Development of diffuse double layers in column-wicking experiments: implications for pH-dependent contact angles on
Christian Weber1, Helge Stanjek
1Clay and Interface Mineralogy, RWTH Aachen University, Bunsenstrasse 8, 52072 Aachen, Germany. christian.weber@cim.rwth-aachen.de
Journal of Colloid and Interface Science
|September 4, 2012
Summary
The study reveals that quartz powder
Area of Science:
- Surface Science
- Colloid and Interface Science
- Physical Chemistry
Background:
- The pH dependence of contact angles in quartz powder beds is complex.
- Direct measurements conflict with predictions from the Washburn equation regarding contact angle minima/maxima at the isoelectric point.
Purpose of the Study:
- To investigate the discrepancy in contact angle behavior of quartz powder beds with varying pH.
- To develop a model accounting for electroosmotic effects on capillary penetration.
Main Methods:
- Column wicking experiments to measure capillary penetration rates.
- Permeability measurements of quartz powder beds using aqueous solutions of varying pH.
- Application of the Washburn equation and a derived equation incorporating electroosmotic counter-pressure.
Main Results:
- Capillary penetration rate and powder bed permeability peak at the isoelectric point of quartz.
- A discrepancy exists between direct contact angle measurements and Washburn equation predictions.
- Electroosmotic counter-pressure influences capillary penetration dynamics.
Conclusions:
- The rate of capillary penetration is significantly affected by powder bed permeability and electroosmotic effects.
- A new equation accurately predicts the contact angle-pH relationship by accounting for electroosmotic counter-pressure.
- This work resolves the conflict between experimental contact angle data and theoretical models.
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