Gexiao Sun | PubMed Health

PubMed2004

Equilibrium interaction of solid surfaces across a polymer melt.

Forces across polymer melts are poorly understood despite their importance for adhesion and fabricating composite materials. Using an atomic force microscope (AFM), this interaction was measured for poly(dimethyl siloxane) (PDMS). The structure of the polymer at the surface changed during the first approximately 10 h. Afterward, short-range attractive forces were observed with short-chain PDMS (M(w) = 4200 g/mol). Using PDMS with a molecular weight (M(w) = 18 000 g/mol) above the entanglement limit, we measured a monotonically decaying repulsive force, which indicates that a quasi-immobilized layer had formed at the solid surface. Due to the small radius of curvature of the tip, forces could be measured in equilibrium.

Dimethylpolysiloxanes↗

PubMed2002

Rupture of molecular thin films observed in atomic force microscopy. II. Experiment.

In atomic force microscope studies of thin films often a defined jump of the tip through the film is observed once a certain threshold force has been exceeded. In particular, on lipid bilayers this is regularly observed. In a previous paper [H.-J. Butt and V. Franz, Phys. Rev. E 66, 031601 (2002)] we presented two complementary models to describe film rupture. The aim of this study was to verify these models. Experiments were done with solid supported bilayers consisting of dioleoyloxypropyl-trimethylammonium chloride (DOTAP) and dioleoylphosphatidylserine (DOPS) in aqueous solutions and with propanol. Both models describe experimental results adequately. In particular, a narrow distribution of yield forces and an increase of the mean yield force with increasing loading rate is correctly predicted. For the lipid bilayers spreading pressures of roughly 20 mN/m (DOTAP) and 5 mN/m (DOPS) were measured. Line tensions for the edge of a lipid bilayer ranged between 3 (DOTAP) and 6 pN (DOPS).

Journal Article↗