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Flow electrification in nonaqueous colloidal suspensions, studied with video microscopy.
V A Tolpekin1, D van den Ende, M H G Duits
1Physics of Complex Fluids group, JM Burgerscentrum for Fluid Mechanics, Faculty of Science and Technology, University of Twente, PO Box 217, Enschede 7500 AE, The Netherlands.
Langmuir : the ACS Journal of Surfaces and Colloids
|September 24, 2004
Summary
Flow electrification in nonaqueous suspensions was observed, changing particle interactions from attractive to repulsive due to acquired charges. This phenomenon, dependent on a glass surface, affects colloidal stability and particle aggregation.
Area of Science:
- Colloid and Surface Science
- Electrochemistry
- Materials Science
Background:
- Flow electrification in nonaqueous suspensions is underreported but crucial for colloidal behavior.
- Electrical charges on particles in low-polarity solvents lead to long-ranged forces due to minimal counterion screening.
- Understanding these phenomena is key to controlling colloidal stability and phase transitions.
Purpose of the Study:
- To investigate flow electrification in concentrated binary suspensions of hydrophobized silica particles in chloroform.
- To elucidate the impact of shear flow on interparticle interactions and colloidal stability.
- To explore the role of surfaces and external electric fields in modulating these effects.
Main Methods:
- Shear flow experiments on concentrated binary suspensions using confocal video microscopy.
- Control experiments with no flow, antistatic agents, and conducting indium tin oxide (ITO) layers.
- Application of external electric fields to aggregated suspensions.
Main Results:
- Shear flow induced flow electrification, altering particle interactions from attractive to strongly repulsive.
- Particle aggregates formed and subsequently disintegrated, with spatial distribution indicating acquired long-range repulsion.
- Control experiments showed continuous aggregate growth without flow electrification, while electric fields induced aggregate movement and segregation.
Conclusions:
- Flow electrification significantly impacts colloidal interactions and stability in nonaqueous suspensions.
- Glass surfaces play a critical role in enabling flow electrification, likely by acquiring negative charges.
- The observed phenomena, including aggregate disintegration and segregation, offer insights into colloidal dynamics and potential control mechanisms.