Year: 2004
Type: dissertation
Abstract: In this thesis, functionalization of polymers with three different types of supramolecular self-assembled nanostructures have been examinated: 1) blends of block copolymers and thermosets, 2) polymer-amphiphile systems, and 3) block copolymer-amphiphile complexes. Morphologies of complexes were characterized preferentially using small- and wide-angle X-ray scattering, and transmission electron microscopy. The effect of nanostructures on mechanical, electrical or optical properties were measured with dynamic mechanical spectroscopy, DC- and AC-conductivity, and UV-Vis spectroscopy. In the first example, the self-assembled diblock and triblock copolymer nanostructures (spherical, "worm-like" cylindrical and lamellar structures) were used to modify the mechanical properties of phenolic resins. Morphology of complexes depended on the weight fraction of microphase separated domain. The storage moduli at room temperature decreased slowly with increasing weight fraction of the microphase separated domain, when the phenolic matrix was continuous. The long period of the structures was of the order of 12-70 nm, depending on the molecular weights of blocks. In the second example, the self-assembled polymer-amphiphile complexes were used to form one-dimensional cylindrical conducting structures with the long period of 3.5 nm using conjugated polymer polyaniline. The conductivity of samples increased rapidly two orders of magnitude when the cylindrical structure was formed. The increase of conductivity is probably due to confinement of polyaniline chains within the cylinders and due to cosolvent effects of the amphiphiles. In the third example, the self-assembled block copolymer-amphiphile structures were used to first achieve molecularly reinforced polyelectrolyte. Complexes formed a lamellar structure, where the conductivity of "liquid-like" polyelectrolyte was decoupled from the segmental motion of the reinforcing glassy domain. Lithium salt was introduced to promote the ionic conductivity. The conductivity levels were relatively low at room temperature probably due to the Coulombic traps and grain boundaries. Finally, the hierarchical structures were used to manipulate optical properties. A high molecular weight block copolymer complexes with surfactants lead to lamellar structure with the long period of ca. 140 nm. All starting materials were almost colourless, but the complexes were predominantly blue pearlescent in reflection to an observer viewing them in ambient. The transmission and reflectance spectra revealed the formation of an incomplete photonic bandgap at ca. 460 nm.
Source: Aaltodoc (Aalto University)
Author: Harri Kosonen
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W73736390