Steric stabilization of colloids

The process of adsorption of polyelectrolytes on solid surfaces has been intensively studied because of its importance in technology, including steric stabilization of colloid particles [3,4]. This process has attracted increasing attention because of the recently developed, sophisticated use of polyelectrolyte adsorption alternate layer-by-layer adsorption [7] and stabilization of surfactant monolayers at the air-water interface [26], Surface forces measurement has been performed to study the adsorption process of a negatively charged polymer, poly(styrene sulfonate) (PSS), on a cationic monolayer of fluorocarbon ammonium amphiphilic 1 (Fig. 7) [27],... 

Adsorption of polyelectrolyte on interfaces is concerned with various applications such as flocculation and steric-stabilization of colloidal particles in an aqueous phase, oil recovery, and soil conditioning. In these cases, both the adsorbance of polyelectrolytes and the conformation of the adsorbed polymer, which is connected with the thickness of the adsorbed layer, are very important. 

Napper DH. Steric stabilization of colloidal dispersions. London Academic Press 1983. 

FIGURE 7.27 Schematic representation of an adsorbed polymer chain at the solid-liquid interface. (From Sato, T. and Ruch, R., in Steric Stabilization of Colloidal Dispersion by Polymer Adsorption, Marcel Dekker, New York, 1980. With permission.)... 

X HE CONFIGURATIONAL PROPERTIES OF WATER-SOLUBLE POLYMERS and their interactions with other polymers and with colloidal particles are relevant to understanding the intermolecular interactions in associative thickeners and steric stabilization of colloidal particles. We used fluorescence spectroscopy to study both the dynamic and the static equilibrium properties... 

A) Steric stabilization. Steric stabilization of colloidal particles is imparted by macromolecules that are attached (e.g. by grafting or by physical adsorption) to the surfaces of the particles. This is represented schematically in Fig. 1.5. Over recent years there have been an impressive number of reviews of steric stabilization to which the reader is referred (Ottewill, 1969 Napper, 1970c Medalia, 1971 Napper and Hunter, 1972 Ottewill, 1973 Vincent, 1973a Vincent, 1973c, 1974 Barrett, 1975 Napper and Hunter, 1975 Napper, 1977 Parfitt and Peacock, 1978 Ottewill, 1980 Tadros, 1980 Laible and Hamann, 1980 Sato and Ruch, 1980 Vincent and Whittington, 1981 Tadros, 1982). These reviews show clearly the rapid expansion in our... 

Figure 4 Steric stabilization of colloidal metal particles by a polymer layer (left) and electrostatic stabilization of colloidal particles (right).

Roan, J.-R. Kawakatsu, T. Self-consistent-field theory for interacting polymeric assemblies. 11. Steric stabilization of colloidal particles. J. Chem. Phys., 2001, 116, 7295-7310. 

In many ceramic systems it is not possible to create a stable suspension simply by controlling pH. Large additions of acid or base can result in dissolution of the particles, or provide a too high ionic strength. Hence, addition of suitable polymeric dispersants is commonly used to create colloidally stable suspensions. These polymeric additives can induce an interparticle repulsion that prevents coagulation. Upon the close approach of two particles covered with adsorbed polymer layers, the interpenetration of the polymer layers give rise to a repulsive force, the so-called steric stabilization (10). There are some simple requirements for steric stabilization of colloidal suspensions, as follows ... 

Explain how and why the molecular weight of an adsorbed polymer may affect its role in the steric stabilization of colloidal particles ... 

Milk is a natural colloidal dispersion that contains casein micelles, self-assembled protein associates with a diameter of about 200 nm [20]. The casein micelles are protected against flocculation by an assembly of dense hairs (often called a brush ) at their surfaces. Polymer brushes can thus provide steric stabilization of colloids. For millennia, man used the fact that milk flocculates and gels when it is acidified, as in yogurt production. Below pH = 5 macroscopic flocculation of the casein micelles in milk is observed [21]. This means that the interactions between casein micelles change from repulsive to attractive. The explanation is that acidification leads to collapse of the casein brushes [22]. In cheese-making the steric stabilization is removed by enzymes, which induce gelation into cheese curd. 

Zhulina, E. B., O. V. Borisov, and V. A. Priamitsyn. 1989. Theory of steric stabilization of colloid dispersions by grafted polymers. J. Colloid Interface Sci. 137 495-511. 

W. Heller and T. L. Pugh. Steric stabilization of colloidal solutions by adsorption of flexible macrranolccules. J. Polym. Sci.. 47. 203-217. 1960. 

Figure 7.6 Polymer adsorption and steric stabilization of colloid systems. Adapted from Wesselingb et al. (2007), with permission from John Wiley Sons, Ltd...

Modification of surfaces by physisorbed, end-attached or grafted-from polymers has long been known to result in striking changes to wettability of such surfaces (see, e.g.. Reference 132), and to the adhesion and interaction forces between them. This latter effect has been widely used in the steric stabilization of colloidal dispersions. Such surface interaction modifications, their modeling, and their implications have been comprehensively reviewed.In this chapter, we have tried rather to focus on recent developments in measuring and understanding surface-attached polymers as modifiers of shear interactions and frictional forces between surfaces. 

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