Interfacial phenomenon

There is no doubt that the discipline of interfacial phenomena is an indispensable part of emulsion polymerization. Thus, the goal of this chapter is to offer the reader an introductory discussion on the interfacial phenomena related to the emulsion polymerization process, industrial emulsion polymerization processes (primarily the semibatch and continuous reaction systems), some important end-use properties of latex products, and some industrial apphcations. In this manner, the reader may effectively grasp the key features of emulsion polymerization mechanisms and kinetics. Some general readings in this vital interdisciphnary research area [1-6] are recommended for those who need to familiarize themselves with an introduction to the basic concepts of colloid and interface science. 

An interface is, as the name suggests, a boundary between phases. Because interfaces are very thin—in most cases only a few molecular diameters thick— we sometimes tend to think of them as two-dimensional surfaces and neglect their thicknesses. But the third dimension is of great significance as well. Indeed, the rapid changes in density and composition across interfaces give them their most important property, an excess free energy or lateral stress which is usually called interfacial tension. 

When three phases are present, three different interfaces are possible, one for each pair of fluids. Sometimes all three interfaces meet, the jimction forming a curve known as a contact line. If one phase is a sohd, the contact line lies along its surface. In this case, the angle that the fluid interface makes with the solid surface is called the contact angle. Since it reflects the wetting properties of liquids on solids, the contact angle is a second fundamental property important in interfacial phenomena. 

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 

The first four chapters thus provide a general background on interfacial phenomena, colloidal dispersions, and surfactants, with emphasis on their equilibrium properties. The remaining chapters deal with the dynamic behavior of interfaces, emphasizing this subject to a much greater degree than most books on interfacial phenomena. 

Chapter 5 considers the stabiUty of fluid interfaces, a subject pertinent both to the formation of emulsions and aerosols and to thdr destruction by coalescence of drops. The closely related topic of wave motion is also diseussed, along with its implications for mass transfer. In both cases, boundary eonditions applicable at an interface are derived—a significant matter because it is through boundary conditions that interfacial phenomena influence solutions to the governing equations of flow and transport in fluid systems. 

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The physical chemist is very interested in kinetics—in the mechanisms of chemical reactions, the rates of adsorption, dissolution or evaporation, and generally, in time as a variable. As may be imagined, there is a wide spectrum of rate phenomena and in the sophistication achieved in dealing wifli them. In some cases changes in area or in amounts of phases are involved, as in rates of evaporation, condensation, dissolution, precipitation, flocculation, and adsorption and desorption. In other cases surface composition is changing as with reaction in monolayers. The field of catalysis is focused largely on the study of surface reaction mechanisms. Thus, throughout this book, the kinetic aspects of interfacial phenomena are discussed in concert with the associated thermodynamic properties. 

B. Widom, Interfacial Phenomena, in Liquids, Freezing and Glass Transition, Les Houches Session LI, 1989, Elsevier, 1991, pp. 507-546. 

K. E. Gubbins, Fluid Interfacial Phenomena, Wiley, New York, 1986. 

J. T. Davies and E. K. Rideal, Interfacial Phenomena, Academic, New York, 1963. 

One fascinating feature of the physical chemistry of surfaces is the direct influence of intermolecular forces on interfacial phenomena. The calculation of surface tension in section III-2B, for example, is based on the Lennard-Jones potential function illustrated in Fig. III-6. The wide use of this model potential is based in physical analysis of intermolecular forces that we summarize in this chapter. In this chapter, we briefly discuss the fundamental electromagnetic forces. The electrostatic forces between charged species are covered in Chapter V. 

P. Becher, in Interfacial Phenomena in Apolar Media, H. Eicke and G. D. Parfitt, eds., Marcel Dekker, New York, 1987 Nonionic Surfactants Physical Chemistry, M. J. Schick, ed., Marcel Dekker, New York, 1987. 

A large number of studies concerned witli tliiol-tenninated molecules has been directed at tire preparation of tailored organic surfaces, since tlieir importance has been steadily increasing in various applications. Films of o> functionalized alkanetliiols have facilitated fundamental studies of interfacial phenomena, such as adhesion [190, 191], corrosion protection [192], electrochemistry [193], wetting [194], protein adsorjDtion [195, 196] or molecular recognition [197, 198, 199, 200 and 201] to mention only a few. 

Cacace M G, Landau E M and Ramsden J J 1997 The Hofmeister series salt and solvent effects on interfacial phenomena Q. Rev. Biophys. 30 241-78... 

M. J. Rosen, Surfactants and Interfacial Phenomena, John Wiley Sons, Inc., New York, 1978. 

Surface properties are generally considered to be controlled by the outermost 0.5—1.0 nm at a polymer film (344). A logical solution, therefore, is to use self-assembled monolayers (SAMs) as model polymer surfaces. To understand fully the breadth of surface interactions, a portfoHo of chemical functionahties is needed. SAMs are especially suited for the studies of interfacial phenomena owing to the fine control of surface functional group concentration. 

Interfacial Phenomena These can significantly affect overall mass transfer. In fermentation reactors, small quantities of surface-active agents (especially antifoaming agents) can drastically reduce overall oxygen transfer (Aiba et al., op. cit., pp. 153, 154), and in aerobic... 

One cannot quantitatively predict the effect of the various interfacial phenomena thus, these phenomena will not be covered in detail here. The following literature gives a good general review of the effects of interfacial phenomena on mass transfer Goodridge and Robb, Ind. Eng. Chem. Fund., 4, 49 (1965) Calderbank, Chem. Eng. (London), CE 205 (1967) Gal-Or et al., Ind. Eng. Chem., 61(2), 22 (1969) Kintner, Adv. Chem. Eng., 4 (1963) Resnick and Gal-Or, op. cit., p. 295 Valentin, loc. cit. and Elenkov, loc. cit., and Ind. Eng. Chem. Ann. Rev. Mass Transfer, 60(1), 67 (1968) 60(12), 53 (1968) 62(2), 41 (1970). In the following outhne, the effects of the various interfacial phenomena on the factors that influence overall mass transfer are given. Possible effects of interfacial phenomena are tabulated below ... 

Acid-base interactions in the most general Lewis sense occur whenever an electron pair from one of the participants is shared in the formation of a complex, or an adduct . They include hydrogen bonding as one type of such a bond. The bond may vary from an ionic interaction in one extreme to a covalent bond in the other. Acid-base interactions and their importance in interfacial phenomena have been reviewed extensively elsewhere [35,78] and will be described only briefly here. 

Jones, F.R., Interfacial aspects of glass fibre reinforced plastics. In Jones, F.R. (Ed.), Interfacial Phenomena in Composite Materials. Butterworths, London, 1989, pp. 25-32. Chaudhury, M.K., Gentle, T.M. and Plueddemann, E., Adhesion mechanism of poly(vinyl chloride) to silane primed metal surfaces. J. Adhes. Sci. Technol, 1(1), 29-38 (1987). Gellman, A.J., Naasz, B.M., Schmidt, R.G., Chaudhury, M.K, and Gentle, T.M., Secondary neutral mass spectrometry studies of germanium-silane coupling agent-polymer interphases. J. Adhes. Sci. Technol., 4(7), 597-601 (1990). 

Second-Order Integral Equations for Associating Fluids As mentioned above in Sec. II A, the second-order theory consists of simultaneous evaluation of the one-particle (density profile) and two-particle distribution functions. Consequently, the theory yields a much more detailed description of the interfacial phenomena. In the case of confined simple fluids, the PY2 and HNC2 approaches are able to describe surface phase transitions, such as wetting and layering transitions, in particular see, e.g.. Ref. 84. 

L. Blum. Structure of the electric double layer. In I. Prigogine, S. A. Rice, eds. Advances in Chemical Physics, Vol. 78, New York Wiley, 1990, pp. 171-222. L. Blum. The electric double layer—a comprehensive approach. In C. A. Croxton, ed. Fluid Interfacial Phenomena. New York Wiley, 1986, pp. 391-436. 

Interfacial Phenomena Equilibrium and Dynamic Effects, Clarence A. Miller and P. Neogi... 

Interfacial Phenomena in Apoiar Media, edited by Hans-Friedrich Eicke and Geoffrey D. Parfitt... 

Interfacial Phenomena in Coal Technology, edited by Gregory D. Botsaris and Yuli M. Glazman... 

Interfacial Phenomena in Petroleum Recovery, edited by Norman R. Morrow... 

Interfacial Phenomena in Biological Systems, edited by Max Bender... 

Interfacial Phenomena in Chromatography, edited by Emile Pefferkorn... 

The interfacial phenomena in LiX/PE systems were studied extensively by Scro-sati and co-workers [3, 53, 130]. They found that the high-frequency semicircle in the impedance spectrum of LiC104/ P(EO)8 electrolyte (EO = ethylene oxide),... 

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