Colloid science, definition

For tire purjDoses of tliis review, a nanocrystal is defined as a crystalline solid, witli feature sizes less tlian 50 nm, recovered as a purified powder from a chemical syntliesis and subsequently dissolved as isolated particles in an appropriate solvent. In many ways, tliis definition shares many features witli tliat of colloids , defined broadly as a particle tliat has some linear dimension between 1 and 1000 nm [1] tire study of nanocrystals may be drought of as a new kind of colloid science [2]. Much of die early work on colloidal metal and semiconductor particles stemmed from die photophysics and applications to electrochemistry. (See, for example, die excellent review by Henglein [3].) However, the definition of a colloid does not include any specification of die internal stmcture of die particle. Therein lies die cmcial distinction in nanocrystals, die interior crystalline stmcture is of overwhelming importance. Nanocrystals must tmly be little solids (figure C2.17.1), widi internal stmctures equivalent (or nearly equivalent) to drat of bulk materials. This is a necessary condition if size-dependent studies of nanometre-sized objects are to offer any insight into die behaviour of bulk solids. 

Simple colloidal dispersions are two-phase systems, comprising a dispersed phase of small particles, droplets or bubbles, and a dispersion medium (or dispersing phase) surrounding them. Although the classical definition of colloidal species (droplets, bubbles, or particles) specifies sizes of between one nanometre and one micrometre, in dealing with practical applications the upper size limit is frequently extended to tens or even hundreds of micrometres. For example, the principles of colloid science can be usefully applied to emulsions whose droplets exceed the 1 tm size limit by several orders of magnitude. At the other extreme, the field of nano-... 

Basic concepts of colloid chemistry that are relevant to soils are discussed in Chap. 10 of G. Sposito, The Chemistry of Soils, Oxford University Press, New York, 1989, and in the first three chapters of R. J. Hunter, Foundations of Colloid Science, Vol. I, Clarendon Press, Oxford, 1987. The definitions of flocculation, floccule, and aggregate given in the present chapter are those of its author. 

A definite prediction of DLVO theory is that charge-stabilized colloids can only be kinetically, as opposed to thermodynamically, stable. The theory does not mean anything at all if we cannot identify the crystalline clay state (d 20 A) with the primary minimum and the clay gel state (d 100 to 1000 A) with the secondary minimum in a well-defined model experimental system. We were therefore amazed to discover a reversible phase transition of clear thermodynamic character in the n-butylammonium vermiculite system, both with respect to temperature T and pressure P. These results rock the foundations of colloid science to their roots and... 

This definition of integral distribution function is common in colloid science, while in polymer science the molecular weight distributions are typically evaluated by the summation of molecular weight smaller than the current value... 

This chapter provides an introduction to the occurrence, properties, and importance of foams as they relate to the petroleum industry. The fundamental principles of colloid science may be applied in different ways to stabilize or destabilize foams. This application has practical importance because a desirable foam that must be stabilized at one stage of an oil production process, may be undesirable in another stage and necessitate a defoaming strategy. By emphasizing the definition of important terms, the importance of interfacial properties of foam making and stability is demonstrated. 

Colloid Stability In colloid science, an indication that a specified process, such as aggregation, does not proceed at a significant rate, which is different from the definition of thermodynamic stability (4). The term colloid stability must be used with reference to a specific and clearly defined process, for example, a colloidally metastable emulsion may signify a system in which the droplets do not participate in aggregation, coalescence, or creaming at a significant rate. 

In setting out to define the scope of colloid science, it should first be said that any attempt to lay down loo rigid a scheme of definitions and nomenclature is likely to be unnecessarily restrictive. Rather than try at the outset to develop a formal definition, it is preferable to describe examples of systems to which the term colloidal is now applied. ... 

The definition of some important terms has been given in the Colloid Science section of this book. Chapter 1. Others are given subsequently. 

Readers not in possession of Volume I will certainly be interested in the meaning of the word Colloid Science and a few other terms in frequent use. Before giving their definitions a short and far from complete historical survey may be included, from which the basic principles, on which the definitions are based may be recognized. 

The above list of definitions contains terms which are used in both volumes I and II of this book. It does not yet discriminate between the different possibilities regarding the nature of the kinetic units of large mass. In the next subparagraph these differences will be considered in the case of sols, in more detail. It will be seen that we may discern three cases, according to wich Colloid Science has to deal with the study of three kinds of objects ... 

The loose connection between the contents of Volume I and II of this book, hitherto based only upon the presence of kinetic units of large mass (See definition Colloid Science on p. 2 1 b), is here reinforced by the apparent single systems of composite nature c. and presumably also by the two phase gels d. 

In colloid science the same applies. In its earlier stages predilections of various kinds prevailed. So for instance the idea that we had to do with a totally new branch of science, further in later stages the idea that all its study objects were disperse two phase systems. Nowadays we must grant that colloid science is not a separate science and that it contains two parts (viz., the contents of Volumes I and II), very loosely bound together by a special chosen wordir of a definition (cf. 1). Further that the main p oints of these two parts must really be incorporated at two different places in the vast body of general physical chemistry. 

Starting from the definition just given, the fact is encountered that not only linear polymers, but globular also can cover a far greater field than that according to the colloidal dimensions. As this book is devoted to colloid science, we will confine ourselves therefore chiefly to macromolecules up to 10 A only in special cases some reference will be made to larger ones. 

There is no doubt that the definition of the concept gel offered here applies to typical gels like gelatin, agar, cellulose and silicic acid gels which are also cl rac-terized by the fact that one of the components of the system is a low molecular fluid. Like almost any definition (particularly in colloid science ) difficulties may arise when considering certain limiting and transitionary cases. Some of these will be referred to below. 

In this chapter, the fundamental concepts of colloid science have been introduced. The definition of colloidal particles, those with sizes (in all directions) ranging from 1 nm to 10 pm, has been presented, and their relevance in soil science is stated. The importance of surface properties was remarked, introducing several definitions. The specific surface area is the area per unit mass the surface tension (or surface free energy) is defined as the Gibbs free energy per unit area. The surface excess of a given species is the amount (in moles per unit area) which is accumulated... 

However, amongst the chemical foundations on which the pioneers of supramolecular chemistry were building, although sometimes without acknowledgment, were the basic principles of colloid science. Colloid chemistry had been long established by the time of the initial development of supramolecular chemistry, and had also focused on the behavior of ensembles of molecules—typically mediated through noncovalent interactions. Indeed, the concept of self-assembly is fundamental in the study and manipulation of colloidal materials. By definition, colloids consist of a dispersed phase (or discontinuous phase) distributed... 

R. E. Johnson, Jr., and R. H. Dettre. In Surface and Colloid Science, Vol 2. (E. Matijevic, Ed.) Wiley-Interscience, New York, 1969, pp. 85—153. Definitions of Terms Relating to Surface Imperfections on Ceramics, Annual Book ofASTM Standards, ASTM F 109—73. American Society for Testing and Materials, Philadelphia, 1981. 

The subject of this chapter represents one of the most diverse areas in soft matter science. Colloidal materials are systems in which small droplets or particles of one material are dispersed in a continuous phase of another material. This definition is deliberately broad as colloidal systems span an extremely wide range of materials, from solid particles suspended in aqueous solution, to droplets of moisture in the air, and foams, and can even be extended to include granular materials like sand. Colloidal science is a subject that is particularly relevant in our everyday lives because it plays an important role in the manufacture of numerous everyday substances. Many of the foods we eat can be described as colloids. Creamy foods, like mayonnaise, sauces, or ice cream, contain tiny droplets of fat dispersed in an aqueous medium food can be foams (liked whipped cream), and it can be a solid sponge (like bread or cake). Personal care products like face creams and toothpastes are colloidal systems, as are household paints and inks. Even the dilute polymer solutions discussed in Chapter 4 can be considered colloids. 

In order to keep the size of this chapter manageable, terms from fundamental colloid and interface science are generally not included here. Most definitions have been given in earlier chapters, and much more comprehensive sources for these definitions are available elsewhere. A good starting point is the recommendations of the IUPAC Commission on Colloid and Surface Chemistry [978-980]. For more comprehensive dictionaries and glossaries of terms in colloid and interface science, see Refs. [9-11,981-985],... 

Some terms are used in other ways by other researchers, or in other countries, and may have legal definitions different from those given here. The distinctions drawn among light, heavy, extra-heavy, and bituminous crude oils were made on the basis of United Nations Institute for Training and Research (UNITAR)-sponsored discussions aimed at establishing such definitions (i-3). For terms drawn from the area of colloid and interface science, much reliance was placed on the recommendations of the lUPAC Commission on Colloid and Surface Chemistry (4), For important emulsion terms that are frequently used in industrial practice, the aim was to be consistent with the standard petroleum dictionaries such as references 5-7. 

The work presented here includes both theoretical and experimental aspects of some of the most significant areas of colloidal silica science and technology. This book constitutes an update in the field since Ralph K. Her, the distinguished silica scientist, published the definitive book on silica chemistry in 1979. This new book includes the 11 plenary lectures presented at an international symposium honoring Iler and 22 related research papers. 

Definition and Classification of Foams. Colloidal species of any kind (bubbles, particles, or droplets), as they are visually defined, have at least one dimension between 1 and 1000 nm. Foams are a special kind of colloidal dispersion one in which a gas is dispersed in a continuous liquid phase. The dispersed phase is sometimes referred to as the internal (disperse) phase, and the continuous phase as the external phase. In practical occurrences of foams, the bubble sizes usually exceed the size limit given, as may the thin liquid-film thicknesses. Table II lists some simple examples of petroleum industry foam types. Solid foams, dispersions of gas in a solid, will not in general be covered in this chapter. A glossary of frequently encountered foam terms in the science and engineering of petroleum industry foams is given at the end of this volume. 

---