Steric stabilization grafting density

The unique density dependence of fluid properties makes supercritical fluids attractive as solvents for colloids including microemulsions, emulsions, and latexes, as discussed in recent reviews[l-4]. The first generation of research involving colloids in supercritical fluids addressed water-in-alkane microemulsions, for fluids such as ethane and propane[2, 5]. The effect of pressure on the droplet size, interdroplet interactions[2] and partitioning of the surfactant between phases was determined experimentally[5] and with a lattice fluid self-consistent field theory[6]. The theory was also used to understand how grafted chains provide steric stabilization of emulsions and latexes. 

The mechanism of action of the hydrophilic PEG chains can be explained in terms of steric interaction that is well known in the theory of steric stabilization. Before considering the steric interaction one must know the polymer configuration at the par-ticle/solution interface. The hydrophilic PEG chains can adopt a random coil (mushroom) or an extended (brush) configuration. This depends on the graft density of the PEG chains as will be discussed below. The conformation of the PEG chains on the nanoparticle surface determines the magnitude of steric interaction. This configuration determines the interaction of the plasma proteins with the nanoparticles. 

Figure 3.8 Potential energy curves for a pair of sterically stabilized colloid particles, separated by a distance h. (a) Repulsive contribution to the free energy, (b) attractive contribution and total free energy. The grafting density decreases from i to iv...

A very effective way of stabilizing colloids is to modify the surface by grafting a polymer.1 In this manner, a high polymer density for which the chains can overlap to form a polymer bmsh can be obtained and this leads to a strong steric repulsion between the colloidal particles. In recent years,-i this-i problem-i has-i received-i attention-" both experimentally2-10 and theoretically.11-42 The theoretical investigations focused firstly on the density profile of a single brush on a flat or curved surface and secondly on the interactions between two brushes. 

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