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Volume 115, Issue 17, 01 November 2001
115(2001); http://dx.doi.org/10.1063/1.1415456View Description Hide Description
Molecular dynamics simulations of supercooled polymer melts are reported for long chains. This is the first simulation study at melt densities where the formation of chain-folded structures resembling the lamellae of polymer crystals is observed. Crystallization and subsequent melting temperatures are related linearly to the inverse lamellar thickness. Analysis of the single chain conformations in the crystal shows that most chains reenter the same lamella by tight backfolds. Simulations are performed with a mesoscopic bead-spring model including a specific angle bending potential. They demonstrate that chain stiffness alone, without an attractive inter-particle potential, is a sufficient driving force for the formation of chain-folded lamellae.
115(2001); http://dx.doi.org/10.1063/1.1415455View Description Hide Description
The fluid mechanics of the movement of the contact line region for non-Newtonian fluids has been analyzed using the method of Joanny and de Gennes [C. R. Acad. Sci., Ser. II: Mec., Phys., Chim., Sci. Univers Terre 299, 279 (1984)] where under lubrication theory approximation the rate of viscous dissipation is equated to the rate of surface work to get the expression for the rate of spreading. Two kinds of fluids are considered, one where the viscosity is dependent on shear rate but there are no normal stresses, and another where there are normal stresses but the coefficients are not dependent on the shear rate. Both show the spreading rates to be independent of the non-Newtonian nature of the fluids to a good approximation, with the zero shear viscosity replacing the Newtonian viscosity in the result of Joanny and de Gennes. This appears to be in keeping with the available experimental data.