Control Of Surface Charge Research Articles

An Investigation of the Mechanisms of Chemical Regeneration of Activated Carbon

The mechanisms underlying chemical regeneration of activated carbon loaded with physisorbed organics have been explored. Using four aromatic adsorbates and five chemical regenerants in batch equilibrium and regeneration experiments, it has been shown that solubility of the organics and surface characteristics of the adsorbent under regeneration conditions strongly influence the regeneration efficiency. Solubility in the regenerant has been enhanced either by the addition of micelles or by the generation of soluble forms of the adsorbate. In general, the latter technique is more effective. It has been demonstrated that soluble forms of the adsorbate can be obtained by pH control or the use of reactive regenerants. pH can also be used to control surface charge characteristics and, consequently, adsorbate affinity for the adsorbent. For adsorbates that are difficult to solubilize or are very strongly bound to the surface, reduced affinity for the adsorbent through a change in surface charge characteristics c...

Cellular Response to Heterogeneously Charged Polystyrene

AbstractCells are sensitive to topological, chemical and electrical properties of substrates on which they are grown. However, most studies of cell-surface interactions have neglected electrical effects or confounded them with other substrate properties. The use of nanofabrication technology has made it possible to fabricate optically transparent surfaces, with controlled chemistry and topology, with active, controllable surface charge density in domains as small as 1–4 um1. Human monocytes incubated on polystyrene with 3.3 um wide strip domains alternately charged, so as to maintain overall charge neutrality, show significant charge density and time dependent increases (greater than twofold) in cell area and cell perimeter after challenge with a phagocytic trigger (human IgG opsonized Zymosan particles). Additional ultrastructural studies on silicon dioxide substrates show charge density dependent qualitative morphological differences. The human monocytes exhibited significant charge density and time dependent hyper-phagocytosis (> 25fold increase over control) of human IgG opsonized Zymosan particles. The charge-induced surfaces modulated the amplitude of the secreted extracellular levels of cytokines and also induced a temporal shift in the kinetics of cytokine release2.These studies demonstrate that human blood peripheral monocytes respond in-vitro to the peak magnitude of local surface charge heterogeneity in the absence of substrate topology and compositional variation.

Determination of near-surface forces in optical polishing using atomic force microscopy

An atomic force microscope was used to measure near-surface forces between individual metal-oxide polishing agent particles and planar optical glass surfaces immersed in aqueous fluids of carefully controlled chemistry. For a given polishing agent, the fluid pH was found to significantly influence the magnitude of the near-surface forces. Generally, if the fluid pH equals the isoelectric point of the polishing agent, then the attractive force between the polishing agent particle and the glass surface is maximized. The pH-driven modulation of near-surface forces was found to be completely reversible, indicating the need to control surface charge during aqueous polishing of optical glass through manipulation of the slurry chemistry.

Dose control system for the Extrion 1000 ion implantation system

The next generation of ion implantation systems requires more stringent controls on the reproducibility and uniformity of dose accuracy on both a day-to-day and batch-to-batch basis. Integration of process controls, vacuum transient immunity, channelling control, and wafer surface charge neutralization in an automated environment will be assumed. This paper describes a dose measurement and control system for Varian's new Extrion 1000 batch process ion implantation system.

Effects of surface density of states in the bandgap of semiconductor electrodes upon capacity curves

Evaluation of the Mott-Schottky capacity plot on semiconductor electrodes usually exhibits a linear 1/ C 2 range which exceeds considerably the semiconductor gap width. This still insufficiently understood phenomenon points either to an extended non-equilibrium space charge layer, and/or to enhanced Helmholtz potential variation. In this paper, initially the latter problem is treated. A broad surface density of states distribution in the bandgap can cause a smooth dependence of (dϕ sc/dϕ h ) at electronic equilibrium upon electrode potential and an extended linear 1/ C 2 range. On the contrary, a sharp surface density peak leads to Fermi level pinning, characterized by a break of (dϕ sc/dϕ h ) and of the observable 1/ C 2 plot. Surface capacity may be suppressed at usual frequencies, due to carrier transport controlled surface charging in the depletion regime.

Electrochemical surface science: The study of monolayers of ad-atoms and solvent molecules at charged metal interfaces

In parallel with the spectacular advances that have been made in recent years in the field of metal/vacuum surface science, there have been corresponding interesting developments of a complementary kind in electrochemical surface science. This article describes recent advances in the latter field, and their experimental and theoretical bases. However, the molecular situation at electrode interfaces is very complex compared with that at a metal/vacuum interface, owing to adsorption and orientation of solvent molecules, and the presence of solvated ions. Hence these topics must be considered as well as the surface science of the metal electrode itself. In comparison with metal/vacuum surface science, electrochemical studies on metal interfaces can utilize the electrode potential as an additional independent variable and thus control surface charge density, coverage by Faradaically deposited ad-atoms, co-adsorption of cations or anions and solvent dipole orientation. Modulations of electrode potential in time allow the kinetic relaxation characteristics of monolayers to be followed, and the potential-modulated reflectivity and spectral absorption of species in the interphase to be studied. Electrochemically controllable sub-monolayer coverages of, e.g., metal ad-atoms have interesting catalytic effects on other continuous electrochemical reactions, such as oxygen reduction or formic acid oxidation. Experiments based on electrochemical potential pulse and sweep, and current pulse methods enable chemisorption of ad-atom monolayers to be studied in fine detail. Multiple state chemisorption in monolayers is commonly observed, even on single crystal surfaces, and fine resolution of the states can be achieved by electrochemical techniques. The kinetics of monolayer deposition and desorption can also be followed, as well as the dynamics of reconstruction processes e.g. in 0 monolayers as a function of time and potential. The electrochemical methods allow direct determination of the differential isotherm for adsorption as well as the usual integral one. The former gives details of multiple state adsorption, and provides information on interaction effects in the monolayer and kinetics of its formation. Ionicity of ad-species can also be evaluated. Recent advances in combining electrochemical systems in situ with high-vacuum LEED, Auger and ESCA apparatus are described. Since electrochemical surface science has necessarily to be able to study processes at the interfaces of metals in contact with liquid solutions, an important area of the field has been the treatment and evaluation of solvent dipole adsorption and orientation as a function of electrode potential or surface charge density.

Emulsifier‐free emulsion polymerization with ionic comonomer

AbstractEmulsion polymerization of styrene in the absence of emulsifier with K2S2O8 as initiator produced uniform latices. Incorporation of ca. 0.5% ionic comonomer (sodium styrenesulfonate) reduced the particle size from the range 0.5–1.0 μm achieved in prior emulsifier free formulations to a range of 0.15–0.40 μm. Some advantages achieved by incorporation of ionic comonomer were higher polymer content and independently controllable surface charge density. Particle diameter varied as the 0.64 power of the ratio of ionic strength to comonomer, as the −0.20 power of initiator concentration, and as the 0.46 power of monomer content. Kinetic data suggest that copolymerization takes place in the aqueous phase, and that nuclei for particle growth are formed by precipitation of the initially water‐soluble copolymer. The latex is stabilized by sulfonic acid groups of the comonomer, as well as by sulfate end groups from the initiator.