Colloidal dispersions aerosols

Colloidal-sized particles in the atmosphere are called aerosols. Those formed by grinding up bulk matter are known as dispersion aerosols, whereas particles formed from chemical reactions... 

Emulsions and suspensions are colloidal dispersions of two or more immiscible phases in which one phase (disperse or internal phase) is dispersed as droplets or particles into another phase (continuous or dispersant phase). Therefore, various types of colloidal systems can be obtained. For example, oil/water and water /oil single emulsions can be prepared, as well as so-called multiple emulsions, which involve the preliminary emulsification of two phases (e.g., w/o or o/w), followed by secondary emulsification into a third phase leading to a three-phase mixture, such as w/o/w or o/w/o. Suspensions where a solid phase is dispersed into a liquid phase can also be obtained. In this case, solid particles can be (i) microspheres, for example, spherical particles composed of various natural and synthetic materials with diameters in the micrometer range solid lipid microspheres, albumin microspheres, polymer microspheres and (ii) capsules, for example, small, coated particles loaded with a solid, a liquid, a solid-liquid dispersion or solid-gas dispersion. Aerosols, where the internal phase is constituted by a solid or a liquid phase dispersed in air as a continuous phase, represent another type of colloidal system. 

Pharmaceutical colloids such as emulsions and suspensions (Fig. 7.1) and aerosols are readily identified (Table 7.1). The disperse phase is the phase that is subdivided. The continuous phase is the phase in which the disperse phase is distributed. Many natural systems such as suspensions of microorganisms, blood, and isolated cells in culture, are also colloidal dispersions. Colloid science is interdisciplinary, for although dealing with complex systems it is nevertheless a unifying discipline as it bridges the physical and... 

Visca, M. and Matijevic, E., Prepai ation of uniform colloidal dispersions by chemical reactions in aerosols. 1. Spherical particles of titanium dioxide, J. Colloid Interf. Sci., 68, 308, 1979. 

The adsorbers should be protected with dust filters to prevent them from becoming filled with particulate material which would add resistance and restrict the flow of air. It is also desirable to make provision for the continuous removal of aerosols because these are not appreciably adsorbed by carbon. Smoke (a typical aerosol) is a colloidal dispersion of tars in air and, unless it is removed as soon as formed, the colloidal tars will deposit on all surfaces—walls, floors, ceilings—from which they will slowly evaporate to cause a persistent odorous environment. A typical example is a smoke-filled room on the morning after. All such after-effects can be avoided by placing... 

Aerosol Colloidal dispersion of liquids or solids in a gas. Distinctions may be made among aerosols of liquid droplets (e.g., fog) and aerosols of solid particles (e.g., smoke and dust). See also Mist. 

The above remarks are couched in very general terms, and apply to some extent to most forms of small metal particle. The available forms are (i) powders, a term which embraces a set of particles of any size, as long as it flows freely (Section 2.2), (ii) aerosols, (iii) colloidal dispersions (Section 2.2), and (iv) supported metals (Section 2.3), including particles formed by condensation of metal atoms onto a flat surface this leads ultimately to a condensed metal film. 

An aerosol is a colloidal dispersion of particles in gas. Fumed or pyrogenic oxides, also known in the case of silica as aerosUs, are powders made by condensing a... 

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. 

Aerosols are colloidal dispersions in which either a solid or a liquid is dispersed in a continuous gas phase. Some examples are given in Tables 1.3, 9.1,10.1,11.1, 12.1,13.1,13.3,14.1 and 15.1. Two principal types of aerosols are distinguished in colloid science and nanotechnology, which are as follows ... 

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. 

Suspensions, and to some degree emulsions, foams and aerosols, play crucial roles in the evolution of the earth s rocks, rivers, streams, lakes, oceans and soils. Table 9.1 lists some examples. In many cases, their role is somewhat disguised in that these colloidal dispersions are the precursors to the ultimate products, the latter having very different final appearances, such as many rocks, sediments and soils. 

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. 

Other types of colloid include aerosols (dispersions of liquid or solid particles in a gas, as in a mist or smoke) and foams (dispersions of gases in liquids or solids). Colloids are analysed theoretically in terms of intermolecular forces. 

Despite their finite stability, dispersed colloidal systems, such as emulsions, dispersions, aerosols and liposomes, have several advantages as drug delivery systems. For example, emulsions offer opportunities for solubilizing relatively large amounts of hydrophobic active... 

In Chapter 1 the importance of the various classes of colloidal systems to modern science and technology was indicated in a general way. Because of the wide variety of colloidal systems one encounters, each having certain unique features that distinguish it from the others, it is convenient to discuss each major classification separately. For that reason, chapters have been devoted to specific systems such as solid dispersions, aerosols, emulsions, foams, lyophilic colloids (i.e., polymer solutions), and association colloids. There is a great deal of overlap in many aspects of the formation, stabilization, and destruction of those systems, and an effort will be made not to repeat more than is necessary. However, for purposes of clarity, some repetition is unavoidable. 

The previous chapters have introduced several classes of colloids and some of the important surface aspects of their formation, stabilization, and destruction. Emulsions, foams, and dispersions are the most commonly treated and intensely studied examples of colloidal systems. They constitute the majority of practical and ideal systems one encounters. There exists one other class of true, lyophobic colloids—the aerosols—which, although seemingly less important in a theoretical or applied sense, are of great practical importance. 

Interfacial effects are especially important in systems where interfadal area is large. This condition is met when one phase is dispersed in another as small drops or particles. With spherical particles, for example, the arearvolume ratio of the dispersed phase is (3/R), where R is the partiele radius. Qearly as R decreases with a given volume of the dispersed matraial present, interfadal area increases. When at least one dimension of each drop or particle decreases to a value in the range of 1 /rm or less, we say that a eoUoidal dispra ion exists. Foams, aerosols, and emulsions are colloidal dispersions involving fluid interfaces that are familiar from everyday life and are important in applieations ranging from food products... 

Colloidal dispersions are those having particles or drops with at least one dimension greater than about 1 nm bnt less than abont 1 rm. These systems are classified as emnlsions when a hquid phase is dispersed in a second liquid, suspensions when a sohd phase is dispersed in a liqnid medinm, foams when a gas is dispersed in a hquid, or aerosols when hqnid droplets or solid particles are dispersed in gas. Other combinations are less common. 

Pollutants are also found in the form of colloidal dispersions the haze in the atmosphere is the result of pollutants dispersed as aerosols. Oils or oily materials are emulsified in the wastewater from refineries and chemical plants and have to be removed before discharging the effluent into rivers or seas. 

This method of formulation by von Smoluchowski and Fuchs is limited to small concentrations of particles. Then the fixed particle can at most feel the presence of one other particle, and (p is equal to the sum of the van der Waals attraction and the electrical double-layer repulsion poteitial, or, as discussed in previous sections. In this limit it is also legitimate to model the reaction as a second-order reaction (i.e., only two-particle collisions can occur and the higher body collisions are virtually nonexistent). In aerosols, which arc colloidal dispersions in air, there is no significant electrical repulsion betwerai particles. Hence the effect of interparticle forces on the initial coagulation rate is negligible, and we find... 

An aerosol is a (colloidal) dispersion of particles in a gas, which for therapeutic aerosols is air. There is no definition for the particle size disttibutimi of an aerosol, but most airborne particles are within the size range between 0.2 and 20 pm. 

The results of the two studies described earlier illustrate a key advantage to the use of fine particle technology for pulmonary delivery of poorly water-soluble drugs. Nanoparticulate colloidal dispersions of poorly soluble drugs can be aerosolized into... 

Arabi-Katbi O.I., Wegner K., Pratsinis S.E. Aerosol synthesis oftitania nanoparticles Effect of flame orientation and configuration. Ann. Chimie, Sci. Mater. 2002 27(6) 37-46 Barnickel P., Wokaun A., Sager W., Eicke H.-F. Size tailoring of silver colloids by reduction in W/0 microemulsions. J. Colloid Interface Sci. 1992 148(1) 80-90 Bender J., Wagner N.J. Reversible shear thickening in monodisperse and bidisperse colloidal dispersions. J. Rheol. 1996 40(5) 899-916... 

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