Poly osmotic compressibility

Fig. 8.8. Osmotic compressibility against volume fraction for various polymers and solvents. Osmotic compressibility means change of osmotic pressure with volume fraction. Horizontal scale is volume fraction 0, relative to 4>. Vertical scale is osmotic compressibility relative to its value in the dilute limit. The scales are logarithmic. Points are combined data on three samples of poly a-methyl styrene in toluene differing by a factor of five in molecular weight [8.14] and one sample of polyisoprene (natural rubber) in cyclohexane [8.1]. The superposition of his data suggests that all long polymers in good solvents have the same osmotic-pressure behavior. The line indicates the expected behavior in the semidilute regime...

The extremely low friction achieved on PLL(20)-g[2.9]-PEG(5) films in SFA experiments is not a unique property of this specific copolymer but has also been observed for other grafted poly(ethylene glycol) films as well as for other polymer-brush systems in a good solvent, such as grafted polystyrene in toluene. The osmotic pressure, which leads to strong repulsive forces as the polymer brushes are compressed, effectively prevents the direct contact of the solid surfaces. At comparable solid surface separations, thin films of water or aqueous salt solutions have been shown to retain a shear fluidity characteristic of the bulk liquid. In a control experiment, this was also observed in 10 mM HEPES buffer solution (data not shown). 

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