On the Size and Shape of Polymers and Polymer Complexes : A Computational and Light Scattering Study

• Main Author: Edvinsson, Tomas
• Format: Doctoral Thesis
• Language: English
• Published: Uppsala universitet, Fysikalisk-kemiska institutionen 2002
• Subjects: Physics; Monte Carlo simulations; grafted polymers; shape description; folding complexity; clustering; percolation algorithm; light scattering; end-capped polymers; inclusion complexes; Fysik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1930; http://nbn-resolving.de/urn:isbn:91-554-5273-6

Detailed characterization of size and shape of polymers, and development of methods to elucidate the mechanisms behind shape transitions are central issues in this thesis. In particular we characterize grafted polymer chains under confinement in terms of the chain entanglement complexity and mean molecular size. Confinement of polymers into small regions can drastically affect the structural and mechanical properties, and make these systems convenient for a large number of applications, including the design of lubricants, coatings, and various biotechnical applications. Using Monte Carlo simulations with a model including both persistence length and intramolecular non-bonded interaction, we find two regimes of polymer behaviour: i) soft mushrooms, where confinement successively flattens the chains with accompanying change in the folding complexity, and ii) hard mushrooms where the compact structures appear to resist confinement and the only way to reorganize the entanglements is by flattening under strong confinement. We also show that a simultaneous use of mean molecular size and chain entanglement complexity renders the possibility to create configurational "phase" diagrams for a wide range of polymers. We have further introduced a new descriptor of folding complexity, the path-space ratio, ζα which captures essential features of molecular shape beyond those conveyed by mean size and asphericity. This thesis also contains results of light scattering measurements on supramolecular complexes formed when mixing an adamantane end-capped star polymer with a β-cyclodextrin polymer. The specific interactions result in an interplay between the association of the end-caps and a strong inclusion interaction between adamantane and β-cyclodextrin.