Ian D. Morrison

Electrical charges in nonaqueous media

Abstract From an explosion at Shells refinery at Pernis to the megahertz oscillations of an electrically charged micelle in hexane to the most advanced of electronic imaging processes, electric charges in nonaqueous media make their presence known. The study of these electric charges has slowly and steadily increased over the last 50 years or so, but the answers to the elementary questions about how charged species are created and how they remain charged are still hotly debated. This review concentrates on the low conductivity solutions and dispersions typical of hydrocarbon media. The model generally accepted for nonaqueous electrolyte solutions is that the electric charges are stabilized against neutralization by being held separate in large structures, such as micelles or complex macroions. Electrical conductivity arises by the field-induced motion of these charged species. The electric-field and concentration dependence of the conductivity depend strongly on their size and structure. Particles acquire electrical charges either by preferentially adsorbing the ion of one sign or the other, possibly still associated with its stabilizing structure, or by an ion dissociating from its surface to be held in some lyophilic structure in the nonaqueous medium. Many aspects of this model are not universally accepted. The influence of water on the creation and stabilization of electrical charges is reviewed. Water plays a key role in the properties of nonaqueous electrolyte solutions and dispersions but its behavior is complex because it influences both the formation of structures such as micelles, the dissociation of ionic molecules, and reactions on particle surfaces. The current theories of the physics of nonaqueous electrolyte solutions and dispersions are reviewed. This review is presented in the form of discussions of twenty-two related topics.

An improved CAEDMON program for the adsorption isotherms of heterogeneous substrates

The numerical analysis of physical adsorption isotherms developed by Ross and Morrison [Surface Sci.52, 103 (1975)] designated CAEDMON (Computed Adsorptive Energy Distribution in the MONolayer), has been improved by incorporating well-established optimization techniques for which uniqueness and convergence criteria exist. The techniques include Dantzigs simplex method for linear programming, a modification of the systematic overrelaxation (S.O.R.) algorithm, Lemkes complementary pivot algorithm, and a nonnegatively constrained linear least squares algorithm. The mathematical bases and the application of these methods are discussed.

On the alleged ideality of szyszkowski-langmuir adsorption

Abstract The Szyszkowski equation for a surface-tension isotherm of a solution is equivalent thermodynamically to the Langmuir adsorption isotherm and also to the Frumkin two-dimensional equation of state. Lucassen-Reynders and van den Tempel (1964) maintained that Szyszkowski-Langmuir adsorption implies ideality of the surface phase. Reasons for disputing the uniqueness of this interpretation and a new interpretation are given.

Thermodynamics of adsorbed solutes

Abstract By considering the surface region of a solution of a surface active solute as a separate phase, the condition of equilibrium, which relates bulk concentration, surface concentration, and surface tension, can be obtained by equating chemical potentials for each component in the system. By applying the boundary condition of pure solvent and choosing an appropriate dividing surface, three formulations may be obtained from which either the bulk concentration, or surface concentration, or surface tension has been eliminated. The name-equations of Szyszkowski, Langmuir, and Frumkin may be obtained from these formulations by more than one set of assumptions about the activity coefficients. Certain sets of assumptions, however, are inconsistent with experimental data, namely, the ones that imply that the name-equations refer to ideal solutions, although this selection has had its proponents. Standard changes in the Gibbs free energy of adsorption can be obtained from the fit of these empirical equations to data if a suitable standard state, appropriate for this (but for no other) purpose be selected.

The equation of state of a foam

Abstract An equation of state of foam relates the six state variables of volume and pressure, moles of gas and temperature, surface area of liquid and surface tension. The equation for several special cases can be established as PV+( 2 3 )σA=nRT Previous attempts to prove this equation as a universal law, applicable to any foam, are reviewed and shown to be limited in their application. Nevertheless, the probability is high that the equation is indeed generally applicable, although a rigorous proof is still lacking.

Ross's rule: Sydney Ross and the phase diagram

Abstract One of Professor Rosss recent publications has the title, Capillarity and the Phase Diagram (J. Colloid Interface Sci., 145 (1991) 301). It describes applications of a fundamental principle first discovered by Ross and coworkers that capillary phenomena occur near certain defined locations within phase diagrams, namely, the phase boundaries. As this principle is a generalization of the Lundelius rule (Kolloid Z., 26 (1920) 145), may we be so bold as to call it Rosss rule? Interestingly, we can now see in the almost sixty years of Professor Rosss published work intimations of this rule in his work on the stabilization of foams and actions of antifoams, the behavior of adsorbed gases, and wetting phenomena near critical points. These earlier contributions are summarized to show the broad usefulness of this rule in colloid science and to justify its name.

ROLE OF PARTICLES AND DISPERSIONS IN ELECTROPHOTOGRAPHY

ABSTRACT The genesis of a 30 billion dollar a year electrophotographic industry can be traced to the sole effort of Chester Carlson who demonstrated in 1938 that dry images could be produced by a new process involving the attraction of charged pigmented particles to an electrostatic image formed on a photoconducting film. Carlsons invention, a particular form of electrophotography, is known as xerography. Most electrophotographic processes are based on the deposition of charged particles in either an air or liquid medium. The marking particles are usually pigments dispersed in a polymer matrix. The various electrophotographic processes are critically dependent on the electrical and mechanical properties of particles and dispersions. We examine the role of particles and dispersions in electrophotographic processes in general, and xerographic processes in particular.