Physical chemistry disperse systems

Basic Principles of Physical Chemistry of Dispersed Systems. 261... 

BASIC PRINCIPLES OF PHYSICAL CHEMISTRY OF DISPERSED SYSTEMS... 

Table 1.6 also lists the radius of gyration. This is an average dimension often used in colloid science to characterize the spatial extension of a particle. We shall see that this quantity can be measured for polydisperse systems by viscosity (Chapter 4) and light scattering (Chapter 5). It is therefore an experimental quantity that quantifies the dimensions of a disperse system and deserves to be included in Table 1.6. Since the typical student of chemistry has probably not heard much about the radius of gyration since general physics, a short review seems in order.

Thin liquid films bordering a gas phase on both sides, or the so-called free films, are one of the oldest objects of research in the physical chemistry of disperse systems. The reason is probably the ease of their formation, simplicity, uniformity of surfaces, etc. Thin films, including foam films, are an efficient and useful model for the study of many surface phenomena. 

The fact that foamed plastic can be classified among fine-dispersed systems is highly important since their structure may be studied not only from the conventional polymer point of view, but also by applying a different novel and promising approach — the physics and chemistry of disperse materials. 

Most of the other basic chemical tools are dispersed in boxes elsewhere in the book, sited where the concept is first needed to understand a term or process. To help you find some of these more easily, Fig. 2.5 maps out the position of some of the key boxes. We have ordered these under three main headings (i) system acidity and oxidation (ii) water and (iii) physical chemistry. 

Surfactants find apphcation in almost all disperse systems that are utilised in areas such as paints, dyestulfs, cosmetics, pharmaceuticals, agrochemicals, fibres, and plastics. Therefore, a fundamental understanding of the physical chemistry of surface-active agents, their unusual properties, and their phase behaviour is essential for most formulation chemists. In addition, an understanding of the basic phenomena involved in the application of surfactants, such as in the preparation of emulsions and suspensions and their subsequent stabilisation, in microemulsions, in wetting, spreading and adhesion, is vitally important to arrive at the correct composition and control of the system involved [1, 2]. This is particularly the case with many formulations in the chemical industry mentioned above. 

Rehbinder, P.A., Selected Works , vol. 2, Surface Phenomena in Disperse Systems. Physical Chemical Mechanics, Nauka, Moscow, 1979 (in Russian)Colloid Chemistry, Nauka, Moscow, 1978... 

This book covers major areas of modern Colloid and Surface Science (in some countries also referred to as Colloid Chemistry) which is a broad area at the intersection of Chemistry, Physics, Biology and Material Science investigating the disperse state of matter and surface phenomena in disperse systems. The book arises of and summarizes the progress made at the Colloid Chemistry Division of the Chemistry Department of Lomonosov Moscow State University (MSU) over many years of scientific, pedagogical and methodological work. 

Although this book significantly differs from the earlier Colloid Chemistry textbook, it nevertheless focuses on the specifics of educational and research work carried out at the Colloid Chemistry Division at the Chemistry Department of MSU. Many results presented in this book represent the art developed in the laboratories of the Colloid Chemistry Division, in the Laboratory of Physical-Chemical Mechanics (headed by E.D. Shchukin since 1967) of the Institute of Physical Chemistry of the Russian Academy of Science, and in other research institutions and industrial laboratories under the guidance of the authors and with their direct participation. Special attention is devoted in the book to the broad capabilities that the use of surfactants offers for controlling the properties and behavior of disperse systems and various materials due to the specific physico-chemical interactions taking place at interfaces. At the same time the authors made every effort to avoid duplication of material traditionally covered in textbooks on physical chemistry, electrochemistry, polymer chemistry, etc. These include adsorption from the gas phase on solid surfaces (by microporous adsorbents), the structure of the dense part of the electrical double layer, electrocapillary phenomena, specific properties of polymer colloids, and some other areas. 

Colloid Chemistry or, alternatively, Colloid and Surface Science, are the established and traditionally used names of the field of science devoted to the investigation of substances in dispersed state with particular attention to the phenomena taking place at interfaces. Peter A. Rehbinder defined colloid chemistry as the chemistry, physics, and physical chemistry of disperse systems and interfacial phenomena [1-6]. 

These are systems in which a distinct phase of colloids is dispersed. Colloidal particles are, according to conventions in physical chemistry (colloidal chemistry and physics), considered to have a size between 1 nm (10 m) and 0.1-1 p (10 M0 m). Colloidal systems therefore show interfaces of mainly very large size. The solvent or matrix is not present in the dispersed phase. Solutions are systems in which solvent and solvated materials are forming one single phase, no phase boundaries are present, the solvated material is present in atomic or molecular scale, a maximum of 1 nm in diameter. 

Adsorption of polymers onto colloidal particles is of great interest for the chemical industry [88] and physical chemistry of disperse systems in cormection with the fundamental problem of colloidal stability [89]. The structure of an adsorbed polymer layer can be probed by neutron [90] or X-ray [91] scattering, while the kinetics of adsorption can be followed by absorption spectroscopy [44]. 

Following these successes an overestimation of the value of explanation b. set in, it being believed valid in all cases. The term Colloid as a class name in Graham s sense of the word became obsolete and "Colloid Chemistry" might subsequently be defined as the physical chemistry of two-phase systems, one of the phases being dispersed to so-called colloidal dimensions in the bosom of the other phase. 

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. 

An interdisciplinary team of leading experts from around the world discuss recent concepts in the physics and chemistry of various well-studied interfaces of rigid and deformable particles in homo- and hetero-aggregate dispersed systems, including emulsions, dispersoids, foams, fluosols, polymer membranes, and biocolloids. The contributors clearly elucidate the hydrodynamic, electrodynamic, and thermodynamic instabilities that occur at interfaces, as well as the rheological properties of interfacial layers responsible for droplets, particles, and droplet-particle-film structures in finely dispersed systems. The book examines structure and dynamics from various angles, such as relativistic and non-relativistic theories, molecular orbital methods, and transient state theories. 

Static electrical parameters of molecules (polarizabilities and hyperpolarizabilities) are quantities which play an important role in the characterization of a wide spectrum of physical-chemistry properties of molecular systems and materials. Among the properties which are particularly relevant to this characterization one should mention the electric polarizability, the optical absorption characteristics, and the intermolecular dispersion interaction (molecule-molecule, molecule-surface, etc) [2, 9, 74]. 

---