Kinetics of interfacial phenomena

This review obviously reflects the preferences of the author in stressing the application of FT - IR to amphiphile phase behavior and the kinetics of interfacial phenomena. In some sense, FT - IR may be considered an emerging technique in studies of the phase behavior of surfactants. However, from the wide range of studies of lipid bilayers mentioned, it seems that the concept of using FT - IR to probe surfactant molecule associative properties in other aggregates such as micelles, gels and vesicles can be considered a logical extension. 

Heterogeneous catalysts preparation, interface (oxide/water), interfacial coordination chemistry, adsorption mechanisms, kinetics of interfacial phenomena. 

The main conclusion of Paciejewska s thesis is the necessity to consider the specific kinetics of interfacial phenomena when evaluating the stability of colloidal suspensions. This applies not only to binary, but to all kinds of colloidal suspensions. A major factor is the dissolution of the dispersed phase(s)—in particular if the solubility and the intrinsic dissolution rate are relatively large. Its relevance is especially pronounced for a large total surface area, which depends on the particle concentration and the specific surface of the particles and which determines the amount of substance that can be dissolved in a given period of time. For many nanoparticle (x < 100 nm) systems (e.g. additives for paints and coatings), it will not be permissible to ignore the influence of dissolution on the interfacial properties and even on suspension stability—independent from the Gibbs-Thomson effect, which becomes relevant at particle sizes below 10 nm (cf. Sect. 3.1.4). 

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. 

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. 

The Frumkin epoch in electrochemistry [i-iii] commemorates the interplay of electrochemical kinetics and equilibrium interfacial phenomena. The most famous findings are the - Frumkin adsorption isotherm (1925) Frumkin s slow discharge theory (1933, see also - Frumkin correction), the rotating ring disk electrode (1959), and various aspects of surface thermodynamics related to the notion of the point of zero charge. His contributions to the theory of polarographic maxima, kinetics of multi-step electrode reactions, and corrosion science are also well-known. An important feature of the Frumkin school was the development of numerous original experimental techniques for certain problems. The Frumkin school also pioneered the experimental style of ultra-pure conditions in electrochemical experiments [i]. A list of publications of Frumkin until 1965 is available in [iv], and later publications are listed in [ii]. 

To access the potential influence of spillover on catalysis and interfacial transport, more qualitative studies are required. Further, it is, for instance, necessary to isolate the individual steps in the phenomena and account for the reaction kinetics of the process. As an example, what is the difference between inter- and intraparticle transport on the support ... 

The rate expressions derived above describe the dependence of die reaction rate expressions on kinetic parameters related to the chemical reactions. These rate expressions are commonly called the intrinsic rate expressions of the chemical reactions. However, as discussed in Chapter 1, in many instances, the local species concentrations depend also on the rate that the species are transported in the reaction medium. Hence, the actual reaction rates are affected by the transport rates of reactants and products. This is manifested in two general cases (i) gas-solid heterogeneous reactions, where species diffusion through the pore plays an important role, and (ii) gas-hquid reactions, where interfacial species mass-transfer rate as wen as solubility and diffusion play an important role. Considering the effect of transport phenomena on the global rates of the chemical reactions represents a very difficult task in the design of many chemical reactors. These topics are beyond the scope of this text, but the reader should remember to take them into consideration. 

The above analysis shows that in the simple case of one adsorbed intermediate (according to Langmuirian adsorption), various complex plane plots may be obtained, depending on the relative values of the system parameters. These plots are described by various equivalent circuits, which are only the electrical representations of the interfacial phenomena. In fact, there are no real capacitances, inductances, or resistances in the circuit (faradaic process). These parameters originate from the behavior of the kinetic equations and are functions of the rate constants, transfer coefficients, potential, diffusion coefficients, concentrations, etc. In addition, all these parameters are highly nonlinear, that is, they depend on the electrode potential. It seems that the electrical representation of the faradaic impedance, however useful it may sound, is not necessary in the description of the system. The systen may be described in a simpler way directly by the equations describing impedances or admittances (see also Section IV). In... 

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