Intersurface force

Forces between polymer-covered surfaces are a subset of the general subject of intermolecular forces, which are more fully discussed elsewhere (Maitland etal. 1981, Israelachvili 1991). Before the SFA and the results obtained from it are discussed, a brief consideration of intersurface forces is needed. If the intermolecular potential energy function between two individual molecules is generated solely by van der Waals forces it is purely attractive and of the form... 

We now present force-thickness curves measured during compression of two identical brushes. The data displayed in Figure 3.4, where we have plotted the intersurface force F, normalized by the radius of curvature R, as a function of brush thickness, have been obtained with 50 nm thick brushes... 

Alternatively to force-based approaches, cell adhesion can be quantified by measuring the intersurface distance between the cell and a planar transparent substrate (Fig. 4.30). Reflection interference contrast microscopy (RICM) is ideally suited for studying cell adhesion characteristics and dynamics in aqueous environment, as it allows for nanometer precise determination of intersurface distances with milliseconds time resolution [62]. It has the added... 

The two experiments are exemplified by the sketches in figure 3.34. In the first, one surface is moved normally to the other in a sinusoidal manner, whereas in the second one surface is moved parallel to the second surface. For the first case, solvent is either squeezed from or drawn into the space between the surfaces until the load applied is balanced by steric repulsion fi-om the increase (decrease) in osmotic pressure due to increase (decrease) in segment concentration in the intersurface volume. Hydrodynamic interactions between the two sinfaces may become dominant and interactions associated with the flow of solvent between the two surfaces are termed lubrication forces. For the geometry of the SFA the hydrodynamic force, Ffi, is related to the velocity of motion of the surfaces normal to each other by... 

We now come to the effect of temperature on F(D) curves. It can be seen in Figure 3.5 that, as the temperature is increased, the onset of repulsive forces occurs at smaller intersurface separations (Figure 3.5a,b), and that hard wall repulsion, i.e., a situation of quasi-fully compressed brushes, occurs at lower normal forces. Such a temperature dependence of the repulsive range shows that the thickness of the brushes indeed decreases as the temperature is increased grafted chains go from a low-temperature swollen state to a high-temperature collapsed state where most of the solvent is... 

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