Introduction to Applied Colloid and Surface Chemistry

Georgios M. Kontogeorgis, Soren Kiil

• Publisher: Wiley
• Year: 2016
• Print ISBN: 9781118881187
• eBook ISBN: 9781118881200
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

Colloid and Surface Chemistry is a subject of immense importance and implications both to our everyday life and numerous industrial sectors, ranging from coatings and materials to medicine and biotechnology.

How do detergents really clean? (Why can't we just use water?) Why is milk "milky"? Why do we use eggs so often for making sauces? Can we deliver drugs in better and controlled ways? Coating industries wish to manufacture improved coatings e.g. for providing corrosion resistance, which are also environmentally friendly i.e. less based on organic solvents and if possible exclusively on water. Food companies want to develop healthy, tasty but also long-lasting food products which appeal to the environmental authorities and the consumer. Detergent and enzyme companies are working to develop improved formulations which clean more persistent stains, at lower temperatures and amounts, to the benefit of both the environment and our pocket. Cosmetics is also big business! Creams, lotions and other personal care products are really just complex emulsions.

All of the above can be explained by the principles and methods of colloid and surface chemistry. A course on this topic is truly valuable to chemists, chemical engineers, biologists, material and food scientists and many more.

1
Introduction to Colloid and Surface Chemistry

1.1 What are the colloids and interfaces? Why are they important? Why do we study them together?

Colloid and surface chemistry is a core subject of physical chemistry. It is a highly interdisciplinary subject, of interest to diverse fields of science and engineering (pharmaceuticals, food, cosmetics, detergents, medicine and biology, up to materials and microelectronics, just to mention a few). Being challenging to teach, it is often either incorporated or presented very briefly in general physical chemistry courses or, even worse, completely neglected (Panayiotou, 1998).

Colloidal systems have a minimum of two components. Colloidal dispersions are systems of particles or droplets with the “right dimensions” (the dispersed phase), which are dispersed in a medium (gas, liquid or solid). The medium is called the continuous phase, which is usually in excess. But which are the “right dimensions”? The particles or droplets have dimensions (or one key dimension) between (typically) 1 nm and 1 μm and their special properties arise from the large surfaces due to precisely these dimensions (Figure 1.1).

Figure 1.1 Scales in colloid and surface science. Typically, colloidal particles have one key dimension between 1 nm and 1 μm (micrometre).

Adapted from Wesselingh et al. (2007), with permission from John Wiley & Sons, Ltd

However, sometimes even larger particles, with diameters up to 10 or even up to 50 micrometre (μm), e.g. in emulsions, or very small particles as small as 5 × 10^–10 m can present colloidal character. Thus, despite the above definition, it is sometimes stated that “If it looks like and if it acts like a colloid, it is a colloid”.

Colloids are characterized by their many interesting properties (e.g. kinetic or optical) as well as by observing their stability over time.

The characteristic properties of colloidal systems are due to the size of the particles or droplets (i.e. the dispersed phase), and not to any special nature of the particles. However, their name is attributed to Thomas Graham (Figure 1.2), who was studying glue-like (gelatinous or gum-like polymeric) solutions (from the Greek word for glue which is “colla”).

Figure 1.2 Thomas Graham (1805–1869), the pioneer in the study of colloidal systems, used the term “colloids” derived from the Greek word for glue (“colla”). He thought that their special properties were due to the nature of the compounds involved. Later, it was realized that the size of particles (of the “dispersed phase”, as we call it) is solely responsible for the special properties of colloidal systems. (Right) T. Graham, H407/0106.

Courtesy of Science Photo Libraryx

Many colloidal systems like milk are easily identified by their colour, or more precisely their non-transparent appearance (Figure 1.3). The optical properties of colloids are very important, also in their characterization and study of their stability – as discussed in later chapters.

Figure 1.3 A non-colloidal (water) and a colloidal liquid system (milk)

Colloidal particles (or droplets) are not always spherical. They can have various shapes (e.g. spherical and rod- or disk-like), as shown in Figure 1.4. Proteinic and polymeric molecules are usually large enough to be defined as colloid particles. Moreover, their shape may be somewhat affected by solvation (hydration) phenomena, where solvent molecules become “attached” to them and influence their final properties. Solutions of proteins and polymers may be stable and they are classified as lyophilic colloids. Many colloidal particles (e.g. Au or AgI) are (near)spherical, but others are not. For example, proteins are often ellipsoids, while many polymers are random coils.

Figure 1.4 Different shapes of colloid particles with molecular weights provided in g mol^–1. Pr J. L. Onclev. Harvard Medical School

1.1.1 Colloids and interfaces

What about surfaces and interfaces? Colloidal systems are composed of small particles dispersed in a medium. The fact that these particles have such small dimensions is the reason that a huge surface (interfac...

Table of contents

• Cover
• Title Page
• Table of Contents
• Preface
• Useful Constants
• Symbols and Some Basic Abbreviations
• About the Companion Web Site
• 1 Introduction to Colloid and Surface Chemistry
• 2 Intermolecular and Interparticle Forces
• 3 Surface and Interfacial Tensions – Principles and Estimation Methods
• 4 Fundamental Equations in Colloid and Surface Science
• 5 Surfactants and Self-assembly. Detergents and Cleaning
• 6 Wetting and Adhesion
• 7 Adsorption in Colloid and Surface Science – A Universal Concept
• 8 Characterization Methods of Colloids – Part I
• 9 Characterization Methods of Colloids – Part II
• 10 Colloid Stability – Part I
• 11 Colloid Stability – Part II
• 12 Emulsions
• 13 Foams
• 14 Multicomponent Adsorption
• 15 Sixty Years with Theories for Interfacial Tension – Quo Vadis?
• 16 Epilogue and Review Problems
• Index
• End User License Agreement