Abstract
The point of zero charge pH of an oxide surface is a fundamental surface chemistry property or solids or metal oxides that determine the nature of interaction at the solid-aqueous solution interface. In colloid chemistry this physical parameter controls the evolution of the electric double layer as well as adsorption and desorption processes.In colloid chemistry a number of methods have been used for the determination of the point of zero charge pH of an oxide surface. This ranges from titrimetric to radiation chemistry approach that deals with scanning electron microscopy.In this study, the direct effect of aqueous solution acidity on the solid-liquid interfacial free energy and the consequence of this effect on spontaneous imbibition of aqueous solution into borosilicate glass have been exploited for the determination of the point of zero charge pH of this type of glass. What is new in this method is that while the traditional titration method relies on neutralization of surface charges, the present method relies on interfacial free energy changes due to aqueous solution pH changes and the effect of this on the wettability of borosilcate glass surface. Result of point of zero charge pH obtained from the present method has been compared with those obtained using traditional methods. The comparison shows close agreements and this proves the technique used in the present work as a novel method for the determination of the point of zero charge pH of oxide surfaces.
Highlights
1.1 Relationship of Capillary Phenomenon to Contact AngleThe point of zero charge pH of an oxide or hydroxide surface is the pH of the aqueous solution in contact with it at which the net surface charge is zero (Sposito, 1998)
The point of zero charge pH of an oxide surface is a fundamental surface chemistry property or solids or metal oxides that determine the nature of interaction at the solid-aqueous solution interface
It is a fundamental surface chemistry property that depends among other things on the dielectric permittivity of the material, metal to oxygen bond length and Pauling bond strength per unit length (Sverjensky, 1994)
Summary
While other methods described above rely on particular principles to measure the point of zero charge pH of a solid surface, the motivation for the present work derives from the dependence sold-liquid interaction and adsorption phenomena (Barrow, Bowden, Posner, & Quirk, 1980) on the point of zero charge of the solid. Integration of the effect of electric field/surface charge density provides a thermodynamic approach involving entropy maximization of the system vapor-liquid-solid This approach has yielded modified equations for Laplace and Young equation (Digilov, 2000). Counting on the works of previous researchers, this paper is motivated to use the electrostatic contribution to wetting changes a step further by considering spontaneous imbibition capillary rise under varying pH conditions. This varying in aqueous solution pH is expected to cause variations in surface charge density, which is expected to cause contributions to Laplace and Young’s equations similar to that dealt with by previous researchers. The prime objective is to link contact angle and capillary rise to pH and to use this as the basis for determining the point of zero charge pH of Borosilicate glass surface through an appropriate mathematical model
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