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Slip of Spreading Viscoplastic Droplets
Maziyar Jalaal1, Neil J Balmforth2, Boris Stoeber3
1Department of Mechanical Engineering, University of British Columbia , Vancouver, British Columbia V6T 1Z4, Canada.
Langmuir : the ACS Journal of Surfaces and Colloids
|September 30, 2015
Summary
This study investigated how complex fluid droplets spread on glass. Modifying the glass surface charge reduced droplet spreading and slip, especially for Carbopol solutions, demonstrating surface charge
Area of Science:
- Rheology and Fluid Dynamics
- Surface Science
- Materials Science
Background:
- Understanding droplet spreading dynamics is crucial for various industrial applications, including coatings, printing, and microfluidics.
- The behavior of complex fluids, such as polymer solutions, is often influenced by surface interactions and fluid properties like viscosity and elasticity.
- Effective slip at fluid-solid interfaces can significantly alter droplet spreading, but its control remains a challenge.
Purpose of the Study:
- To experimentally investigate the spreading of axisymmetric viscoplastic droplets (Carbopol and xanthan gum solutions) on glass surfaces.
- To quantify the effect of surface charge modification on droplet spreading dynamics and interfacial slip.
- To correlate fluid rheology and surface properties with observed spreading behavior.
Main Methods:
- Utilized shadowgraphy and swept-field confocal microscopy for visualizing droplet spreading.
- Employed particle image velocimetry (PIV) with neutrally buoyant tracers to measure radial velocity profiles.
- Conducted experiments on both untreated and positively charged glass surfaces to study the impact of surface adhesion.
Main Results:
- On untreated glass, both Carbopol and xanthan gum solutions exhibited significant effective slip.
- On positively charged glass surfaces, droplet spreading was reduced, leading to smaller radial distances.
- PIV measurements confirmed a substantial reduction in slip on the treated surface; effective slip was eliminated for Carbopol and significantly reduced for xanthan gum.
Conclusions:
- Surface charge plays a critical role in controlling the spreading of viscoplastic droplets on solid surfaces.
- Promoting adhesion via surface charge modification effectively suppresses interfacial slip, thereby altering spreading dynamics.
- The degree of slip reduction depends on the specific complex fluid, with Carbopol showing complete slip elimination under the experimental conditions.
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