Journal of Colloid Science最新文献

Electron microscopy and electron diffraction were used in conjunction with a radioactive tracer to investigate experimentally the adsorption of undecanoic acid and nonadecanoic acid from cyclohexane solution on the carefully characterized (100), (110), (111), and (311) faces of copper and oxidized copper crystals. Nonadecanoic acid was isotropically adsorbed on the copper crystal with the molecules virtually perpendicular to the adsorbent in islands. As the adsorption continued, these islands grew laterally until after about 64 hrs. a continuous monolayer was formed. The equivalent of a monolayer of undecanoic acid was absorbed on the copper crystal after about 64 hr., but the (100) face adsorbed more of this acid than either of the other three faces for adsorption times less than 17 hrs. The (100) face was roughened the most by oxidation, and this face of the oxidized crystal was outstanding in its adsorption of both acids. The equivalent of a monolayer of undecanoic acid that followed the irregularities of the surface was not adsorbed after 128 hr. on any of the faces of the oxidized crystal. Approximately the equivalent of a monolayer of nonadecanoic acid was adsorbed after 1 min. on the oxidized surface, but the adsorbate rapidly desorbed into the solution.

A stabilized gas bubble resting at a gas/liquid interface decreases in size owing to outward diffusion of gas across the liquid film at the top of the bubble. Brown, Thuman, and McBain used the rate of shrinkage to calculate the permeability of the film to air but the theory employed is inexact.

An improved theory is presented here which takes into account the exact shape of the bubble and, in the case of multicomponent gases such as air, the changing composition. It is shown that after a short period the composition of the gas in the bubble adjusts itself so that the observed permeability becomes constant.

If the equilibrium thickness of the film is known, the method can be used to measure the permeability of the monolayers on both sides of the film.

The experimental results support the modified theory. The method appears to produce accurate and reproducible values of the film permeability, and values for a number of gases at various concentrations of surfactant, at various temperatures, and with added electrolytes are presented.

A critical analysis was made of the extensive experimental data on the relative viscosity of suspensions of uniform spherical particles. By appropriate extrapolation techniques, non-Newtonian, inertial, and nonhomogeneous suspension effects were minimized. As a result, the scatter of the data was reduced from ±75% to ±13% at a volume fraction solids of 0.50. The coefficients of different power series relating relative viscosity and volume fraction solids were determined using a nonlinear least squares procedure. It was shown that a new expression containing three terms of a power series with coefficients determined from previous theoretical analyses and an exponential term with two adjustable constants fit the data as well as a power series with six terms, either three or four of which were adjustable constants with the remaining coefficients being theoretical values.

The equilibrium shape of a liquid or gas drop (Phase 1 of density d₁) at a horizontal interface separating two fluid phases (Phases 2 and 3 of densities d₂ and d₃) can be calculated from the principles of capillarity. In the most general system these calculations are extremely complicated, and solutions have been obtained only for some special cases (very small drops; systems with d₁ = d₃; and very large drops when d₃ < d₁ < d₂).

When d₁ < d₃ there is a critical drop size above which the drop cannot be supported by the interface and ascends to the top of the system. This is illustrated with the model system of an infinitely long cylinder at an interface. The same model system is used to illustrate the experimental observation that a cluster of two or more drops, each of which is below the critical size, may cross the interface.