Meniscus Of Solution Research Articles

Mechanical and Current Oscillations in Corroding Electrodes

Mechanical oscillations of the solution meniscus risen around a corroding wire electrode were observed in synchronism with electrical current oscillations. Scanning electron microscopy coupled to microprobe analysis was used to investigate the topochemistry of the system under study. Solution capillarity effects on iron and on iron compounds are related to the oscillations detected in this system.

Investigations of hydrogen ionization on platinum with the help of micro-electrodes

With the help of a micro-electrode placed in the thin electrolyte film above the solution meniscus, limiting diffusion current values, an order of magnitude higher than the values obtained on rotating disk electrodes, were realized. The dependence of the hydrogen exchange current on pH was determined. The experimental data may be explained by the assumption of two overlapping reaction courses: one depending on θH (through intermediate formation of hydrogen atoms by dissociative molecular adsorption) and another, not depending on θH (for example, an electron transfer reaction before dissociation). The connection between surface coverage with anions (iodide and bromide) and hydrogen ionization rate was quantitatively investigated; it was shown that adsorption leading to the displacement of adsorbed hydrogen atoms (the case of iodide) inhibits hydrogen ionization much more than adsorption leading to a redistribution of the hydrogen-surface bond energies (for bromide).

Sedimentation velocity of polymer solutions—II. Pressure dependence of the sedimentation coefficient

The dependence of the sedimentation coefficient upon the hydrostatic pressure in the solution has been studied in the three polymer-solvent systems: (I) polymethylmethacrylate in n-butyl chloride at 35°, (II) polystyrene in cyclohexane at 34° and (III) polyisobutylene in cyclohexane at 34°, The first two are θ-systems. Analysis of the experimental data in terms of the Fujita equation yielded values for the pressure dependence parameter m. The pressure dependence coefficient (μ) was obtained from the equation m/ r 0 2 = (0·5) ρ 1. μ, ω 2 where ρ 1 is the solute density at atmospheric pressure, r 0 the distance between the axis of rotation and solution meniscus and ω the angular velocity of the rotor. For the three systems, μ depended upon ω and for system (I), upon the solute concentration, although allowance had been made for the concentration dependence of the sedimentation coefficient. The reason for this may lie in the polydispersity of the solute or incorrect assumptions implicit in the Fujita equation or its application to these systems.

A convenient small osmometer

A description is given of a simple, rugged instrument for determining the osmotic pressure developed by a solution of a high polymer. Other small osmometers described previously [1, 2, 3, 4, 5]/ have been, in some respects, too inconvenient to use. Although relatively easy to make, glass osmometers are fragile and may require frequent repairs. Small metal osmometers, in addition to being rugged, can be designed for easy and rapid assembly and simplicity of operation. The instrument described here is a modification of the apparatus described by Sands and Johnson [4]. The new design permits the instrument to be assembled, rinsed, and filled conveniently, while keeping the membrane wet with solvent at all times., The total volume of the solution cell is less than 2 ml so that a relatively small quantity of polymer suffices for a complete osmotic pressure curve. The Zimm and Myerson osmometer [5] has been used in the Bureau for some time. The outstanding advantages of this instrument are the ease of adjusting the solution meniscus and its relative speed in attaining equilibrium compared with other small osmometers. On the other hand, its assembly is tedious and time consuming. Particularly in rinsing the cell, it is difficult to empty the osmometer without risk of drying the membrane. After the instrument is finally filled with polymer solution, air bubbles must be removed from each osmometer. Because considerable clamping pressure on the membrane (which serves as its own gasket) is required to insure an adequate seal, there is danger that the glass edges may be chipped. This is especially likely if the plane of the membrane is not exactly perpendicular to the axis of the cylinder forming the cell of the Zimm osmometer.