Generic Properties of Polymer Solutions

Doctoral thesis, 2007

Polymer solutions are abundantly present in our daily life, for example in paints, jellies, contact lenses and even in the living cells. Despite their ubiquity, we still have a poor understanding of the physical properties of solutions due to the extremely large number of internal degrees of freedom. To understand the physical properties, concepts such as coarse-grained models are thus essential tools. This thesis is focused on consequences of the work of de Gennes (Nobel Prize 1991) on the blob model, which describes the static and dynamic network structure of non-dilute solutions, i.e. solutions where the polymer chains overlap. The blob model gives universal predictions based on a few assumptions. Here, a thorough investigation of solutions of typical synthetic polymers such as poly(methyl methacrylate) (PMMA) and polystyrene (PS), and a biological polymer DNA is presented. We demonstrate, primarily using photon correlation spectroscopy, that non-dilute polymer solutions have generic properties. The blob model is extremely useful and robust although the model was originally proposed only for the so-called semi-dilute solutions of flexible long chains. We find that also highly concentrated solutions of PS and PMMA can be universally described using the model, when taking into account the local solvent viscosity. Solutions of styrene chains with various lengths are also found to be well described by the model, even though the network structure is dramatically changed with decreasing chain length due to an increasing importance of the local segmental stiffness. This provides new insights into the properties of the solutions of so-called semi-flexible polymers. Insights that we also show can successfully be applied to the network structures of DNA molecules in solution. Finally, we find a new class of dynamics, superdiffusion, in cross-linked PMMA solutions and entangled DNA solutions. This behavior can also be explained on basis of the polymer network predicted by the blob model, as a consequence of the restoring force of the cross-linked or entangled network coupling concentration fluctuation over large length scales.