Surface Chemistry and Colloidal Stability

Adsorbed water promotes self adhesion of Fe oxide particles in powders (e. g. cosmetics) which can lead to problems with clumping (Tsugita et al., 1990). 

The surface hydroxyl groups (whether they arise from adsorption of water or from structural OH) are the Junctional groups of iron oxides, i. e. they are the chemically re- 

1) A Lewis base is a molecule or atom (for example H2O, NH3 or pyridine) that can donate an 

The Iron Oxides Structure, Properties, Reactions, Occurences and Uses. R. M. Cornell, U. Schwertmann Copyright 2003 WILEY-VCH Verlag GmbH Co. KGaA,Weinheim ISBN 3-527-30274-3 

The surface hydroxyl groups can be replaced by silane groups (Micale et al, 1985) or by titanate groups (Hotta et al, 1991) e. g. 

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Because of the high particle concentration and small particle sizes involved in the precipitation systems, the surface chemistry and colloidal stability of the resulting dispersed systems are of particular importance. In general, particle aggregation, and thus the stability of the system, is determined by the prevailing forces between the solid particles in the dispersion. These forces between particles can be repulsive or attractive (Hunter 1987). 

The dispersion stability, rheology, and consolidation of numerous aqueous and non-aqueous Si3N4 suspensions have been studied extensively [251-257]. Recently a novel class of dispersants for Si3N4 powders in non-aqueous media has been designed and its interactions with the powder surface have been characterised systematically on the basis of surface chemistry and fundamentals of colloidal stabilisation [255, 258]. 

Gore, A.Y. Banker, G.S. Surface chemistry of colloidal silica and a possible application to stabilize aspirin in solid 68. matrixes. J. Pharm. Sci. 1979, 68, 197-202. 

Lyklema, J. (1978) Surface Chemistry of Colloids in Connection with Stability. In The Scientific Basis of Flocculation, K. J. Ives, Ed., Sijthoff and Noordholf, The Netherlands, pp. 3-36. 

With these considerations in mind, the goals of contemporary metal colloid research, the approaches to whidi will be covered in this chapter, may be stated as the search for synthetic methods for metal particles which are stabilized in the 1-20 nm size range, the application of characterization methods to identify the potential novelty of the partides (structural methods, electronic properties, surface chemistry), and finally the ap cation of these properties to various fields of chemistry and physics. Perhaps the field for which the renaissance in transition metal colloid chemistry has the most potential impact is catalyds. It has been... 

Atomic force microscopy (AFM) [20] has recently been used to image interfacial aggregates directly, in situ and at nanometer resolution [21, 22], The key to this application lies in an unusual contrast mechanism, namely a pre-contact repulsive force ( colloidal stabilization force ) between the adsorbed surfactant layers on the tip and sample. In contrast to previous adsorbate models of flat monolayers and bilayers, AFM images have shown a striking variety of interfacial aggregates - spheres, cylinders, half-cylinders and bilayers - depending on the surface chemistry and surfactant geometry. I review the AFM evidence for these structures and discuss the possible inter-molecular and molecule-surface interactions involved. 

R. J. Pugh, Dispersion and Stability of Ceramic Powders, in Surface and Colloid Chemistry in Advanced Ceramics Processing, Marcel Dekker, New York, 1994, Chapter 4. 

In the past decades, it has become more and more obvious that students and scientists of chemistry and engineering should have some understanding of surface and colloid chemistry. The textbooks on physical chemistry tend to introduce this subject insufficiently. Modern nanotechnology is another area where the role of surface and chemistry is found of much importance. Medical diagnostics applications are also extensive, where both microscale and surface reactions are determined by different aspects of surface and colloid chemical principles. Drug delivery is much based on lipid vesicles (self-assembly structure) that are stabilized by various surface forces. 

The primary methods for analysis were usually gravimetric, thermal, and spectroscopic in nature but not necessarily correlated with in situ analysis (XPS, AFM, TEM, etc.) or ex situ analysis of surface-bound polymers by de-grafting (NMR, MW, polydispersity, etc.). Colloidal stability and homogeneity of the grafting process is a primary concern. A range of these systems were analogous to what has been done in solution and in bulk and should be thoroughly examined in terms of chemistry on flat substrate surfaces. Several examples follow. 

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