Stability of Colloidal Particles

The repulsion between two double layers is important in determining the stability of colloidal particles against coagulation and in setting the thickness of a soap film (see Section VI-5B). The situation for two planar surfaces, separated by a distance 2d, is illustrated in Fig. V-4, where two versus x curves are shown along with the actual potential. 

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],... 

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

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. 

For studying the stability of colloidal particles in suspension (Chapter 13) or for determining the potential at the surface of particles (Chapter 12), one often needs expressions for potential distributions around small particles that have curved surfaces. Solving the Poisson-Boltzmann equation for curved geometries is not a simple matter, and one often needs elaborate numerical methods. The linearized Poisson-Boltzmann equation (i.e., the Poisson-Boltzmann equation in the Debye-Hiickel approximation) can, however, be solved for spherical electrical double layers relatively easily (see Section 12.3a), and one obtains, in place of Equation (37),... 

Proteins are both colloids and polymers. Therefore, attempts have been made to understand the phenomenon of protein aggregation with the help of models from the polymer and colloid fields such as DLVO theory, describing the stability of colloidal particles, or phase behavior and attraction-repulsion models from polymers (De Young, 1993). For faster progress, more phase diagrams for equilibrium protein precipitation, in both the crystalline and the non-crystalline state, as well as more data on observations of defined protein oligomers or polymers, are required. 

Electrical Double Layer and Stabilization of Colloidal Particles... 

The results from the above mentioned approaches are that the stability of colloidal particles is diminished if the electrostatic repulsion is reduced by... 

The conditions of stability of colloidal particles with respect to further dispersion down to molecular sizes can be found by analyzing the A (d) dependence at d - b. If the value of a does not change with the decrease in d down to the molecular dimensions, and if a can be used to describe the work of dispersing, further dispersion of particles down to molecular sizes is thermodynamically favorable. In a real polydisperse system the dispersed particles of colloidal range with some defined particle size distribution may, however, also fluctuationally form at a = const. 

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... 

Fowkes and Lee and Rives [2,3] showed that ion formation in a nonaqueous medium is appreciably higher than predicted by Eq. (1). Steiic stabilization of colloidal particles is achieved by adsorption of long-chain molecules on solid surfaces [4]. For an effective steric stability by the adsorbed molecules, there are several basic requirements (1) long chain of the adsorbate molecule, (2) strong adsorption of the adsorbate on the solid particle surface, and (3) good solubility of the chain in the medium [4]. 

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... 

Fig. 2.1. Diagrammatic representation of the stabilization of colloidal particles by oleic add in nonaqueous media as depicted by Verwey and de Boer (1938).

If, near to the CFPT, the configurational entropy of the particles contributes to the stability of colloidal particles stabilized by low molecular weight species, then it is reasonable to ask why this configurational entropy... 

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

The term steric stabilization is now used to embrace all aspects of the stabilization of colloidal particles by adsorbed non-ionic macromolecules, and is equally effective in aqueous and non-aqueous media. 

The stability of colloidal particles in biological fluids containing proteins and enzymes is a crucial issue, because the size of the nanoparticles plays an important role in its ability to interact with mucosal surfaces and, in particular, with the ocular mucosa (Figure 51.27). ... 

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. 

Figure 8.3. Electrostatic stabilization of colloidal particles (a) schematic representation of the electrostatic interaction energy-distance curve for two approaching particles (not to scale) (b) calculated electrostatic interaction curves according to equations (8.20a-8.20c)...

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

Polymers are often applied to promote either stabilization or aggregation. Examples of polymer-induced aggregation are found in water purification, clarification of wine and fruit juices, and in papermaking. Stabilization of colloidal particles by polymers is applied in foodstuffs, paints, and dyes, in the dispersion of particles on magnetic tapes and photographic paper, as well as in many cosmetic and medical salves and lotions. A rather recent development is the use of polymers to reduce or prevent the deposition of protein molecules and biological cells on surfaces in order to avoid biofouling and, hence, improve the biocompatibility of these surfaces. 

Steric stabilization is the term used to describe the stabilization of colloidal particles which results from the interaction between uncharged polymer chains ad-... 

The stability of colloidal particles in suspension has been the focus of many research problems in literature. Central to many of these studies is the DLVO model, named after the pioneering work ofDerjaguin and Landau (1941) and Verwey and Overbeek (1948). The main idea of this theory is that the total interaction energy of coUoidal particles is given by the sum of the van der Waals and electrostatic interactions. 

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