Contents 8 Fundamental Constants

Throughout most of this chapter the emphasis has been on the evaluation of zeta potentials from electrokinetic measurements. This emphasis is entirely fitting in view of the important role played by the potential in the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. From a theoretical point of view, a fairly complete picture of the stability of dilute dispersions can be built up from a knowledge of potential, electrolyte content, Hamaker constants, and particle geometry, as we discuss in Chapter 13. From this perspective the fundamental importance of the f potential is evident. Below we present a brief list of some of the applications of electrokinetic measurements. 

Soon after vinyl BR s were first introduced commercially, it was recognized that the vinyl structure imparted non-typical dynamic properties. In particular, their vulcanizates showed improved resistance to heat build-up when compared to emulsion SBR. j O Before relating the special contribution of the vinyl structure to properties, it is informative to first determine the influence of styrene content (at constant vinyl) on the two fundamental properties of interest Tg and tan 6, as shown in Figure 14. As expected, both Tg and tan 6 increase almost linearly with styrene content. Thus like a conventional tire tread rubber, the rolling resistance of solution SBR s prepared using lower amounts of styrene is accompanied by a decrease in the wet traction of the rubber. 

Reaction of dissolved gases in clouds occurs by the sequence gas-phase diffusion, interfacial mass transport, and concurrent aqueous-phase diffusion and reaction. Information required for evaluation of rates of such reactions includes fundamental data such as equilibrium constants, gas solubilities, kinetic rate laws, including dependence on pH and catalysts or inhibitors, diffusion coefficients, and mass-accommodation coefficients, and situational data such as pH and concentrations of reagents and other species influencing reaction rates, liquid-water content, drop size distribution, insolation, temperature, etc. Rate evaluations indicate that aqueous-phase oxidation of S(IV) by H2O2 and O3 can be important for representative conditions. No important aqueous-phase reactions of nitrogen species have been identified. Examination of microscale mass-transport rates indicates that mass transport only rarely limits the rate of in-cloud reaction for representative conditions. Field measurements and studies of reaction kinetics in authentic precipitation samples are consistent with rate evaluations. 

MW/cm2). The solid line is a best fit to the data assuming a cubic dependence of the third harmonic intensity on the fundamental intensity. The constant of proportionality is 4.3 x 10 6. The inset shows the spectral content of the third harmonic intensity showing a resolution limited peak at 355 nm. Using Q-switched, modelocked pulses, we have extended the measurement to peak pump powers in excess of 10 GW/cm2 without damage to the sample. 

As a first step in assessing the potential importance of nanoparticle reactions, we compare the volume and surface areas of these particles with the same values from other condensed phases with known chemical effects. We first consider nanoparticle volumes. As an upper limit, we consider an urban air parcel containing 20-nm diameter nanoparticles at a number concentration of 10 cm. Under this scenario, the nanoparticle volume is a small fraction (10 of the total air parcel volume. Thus the nanoparticle reaction rate (in units of mol m -air s ) would have to be ca. 10 times as fast as the equivalent gas phase reaction (mol m -air s ) to have a comparable overall rate in the air parcel. For comparison, clouds typically have liquid water contents of 10 to 10 (volume fraction) and can have significant effects upon atmospheric chemistry (Seinfeld and Pandis 1998). For simplicity of argument, if the medium of the cloud droplets and nanoparticles are assumed similar (e.g., dilute aqueous), then the fundamental rate constants in each medium are similar. Under this condition, reactant concentrations in the nanoparticles would need to be enhanced by 10, as compared to the cloud droplets, to have equal rates. Based on this analysis, it appears unlikely that reactions occurring in the bulk of nanoparticles could affect the composition of the gas phase. 

Theory and kinetic analysis (38 entries). Many aspects of the theory of kinetic analysis were discussed (27 entries). Some papers were specifically concerned with discrimination of fit of data between alternative kinetic expressions or with constant reaction rate thermal analysis. Other articles (11 entries) were concerned with aspects of the fundamental theory of the subject and with the compensation effect. The content of papers concerned with kinetic analyses appeared to accept the common basis of the applicability of the rate equations listed in Table 3.3. 

Weiss and co-workers reported solubilities for He, " He, Ne, Ar, Kr as well as for O2 and N2 as a function of temperature and salinity for fresh and ocean waters (Table 1 Weiss 1970, 1971 Weiss and Kyser 1978). As this fundamental piece of work was strongly motivated by practical oceanographic research, the noble gas solubilities were expressed in the form of equilibrium concentrations with moist atmospheric air. For the atmosphere, it is justified to assume that its major elemental composition remains constant over the relevant time scales controlling gas exchange. Hence the gas partial pressure pi can be expressed by the total atmospheric pressure ptot corrected for water vapor content, Cw(T), and the volume or mole fraction Zi of the gas i in dry air (Ozima and Podosek 1983). 

The kinetic models of Jander and Ginstling were developed by Komatsn [11]. He had assumed that the reaction starts in the places of inteigrannlar contact (Fig. 2.7). The fundamental role in the reaction has the number of these contacts, thus the fineness of the mixture. If the number of contacts is constant in time, the formula derived by Komatsu is reduced to lander s equation, in which, however, the k constant is the function not only of the temperature but also the ratio of grains sizes and of both components as well as the content ratio of these components in the mixture. 

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