Colloidal metal nanoparticles are a class of materials with myriad applications: drug delivery, medical imaging, catalysis and for antimicrobial purposes, to name just a few. They also show potential as strain gauges. A monolayer of colloidal gold nanoparticles on a flexible substrate offers an interesting alternative to currently used resistive strain gauges. Researchers at the Slovak Academy of Science and STU Centre for Nano-diagnostics show that they provide a fast and linear response is a wide strain range.
Small-Angle X-ray Scattering (SAXS) gives insight into the electrical response of this new type of gauges by efficiently probing the structural changes of the nanoparticle assemblies induced by stress on the gauge. The use of a high intensity MetalJet X-ray source uniquely enables the researchers to study this system out of equilibrium, during the stretching of the foil. The images below show the 2D scattering pattern (a) of the used gold particles suspended in hexane. Fitting of the radially averaged 1D curve (b) reveals the shape and diameter of the particles.
The MetalJet is available with a gallium-rich (l = 1.34 Å) and an indium-rich (l = 0.51 Å) target. These low wavelengths result in lower absorption, and thereby an increase in the scattering signal. This is especially interesting for high-Z materials such as most metals, which are challenging to measure using a copper source. Furthermore, using these short wavelengths, smaller structures can be probed, air scattering is minimized, which makes in-air measurements more attractive.
These properties, together with the high flux, ensure that short measurements of only 10 seconds, provide sufficient statistics for the analysis of the gold particle monolayers on Mylar foil exposed to uniaxial stress. The in-situ measurements allow the correlation of interparticle distance with the simultaneously measured stress-strain curve, hereby enabling comparison of the macroscopic and microscopic properties of the gauge.
The SAXS measurements were performed in vacuum on a Bruker-AXS Nanostar instrument equipped with a Ga liquid metal-jet X-ray microfocus source.