Journal of Colloid Science最新文献

A previously developed description of multi-process near-equilibrium systems in terms of individual kinetically independent processes is extended to some membrane processes. For the examples considered it is shown that this description is at least as convenient as the application of irreversible thermodynamics; for example, it leads to quite obvious criteria for “anomalous” osmosis. Moreover, irreversible thermodynamics does not properly describe systems in which solution leaks through the membrane. A by-product of the process description is that it aids in understanding equilibrium systems such as classical Donnan equilibria and the electromotive force of Donnan cells both with and without the separating membrane.

The interaction of nitrous oxide with real (oxide-coated) surfaces of both n- and p-type germanium has been investigated in the range of 10–300 torr and 200–400°C. The n-type samples promoted greater decomposition than the p-type samples. In all cases studied, not a trace of oxygen resulting from the decomposition could be detected in a mass spectrometer; obviously, the oxygen was incorporated in further oxide film formation. Pretreatment of germanium with oxygen decreased the extent of its interaction with nitrous oxide.

Experiments with a 34% enriched ¹⁵N¹⁴N¹⁶O clearly showed that the decomposi tion mechanism primarily consists of the rupture of the NO bond to set a nitrogen molecule free.

The mathematical relationships have been developed for describing the penetration of fluids into the void spaces of a collection of uniform solid spheres. The pressure required for initial penetration or “breakthrough” pressure is defined in terms of the porosity of the spherical model and the contact angle of the fluid. Calculated data, covering the porosity range of 47.64% to 25.95%, and contact angles of 90° to 180°, are presented. These relationships allow the determination of particle radius from standard mercury penetration and porosity data.

Isotherms for the adsorption of nitrogen and argon on poly(methylmethacrylate) were obtained at three temperatures over a pressure range from a few microns to the saturated vapor pressure of the adsorbing gas. Differential and integral enthalpies and entropies were calculated and indicate a heterogeneous surface with adsorption energies higher than those observed for unsubstituted hydrocarbons. Clustering functions were calculated and indicate that the adsorption occurred in clusters throughout the range investigated.

The absolute angular scattered intensities for a Mie scattering system have been determined. A Dow polystyrene latex of large diameter (D_EM = 1.305 μ) was studied with unpolarized, vertically polarized, and horizontally polarized incident light. The necessary expressions relating the geometrical, optical, and calibration constants of a Brice-Phoenix photometer with the quantities directly related to the Mie intensity functions were developed. Two features of the experimental technique were explored in detail: the use of polarized incident radiation and the effect of the solid angle subtended by the receiver aperture. Generally, excellent agreement between the theoretical Mie intensity functions and the corresponding experimental absolute intensities was obtained over the whole angular range.

Adsorption-desorption isotherms for water vapor and a high charge density sodium vermiculite were determined at 25°C. and at 50°C. X-ray patterns were obtained at various stages of hydration of the clay. Heats of immersion were determined calorimetrically for the dry clay and for partially hydrated samples. The adsorption of water appears to take place in two distinct steps corresponding with the intercalation of the lattice with one and with two monomolecular layers of water. The shape of the isotherms can be seen as the superposition of two Langmuir-type isotherms. The observed hysteresis is attributed to a retardation of the adsorption process owing to the development of elastic stresses in the crystallites during the initial peripheral penetration of water between the unit layers. On the assumption that the desorption isotherm represents equilibrium values, the thermodynamic constants for the sorption process were determined.

The calorimetric data suggest that the integral heats of sorption per mole of water are constant during the formation of each layer of water, the heat of sorption for the first layer per mole of water being about twice that for the second layer. Agreement between the calorimetric data and the heats determined from the isotherms at two temperatures is reasonable for the first stage, and good for the second.

The integral entropy of sorption is negative with respect to the entropy of liquid water. Since the system was treated as a one-component system (the adsorbate), the computed integral entropy includes entropy changes in the solid due to the parting of the unit layers and changes in the positions of the interlayer cations.

From the isotherms the net work of unit layer interaction can be computed as a function of unit layer distance, from which the pressures required to squeeze out the water layers are derived. The net work consists of the hydration energy proper minus the potential energy of electrostatic and van der Waals unit layer attraction. From an estimate of the attraction energy, the hydration energy is estimated to be considerably smaller than ion hydration energy in bulk solution.

The theory for the kinetics of coagulation of particles in Brownian motion is reviewed briefly. The relationship between the classical solution of Smoluchowski and the similarity solution to the kinetic equation is discussed. When the classical result is placed in the form of the similarity solution, a simple exponential expression results. In spite of the theoretical limitations, this expression for Smoluchowski's relation can be used to predict satisfactorily a substantial range of the size distribution which has a similar or a self-preserving form.

In an earlier paper, monolayer permeability was derived on the basis of the fluctuations that occur in monolayer density at equilibrium. In this paper, the same model is used to derive the monolayer transport properties. First, expressions are developed for the probability and for the frequency of local expansions. These expressions are then used to derive the self-diffusion coefficient (D), the viscosity (η), and the thermal conductivity (κ) of a monolayer in terms of properties that are related to the surface isotherm. Whereas D has a reasonable magnitude, η is extremely small and many orders of magnitude lower than measured surface viscosities. The differences are discussed in terms of the monolayer model and the effect of the subphase. The utility of the model for processes involving natural membranes is also considered.

A thermodynamic analysis of adsorption from a single-component fluid, either vapor or liquid, on the surface of a single-component solid is systematically developed. The analysis is based on the Gibbsian treatment of surface regions and assumes only that the interfaces are planar, that the solid and fluid phases are mutually insoluble, and that the solid is inert. The treatment is then applied to the interpretation of adhesional wetting (contact angle) and immersional wetting (heat of wetting) measurements. A relationship between the quantities obtained from these two types of wetting measurements is derived. This relationship is of the GibbsHelmholtz form and involves the dependence of the contact angle on temperature. Problems which arise in a proposed experimental test of the relationship are discussed.