Confined flow of polymer blends

Area of Science:

• Rheology
• Materials Science
• Fluid Dynamics

Background:

• Investigating emulsion morphology under shear is crucial for understanding complex fluid behavior.
• Confinement effects on droplet dynamics in emulsions are not fully understood.
• Existing models often fail to predict behavior in confined geometries.

Purpose of the Study:

• To investigate the influence of confinement on the steady-state morphology of polybutene (PB) and polybutadiene (PBD) in polydimethylsiloxane (PDMS) emulsions.
• To analyze the effects of shear rate and concentration on droplet arrangement and morphology.
• To compare experimental results with existing and modified theoretical models.

Main Methods:

• Shearing two types of emulsions (PB in PDMS, PBD in PDMS) between parallel plates with controlled gap spacing (40 microm).
• Systematic investigation of varying concentrations and shear rates.
• Analysis of droplet morphology using optical micrographs and comparison with theoretical models.

Main Results:

• Decreasing shear rate leads to increased droplet coalescence and confinement.
• Droplets transition from bulk behavior to layered structures (two layers, then a single layer) as confinement increases.
• Droplets self-assemble into superstructures like pearl necklaces and strings.
• The Maffettone-Minale (MM) model fails to predict deformation in confined flow above a critical confinement level.
• A modified model (mM model) incorporating effective viscosity accurately describes experimental observations in confined flow.

Conclusions:

• Confinement significantly impacts emulsion morphology and droplet arrangement under shear.
• A new mM model accurately predicts the behavior of emulsions in confined shear flow, outperforming previous models.
• Understanding these confined flow dynamics is essential for applications involving emulsions in constrained environments.