Microscopic mechanisms of deformation transfer in high dynamic range branched nanoparticle deformation sensors

Shilpa N Raja,Sanjay Govindjee,Xingchen Ye,Robert O Ritchie,Liwei Lin,Matthew R Jones

doi:10.1038/s41467-018-03396-5

Abstract

Nanoscale stress sensing is of crucial importance to biomechanics and other fields. An ideal stress sensor would have a large dynamic range to function in a variety of materials spanning orders of magnitude of local stresses. Here we show that tetrapod quantum dots (tQDs) exhibit excellent sensing versatility with stress-correlated signatures in a multitude of polymers. We further show that tQDs exhibit pressure coefficients, which increase with decreasing polymer stiffness, and vary >3 orders of magnitude. This high dynamic range allows tQDs to sense in matrices spanning >4 orders of magnitude in Young’s modulus, ranging from compliant biological levels (~100 kPa) to stiffer structural polymers (~5 GPa). We use ligand exchange to tune filler-matrix interfaces, revealing that inverse sensor response scaling is maintained upon significant changes to polymer-tQD interface chemistry. We quantify and explore mechanisms of polymer-tQD strain transfer. An analytical model based on Mori-Tanaka theory presents agreement with observed trends.

Highlights

Nanoscale stress sensing is of crucial importance to biomechanics and other fields
We studied 17 material systems, which included fibers and films, as well as a variety of different tetrapod quantum dots (tQDs) concentrations and dispersions in multiple tQD-ligand-polymer systems
Electrospinning was used for PLLA, poly(ethylene oxide) (PEO), SEBS, and PCL; a viscous polymer chloroform solution was mixed with a chloroform solution of nanoparticles to create viscous solutions of 4–12% by weight polymer, and 0.05–20% by weight/0.01–5% by volume tQDs; droplets of the highly viscous solution were subject to high electric fields (15 kV/cm) to form aligned arrays of fibers using the dual-rod geometry of Li et al.[4,32]

Summary

Introduction

Nanoscale stress sensing is of crucial importance to biomechanics and other fields. An ideal stress sensor would have a large dynamic range to function in a variety of materials spanning orders of magnitude of local stresses. Current techniques[7,8] for examining such nanoscale stresses such as Raman spectroscopy[5], mechanochromic gels[9], atomic force microscopy (AFM)[10], electronic skins[11], metal nanoparticle chains[12], stress-sensitive small molecules[13], and others[9] have limitations, which constrain their utility in practical situations[4,6,7,8,14] These include being invasive, having low signal-to-noise ratio, or being limited to specific laboratory settings, material systems, or geometries. Studies were only performed with native ligands, i.e., no ligand exchange was performed to change tQD surface chemistry and alter the interfacial strength between the tQD and polymer matrix[4,6,8] To rectify this situation, we report here on a study using a very wide selection of host materials with varied interfacial conditions

Objectives

Methods

Results

Conclusion