Nonlinear Rheology of Unentangled Polymer Melts Reinforced with High Concentration of Rigid Nanoparticles

Area of Science:

• Polymer Science
• Materials Science
• Rheology

Background:

• Understanding the nonlinear rheology of polymer melts with high particle concentrations is crucial for material design.
• Existing models often struggle to capture the complex interplay between polymer chains and filler particles under deformation.

Purpose of the Study:

• To develop a scaling model for analyzing the nonlinear viscoelasticity of unentangled polymer melts filled with high concentrations of small spherical particles.
• To elucidate the mechanisms driving the nonlinear response, specifically chain stretching and desorption.

Main Methods:

• Development of a scaling model based on the assumption of reversible chain adsorption to particle surfaces.
• Analysis of the composite system under 2D shear flow to observe viscoelastic responses.
• Investigation of steady-state shear viscosity and dynamic moduli (storage and loss) under varying shear rates and strain amplitudes.

Main Results:

• Nonlinearity in viscoelastic response arises from the stretching of adsorbed polymer chains and increased desorption rates under deformation.
• Steady-state shear viscosity exhibits a power-law shear-thinning behavior: η ∼ ɣ̇(-½).
• Storage and loss moduli scale with strain amplitude as G' ∼ ɣ(0)(-1) and G″ ∼ ɣ(0)(-½) at large amplitudes.

Conclusions:

• The proposed scaling model successfully explains the nonlinear rheological behavior of particle-filled polymer melts.
• Chain adsorption-desorption dynamics are key to understanding shear thinning and modulus changes in these composite materials.
• The findings provide a theoretical framework for predicting and controlling the mechanical properties of filled polymer systems.