| dc.description.abstract | The research is to study the morphologies of poly(3-hexylthiophene)(P3HT) homopolymers and its block copolymers since these materials can be used as potential materials for applications such as organic field-effect transistors(OFET), organic photovoltaics(OPV) and organic light-emitting diodes(OLED). In order to fit the devices’ design and to well control the photoelectric properties, it is necessary to understand how to finely tailor the mesoscale structures of P3HT in solutions and thin films. In the thesis, three investigated systems were arranged as follows：
Crystallization of P3HT homopolymers at various fractions in anisole：P3HT crystallographic mismatch nucleation and growth in solution were dominated by effect of the polymer concentration in anisole. At high P3HT concentrations, the degree of supersaturation in solution can be easily reached upon cooling to form network-like structures. As a result, the solutions containing large mass fractions of P3HT were in a gel state. By contrast, at low P3HT concentrations, the degree of supersaturation was low. The low supersaturation led P3HT to form fibrillar networks that can be dispersive in solution. The networks are comprised of fibrillar bundles with a high density of tip- and side-branches. In order to reduce the tip- and side-branches to grow single P3HT fibers in solution, two strategies were designed.
Mixtures of P3HT and insulating polymers：Blending insulating polymers (PMMA, PS and PSA) with various solubility parameters can affect P3HT crystallographic mismatch nucleation and growth in anisole. At low P3HT concentrations in anisole, adding small amounts of PS, PMMA and PSA can reduce the densitiy of tip- and side-branches within P3HT crystallites and cause the growth of single P3HT fibers. However, at high P3HT concentrations, as large amounts of PMMA were added into the P3HT mixture, the incompatibility between PMMA and P3HT caused high degree of crystallographic mismatch nucleation and growth, giving rise to amorphous P3HT agglomeration in solution.
Morphological study of poly(3-hexylthiophene)-block-poly(stearyl acrylate), P3HT-b-PSA, block copolymers in organic solvents：The morphology of P3HT-b-PSA was controlled by three factors：solvent quality, rod/coil length ratio and copolymer concentration. For the block copolymers with short PSA chains, increasing the solvent quality and lowering the polymer concentration favored the gowth of single P3HT fibers. By contrast, for the block copolymer with long PSA chains in anisole, shish-kebab stuctures formed at high concentrations whereas rod-like aggregations grew at low concentrations. In methanol/THF mixtures, where THF is good for both P3HT and PSA, and methanol is poor for both P3HT and PSA, P3HT-b-PSA tends to form fiber agglomeration. | en_US |