Droplet diffusion coefficient

Dynamic light scattering has been utilized to directly measure droplet diffusion coefficients in near-critical and supercritical fluids. Blitz et al.f and Fulton et measured the effect of pressure on... 

Tuning of aggregation of microemulsion droplets and silica nanoparticles can be achieved using solvent mixtnres. The state of aggregation can be correlated with the effective molecular volnme of the solvent mixtore. This is because the droplet diffusion coefficient increases and the apparent diameter of microemnlsion droplets decreases when effective molar volnme of solvent mixtore decreases. Attractive interactions are increased, when the effective molar volnme of the solvent is increased. ... 

The oil droplets in a certain benzene-water emulsion are nearly uniform in size and show a diffusion coefficient of 3.75 x 10 cm /sec at 25°C. Estimate the number of benzene molecules in each droplet. 

Here, S0 is the signal when G = 0, D is the self-diffusion coefficient, yG is the gyromagnetic ratio and am are roots of the Bessel function equation amaf3 2(ama) — (l/2)J3/2(a ma) = 0. If the system is polydisperse, the signal decay is due to contributions from droplets of different sizes. Then, the signal attenuation is given by the volume average over all sizes as... 

The flow artifacts detected in the droplet size measurements are similar to those reported by Goux et al. [79] and Mohoric and Stepisnik [80]. In their work natural convection effects led to an increase in the decay of signal attenuation curves, causing over-prediction in the self-diffusion coefficient of pure liquids. In order to avoid flow effects in droplet size distributions, flow compensating pulse sequences such as the double PGSTE should be used. It has been demonstrated recently that this sequence facilitates droplet size measurements in pipe flows [81]. 

Batch operation For the design of batch reactors for biphasic conversion the type of stirring device is an essential aspect to generate a narrow distribution with small droplet sizes which is equivalent to high surfaces [36]. Together with the diffusion ability (diffusion coefficient) of the used sol-... 

In that case the self diffusion coefficient - concentration curve shows a behaviour distinctly different from the cosurfactant microemulsions. has a quite low value throughout the extension of the isotropic solution phase up to the highest water content. This implies that a model with closed droplets surrounded by surfactant emions in a hydrocarbon medium gives an adequate description of these solutions, found to be significantly higher them D, the conclusion that a non-negligible eimount of water must exist between the emulsion droplets. 

Diffusion into the bulk. This is determined by the diffusion coefficient in the liquid (D,). Diffusion within the bulk aqueous phase is much slower than gas-phase diffusion and can be rate-limiting under conditions of high reactant concentrations where the rate of the chemical reaction is high. This appears to have been a problem in some experimental studies of some aqueous-phase reactions relevant to the atmosphere where either bulk solutions or large droplets and reactant concentrations higher than atmospheric were used (Freiberg and Schwartz, 1981). 

This relation has been used for the calculation of diffusion coefficients by the rate of evaporation of liquid droplets suspended in a still gas (S9, p. 17). Clearly Eq. (122) does not describe the situation properly if the diffusion produces free convection owing to changes in density. 

The last case in this section deals with the sudden exposure of a spherical system A (particle, droplet, etc.) with initial concentration, CJ(, to a constant exterior concentration, Cg (Fig. 18.6). Here again we assume that the equilibrium situation is represented by = 1. At time t = 0, for the case in which C°h < Cg, the substance begins to move into the spherical system by diffusion (coefficient D). Now we are interested in the temporal evolution of the concentration inside the sphere and in the total exchanged mass at time t. 

Diffusion coefficients of moisture and fat in cheese were measured and restricted feature of fat signal facilitated estimation of fat droplet size distribution [50], while the water diffusion was suggested to be confined to the surface within the protein matrix [50]. 

Packer and Rees [3] extended the work of Tanner and Stejskal by the development of a theoretical model using a log-normal size distribution function. Measurements made on two water-in-oil emulsions are used to obtain the self-diffusion coefficient, D, of the water in the droplets as well as the parameters a and D0 0. Since then, NMR has been widely used for studying the conformation and dynamics of molecules in a variety of systems, but NMR studies on emulsions are sparse. In first instance pulsed field gradient NMR was used to measure sdf-diffusion coefficients of water in plant cells (e.g. ref. [10]). In 1983 Callaghan... 

Flocculation kinetics can be described in different ways. Here we introduce a treatment first suggested by Smoluchowski [547], and described in Ref. [538], p. 417. The formalism can also be used to treat the aggregation of sols. A prerequisite for coalescence is that droplets encounter each other and collide. Smoluchowski calculated the rate of diffusional encounters between spherical droplets of radius R. The rate of diffusion-limited encounters is SttDRc2, where c is the concentration of droplets (number of droplets per unit volume). For the diffusion coefficient D we use the Stokes-Einstein relation D = kBT/finr/R. The rate of diffusion-limited encounters is, at the same time, the upper limit for the decrease in droplet concentration. Both rates are equal when each encounter leads to coalescence. Then the rate of encounters is given by... 

In conventional RE processes, the diffusive resistance is concentrated mainly inside the droplet, whereas the aqueous-side resistance can be neglected. This has been proven in Ref. 203 using the laser-induced-fluorescence (LIF) technique. Usually the organic phase is more viscous and the diffusion coefficients of the organic complexes are larger than those at the aqueous side, which supports this finding. 

The mass transfer within a rigid droplet is determined by the Maxwell-Stefan diffusion. The appropriate diffusion coefficients experimentally determined... 

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