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

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.

Atomic Resolution Imaging of Nanoscale Chemical Expansion in PrCeO during In Situ Heating.

Thin film nonstoichiometric oxides enable many high-temperature applications including solid oxide fuel cells, actuators, and catalysis. Large concentrations of point defects (particularly, oxygen vacancies) enable fast ionic conductivity or gas exchange kinetics in these materials but also manifest as coupling between lattice volume and chemical composition. This chemical expansion may be either detrimental or useful, especially in thin film devices that may exhibit enhanced performance through strain engineering or decreased operating temperatures.

Characterizing Photon Reabsorption in Quantum Dot-Polymer Composites for Use as Displacement Sensors.

The reabsorption of photoluminescence within a medium, an effect known as the inner filter effect (IFE), has been well studied in solutions, but has garnered less attention in regards to solid-state nanocomposites. Photoluminescence from a quantum dot (QD) can selectively excite larger QDs around it resulting in a net red-shift in the reemitted photon. In CdSe/CdS core/shell QD-polymer nanocomposites, we observe a large spectral red-shift of over a third of the line width of the photoluminescence of the nanocomposites over a distance of 100 μm resulting from the IFE.

Tracking Nanoparticle Diffusion and Interaction during Self-Assembly in a Liquid Cell.

Nanoparticle self-assembly has been well studied theoretically, but it remains challenging to directly observe and quantify individual nanoparticle interactions. With our custom image analysis method, we track the trajectories of nanoparticle movement with high precision from a stack of relatively noisy images obtained using liquid cell transmission electron microscopy. In a time frame of minutes, Pt-Fe nanoparticles self-assembled into a loosely packed hcp lattice.

Encapsulation of Perovskite Nanocrystals into Macroscale Polymer Matrices: Enhanced Stability and Polarization.

Lead halide perovskites hold promise for photonic devices, due to their superior optoelectronic properties. However, their use is limited by poor stability and toxicity. We demonstrate enhanced water and light stability of high-surface-area colloidal perovskite nanocrystals by encapsulation of colloidal CsPbBr quantum dots into matched hydrophobic macroscale polymeric matrices.

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

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.

Structural diversity in binary superlattices self-assembled from polymer-grafted nanocrystals.

Multicomponent nanocrystal superlattices represent an interesting class of material that derives emergent properties from mesoscale structure, yet their programmability can be limited by the alkyl-chain-based ligands decorating the surfaces of the constituent nanocrystals. Polymeric ligands offer distinct advantages, as they allow for more precise tuning of the effective size and 'interaction softness' through changes to the polymer's molecular weight, chemical nature, architecture, persistence length and surrounding solvent. Here we show the formation of 10 different binary nanocrystal superlattices (BNSLs) with both two- and three-dimensional order through independent adjustment of the core size of spherical nanocrystals and the molecular weight of densely grafted polystyrene ligands.

Influence of three-dimensional nanoparticle branching on the Young's modulus of nanocomposites: Effect of interface orientation.

With the availability of nanoparticles with controlled size and shape, there has been renewed interest in the mechanical properties of polymer/nanoparticle blends. Despite the large number of theoretical studies, the effect of branching for nanofillers tens of nanometers in size on the elastic stiffness of these composite materials has received limited attention. Here, we examine the Young's modulus of nanocomposites based on a common block copolymer (BCP) blended with linear nanorods and nanoscale tetrapod Quantum Dots (tQDs), in electrospun fibers and thin films.

Tetrapod nanocrystals as fluorescent stress probes of electrospun nanocomposites.

A nanoscale, visible-light, self-sensing stress probe would be highly desirable in a variety of biological, imaging, and materials engineering applications, especially a device that does not alter the mechanical properties of the material it seeks to probe. Here we present the CdSe-CdS tetrapod quantum dot, incorporated into polymer matrices via electrospinning, as an in situ luminescent stress probe for the mechanical properties of polymer fibers. The mechanooptical sensing performance is enhanced with increasing nanocrystal concentration while causing minimal change in the mechanical properties even up to 20 wt % incorporation.

Nanotwinned gold nanowires obtained by chemical synthesis.

We demonstrate a facile method for synthesizing and isolating Au nanowires with a high density of twin boundary defects normal to the growth axis. In this process, oleylamine conveniently plays the role of the solvent, the reducing agent and the ligand. The geometry of the twin boundaries in the nanowires is in sharp contrast with the pentagonal twinning commonly observed in metal nanowires, and is of particular interest for its ultrahigh tensile strength.