Particle interface

A convenient way to understand particle dispersion is to consider the process in four successive parts the nature of particles and surfaces, adsorption onto particles, interface properties, and forces of attraction and repulsion. 

It is particularly significant that no evidence is found for localized melting at particle interfaces in the inorganic materials studied. Apparently, effects commonly observed in dynamic compaction of low shock viscosity metals are not obtained in the less viscous materials of the present study. To successfully predict the occurrence of localized melting, it appears necessary to develop a more realistic physical model of energy localization in shock-compressed powders. 

Solomatov et al. [131] derived an equation for strength at the polymer - spherical particle interface ... 

R. F. Haglund Jr., Quantum-dot composites for nonlinear optical applications, in R. E. Hummel, P. Wissmann (eds.) Handbook of Optical Properties II Optics of Small Particles, Interfaces, and Surfaces, Vol. 2, CRC Press, New York, 1997, 191. 

Pant and Levinger have measured the solvation dynamics of water at the surface of semiconductor nanoparticles [48,49]. In this work, nanoparticulate Zr02 was used as a model for the Ti02 used in dye-sensitized solar photochemical cells. Here, the solvation dynamics for H2O and D2O at the nanoparticle surface are as fast or faster than bulk water motion. This is interpreted as evidence for reduced hydrogen bonding at the particle interface. 

Polymers interpenetration of polymer chains, phase separation, compatibility between polymers, interdiffusion of latex particles, interface thickness in blends of polymers, light-harvesting polymers, etc. 

In Chapter 4, we saw how conservative chemicals are used to trace the pathway and rates of water motion in the ocean. True conservative behavior is exhibited by a relatively small number of chemicals, such as the major ions and, hence, salinity. In contrast, most of the minor and trace elements display nonconservative behavior because they readily undergo chemical reactions under the environmental conditions found in seawater. The rates of these reactions are enhanced by the involvement of marine organisms, particularly microorganisms, as their enzymes serve as catalysts. Rates are also enhanced at particle interfaces for several reasons. First, microbes tend to have higher growth rates on particle surfaces. Second, the solution in direct contact with the particles tends to be highly enriched in reactants, thereby increasing reaction probabilities. Third, adsorption of solutes onto particle surfaces can create fevorable spatial orientations between reactants that also increases reaction probabilities. 

Andrade and Molina [46] have performed electrochemical impedance studies of mercury electrodes with hematite particles adhered at different electrode potentials. Adhesion of such particles was strong and the decrease in the impedance was accompanied by an increase in the number of attached particles. Experimental results were analyzed in terms of an equivalent circuit including the constant phase element (CPE), the magnitude of which appeared to be directly related to the electrode coverage. A pore model for the metal/hematite particles interface has been proposed. 

Here, issues in relation to the trickle flow regime—isothermal operation and plug flow for the gas phase—will be dealt with. Also, it is assumed that the flowing liquid completely covers the outer surface particles (/w = 1 or aLS = au) so that the reaction can take place solely by the mass transfer of the reactant through the liquid-particle interface. Generally, the assumption of isothermal conditions and complete liquid coverage in trickle-bed processes is fully justified with the exception of very low liquid rates. Capillary forces normally draw the liquid into the pores of the particles. Therefore, the use of liquid-phase diffusivities is adequate in the evaluation of intraparticle mass transfer effects (effectiveness factors) (Smith, 1981). 

Source-Limited Coarsening. During source-limited coarsening, the interfaces surrounding the particles behave as poor sources and sinks, and the coarsening rate then depends upon the rate at which the diffusion fluxes between the particles can be created or destroyed (accommodated) at the particle interfaces. In a simple model, the same assumptions can be made about the source action at the particles as those that led to Eq. 13.24. The rate of particle growth can then be written... 

Solution. Let yLP, yLS. and ysp be the energies (per unit area) of the liquid/particle, liquid/solid, and solid/particle interfaces, respectively. From Section 19.2.1 the volume of the solid nucleus is Vs = (2 — 3 cos 6 + cos3 8), the spherical liquid/solid... 

It is accepted that the radical entry rate coefficient for miniemulsion droplets is substantially lower than for the monomer-swollen particles. This is attributed to a barrier to radical entry into monomer droplets which exists because of the formation of an interface complex of the emulsifier/coemulsifier at the surface of the monomer droplets [24]. The increased radical capture efficiency of particles over monomer droplets is attributed to weakening or elimination of the barrier to radical entry or to monomer diffusion by the presence of polymer. The polymer modifies the particle interface and influences the solubility of emulsifier and coemulsifier in the monomer/polymer phase and the close packing of emulsifier and co emulsifier at the particle surface. Under such conditions the residence time of entered radical increases as well as its propagation efficiency with monomer prior to exit. This increases the rate entry of radicals into particles. 

These results on viscosity behavior are in good agreement with the results of the latex characterization by conductometric titration (see Figures 5 6), which showed that the carboxyl groups are uniformly distributed within the particle for the semi-continuous latex, whereas in the batch latex the carboxyl groups are concentrated at the water-particle interface. 

It should be noted that because of the insolubility of the polymer, there is no change in monomer concentration at the particle interface in... 

If it is assumed that for a junction rubber the energy loss takes place near the circular peripherals of the rubber-filler particle interface, the dissipated energy for a cyclic displacement of amplitude Ax and strain rate d/dt (x/hg) can be estimated to be... 

Homogeneous nudeation occurs in the absence of a solid interface heterogeneous nudeation occurs in the presence of a solid interface of a foreign seed and secondary nudeation occurs in the presence of a solute particle interface. The mechanisms governing the various types of primary and secondary nudeation are different and result in different rate expressions. The relative importance of each type of nudeation varies with the precipitation conditions. 

While the above criteria are useful for diagnosing the effects of transport limitations on reaction rates of heterogeneous catalytic reactions, they require knowledge of many physical characteristics of the reacting system. Experimental properties like effective diffusivity in catalyst pores, heat and mass transfer coefficients at the fluid-particle interface, and the thermal conductivity of the catalyst are needed to utilize Equations (6.5.1) through (6.5.5). However, it is difficult to obtain accurate values of those critical parameters. For example, the diffusional characteristics of a catalyst may vary throughout a pellet because of the compression procedures used to form the final catalyst pellets. The accuracy of the heat transfer coefficient obtained from known correlations is also questionable because of the low flow rates and small particle sizes typically used in laboratory packed bed reactors. 

Consider two cases of spherical particles, one of KRO-1 morphology of a volume fraction of 0.23 of randomly wavy PB rods, and the other pure PB — both occupying a volume fraction of 0.22 in PS. We are interested in the craze initiation condition for these two particles at room temperature under a uniaxial tensile stresso. We consider the state of stress at a typical equatorial point A along the particle interface, on the PS side of the particle, as shown in Fig. 33. We determine first by standard methods the elastic properties of the particles and their thermal expansion coefficients, together with the elastic properties and thermal expansion coefficients of the composite matrix as a whole consisting of particles and the majority phase of PS. 

Excitation of TiO particles with ionizing radiation is equivalent to their photoexcitation [69] and generates electron-hole (e /h ) pairs that can be exploited in various processes at the particle interface (Eq. (17)) ... 

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