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Thermodynamics and Dynamics of Branched Polystyrenes and Their Mixtures
| Title: | Thermodynamics and Dynamics of Branched Polystyrenes and Their Mixtures |
| Author: | Yang, Sewoo |
| Description: | The effect of long-chain branching on the bulk and surface thermodynamics of polymer blends, as well as its effect on dynamics of pure melts, has been studied using well-defined polystyrene chains synthesized using anionic polymerization. Three specific aspects of branching were addressed: i.) the effect of changing chain end chemistry, ii.) the effect of changing branch point chemistry, and iii.) the effect of altering the distance between junction points in a molecule that is otherwise identical. Variations in values of the interaction parameter for isotopic linear blends, measured using small angle neutron scattering, were found, but their magnitudes were small. For chains of 30,000 molecular weight any differences in surface segregation arising from changes in chain end and branch point chemistry were not larger than the isotopic labeling effect. Shortening the central linear portion of a pom-pom chain while keeping overall molecular weight constant reduced the hydrodynamic radius of the chain. The contribution due to architecture to the interaction parameter for isotopic binary blends of linear and branched chains increased with a growing disparity in hydrodynamic volumes. A Gaussian field theory captures this effect. The strength of segregation to the surface of a blend film is seen with neutron reflectivity to increase with a reduced length of the central linear portion of the pom-pom, rather than depending on only the number and type of chain ends and junction points as approximated by the existing linear response theory. While in most cases the contribution to the interaction parameter due to architecture alone was estimated by subtracting an estimate of the isotopic effect from the overall interaction parameter, measurements were also done that allowed us to extrapolate data measured in blends of branched PS and linear PS-r-deuterated PS random copolymers to zero deuterium labeling. Relaxation times for the surface fluctuations of films of highly branched PS were measured using X-ray photon correlation spectroscopy. These revealed trends different from those for bulk viscosity measurements when film viscosities were calculated assuming a continuum model for surface capillary waves applied. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=akron1212601903
http://hdl.handle.net/2374.OX/103746 |
| Date: | 2008 |
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