Transient interfacial tension and morphology evolution in partially miscible polymer blends

Area of Science:

• Polymer science
• Materials science
• Physical chemistry

Background:

• Interfacial tension is crucial for polymer blend morphology.
• Molecular weight asymmetry across interfaces can lead to transient interfacial tension behavior.
• Understanding diffusion dynamics is key to predicting blend properties.

Purpose of the Study:

• Investigate the influence of molecular weight asymmetry on transient interfacial tension.
• Analyze the role of diffusion in interfacial tension changes for polymer blends.
• Study the impact of evolving interfacial tension on blend morphology development.

Main Methods:

• Utilized pendent/sessile drop apparatus to measure interfacial tension over time at varying temperatures.
• Employed discrete diffusion equation solutions and literature kinetic models to estimate diffusion times.
• Applied in situ small angle light scattering (SALS) and optical microscopy (OM) to study morphology evolution in dilute blends.

Main Results:

• Transient interfacial tension variations were observed, primarily driven by diffusion of lower molecular weight components.
• The most significant changes occurred in highly diffusive systems (low molecular weight, high polydispersity) when diffusion was from drop to matrix.
• Morphology development was found to be dominated by either diffusion or coalescence, depending on system diffusivity.

Conclusions:

• Interfacial tension evolution is a critical factor in polymer blend morphology, particularly for diffuse interfaces.
• Existing sharp-interface models are inadequate for diffuse blends, necessitating improved models for critical film thickness.
• The study provides insights into the relationship between molecular diffusion, interfacial tension dynamics, and blend microstructure.