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Biomedical subjects

D Gersappe

Publications and source records attributed to D Gersappe.

8 recordsLinked to original sources
PubMed2006

Substrate effect on the melting temperature of thin polyethylene films.

Strong dependence of the crystal orientation, morphology, and melting temperature (Tm) on the substrate is observed in the semicrystalline polyethylene thin films. The Tm decreases with the film thickness decrease when the film is thinner than a certain critical thickness, and the magnitude of the depression increases with increasing surface interaction. We attribute the large Tm depression to the decrease in the overall free energy on melting, which is caused by the substrate attraction force to the chains that competes against the interchain force which drives the chains to crystallization.

Crystallization↗
PubMed2005

Molecular dynamics study of the effect of surfactants on droplet deformation in shear flows.

We use molecular dynamics simulations to study the effect of surfactants on the mechanism of drop deformation in shear flows. Our results show deviations from fluid mechanics predictions, in both the high and the low surfactant concentration limits. We find that these deviations are a result of the local conformation of the surfactant layer which mediates the stress transfer across the interface. We show that the ability of the surfactant to affect the stress transfer across the interface is a result of the interplay between the architecture of the surfactant and the surface coverage.

Journal Article↗
PubMed2001

Mobility of polymer chains confined at a free surface.

Dynamic secondary ion mass spectrometry was used to investigate the chain mobility of polystyrene (MW ranging from 4.3 to 957 kg/mol) at the free surface. The data show that the diffusion coefficient was reduced relative to the bulk value within a distance, d < or = 4R(g), from the surface and scaled as 1/N(2.5) at fixed d. These results are in excellent agreement with self-consistent field calculations of the surface segmental distribution and provide the first direct confirmation of various theoretical models that predict asymmetric segmental fluctuation which arises from surface induced orientation of polymer chains.

Journal Article↗
PubMed2000

DNA electrophoresis on a flat surface.

We report a new approach for performing DNA electrophoresis. Using experimental studies and molecular dynamics simulations, we show that a perfectly flat silicon wafer, without any surface features, can be used to fractionate DNA in free solution. We determine that the ability of a flat surface to separate DNA molecules results from the local friction between the surface and the adsorbed DNA segments. We control this friction by coating the Si surface with silane monolayer films and show that it is possible to systematically change the size range of DNA that can be separated.

DNA↗