Colloids practical aspects

Interactions of solutes with monodispersed colloids - practical aspects ... 

Of course, the processing engineer or the colloid chemist seldom worries about the fundamental aspects of the microstructure of the product and its relation to rheology, but many of the topics we discuss in this chapter are useful for gaining the conceptual basis necessary to deal with the practical aspects of dispersion rheology. 

The book contains 45 chapters. The intention has been to cover all practical aspects of surface and colloid chemistry. For convenience the content material is divided into five parts. 

This book is divided into two parts, including the theoretical basis of linear-dichroic infrared (IR-LD) spectroscopy (Chapter 1), the orientation method as colloid suspension in nematic hosts (Chapter 2), and practical aspects (Chapters 3 through 6) associated with the use of the method for the characterization of inorganic chemicals and glasses as well as various classes of organic compounds. In all of the examples, the scope and limitation of the method are discussed and summarized. Therefore, this text can serve as a useful source of information not only for specialists in IR spectroscopy but also for other scientists as well as Ph.D. students working in the field of structural analysis. It can also be successfully used by B.Sc. and M.Sc. students who attend courses for advanced physical methods of analysis. 

In addition to their practical importance, colloidal suspensions have received much attention from chemists and physicists alike. This is an interesting research area in its own right, and it is an important aspect of what is referred to as soft condensed matter physics. This contribution is written from such a perspective, and although a balanced account is aimed for, it is inevitably biased by the author s research interests. References to the original literature are included, but within the scope of this contribution only a fraction of the vast amount of literature on colloidal suspensions can be mentioned. 

In a number of recent publications (1, 2) microcrystailine cellulose dispersions (MCC) have been used as models to study different aspects of the papermaking process, especially with regard to its stability. One of the central points in the well established DLVO theory of colloidal stability is the critical coagulation concentration (CCC). In practice, it represents the minimum salt concentration that causes rapid coagulation of a dispersion and is an intimate part of the theoretical framework of the DLVO theory (3). Kratohvil et al (A) have studied this aspect of the DLVO theory with MCC and given values for the CCC for many salts, cationic... 

An important aspect of porphyrin assembly chemistry is the interaction of porphyrins with colloids and polymers. For years it has been recognized that chlorophyll a is practically insoluble as a monomer and nonfluorescent in hydrocarbon solvents unless a polar activator is present Concentrated... 

The term colloid does not define a molecular species as do the names acids, bases, salts, and esters. Instead the name colloid describes a state in which practically any substance can abide if suitable conditions are provided. In brief, colloid describes a characteristic manner in which one substance can be dispersed in another. Our interest is primarily in what are known as organic colloids. As this is a vast subject for which comprehensive texts are available, here we will give only a brief outline of aspects known to be factors in the industrial use of activated carbon. 

Regulation of the physico-chemical properties of colloid dispersions by polyelectrolytes is of great interest from the theoretical and practical points of view [89]. A consideration of the peculiarities of absorption of polyelectrolytes on disperse particles can be of help to clarify some aspects of kinetics and mechanism of flocculation, elemental acts of flocculation, as well as to provide the se-... 

In a preferred aspect of the process of this invention, the supplementary electrolyte of sodium sulfate is employed at a concentration of about 0.03-0.08 normal. Within this concentration range, the sol electrolyte has a sufficiently low electrical resistivity to permit the use of a practically low voltage on the cell, while at the same time the colloidal silica concentration can be greatly increased in the course of the process by the continued addition of concentrated sodium silicate solution, so that a silica sol containing as much as 35 g or more of Si02 per 100 ml, can be obtained without appreciable deposition of silica on the ion exchange membranes or formation of silica aggregates or gel. 

Standard latexes now are used routinely by colloid scientists as model colloids in experimental studies, a use which has facilitated a much deeper understanding of both practical and theoretical aspects of colloid science than would otherwise have been possible. Standard latexes also are widely used for calibration of instruments which measure particle size. 

This book is intended as a comprehensive reference work on surface and colloid chemistry. Its title, Handbook of Applied Surface and Colloid Chemistry , implies that the book is practically oriented rather than theoretical. However, most chapters treat the topic in a rather thorough manner and commercial aspects, related to specific products, etc. are normally not included. All chapters are up-to-date and all have been written for the specific purpose of being chapters in the Handbook . As will be apparent to the user, the many topics of the book have been covered in a comprehensive way. Taken together, the chapters constitute an enormous wealth of surface and colloid chemistry knowledge and the book should be regarded as a rich source of information, arranged in a way that I hope the reader will find useful. 

Somewhat surprisingly, considering its inherent importance, this neglected dimension has historically been shorthanded in terms of scientists and technicians formally trained in the theoretical and experimental aspects of the discipline. As a result, one can speculate that large amounts of time, money, and other resources have been wasted over the years simply because chemists, physicists, biologists, engineers, and technical operators were ignorant of certain basic ideas about interfaces and colloids that could have solved or helped solve many practical and theoretical problems. 

The previous chapters have introduced several classes of colloids and some of the important surface aspects of their formation, stabilization, and destruction. Emulsions, foams, and dispersions are the most commonly treated and intensely studied examples of colloidal systems. They constitute the majority of practical and ideal systems one encounters. There exists one other class of true, lyophobic colloids—the aerosols—which, although seemingly less important in a theoretical or applied sense, are of great practical importance. 

Aerosols, like foams, emulsions, and dispersions, may be either advantageous or detrimental, depending on the situation. The previous discussion introduced some of the fundamental aspects of aerosol formation. Of equal or perhaps greater practical importance is the question of the suppression of aerosol formation, the destruction of unavoidable aerosols, or the controlled deposition of aerosols onto surfaces. Perhaps the best approach to solving such problems is through an understanding of some of the general principles involved in their stabilization and destruction. In that context, some of the mechanisms of destruction involved will be essentially the same as those for other colloidal systems flocculation and coalescence. 

This class of association colloids can be further divided into several subgroups, which include micelles, vesicles, microemulsions, and bilayer membranes. Each subgroup of association colloids plays an important role in many aspects of colloid and surface science, both as theoretical probes that help us to understand the basic principles of molecular interactions, and in many practical applications of those principles, including biological systems, medicine, detergency, crude-oil recovery, foods, pharmaceuticals, and cosmetics. Before undertaking a discussion of the various types of association colloids, it is important to understand the energetic and structural factors that lead to their formation. 

Vignes-Alder, M. and Brenner, H., A micromechanical derivation of the differential equations of interfacial statics. III. line tension, 7. Colloid Interface Sci., 103,11,1985. Vogler, E.A., Practical use of concentration-dependent contact angles as a measure of solid-liquid adsorption. 1. Theoretical aspects, Langmuir, 8, 2005, 1992. Vrbanac, M.D. and Berg, J.C., The use of wetting measurements in the assessment of acid-base interactions at solid-liquid interfaces, J. Adhesion Sci. TechnoL, 4, 255, 1990. 

This book tries to regard most of these aspects. Internationally recognized scientists describe those fields of cluster and colloid research in which they have been working for many years and therefore are endowed with fundamental knowledge. The book is intended for those scientists working in research as well as in practice who wish to gain a fundamental insight into one or more areas of the world of small metal particles. However, it is addressed to advanced students in physics, chemistry, or materials sciences as well. 

---