Colloidal behaviour

Clearly the improved understanding of colloidal behaviour within living systems that we are developing offers the eventual prospect of our being able to manipulate such systems. The control of microarchitecture in both living and synthetic systems has many potential applications. The most important aspect is the ability to define the particular conditions under which a certain pattern or structure will be formed such that the products will be uniform. This clearly happens in Nature, but natural systems have been subject to trial and error for considerably longer than any experiment involving synthetic systems. 

It has been established that plutonium hydrolysis products exhibit colloidal behaviour (147-151) and may adsorb onto minerals and other surfaces to form radiocolloids. However, it is difficult to determine whether a radiocolloid is a true colloid or a pseudocolloid formed by adsorption of the plutonium species onto other colloidal impurities in the solution (152). In some cases both forms may be present... 

There have been many investigations into the colloidal behaviour of plutonium and much of these data have been thoroughly summarised by Andelman and Rozzell... 

The colloidal behaviour of iron oxides is of great importance in the environment. 

Ternary adsorption of humic molecules and Ca ions modified the surface charge and the colloidal behaviour of goethite (Tipping and Cooke, 1982). Fe oxides in natural environments often form in the presence of or through the activity of, micro-organisms (see Chap. 17). The adsorption properties of the oxides may, therefore, be modified by adsorbed organic molecules and ternary Fe-OCO-M complexes (CO-org. 

The essential differences between the properties of matter when in bulk and in the colloidal state were first described by Thomas Graham. The study of colloid chemistry involves a consideration of the form and behaviour of a new phase, the interfacial phase, possessiug unique properties. In many systems reactions both physical and chemical are observed which may be attributed to both bulk and interfacial phases. Thus for a proper understanding of colloidal behaviour a knowledge of the properties of surfaces and reactions at interfaces is evidently desirable. 

In this monograph an attempt has been made to present the subject from this point of view, and whilst the text is admittedly incomplete as a compendium on colloid chemistry yet it is hoped that the elaboration of the physics and chemistry of these degraded two-dimensional systems may prove of value to those concerned in problems of colloidal behaviour. 

Until the last few decades colloid science stood more or less on its own as an almost entirely descriptive subject which did not appear to fit within the general framework of physics and chemistry. The use of materials of doubtful composition, which put considerable strain on the questions of reproducibility and interpretation, was partly responsible for this state of affairs. Nowadays, the tendency is to work whenever possible with well-defined systems (e.g. monodispersed dispersions, pure surface-active agents, well-defined polymeric material) which act as models, both in their own right and for real life systems under consideration. Despite the large number of variables which are often involved, research of this nature coupled with advances in the understanding of the fundamental principles of physics and chemistry has made it possible to formulate coherent, if not always comprehensive, theories relating to many of the aspects of colloidal behaviour. Since it is important that colloid science be understood at both descriptive and theoretical levels, the study of this subject can range widely from relatively simple descriptive material to extremely complex theory. 

Monodispersed sols containing spherical polymer particles (e.g. polystyrene latexes22"24, 135) can be prepared by emulsion polymerisation, and are particularly useful as model systems for studying various aspects of colloidal behaviour. The seed sol is prepared with the emulsifier concentration well above the critical micelle concentration then, with the emulsifier concentration below the critical micelle concentration, subsequent growth of the seed particles is achieved without the formation of further new particles. 

Benes, P. and Jiranek, V., Adsorption and colloidal behaviour of carrier-free Be in aqueous solutions, Radiochim. Acta, 21, 49, 1974. 

Before proceeding further, it will be helpful to introduce a number of additional terms which are widely used in the description of colloidal behaviour. 

Theories of interparticle forces play a fundamental part in many theoretical aspects of colloidal behaviour. It is therefore of great importance to have experimental evidence for the validity of these theories. One approach to this is to study the forces between macroscopic objects, to which the same theoretical equations should apply. Since these forces arc exceedingly small until the bodies come into very close proximity, work in this area has faced considerable experimental difficulties. Experiments on the force between two plates and between a plate and a lens have been of limited validity because of the difficulty in achieving adequate surface smoothness and in completely eliminating dust. The... 

Colloidal behaviour is affected by the type of electrolytes present in the bulk solution, since dispersion occurs in the presence of monovalent cations, while with calcium ions the myo-inositol hexakisphosphate-goethite complexes flocculate (Celi et al., 2001). These findings have important environmental implications, since the charge-... 

Evidently it is not sufficient simply to state that one clay is finer than another it is necessary to specify the range of particle sizes for which this statement is true. For example (Table 12) the South Devon clays contain 81.9% material less than 1.0(x in radius—slightly more than the Dorset clays (81.1%), and on this basis the former might be considered the finer of the two. But the Dorset clays contain much more material in the ranges <0.0S(ji and 0 05-0-10(i. since these lower ranges are more important for colloidal behaviour, the Dorset clays may well be considered to be the finer . 

T. W. Healy, D. Chan., and L. R. White, Colloidal behaviour of materials with ionizable group surfaces, Pure Applied Chem. 52 1207 (1980). 

It is clear that the colloidal behaviour of pol3uners will be largely dependent on the distribution of the molecular sizes. In Fig. 16 the change of this distribution with increasing q is shown for an esterification reaction. 

J. Loeb, Proteins and the theory of colloidal behaviour Me Graw-Hill Publishing Co, Ltd., London, 1922. 

We may speak of an apparent equivalent weighty playing for colloid behaviour towards added salts a role similar to the true equivalent weight, if not all ionogenic groups are ionised but only a fraction of them. 

There is a continuous transition in the physical properties of solutions of polyphosphates on passing from lower- to higher-molecular-weight species. Apart from the first few members of the series, they all exhibit typical properties of polyelectrolytes. Colloidal behaviour is not exhibited by polyphosphates, however, until the average chain lengths are of the order of hundreds. 

Based on the DLS measurements it is possible to find particle size distributions of polymers and proteins, particle aggregation phenomena, micellar systems and their stability, micro-emulsion technology, colloid behaviour, nucleation processes and protein crystallization. DLS is a non-destructive and convenient method and so it can find application in various branches of science. In chemistry it finds application in topics of colloids, polymers, emulsions, suspensions, nanoparticles, and in physics, applications such as in astrophysics and atmosphere physics and in biology it involves biophysics and biomedicine applications. 

Journal of Applied Polymer Science 76, No.ll, 13th June 2000, p.1677-82 CATIONIC LATEX COLLOIDAL BEHAVIOUR AND INTERACTION WITH ANIONIC PULP FIBRES... 

Styrene-butadiene latices were prepared by emulsion-free polymerisation in the presence of N,N-diethylaminoethyl methacrylate to supply a positive charge and their colloidal behaviour and interaction with anionic pulp fibres investigated. It was found that the latices were positively charged and stabilised by electrostatic repulsion and deposited readily on anionic fibres suspended in water, forming a monolayer on the fibre surface. Dewatering and drying resulted in coalescence of the particles and fibres covered with a polymeric film, which improves the bonding between the fibres. 9 refs. CANADA... 

Khan TN, Mobbs RH, Price C, Quintana JR, Stubbtasfield RB (1987) Synthesis and colloidal behaviour of a polystyrene-b-poly(ethylene oxide) block copolymer. Eur Polym J... 

Bentonite is mentioned by Heaton (1928) in his discussion of china clay (. v.), apparently as an equivalent material he also states that large deposits [of bentonite] have been exploited recently in Western Canada , which may indicate the sphere of usage. The colloidal behaviour was thought to be suited to preparation of lake pigments. 

A large number of drugs have been found to exhibit typical colloidal behaviour in aqueous solution in that they accumulate at interfaces, depressing the surface tension, and form aggregates in solution at sufficiently high concentrations. The biological and pharmaceutical implications of this behaviour have been reviewed [1-3] and are discussed later in this chapter. The first part of the chapter will be concerned primarily with the solution properties of the colloidal drugs, with particular emphasis on their mode of association. 

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