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accurate knowledge of 6, and the difficulty in taking account of desorption and changes in chain conformation or solvation during interaction. When the steric contribution is combined with the electrostatic and van der Waals interactions, a minimum in the energy at large separations still obtains, but repulsion is generally evident at all shorter distances, provided that the adsorbed macromolecules or surfactants do not desorb into the continuous phase or otherwise move away from the points of interaction (Fig. 7.8).

For particles with a hydrated stabilising layer of thickness 6, the volume of the overlapping region (Vov) is as derived in Fig. 7.9:

2x1 H\21 H

relationships, xE = RTBc2

where B is the second virial coefficient. Now the free energy of mixing is

and therefore

XEdV = 2xEVov

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