Getting in shape: molten wax drop deformation and solidification at an immiscible liquid interface

Area of Science:

• Materials Science
• Fluid Dynamics
• Chemical Engineering

Background:

• Controlled synthesis of non-spherical particles is crucial for applications in food processing, drug delivery, and optical sensing.
• Existing methods often lack precise control over particle morphology.
• Understanding the physics of droplet deformation and solidification is key to tailored particle production.

Purpose of the Study:

• To investigate the deformation and solidification of molten wax drops impacting an immiscible liquid interface.
• To identify the key parameters influencing the final shape of solidified wax particles.
• To establish relationships between process variables and particle morphology.

Main Methods:

• Experiments involving millimeter-sized molten wax drops impacting a higher-density cooling liquid bath.
• Systematic variation of parameters: initial temperature, viscoelasticity, drop size, impact velocity, bath fluid viscosity and temperature, and interfacial tension.
• High-speed imaging to capture drop deformation dynamics.
• Construction of phase diagrams correlating dimensionless numbers (Weber, Capillary, Reynolds, Stefan) with particle shapes.
• Simplified heat transfer analysis to estimate solidification time.

Main Results:

• Spherical molten wax drops transformed into non-spherical shapes (ellipsoid, mushroom, disc, flake) upon impact and cooling.
• Particle morphology was found to be dependent on a balance of interfacial, inertial, viscous, and thermal forces.
• Cursory phase diagrams were constructed, mapping particle shapes against dimensionless numbers.
• Solidification time was estimated and correlated with drop deformation history.

Conclusions:

• The final morphology of solidified wax particles is determined by a complex interplay of fluid dynamics and heat transfer.
• Controlling impact conditions and fluid properties allows for the directed synthesis of various non-spherical particle shapes.
• This study provides a framework for understanding and designing processes for controlled non-spherical particle generation.