Forces between solid surfaces across polymer melts are poorly understood despite their importance for adhesion and composite materials. Using an atomic force microscope (AFM) this force was measured for poly(dimethyl siloxane) (PDMS) on silicon oxide. The influence of molecular weight (4.0-40 kDa) was studied. Forces are attractive for low and repulsive for high molecular weight. In addition, changing the terminal methyl group for a hydroxyl group leads to an increased probability of bridging.

Using an atomic force microscope (AFM) the interaction between an AFM tip and a planar silicon oxide surface has been measured across poly(dimethylsiloxane) (PDMS, MW=18000). Due to the small radius of curvature of the AFM tip the hydrodynamic repulsion of the tip was negligible and forces could be measured in equilibrium. This is confirmed by the fact that force-versus-distance curves measured at different approaching velocities were indistinguishable. In equilibrium a repulsive force was observed which could best be described by a power law, F∝1/d2.5 where d is the distance.

The adhesion of solid surfaces across polymer melts has been studied with an atomic force microscope (AFM). As polymers we used poly(dimethylsiloxane) (PDMS, M-w = 18 000), poly(ethylmethylsiloxane) (PEMS, M-w = 16 800), and a diblock copolymer (PDMS-b-PEMS, M-w = 15 100). Upon retraction, adhesion peaks were observed which we interpret as bridging of single polymer chains. Bridging occurred seldom (in each 20th force curve) in PDMS and more often in PEMS (in each 8th force curve) and was most prominent in the diblock copolymer, where a typical force curve contained 5-10 adhesion peaks. The mean detachment force decreased with increasing retraction velocity, indicating that the bond to the surface or tip is not a direct contact with the solid surface.

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.

Recently, molecular similarity, as an important tool of computer-aided drug design has developed rapidly. Its calculation has also developed from planar, rigid. 2D molecules to steric, flexible, 3D molecules. However, 3D molecular similarity calculation is easy to fall into local optima and the calculation is always time-consuming.In this paper. a method of flexible 3D molecular similarity calculation through the evaluation of molecular electrostatic potentials (MEP) with principal component analysis (PCA), genetic algorithm (GA) and Tabu search (TS) was presented. PCA was used to preprocess, GA was used to align two molecules and TS was used to decrease the probability of falling into local optima.The authors calculated the molecular similarities of benzene and its derivatives, a group of insecticides and a series of acetylcholinesterase inhibitors. To further evaluate the method, the authors calculated the similarities of HIV-1 protease inhibitors TIBO derivatives and predicted the pIC50 values. in which the linear relationship between similarities and logP values was also discussed. (C) 2003 Elsevier B.V. All rights reserved.

The force profile between a glass microsphere and mica in 1-propanol has been measured with the colloidal probe technique. Oscillatory solvation forces indicate a layered structure of the confined propanol for at least three layers. In the same experiment, hydrodynamic forces were measured at high approaching velocity. Comparing measured force curves with calculations we found a significant effective slip, which could be described by a slip length of 10-14 nm. (C) 2002 American Institute of Physics.

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).