OpTiDDM (Optical Tweezers integrating Differential Dynamic Microscopy) maps the spatiotemporal propagation of nonlinear stresses in polymer blends and composites

TL;DR

This paper introduces OpTiDDM, a novel method combining optical tweezers and differential dynamic microscopy to map how stresses propagate in polymer fluids, revealing complex resonant behaviors influenced by polymer type and strain rate.

Contribution

The study presents a new integrated approach, OpTiDDM, enabling simultaneous stress application, force measurement, and polymer motion analysis in macromolecular materials, uncovering previously unknown stress propagation phenomena.

Findings

Resonant stress response maximized at strain rates near entanglement rates.

Microtubules alter stress buildup, flow, and dissipation in polymer blends.

OpTiDDM reveals multi-scale coupling of mechanics and dynamics in polymers.

Abstract

How local stresses propagate through polymeric fluids, and, more generally, how macromolecular dynamics give rise to viscoelasticity are open questions vital to wide-ranging scientific and industrial fields. Here, to unambiguously connect polymer dynamics to force response, and map stress propagation in macromolecular materials, we present a powerful approach-Optical Tweezers integrating Differential Dynamic Microscopy (OpTiDMM)-that simultaneously imposes local strains, measures resistive forces, and analyzes the motion of the surrounding polymers. Our measurements with blends of ring and linear polymers (DNA) and their composites with stiff polymers (microtubules) uncover a surprising resonant response, in which affine alignment, superdiffusivity, and elastic memory are maximized when the strain rate is comparable to the entanglement rate. Microtubules suppress this resonance, while substantially increasing elastic force and memory, due to varying degrees to which the polymers buildup, stretch and flow along the strain path, and configurationally dissipate stress. More broadly, the rich multi-scale coupling of mechanics and dynamics afforded by OpTiDDM, empowers its interdisciplinary use to elucidate non-trivial phenomena that sculpt stress propagation dynamics-critical to commercial applications and cell mechanics alike.