The Surface Thermodynamic Properties of Some Volcanic Ash Colloids

Abstract

The surface tension components and parameters for nine naturally occurring colloidal-sized volcanic ash samples were determined by thin-layer wicking. These materials include rhyolites, trachytes, phonolites, and an andesite, and were collected from deposits in California, Arizona, Italy and Martinique. The samples are principally volcanic glass (with minor amounts of mixed materials of various compositions) with silica contents ranging (average values) from 74% (rhyolite) to 57% (andesite). The surface tension components were determined by means of thinlayer wicking to provide contact angles which were used to solve the Yeung-Dupre equation. The Lifshitz-van der Waals component of the surface tension, 'Y LW , for these ash samples varies between 26.6 mJ/m 2and 38.7 ml/m''. The Lewis acid parameter, 'Y Ill , values are small with values ranging from 0 mJ/m 2to 1.8 ml/rn", while the Lewis base parameter, 'Y e , values varied between 15.6 mJ/m 2and 45.6 mJ/m 2. Of the nine samples, five were hydrophobic and the other four were hydrophilic. The hydrophobic ashes were produced by eruptions with a dominantly 223 Copyright 0 1997 by Marcel Dekker, Inc. 224 LI ET AL.magmatic rupture mechanism: pyroclastic flow, nuee ardente, ash cloud surge. The hydrophilic ashes were generated by a strong hydromagmatic mechanism and most formed accretionary lapilli. The <:-potential values were determined from the electrophoretic mobility, and varied between -32.1 mV and -55.2 mY. Utilizing the surface tension values and the <:-potential, an extended DLVO-type (XDLVO) calculation of the free energy of interaction versus distance, including the Lewis acid-base contribution, between 1 I'm spherical particles, showed that for the five hydrophobic ash samples there is a net attraction between particles in the presence of water, and for the four hydrophilic samples there is a strong net repulsion between particles. Assuming that the stability of an ash deposit (in the presence of water) on an inclined slope is related to the forces acting between neighboring ash particles, those deposits with repulsive interparticle forces would be more mechanically unstable and pose a risk of forming mud flows on remobilization.

Wettability and Topography of Phospholipid DPPC Multilayers Deposited by Spin-Coating on Glass, Silicon, and Mica Slides

“…The physicochemical properties of solid-supported phospholipid layers are important for the characterization and development of novel biomolecular materials (e.g., biosensors). The changes in the surface wettability of DPPC layers deposited on glass, silicon, and mica can be evaluated from their surface free energy determined by means of the two approaches and using the measured contact angles and surface tension as well as the components of the probe liquids …”

Topography and Surface Free Energy of DPPC Layers Deposited on a Glass, Mica, or PMMA Support

“…In the first approach, only the advancing contact angles are used, and in the second, both the advancing and receding ones are used. For the surface free energy calculations, the literature data on surface tension and its components for the probe liquids were taken, and they are listed in Table . The calculated values of the surface free energy and its components for bare surfaces of the substrates are shown in Figure .…”

Surface Aggregation ofCandida albicanson Glass in the Absence and Presence of AdheringStreptococcus gordoniiin a Parallel-Plate Flow Chamber: A Surface Thermodynamical Analysis Based on Acid–Base Interactions

“…The necessary input data concerning the Lifshitz-van der Waals and acid-base interactions can be derived from contact angles with liquids and the electrostatic interactions from streaming potential measurements (12) or particulate microelectrophoresis (13). Although the extended DLVO approach has proven merits for explaining adhesion in general (14,15) and microbial adhesion in particular (16), it is increasingly being recognized that chemical heterogeneities and structural features on microbial cell surfaces may impede a straightforward application of the extended DLVO approach (17,18).…”