-butanol, was used as standard electrolyte solution for the performance of the electrochecmical polymerization of polyanilines within the cylindrical nanopores. Moreover, the formation of templated polyaniline was traced by the in-situ cyclic voltammery analysis. As observed, the growth rate of polyanilines can be effectively controlled by the working voltage of electroplating (the minimum active voltage ~ 0.72 V). As a result, polyaniline nanoarrays with interesting light bulb-like textures can be obtained within the cylindrical nanopores by gentle electroplating at 0.8 V. Because of the non-uniformly diffused field of aniline monomers in the electrolytes, it is difficult to define the average growth rate of polyanilines within each cylindrical nanopore by traditional potentiostatic method. Consequently, advanced pulse plating was carried out to improve diffused efficiency of aniline monomers. Instead of continuous electroplating, the pulse mode applied a periodic electroplating and a diffused sequence so as to equalize concentration gradient of aniline monomers within the cylindrical nanopores. As a result, well-defined conducting polymer nanoarrays can be obtained. Here we demonstrated a novel way for the formation of conducting polymer nanoarrays by the integration of nanopatterning and electroplating; it is appealing in the practical application such as solar cell, flexible electrode and field-emitted display.