James R. Larson

Space‐charge‐perturbed electrophoresis in nonpolar colloidal dispersions

This paper reports the observation of bipolar, space‐charge‐perturbed transport in colloidal dispersions using an experimental technique that time‐resolves electrophoresis in nonpolar colloidal systems. Unlike existing methods for studying electrophoresis, this technique can be applied to dispersions of diverse types and concentrations over a wide range of electric fields, including the space‐charge‐perturbed conditions often encountered in practical applications. The phenomenon is investigated as a special case of dielectric relaxation in a leaky capacitor connected in series to a perfect one. Using the first principle charge transport theory, such dielectric relaxation, occurring under the non‐Ohmic supply and space‐charge‐perturbed transport conditions, is shown to differ from that expected by the conventional equivalent‐circuit treatment. The combined theoretical analysis and the experimental technique provides a means for independently determining the densities and mobilities of charged species in su...

Advances in liquid toner charging mechanism

Particles dispersed in a hydrocarbon liquid become charged by the addition of a charge director, a hydrocarbon soluble ionic surfactant, which aggregates into inverse micelles in non-polar media. This effect is utilized in liquid electrostatic developers for imagewise particle deposition which enables electrostatic printing. The charge director micelles ionize to form both positive and negative micelles which can compete with particles of the same sign for image charge during the image development process. Several techniques are available for the measurement of particle charges. These include methods by which particles are electrophoretically developed and the transient current monitored, one method where micelle counter ions are stripped from the particles by fluid flow, and particle charge can be related to particle mobility which can be measured by a number of techniques. All of these methods have some utility but their effectiveness will depend on how well they account for all of the charged species in the particle dispersion and other factors which effect charge on the particle. In this report a discussion of the influence of micelle ionization and the affect applied field have on the charge of particles is presented and how these phenomena might impact the measurement of the particle charge.

Halftone dot gain in liquid electrostatic printing systems

The development of an electrostatic printing system that is intended to emulate conventional printing must not only reproduce the color of the ink and the optical density of the printed solid area it must also obtain midtone dot gains and dot gain curves essentially identical to those obtained with conventional printing. In electrostatic printing halftone dot size may be affected by image change decay which is accelerated in small features, enhanced toner development along edges due to electrostatic fringe fields, and by the transfer of the image to paper. This report will show how these phenomena are dependent on the size of the halftone dots and how they combine to impact dot gain in a liquid electrostatic printing system. Specifically, it is demonstrated that differences observed in midtone dot gains on prints obtained with two different electrostatic masters are primarily the result of toner transfer from the masters to paper, while differences observed in the shape of the dot gain curves on prints obtained from the two masters are primarily due to the charge decay and toner development characteristics for halftone dots of the two masters.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.