Abstract
Nanostructured materials have drawn intensive attention because of their unique properties resulting from nanoscale features. One of the convenient ways to generate nanostructured materials is to use self-assembled degradable block copolymers (polystyrene-b-poly(L-lactide) (PS-PLLA)) after hydrolysis as templates for the reactions carrying out within the templates (i.e., the concept of nanoreactor). In this study, we focused on the execution of electroplating of low-cost and large-area poly-3(hexylthiophene) (P3HT) within the nanoporous PS to demonstrate the feasibility and generality of fabricating nanostructured thin films with P3HT nanoarrays. The electroplating process for the polymerization of 3-hexylthiophene (3HT) monomer was carried out within the PS template on the top of ITO glass by controlling the diffusion of reactive monomers along the nanochannels driven by capillary force. Instead of using continuous electroplating, a pulse mode having a periodic electroplating and a diffused sequence was applied to equalize the concentration gradient of 3HT monomer within nanopores. As a result, electropolymerization of P3HT can be carried out in the electroplating conditions with micro current, as evidenced by chronoamperogram recorded in the pulse plating. Moreover, the formation of templated P3HT was characterized by using Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS) and Nuclear Magnetic Resonance Spectroscopy (NMR). Herein, we demonstrate 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. In addition to the fabrication of cylindrical P3HT nanoarrays, we aim to fabricate large-size thin films with gyroid-forming PS-PLLA diblock copolymer. The thin-film morphologies after casting are very different to that of bulk samples from the self-assembly of the PS-PLLA at which disorder-like microphase-separated texture is usually found. As a result, thermal annealing was carried out to induce the ordering of the cast samples. Interestingly, the thermal-annealed morphologies are strongly dependent upon the film thickness at which the confinement effect on self-assembled morphologies might be effective once the film thickness reaches a minimum. Consequently, the formation of bicontinuous phase can be successfully achieved by thermal annealing with controlled annealing time and suitable thickness due to the increasing of mobility for reorganization of self-assembled morphologies to reach energetic stable state. To achieve the formation of gyroid texture (i.e., higher-order morphology), it is necessary to increase the annealing time or to enhance the chain mobility of BCPs. Nevertheless, it is noted that thermal degradation of PLLA may occur once the thermal annealing is over 2hrs or the annealing temperature is over 220oC, as evidenced by the results of gel permission chromatography(GPC) so as to result in the formation of micelle texture.