String formation in sheared polymer blends: coalescence, breakup, and finite size effects

Area of Science:

• Rheology and Polymer Science
• Soft Matter Physics

Background:

• Concentrated polymer blends exhibit complex flow behaviors.
• Droplet deformation and breakup are critical phenomena in multiphase fluid dynamics.

Purpose of the Study:

• To investigate the droplet-string transition in concentrated polymer blends.
• To elucidate the mechanism and stability of string formation under shear.

Main Methods:

• Experimental observation of droplet behavior in concentrated polymer blends under shear.
• Analysis of droplet size, gap width, and shear effects.
• Investigation of the kinetic process and stability mechanisms.

Main Results:

• A droplet-string transition was discovered in concentrated polymer blends.
• The transition occurs when droplet size is comparable to the gap width.
• String formation involves a four-stage kinetic process and results in stable strings with hysteresis.
• Rayleigh-Tomotika instability is suppressed by finite size effects and shear-induced advection.

Conclusions:

• The droplet-string transition is an abrupt phenomenon driven by confinement and shear.
• Shear-induced strings are stabilized by suppressed instabilities, offering insights into complex fluid behavior.