Tuning the Viscoelasticity and Conformational Structure through Electric Field: From Unentangled to Entangled Polymers

Electroactive polymers offer versatile functionality, yet how electric fields modulate their viscoelasticity remains unclear. Here, we unveil molecular-weight-dependent electrorheological (ER) effects in poly(methyl methacrylate) (PMMA) melts and PMMA/titanium dioxide (TiO2) composites. The ER efficiency shows a decreasing trend with increasing molecular weight, and the addition of TiO2 particles significantly enhances ER efficiency, particularly in unentangled polymers, exhibiting its promising potential as a matrix in ER fluids. In frequency sweep tests, the electric fields stabilize transient microstructures, yielding a modulus plateau (∼102 Pa) in unentangled systems, whereas entangled systems exhibit increased moduli due to amplified intermolecular interactions. Crucially, entangled melts display a two-step structural recovery under large deformations: the initial rapid recovery corresponds to Hookean elasticity, while the subsequent slower phase reflects conformational recovery linked to entropic elasticity. These findings demonstrate tunable viscoelasticity through controlling molecular weight and applying an electric field, advancing soft materials with dynamically controllable mechanics.