Steric stabilization surface chemistry

A basic fact of nanoscale materials chemistry is that nanoparticies arc only metastable. The stable state is bulk material. Surface stabilizers are necessary to prevent the particles in a colloidal dispersion from colliding and sticking together. Stabilizers act by an electrostatic mechanism or a steric mechanism or both (16). Particles with like charged surfaces electrostatically repel one another. By the steric mechanism solvated polymer chains extending from the surfaces of two different particles repel one another because the entropy of the system decreases if the polymer chains occupy the same volume. Colloidal dispersions are stable in water or in organic solvents when the stabilizer coordinates to the particle surface and is well solvated. 

In this section, guests confined within the zeolite cavities will be discussed, i.e., guests of sizes larger than the portals formed by the pore aperture, so that they are unable to escape. Steric restrictions and the strong intrazeolitic electric fields affect the chemistry in these nanoreaction chambers and may cause structures and properties that are modified compared to those obtained in solution or on external surfaces. Furthermore, entrapping hinders interaction between the clusters and enhances their stability. 

Chapters 10 and 11 are devoted entirely to aspects of colloid stabihty. First, the essential concepts of the electrical and van der Waals forces between colloid particles are presented with special emphasis on the concepts of the zeta potential, double-layer thickness and Hamaker constants. Then, the DLVO theory for colloidal stability is presented. This is a major tool in colloid chemistry and we discuss how stability is affected by manipulating the parameters of by the classical DLVO theory. Chapter 11 closes with a presentation of kinetics of colloid aggregation and structure of aggregates. Chapters 12 and 13 are about emulsions and foams, respectively - two important categories of colloid systems where DLVO and other principles of colloid and surface science are apphed. In this case, DLVO is often not sufficient. Steric forces and solvation effects are not covered by the classical DLVO and their role in colloid stabihty is also discussed in Chapter 12. 

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