Colloidal Properties of Aerosols

In a first analysis, we can identify at least four basic differences between aerosols and other colloids related to the dispersion medium (1) buoyancy effects, (2) the effects of movement of the dispersing medium, (3) particle mobility in undisturbed conditions (i.e., free fall), and (4) modification of interactions by the intervening medium. In emulsions, foams, and sols we have seen that buoyancy can be important in determining the stability of a system (i.e., matching the densities of dispersed and continuous phases can retard creaming or sedimentation). In aerosols, where the density of the continuous phase will always be significantly less than that of the dispersed particle, such effects are practically nonexistent—the colloid is essentially left to its own devices the usual interactions found for all colloids, the constant  

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Hygroscopic, Surface, and Colloidal Properties of Organic Aerosols 474... 

Shinoda K, Kunieda H. The effect of salt concentration, temperature and additives on the solvent property of aerosol-OT solutions. J Colloid Interface... 

When trying to understand and to manipulate matter and materials, chemistry does not start by looking at the natural world in all its complexity. Rather, it seeks to establish what have been termed exemplar phenomena ideal or simplified examples that are capable of investigation with the tools available at the time (Gilbert, Borrlter, Elmer, 2000). This level consists of representatiorrs of the empirical properties of solids, liquids (taken to include solutions, especially aqueous solutiorts), colloids, gases and aerosols. These properties are perceptible in chemistry laboratories and in everyday life and are therefore able to be meastrred. Examples of such properties are mass, density, concentration, pH, temperatrrre and osmotic presstrre. 

In what follows, heterogeneous transformations are understood as chemical or physical-chemical transformations that take place on some surfaces, for example, on interfaces or surfaces possessing catalytic properties. This wide understanding of the term heterogeneous transformation includes surface catalytic reactions, adsorption and desorption on solid and fluid surfaces, dissolving of crystals in fluid, electrochemical reactions on the surface of an electrode in electrolyte, sublimation and condensation, sedimentation of aerosols and colloids, etc. Chemical transformations taking place in the bulk of fluid will be called homogeneous transformations or volume chemical reactions. 

In systems with liquid dispersion medium, i.e. in foams, emulsions, sols and suspensions, there is a broad variety of means to control colloid stability. In these systems the nature of colloid stability depends to a great extent on the aggregate state of dispersed phase. Similar to aerosols, foams are lyophobic, but in contrast to them can be effectively stabilized by surfactants. Properties of emulsions, and, to some extent, those of sols may be quite close to the properties of thermodynamically stable lyophilic colloidal systems. In such systems a high degree of stability may be achieved with the help of surfactants. 

In addition to the advancement in knowledge of the chemical composition of cigarette smoke was the advancement in the knowledge of its physical properties, that of an aerosol. An aerosol is defined as a colloidal system of dispersed liquid or solid material in a gaseous medium. Cigarette smoke is an aerosol comprising liquid droplets in a gas. 

Definition Aerosols are snspensions of solid or liquid particles in a gas. Dust, smoke, mists, fog, haze, and smog are various forms of common aerosols. Colloids are suspensions of solid particles in a liquid. Colloidal particles are typically in the range of nanometers to few microns. The rheological properties of colloidal suspensions are strongly affected by the donble-layer forces. Emulsions are suspensions of droplets of liquids in another immiscible liquid. 

Applications of microparticles can be found in medicine, biochemistry, colloid chemistry, and aerosol research [48]. Some uses include separation media for chromatographic application, high surface area substrates for immobilized enzymes, standards for calibration, spacers in optical cavities and liquid crystal displays, and three-dimensional microenvironments for cell encapsulation. It should be stressed that even a scaled-up MF synthesis enables generation of a relatively small amount of particles, in comparison with conventional emulsion, dispersions, or suspension polymerizations. Thus, most practical applications of such microbeads should utilize their high-value unique properties, for example, a uniform distribution of sizes and control of morphology, structure, and shape. Therefore, some of the demonstrated applications of polymer microbeads are still in the proof-of-concept stage. 

It is because of the subdivision of matter in colloidal systems that they have special properties. The large surface-to-volume ratio of the particles dispersed in a liquid medium results in a tendency for particles to associate to reduce their surface area, so reducing their contact with the medium. Emulsions and aerosols are thermodynamically unstable two-phase systems which only reach equilibrium when the globules have coalesced to form one macro-phase, for which the surface area is at a minimum. Many pharmaceutical problems revolve around the stabilisation of colloidal systems. 

This book is focused on emulsions, foams, suspensions and aerosols, and then-fundamentals and apphcations. The variety of systems represented or suggested by Tables 1.2 and 1.3 underscores the fact that the problems associated with colloids are usually interdisciplinary in nature, and that a broad scientific base is required to understand them completely. A wealth of literature exists on the topic of colloidal dispersions, including a range of basic colloid reference texts [12—29], dictionaries [5-8, 30,31] and treatises on the myriad of apphed aspects, of which only a few are cited here [32-43]. The widespread importance of emulsions, foams and suspensions, in particular, and scientific interest in their formation, stability and properties have precipitated a wealth of specialized publications dedicated to each of emulsions [44-49], foams [50-54], suspensions [32,55-58] and aerosols [10, 59-63], of which only a few representative examples are given here. 

In colloidal dispersions a thin intermediate region or boundary, known as the interface, lies between the dispersed and continuous phases. Each of emulsions, foams, suspensions, and aerosols represent colloidal systems in which interfacial properties are very important because droplets, bubbles and particles can have very large interfadal areas. 

This book provides an introduction to the colloid and interface science of four of the most common types of colloidal dispersion emulsions, foams, suspensions and aerosols. The initial emphasis covers basic concepts important to understand-ing most kinds of colloidal dispersions, not just emulsions, foams, suspensions and aerosols, and is aimed at providing the necessary framework for understanding their applications. The treatment is integrated for each major physical property class, the principles of colloid and interface science common to each dispersion type are presented first, followed as needed by separate treatments of features unique to emulsions, foams, suspensions or aerosols. The second half of the book provides examples of the applications of colloid science, again in the context of emulsions, foams, suspensions and aerosols, and includes attention to practical processes and problems in various industrial settings. 

The applications of, or problems caused by, emulsions, foams, suspensions and aerosols in industry area are quite diverse and have great practical importance. The different industrial application settings share some important common themes as well. Colloidal dispersions can be found, may require treatment or may be applied to advantage throughout most, if not all, of the process industries. In each case, the nature, properties or even the presence or absence of these dispersions can determine both the economic and technical successes of the industrial process concerned. In this book, a wide range of applications areas are summarized. 

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