Mechanisms of Local Stress Sensing in Multifunctional Polymer Films Using Fluorescent Tetrapod Nanocrystals

Abstract

Nanoscale stress-sensing can be used across fields ranging from detection of incipient cracks in structural mechanics to monitoring forces in biological tissues. We demonstrate how tetrapod quantum dots (tQDs) embedded in block copolymers act as sensors of tensile/compressive stress. Remarkably, tQDs can detect their own composite dispersion and mechanical properties with a switch in optomechanical response when tQDs are in direct contact. Using experimental characterizations, atomistic simulations and finite-element analyses, we show that under tensile stress, densely packed tQDs exhibit a photoluminescence peak shifted to higher energies ("blue-shift") due to volumetric compressive stress in their core; loosely packed tQDs exhibit a peak shifted to lower energies ("red-shift") from tensile stress in the core. The stress shifts result from the tQD's unique branched morphology in which the CdS arms act as antennas that amplify the stress in the CdSe core. Our nanocomposites exhibit excellent cyclability and scalability with no degraded properties of the host polymer. Colloidal tQDs allow sensing in many materials to potentially enable autoresponsive, smart structural nanocomposites that self-predict impending fracture.

Dynamic Phosphorescent Probe for Facile and Reversible Stress Sensing

“…The relative contribution of monomer and excimer to the overall emission was found to be directly linked to sample deformation and mirrored the stress–strain curve. A separate class of deformation sensitive PL sensors employed nanocrystalline probes including ZnO and CdSe‐CdS nanocrystals, core–shell quantum dots, and doped alumina nanocomposites . The common feature of the majority of PL‐based sensors is their reliance on the structural rearrangements of the PL probe to detect deformation that is typically proportional to stress.…”

Type I vs. quasi-type II modulation in CdSe@CdS tetrapods: ramifications for noble metal tipping

“…49,51 While more challenging to prepare than nanorods systems, CdSe@CdS tetrapods have been studied for stress-sensing, photovoltaic, and LED applications in recent years. 1,3,12,16,52 Particularly, the seminal work of Alivisatos and Chan have reported on the synthesis and spectroscopic characterization of CdSe@CdS TPs with 4.0 nm and 3.0 nm zincblende CdSe NC seeds, respectively, leading to applications in mechanical stress sensing and dual emission lightemitting diodes. 1,3,12,52 These studies pointed to the possibility of modulating energetics of CdSe@CdS TPs by variation of ZB CdSe NC size from 2-6 nm.…”

“…1,3,12,16,52 Particularly, the seminal work of Alivisatos and Chan have reported on the synthesis and spectroscopic characterization of CdSe@CdS TPs with 4.0 nm and 3.0 nm zincblende CdSe NC seeds, respectively, leading to applications in mechanical stress sensing and dual emission lightemitting diodes. 1,3,12,52 These studies pointed to the possibility of modulating energetics of CdSe@CdS TPs by variation of ZB CdSe NC size from 2-6 nm. However, synthetic accessibility to both welldefined ZB CdSe NC sizes and subsequent CdSe@CdS TPs have limited further studies to enable correlation of type I vs. quasi-type II energetics with ZB CdSe seed size.…”

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

“…Further, it is important for ensuring reproducible, tailored material synthesis 4 . In order to study such nanoscale stresses, an appropriate tool is needed that is sensitive, versatile, and does not alter the properties of the host matrix 4 , 6 . Further, the ideal nanoscale stress sensor should exhibit stress sensitivity over a large dynamic range, enabling it to detect equally well kilopascal (kPa) stresses in biological systems as well as larger megapascal (MPa) stresses in structural materials.…”

“…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 – 8 , 14 . These include being invasive, having low signal-to-noise ratio, or being limited to specific laboratory settings, material systems, or geometries.…”