Journal of Colloid Science最新文献

The effect of autoxidation of a linoleic acid monolayer on the contact angle with water depended upon the conditions of oxidation and the type of surface upon which the monolayer was formed. For monolayers on a glass surface with which the carboxyl group did not react, autoxidation in air of 0.02% R.H. increased the contact angle with water from zero to 56°. However, on copper where reaction between the surface and the carboxyl group occurred, autoxidation under the same conditions decreased the contact angle from 86° to 76°. Autoxidation in air of 50% R.H. caused no change in the initial contact angle of zero with water when the monolayer was on glass. On copper, aging under these conditions caused the angle to increase from an initial value of 86° to 92°. Contact angles between methylene iodide and the monolayers were not greatly affected by autoxidation under any of the afore-mentioned conditions. Ultraviolet spectra and reductive polarography indicated that secondary oxidation of the initially formed 9- or 13-hydroperoxide of the conjugated octadecadienoic acid occurred to a much greater extent in the drier air. The hypothesis presented explains the wettability results in terms of the ability of the oxidation products to produce a solid, coherent monolayer structure, taking into account the location in the hydrocarbon chain of oxygen-containing functional groups introduced by autoxidation.

The results of a light scattering study of four rubber latex samples using a dissymmetry technique are reported. Particle diameters found from the Rayleigh-Gans-Debye and Mie theories were in the range 1,400 to 2,000 A. In water the relative refractive index of these particles was m = 1.15 so that for particles of this size, the two accepted theoretical limitations for the RGD theory were exceeded. However, the results indicate that this theory can still be used to give particle sizes to within 5% for values of m approaching 1.15 and for diameters of up to 2,000 A.

On the assumption that pseudoplastic flow is associated with the formation and rupture of structural linkages a new flow equation is derived. The equation takes the form $\text{ƞ = ƞ}{}_{\mathrm{\infty }}\text{+}\text{ƞ}{}_0\text{− ƞ}{}_{\mathrm{\infty }}\text{1 + αD}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{,}$ where D = rate of shear, η₀ = limiting viscosity at zero rate of shear, η_∞ = limiting viscosity at infinite rate of shear, and α is a constant associated with the rupture of linkages.

Graphical methods for evaluating the three constants η₀ , η_∞ , and α are presented.

Experimental data are presented on a wide range of pseudoplastic systems, ranging from suspensions to optically clear solutions, in both aqueous and nonaqueous media. In all cases the results conform to the equation with a high degree of accuracy over a wide range of shear rates.

An apparatus is described for compressing and expanding insoluble monolayers, or films, present at an oil/water interface. Typical results for polymethylmethacrylate and pepsin monolayers at a petroleum ether/water interface are described.

A new design is presented of an improved mass-transport cell for the measurement of electrophoretic mobilities of concentrated suspensions of particles. The results obtained with three different suspensions are compared with those from a Burton cell (moving-boundary method) and found to give good agreements. The advantages and disadvantages of the new cell are pointed out.

The effect of urea on the c.m.c. of polyoxyethylene straight-chain alkanols has been reported in a previous investigation. The observed increments in c.m.c. values have been attributed to increased hydration of the ethylene oxide chain caused by a reduction of the cooperative structure of water. On the basis of analogous results obtained in this investigation with polyoxyethylene branched-chain nonylphenols, the possibility of channel compound formation in these highly concentrated urea solutions has been excluded. Comparable increments in c.m.c. values have also been observed with guanidinium chloride and dioxane at lower concentration levels than with urea. The former presents additional evidence for attributing these changes to increased hydration of the ethylene oxide chain caused by a reduction of the cooperative structure of water.