Journal of Colloid Science最新文献

The anisotropy effect of the electrical conductivity occurs in solutions of anisometric polyelectrolytes under the influence of the orienting forces of a velocity gradient. A Couette-type apparatus for the generation of velocity gradients up to 20,000 sec.⁻¹ is described which permits measurements of the conductivity in three orthogonal directions. Evaluation of the curves obtained yields shape, size, and stability of the particles. A convenient method for the evaluation on the basis of Schwarz' theory (1, 2) is presented. Furthermore, the size of the particles may be calculated from the relaxation of the conductivity changes after the flow is stopped. The theory is extended to relaxation processes of nonuniform particles, and a method for the evaluation of the relaxation curves is developed which yields the average size and the size distribution of the particle assembly. The range of application of the flow method and the relaxation method is discussed; both methods may be applied to charged particles in the size range between 10⁻⁵ and 10⁻² cm. The application is demonstrated on rod-shaped and disc-shaped polyelectrolytes (sodium thymonucleinate and graphitic acid, respectively), and the results are found to be in agreement with electron microscope determinations. The methods proved to be useful for the investigation of the micellar state of amphiphilic substances in solution.

The conductimetric method of determining the critical micelle concentration of ionic surfactants has been used at very high ionic strengths. Data on sodium decyl and dodecyl sulfates in the presence of up to 1.0 and 0.3N NaCl, respectively, were obtained. The problems involved in these determinations are discussed. The principal one is the unexpected equality of the equivalent conductances of micelles and monomers in the presence of about 0.35N NaCl.

The hydrolysis of beryllium ion was investigated by means of the coagulation method. The charge of the the hydrolyzed species is found to be +3. This finding has been compared with the results of Sillén and collaborators and the differences have been discussed.

A quantitative linear relation between the heat of immersion and the pH of the zero point of charge (zpc) of inorganic oxides has been derived. The validity of the derivation has been substantiated by literature values of the two quantities for the inorganic oxides. The basis of the correlation is examined in terms of the electrostatic field strengths of the oxide surfaces, and the role of this field strength in determining both heat of immersion and zpc phenomena is discussed. The field is considered to control both the adsorption and dissociation of water molecules at the solid-liquid interface.

Jeffery's calculation of the energy dissipation in a suspension of noninteracting spheroids undergoing slow shear flow is extended for prolate spheroids in Couette flow, when they are prevented from rotating by an external torque, the spheroid axes being perpendicular to the fluid vorticity. The intrinsic-viscosity coefficient (2.5 for freely rotating spheres) is 4 for fixed spheres and 2 for long rods parallel to the fluid streamlines, and becomes indefinitely large for long rods perpendicular to the streamlines. It always exceeds the minimum value for free rotation. A suspension such as this provides a realizable model of a fluid having an unsymmetric stress tensor.