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Dip coating of shear-thinning particulate suspensions
D Ding1, C T Gabbard2, J B Bostwick1
1Department of Mechanical Engineering, Clemson University, Clemson, SC 29634, USA. jbostwi@clemson.edu.
Soft Matter
|October 2, 2024
Summary
Dip coating with shear-thinning fluids entrains particles, enabling filtration and sorting. A new model predicts particle capture based on fluid properties and withdrawal speed, validated by experiments.
Area of Science:
- Fluid dynamics
- Colloid science
- Materials science
Background:
- Dip coating is a versatile technique for applying thin films.
- Particle suspension behavior in non-Newtonian fluids is complex.
- Understanding particle entrainment is crucial for filtration and sorting applications.
Purpose of the Study:
- To investigate particle entrainment during dip coating of shear-thinning fluids.
- To develop a predictive model for particle entrainment criteria.
- To explore particle sorting in bidisperse suspensions.
Main Methods:
- Experimental dip coating of monodisperse and bidisperse particle suspensions (Xanthan Gum solutions).
- Development of a theoretical model using lubrication theory for an Ostwald power-law fluid.
- Analysis of particle entrainment based on coating thickness, particle size, and fluid rheology.
Main Results:
- Particle entrainment occurs when coating thickness exceeds particle diameter.
- A modified Landau-Levich-Derjaguin (LLD) law predicts film thickness, dependent on capillary number (Ca).
- Critical withdrawal velocity correlates with particle size and fluid rheology (Ca and bond number, Bo).
- Particle sorting observed in bidisperse suspensions, with smaller particles preferentially entrained.
Conclusions:
- The developed model accurately predicts particle entrainment criteria for shear-thinning fluids.
- Dip coating offers a method for particle filtration and sorting based on size.
- Fluid rheology and process parameters (Ca, Bo) control particle entrainment and sorting efficiency.
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