Wolfgang Haller

Rearrangement Kinetics of the Liquid—Liquid Immiscible Microphases in Alkali Borosilicate Melts

Probability calculations are presented which show the high degree of mutual intersection within a population of spheres grown from randomly placed nuclei. It is proposed that the observed networklike structures of the phases of certain liquid—liquid immiscible systems may be due to this statistical lumping. It is further proposed that interfaces of opposite curvature facilitated by this structure rather than polydispersisity give rise to transport phenomena resulting in observable rearrangements in these systems. Equations for a number of transport models are derived.Liquid—liquid phase separation was induced in alkali borosilicate melts by cooling below immiscibility temperature. Progressive stages of the geometric rearrangements within the microdisperse phases were arrested by undercooling. The kinetics of the decrease in interfacial area between the phases was studied by gas adsorption on the isolated silica‐rich phase. It is found that interfacial area is proportional to the reciprocal of the square r...

The electrokinetic potential of glasses in aqueous electrolyte solutions

Abstract Electrokinetic potentials of several glasses of well defined bulk composition in aqueous electrolyte solutions were computed from streaming current measurements. The composition of the bulk is reflected in the magnitude of the potential and in the shape of the curves relating the electrokinetic potential and the pH of the solution. No differences have been found between the crystalline and the vitreous state of silica. Addition of Al 2 O 3 to the bulk results not in doping effects but rather in surface neutralization making the surface less acidic. Glasses with an appreciable amount of B 2 O 3 have higher negative potentials at the same pH, and the derivatives of electrokinetic potential vs pH show them to belong to a different type of surface than vitreous or crystalline silica. Studies involving controlled pore glasses of various pore sizes have shown the importance of below-the-surface ionic penetration and/or adsorption in the pores in establishing the solid-movable liquid interfacial electrical equilibrium.

Correlation between chromatographi and diffusional behavior of substances in beds of pore controlled glass : Contribution to the mechanism of steric chromatography

Abstract Chromatography and diffusion experiments were performed with columns and suspensions of grains of pore-controlled glass 620 A pore diameter. The elution positions of tobacco mosaic virus and of benzyl alcohol coincide with the actual void volume and the total fluid volume of the column. A spherical virus (MS2) of 260 A diameter eluted at a normalized elution volume of ke = 0.44 and its peak position shifted only very slightly over a wide range of elution rates. The diffusional uptake of virus (MS2) by the porous glass grains from a well stirred suspension indicated that the total pore volume of the glass was accessible to the virus. It took approximately 30 sec for one half of the ultimated amount of virus to penetrate the glass. In the light of these results it is very unlikely that a volume exclusion of uniform and controlle pore size display elution spectra similary to those of gel columns, it is also unlikely that volume exclusion governs the elution spectrum in steric chromatography on gels.

Mechanism of inactivation of bacteriophages by metals

Abstract The sensitive RNA bacteriophages MS2 and f2 and, to a lesser extent, the single-stranded DNA phage S13 are inactivated when their dilute suspensions come into contact with an aluminum alloy surface or when diluted with fluids which have been in contact with aluminum, zinc, or magnesium. The inactivation is believed to result from the simultaneous action of traces of Cu2+ and electrolytically formed H2O2 and may be stimulated by addition of both of these agents, although neither alone is fully active when present in trace amounts. The phages are protected by adding either catalase or EDTA, which is further support for the suggested mechanism.

Characterization of active sites at chemically modified glass surfaces

Abstract Chemically modified surfaces of silica glass samples of controlled pore size (CPG) were studied by gas (argon, H 2 O) adsorption, and by adsorption of organic amino and hydroxyl functional compounds having ESR active nitroxide groups. Chemical modification of surfaces was achieved using triethoxy or trichloro alkyl, allyl, and phenyl silanes. The results allow the quantitative and qualitative estimation of the number of active sites on modified surfaces of CPG.

Surface conductivity of glass at the solid/liquid interface☆

Abstract The electrokinetic phenomenon of surface conductivity was studied for capillaries of pure fused silica and of a borosilicate glass, in water, dilute aqueous solutions of HCl and NaCl, in methanol and acetonitrile. Measurements were done in the temperature range between 5 and 30°C by a dc linear voltage sweep technique at a rate of 0.2 V/sec or less, and with applied polarization voltages up to ±40 V. Surface conductivity was calculated from the total specific conductivity measured by two bright platinum electrodes at the mouths of the capillary and from the specific bulk conductivity of the liquid medium measured by a separate pair of Pt electrodes at the same temperature. Absolute values of the surface conductivity were between 10 −9 and 10 −10 ohm −1 . Energies of activation were calculated from the slopes, S , of log κ vs 1 T curves, observed within a temperature range from 5 to 30°C. The energies E defined as S = E / k were: 45–55 kJ/mole for the borosilicate glass, and 25–34 kJ/mole for fused silica in water, in aqueous solutions, and in methanol. In acetonitrile they were 105 kJ/mole for borosilicate glass and 59 kJ/mole for fused silica. The results were interpreted on the basis of the assumption that protonic conductivity is the predominant mode of surface charge transfer, with the rotation of water molecules in the first liquid layer as the rate-determining step.

Adsorption phenomena on glass surfaces. IV: Surface acidity of silica and glasses

Abstract Batch and flow microcalorimetry were used to study adsorption of aliphatic amines on silica gel, controlled pore glass (CPG), high alumina glass, and surface-derivatized controlled pore glass. The adsorption of basic aliphatic amines is indicative of the acidity of the surface. Silica gel and controlled pore glass show the same average heat of adsorption for butylamine, 35 ± 2 kJ mole −1, but the CPG, in contrast to the silica gel has nearly homoenergetic surface. High alumina glass (17% Al2O3) has a less acidic surface, and the relevant value for the heat of adsorption of butylamine is only 4.7 kJ mole−1. Surface derivatization with a long-chain aliphatic silane (octadecylsilane) produces a highly hydrophobic surface, when water molecules are used as probes. Interaction with butylamine remains strong, as in the original state of CPG. Derivatization with aminopropylsilane yields a basic surface and the interaction with butylamine is weak, showing a heat of adsorption of only 3–4 kJ mole−1. The paper indicates that surface acidity of silica and glasses can be understood only as an interactive process between the surface and the adsorbate.

Investigation of liquid-liquid phase transitions in oxide melts by viscosity measurements

Results from viscosity measurements conducted both above and below the liquid-liquid phase transition of a series of molten oxide glasses are reported in order to analyze the effect of supercritical composition fluctuations on viscous flow, and to investigate the mechanisms of phase separation. Measurements of four oxide mixtures with similar high temperature structures and widely different critical temperatures, revealed an anomalous increase in viscosity at temperatures above the critical point. The anomalous increase occurs when large composition fluctuations characterizing the critical point are present. The effect is explained in terms of an interaction between viscous flow and the supercritical fluctuations through the structural relaxation process. An analysis of this interaction is presented.Measurements conducted at temperatures slightly below the critical point of one of these glasses indicate that the microstructure resulting from the phase separation is highly sensitive to the preceding heat-treatment. Phase separation by the formation of isolated spheres of the silica-rich component is identified a few degrees below the critical point. Further measurements of viscosity by a fibre elongation method, conducted far below the critical temperature, are reported in order to analyze the growth mechanisms occurring in the separated phases. In this case, the rearrangement stage of phase separation is characterized by a growing interconnected structure.

Glassy Optical Coatings By Multisource Evaporation

In this presentation, the concepts of bulk glass formation are discussed in light of their possible application to the production of glassy thin films for optical applications. Specifically, the systems Zr02-Si02 and Zr02-Mg0 were explored using electron beam coevap-oration for the film production. The films so produced were characterized using x-ray dif-fraction and scanning electron microscopy. It was found that while coevaporation of a traditional bulk glass former (Si02) to Zr02 was more effective in producing an amorphous mixture coating, other dopants (Mg0) could also achieve the same end if used in higher con-centrations. Key words: Ceramic coatings; Glassy; MgO; Si02; Thin films; and Zr02.

Application of a general equation for controlled pore glass permeation chromatography to an aggregating, spherical virus

A semi-empirical permeation chromatography equation relating pore size, species size and elution coefficient, which had previously been derived from chromatographic data of narrow-molecular-weight dextrans on controlled pore glass, was applied to the chromatography of an aggregating virus particle. A large number of chromatographic runs on columns of different pore sizes were combined and statistically evaluated. The resulting diameter distribution versus infectivity curve for the virus particle population shows distinct maxima at multiples of 50 nm. This unit size agrees with electron microscopical observations and confirms the applicability of the chromatography equation.