Water volume fraction

B. Interface surface area, oil-water volume fraction 696... 

B. Interface Surface Area, Oil-Water Volume Fraction... 

The line = 0 can be considered as a borderline for applicability of the basic model, in which the Gaussian curvature is always negative. Recall that in the basic model the oil-water interface is saturated by the surfactant molecules by construction of the model. Hence, for equal oil and water volume fractions the Gaussian curvature must be negative, by the definition of the model. 

According to Evans and Haisman (1982), there are two phases of water in starch granules (1) the "tightly" bound phase, approximately 20% of the amoimt, absorbed by granules and (2) a "loosely" bound phase that is available for gelatinization. They foimd that the DSC measured onset temperature (Tq) increased rapidly below 0.6 g water per 1 g starch ( 29% water volume fraction) and stayed essentially constant between 0.6 and 2.0 g water per 1 g starch (29-57% water volume fraction) (Eig. 5.10). Changes observed in and Tp, and the peak separation pattern... 

FIGURE 5.1 Separation of PAH isomers of relative molecular mass 302 on (a) monomeric Cl8 column and (b) polymeric Cjs colurtm. Conditions 90 10 acetonitrile/water (volume fraction) to acetonitrile over 10 min. (Adapted from Wise, S.A., et al.. Anal. Chem., 60, 630, 1988. With permission.)... 

Proton mobility (D J and water self-diffusion coefficient (D q) as a function of the water volume fraction (X ) in Nafion and SPEEKK, where X, = volume of water in membrane divided by volume of wet membrane. (From Kreuer, K. D. 2001. Journal of Membrane Science 185 29-39.)... 

The above differences observed with the various cosurfactants are reflected in the conductivity - water volume fraction This is shown in Figures 5 and 6. It can be... 

InrxLiences of alcohol isomery on the conductivity - water volume fraction curve (symbols are the same as those for Figure 4). 

Thus, in summary, self diffusion measurements by Lindman et a (29-34) have clearly indicated that the structure of microemulsions depends to a large extent on the chain length of the oosurfactant (alcohol), the surfactant and the type of system. With short chain alcohols (hydrophilic domains and the structure is best described by a bicontinuous solution with easily deformable and flexible interfaces. This picture is consistent with the percolative behaviour observed when the conductivity is measured as a function of water volume fraction (see above). With long chain alcohols (> Cg) on the other hand, well defined "cores" may be distinguished with a more pronounced separation into hydrophobic and hydrophilic regions. 

The highest level, at structural scales >10 nm, is that over which long-range transport takes place and diffusion depends on the degree of connectivity of the water pockets, which involves the concept of percolation. The observed decrease in water permeation with decreasing water volume fraction is more pronounced in sulfonated poly(ether ketone) than in Nafion, owing to differences in the state of percolation. Proton conductivity decreases in the same order, as well. 

Plots of D versus water volume fraction " show that the concentration dependence of D is in fact described well by the Fujita free volume equation. " This was surprising considering that the underpinning of this equation simply involves available free volume for molecular hopping. The interpretation is that water molecules plasticize the perfluoroalkyl ether side chain domains and this increases D with increasing water content. D for water varied from... 

Figure 12. Water self-diffusion coefficient of Nafion 117 (EW =1100 g/equiv), as a function of the water volume fraction Xy and the water diffusion coefficient obtained from a Monte Carlo (MC) simulation (see text). The proton conductivity diffusion coefficient (mobility) is given for comparison. The corresponding data points are displayed in Figure 14.

The transport properties that are most significantly affected by changes of the water volume fraction are the water/methanol electro-osmotic drag and permeation, both of which have significant contributions from viscous flow (see Section 3.2.1.1). For DMFC applications (where the membrane is in contact with a liquid water/methanol mixture), this type of transport determines the crossover, which is only acceptably low for solvent volume fractions smaller than 20 vol % (see Figures 14 and 15). Consequently, recent attempts have been focused on strengthening... 

For microemulsions with low water volume fractions (typically <0.02), the absolute amount of dissolved hydrophiles can be somewhat small, and this can limit phase-transfer reactions between C02 and aqueous phases (Jacobson et al., 1999b). Recently, highly concentrated w/c microemulsions Up 0.5) have been formed (Lee et al., 1999a), providing for much greater... 

EFFECT OF WATER VOLUME FRACTION ON ELECTRICAL CONDUCTIVITY AND ION DIFFUSIVITY IN AGAROSE GELS... 

The electrical conductivity of agarose gel increased with increasing water volume fraction, Figure 1. This is attributed primarily to the dependence of ion diffusivity on water volume fraction [14], An empirical model for relative ion diffusivity (D/Do) is proposed to be a function of the hydrodynamic radius ( rs) of solute and intrinsic Darcy permeability (k) of gel ... 

Effect of Water Volume Fraction on Electrical Conductivity and Ion... 

Figure 6. Rate of aqueous-phase oxidation of S(IV) by O3 (30 ppb) and H2O2 (l ppb), as a function of solution pH. Gas-aqueous equilibria are assumed for all reagents. R/PSO2 represents aqueous reaction rate per ppb of gas-phase S02 P/L represents rate of reaction referred to gas-phase SO2 partial pressure per cm3 m 3 liquid water volume fraction.

Alany et al. [11,35] reported on the phase behavior of two pharmaceutical ME systems showing interesting viscosity changes. The viscosity of both systems increased with increasing volume fraction of the dispersed phase to 0.15 and flow was Newtonian. However, formation of LC in one of the two systems, namely the cosurfac-tant-free system, resulted in a dramatic increase in viscosity that was dependent on the volume fraction of the internal phase and a change to pseudoplastic flow. In contrast, the viscosity of the bicontinuous ME was independent of water volume fraction. The authors used two different mathematical models to explain the viscosity results and related those to the different colloidal microstructures described. 

Figure 5 is a plot of R versus H2 0. It is important to compare the results obtained in this present study with those reported in the literature. In most of the water in oil microemulsion systems studied by scattering methods, the ratio of water to surfactant was kept constant. In these cases it was found that an increase in the water volume fraction did not change the size of the droplets. Cebula et al.(J ), again with a constant ratio of water to surfactant, were the first to show that the droplet size of microemulsions increases close to the phase boundary, as was noticeable in our results. Baker et al.(l ) have measured the droplet size radius at a fixed surfactant concentration. It was found that the size of the microemulsion droplets Increases as the volume fraction of water increases. However, at a fixed ratio of water to surfactant the droplet size was constant. The results presented here are the droplet size as a function of water concentration for a fixed surfactant concentration. The results show that the droplet size increases slowly with increasing water concentration (this is a result of the droplets swelling as more water is added to the system), in agreement with the results of Baker et l ( ). In addition, close to the phase boundary the droplet size Increases more markedly the size of the droplets Increases by 50%, as was observed by Cebula et al. (19). 

Figure 4. Computer line drawings (without hidden line removal) of three representatives of the I-WP family of constant mean curvature surfaces. These surfaces are invoked to describe the polar/apolar dividing surface in the DDAB / water / hydrophobe cubic phases, at water volume fractions of a) 35% b) 47% c) 65%.

The liquid and bound water volume fractions are calculated from the water content divided by the intrinsic density of water (1000 kg/m ). The volume fraction of gas, i.e. the porosity, is given both by the gas law (i.e the gas density in Equation 14) and the volume of gas (i.e. structural changes arising from Equation 13). The solid volume fraction is calculated from Equation (12). 

Given a soil containing a few percent of one or more sorbing phases, and with the pore-water volume fraction and soil-water composition known, describe in detail what you would need to know to compute the adsorption of a contaminant cation or anion by the soil using ... 

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