Principles of Colloid and Surface Chemistry, Revised and Expanded

Paul C. Hiemenz, Raj Rajagopalan, Paul C. Hiemenz, Raj Rajagopalan

• Editore: CRC Press
• Anno: 2016
• ISBN:
  9781351990738
• Edizione: 3
• Argomento: Physical Sciences
• Categoria: Physical & Theoretical Chemistry

This work aims to familiarize students with the fundamentals of colloid and surface science, from various types of colloids and colloidal phenomena, and classical and modern characterization/measurement techniques to applications of colloids and surface science in engineering, technology, chemistry, physics and biological and medical sciences. The Journal of Textile Studies proclaims "High praise from peers...contains valuable information on many topics of interest to food rheologists and polymer scientists …[The book] should be in the libraries of academic and industrial food research organizations" and Chromatographia describes the book as "…an excellent textbook, excellently organised, clearly written and well laid out."

1

Colloid and Surface Chemistry:

Scope and Variables

Next … come the Nobility, of whom there are several degrees, beginning at Six-Sided Figures, … and from thence rising in the number of their sides till they receive the honorable title of Polygonal…. Finally when the number of sides becomes so numerous, and the sides themselves so small, that the figure cannot be distinguished from a circle, he is included in … the highest class of all.

From Abbott’s Flatland

1.1 INTRODUCTION

“Yesterday, I couldn’t define colloid chemistry; today, I’m doing it.” This variation of an old quip could apply to many recent chemistry and engineering graduates on entering employment in the “real world.” Two facts underlie this situation. First, colloid and surface science, although traditional parts of physical chemistry, have largely disappeared from introductory physical chemistry courses. Second, in research, technology, and manufacturing, countless problems are encountered that fall squarely within the purview of colloid and surface science. In this section we enumerate some examples that illustrate this statement. The nine “vignettes” included in this chapter also illustrate the importance of colloid and surface science in a broad range of scientific and technological areas.

The paradoxical situation just described means that it is entirely possible for a science or an engineering student to have completed a course in physical chemistry and still not have any clear idea of what colloid and surface science are about. A book like this one is therefore in the curious position of being simultaneously “advanced” and “introductory.” Our discussions are often advanced in the sense of building on topics from physical chemistry. At the same time, we have to describe the phenomena under consideration pretty much from scratch since they are largely unfamiliar. In keeping with this, this chapter is concerned primarily with a broad description of the scope of colloid and surface science and the kinds of variables with which they deal. In subsequent chapters different specific phenomena are developed in detail.

1.1a Colloid and Surface Chemistry: Some Definitions

1.1a.1 Definition of Colloids

Our first tasks are to define what we mean by colloid science and how this is related to surface science. For our purposes, any particle that has some linear dimension between 10⁻⁹ m (10 Å) and 10⁻⁶ m (1 μm or 1 μ)* is considered a colloid. For us, linear dimensions rather than particle weights or the number of atoms in a particle will define the colloidal size range; however, other definitions may be encountered elsewhere. It should be emphasized that these limits are rather arbitrary. Smaller particles are considered within other branches of chemistry, and larger ones are considered within sciences other than chemistry. The statement above may be expanded still further. Colloid science is interdisciplinary in many respects; its field of interest overlaps physics, biology, materials science, and several other disciplines. It is the particle dimension – not the chemical composition (organic or inorganic), sources of the sample (e.g., biological or mineralogical), or physical state (e.g., one or two phases) – that consigns it to our attention. With this in mind, it is evident that colloid science is the science of both large molecules and finely subdivided multiphase systems.

1.1a.2 Surfaces and Interfaces

It is in systems of more than one phase that colloid and surface science meet. The word surface is thus used in the chemical sense of a phase boundary rather than in a strictly geometrical sense. Geometrically, a surface has area but not thickness. Chemically, however, it is a region in which the properties vary from those of one phase to those of the adjoining phase. This transition occurs over distances of molecular dimensions at least. For us, therefore, a surface has a thickness that we may imagine as shrinking to zero when we desire a purely geometric description. The term interface is also used in this context. This term simply highlights the fact that the surface of interest is the dividing region between two phases.

It is self-evident that the more finely subdivided a given weight of material is, the higher the surface area will be for that weight of sample. In the following section we discuss this in considerable detail since it is the basis for combining a discussion of surface and colloid science in a single book.

1.1a.3 Other Concepts and Classification of Colloids

In subsequent sections of this chapter, we discuss further the distinction between macromolecular colloids and multiphase dispersions (Section 1.3), the use of the term stability in colloid science (Section 1.4), the size and shape of colloidal particles, the states of aggregation among particles, and the distribution of particle sizes that is typical of virtually all colloidal preparations (Section 1.5). The fact that particles in the colloidal size range are not all identical in size also requires a preliminary discussion of statistics, which is the subject of Section 1.5c and Appendix C.

VIGNETTE I.1 ENVIRONMENTAL SCIENCES: Colloid-Enhanced Transport in Unconsolidated Media

Contaminated bed sediments exist at numerous locations in the United States and around the world. These result mainly from past indiscriminate pollution of our aquatic environments and consist of freshwater and marine bodies including streams, lakes, wetlands, and estuaries. The bed sediments contain many hydrophobic organic compounds and metal ions that in the course of time act as sources of pollutants of the overlying aqueous phase. There are a number of transport pathways by which pollutants are transferred to the aqueous phase from contaminated sediments. One of the lesser known, but potentially important, modes of transport of pollutants from bed sediments is by diffusion and advection of contaminants associated with colloidal-size dissolved macromolecules in pore water. These colloids are measured in the aqueous phase as dissolved organic compounds (DOCs). (These are defined operationally as particles with a diameter smaller than 0.45 micrometer.)

The facilitated transport of compounds by colloids, illustrated schematically in Figure 1.1, is important in several areas and especially in the study of the fate and transport processes of hydrophobic organic compounds and metal ions in the environment. This facilitated transport also has implications in other areas in which colloid diffusion through porous media is important, such as those processes utilizing porous sorbents to clean up water and in situ flushing of subsurfa...