Solid/liquid dispersions

Sample requirements Solids, liquids (dispersed or evaporated on a substrate), or powders must be vacuum compatible... 

Liquid-liquid dispersion, Solid-liquid dispersion. Local shear... 

Solid-Liquid Dispersions, Bohuslav Dobias, Xueping Qiu, and Wolfgang von Rybinski... 

Disperse systems can be classified in various ways. Classification based on the physical state of the two constituent phases is presented in Table 1. The dispersed phase and the dispersion medium can be either solids, liquids, or gases. Pharmaceutically most important are suspensions, emulsions, and aerosols. (Suspensions and emulsions are described in detail in Secs. IV and V pharmaceutical aerosols are treated in Chapter 14.) A suspension is a solid/liquid dispersion, e.g., a solid drug that is dispersed within a liquid that is a poor solvent for the drug. An emulsion is a li-quid/liquid dispersion in which the two phases are either completely immiscible or saturated with each other. In the case of aerosols, either a liquid (e.g., drug solution) or a solid (e.g., fine drug particles) is dispersed within a gaseous phase. There is no disperse system in which both phases are gases. 

The observed values of the mass transfer coefficient- in three-phase systems between solid and liquid for the conventional impellers and a typical baffled vessel (e.g. Rushton turbine, propeller) are between the values predicted by Hiraoka (liquid-liquid dispersion, eq. (3.267)) and Levins and Glastonbuty (solid-liquid dispersion, eq. (3.118)) correlations. However, as an approximation, the Levins and Glastonbuty correlation could be used for three-phase systems (Smith, 1981). 

Vincent, B. The Stability of Solid/Liquid Dispersions in the Presence of Polymers in Solid/Liquid Dispersions, Tadros, Th. F. (Ed.), Academic Press New York, 1987, pp. 147— 162. 

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. 

The adsorption of surfactants at the liquid/air interface, which results in surface tension reduction, is important for many applications in industry such as wetting, spraying, impaction, and adhesion of droplets. Adsorption at the liquid/liquid interface is important in emulsification and subsequent stabilization of the emulsion. Adsorption at the solid/liquid interface is important in wetting phenomena, preparation of solid/liquid dispersions, and stabilization of suspensions. Below a brief description of the various adsorption phenomena is given. 

FIGURE 4.29 Adsorption isotherms of nonionic surfactants on the polar and nonpolar solid surfaces. [Graph reconstructed from data by T. F. Tadros, Solid/Liquid Dispersions, Academic Press, New York, 1987.]... 

T. F. Tadros (Ed.), Solid/Liquid Dispersions, Academic Press, New York, 1987. 

In natural systems, solid-liquid dispersions are the most common colloidal dispersions. 

Equations (5) and (6) were derived for solid-liquid dispersions. These can be easily adapted to any other multiphase system such as gas-solid and gas-liquid systems. The one-dimensional equation of motion for solid phase in terms of instantaneous quantities is given by... 

Under conditions of the homogeneous regime, the steady-state conditions for solid-liquid dispersion are given as follows. 

Emulsion systems can be considered a subcategory of lyophobic colloids. Like solid-liquid dispersions, their preparation requires an energy input, such as ultrasonication, homogenization, or high-speed stirring. The droplets formed are spherical, provided that the interfacial tension is positive and sufficiently large. Spontaneous emulsification may occur if a surfactant or surfactant system is present at a sufficient concentration to lower the interfacial tension almost to zero. 

Myburgh JA, McCarthy TJ. The influence of suspending agents on preservative activity in aqueous solid/liquid dispersions. Pharm Weekbl (Sci) 1980 2 143-148. 

The power dissipated by the impeller in solid-liquid dispersions can be calculated from an equation similar to Eq. (2), i.e.. 

Tadros, T.F. (ed.) (1987) Solid/Liquid Dispersions, Academic Press, London. Tadros, T. (ed.) (2013) Emulsion Formation and Stability, Wiley-VCH Verlag GmbH, Weinheim. 

The above polymeric dispersants are essential materials for the preparation of most disperse systems, of which should be mentioned dyestuffs, paper coatings, inks, agrochemicals, pharmaceuticals, personal care products, ceramics, and detergents [1]. One of the most important applications of polymeric surfactants is in the preparation of oil-in-water (O/W) and water-in-oil (W/O) emulsions, as well as solid/liquid dispersions [2, 3]. In this case, the hydrophobic portion of the surfactant molecule should adsorb strongly at the O/W or become dissolved in... 

Lyklema, J. (1987) Structure of the solid/liquid interface and the electrical double layer, in Solid/Liquid Dispersions (ed. T.F. Tadros), Academic Press, London. 

Two main processes are utilised for the preparation of solid/liquid dispersions ... 

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