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Diblock-copolymer melts at patterned surfaces and dilute polymer solutions under shear

Dirk Petera, University of Massachusetts Amherst


Diblock-Copolymer Melts at patterned surfaces are investigated. Above the order-disorder transition (ODT) of the bulk, density-functional theory is used to calculate the density profile at the surface. Below the ODT self-consistent field theory (SCFT) is employed to extract numerically possible density variations across a thin film. The orientation of the diblocks and lamellar morphology at the surface depends on the ratio of natural lamellar bulk period to surface period [special characters omitted]. The diblocks can be either perpendicular or parallel to the surface, inducing parallel or perpendicular lamellar morphology. Individual polyelectrolytes and their counterions are studied with SCFT. Scaling behavior and density distribution are numerically calculated and compared to known results. Although the scaling roughly agrees with expected results, the density distribution and the end-to-end vector distribution do not. Apparently, fluctuations significantly contribute to angular averaged SCFT of an individual polymer. Dilute polymer solutions under shear are investigated with renormalization group theory of the Gaussian model and with Brownian dynamics simulations of the bead-rod model. The material functions derived from the first model using coupled Langevin equations agree qualitatively with the ones derived from the diffusion equation of the same model. They exhibit shear thickening for high shear rates due to the unrestricted extensibility of the chain. The excluded volume interaction is responsible for shear thinning at intermediate shear rates. The simulations yield shear thinning behavior for all shear rates, independent of the presence or absence of excluded volume or hydrodynamic interactions. A good agreement with experiments is obtained for the relative extension with increasing shear rate. In theta-solutions an unexpected shrinkage of the chain is observed for high shear rates.

Subject Area


Recommended Citation

Petera, Dirk, "Diblock-copolymer melts at patterned surfaces and dilute polymer solutions under shear" (1999). Doctoral Dissertations Available from Proquest. AAI9920640.