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Critical role of flow-modified permittivity in electrorheology: model and computer simulation
Ujitha M Dassanayake1, Stella S R Offner, Yue Hu
1Complex Fluids Group, Physics Department, Brandeis University, Waltham, Massachusetts 02454, USA.
Summary
This study reveals how flow-modified permittivity impacts electrorheology (ER) effects. At high Mason numbers, particle dipole misalignment, not just chain deformation, drives ER, even causing negative effects.
Area of Science:
- Rheology
- Materials Science
- Computational Physics
Background:
- Electrorheology (ER) describes fluids whose viscosity changes with an applied electric field.
- Existing models often focus on particle chain formation and deformation.
- The role of fluid flow in modifying material properties within ER fluids is less understood.
Purpose of the Study:
- To develop and validate a computational model for electrorheology that incorporates flow-modified permittivity (FMP).
- To elucidate the mechanisms governing ER effects across a range of Mason numbers.
- To identify conditions leading to both positive and negative ER phenomena.
Main Methods:
- Development of a novel computer simulation model.
- Analysis of electrorheological behavior as a function of Mason number.
- Investigation of particle chain structure and dipole moment alignment.
Main Results:
- For Mason numbers < 0.1, ER effects are dominated by particle chain deformation, consistent with prior research.
- At higher Mason numbers (> 0.1), FMP-induced misalignment of particle dipoles with the electric field becomes the primary driver of ER.
- Conditions for observing negative electrorheological effects at large Mason numbers were identified.
Conclusions:
- Flow-modified permittivity is a critical factor in electrorheology, especially at higher shear rates.
- The model successfully explains ER mechanisms beyond simple chain deformation.
- This work provides new insights into controlling and predicting ER fluid behavior.