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Fixed-Path Length Laser-Induced Sound Pinging: A Streamlined Method for Sound Speed Determination in Arbitrary Liquids
摘要： Recently, we introduced laser-induced sound pinging (LISP) as a simple photoacoustic technique for the expedient and fairly rapid (2?3 min) measurement of the speed of sound traversing low-volume samples (25?1000 μL), built around an inexpensive tattoo-removal source (Sens. Actuators B-Chem. 2019, 291, 401?410). In this report, we expand on the utility of this technique by improving the facility of measurement and speed of analysis by adopting a ?xed-path length (FPL) architecture which allows for much faster analysis (1?5 s) of similar sample volumes. The FPL-LISP setup was employed to determine the speeds of sound at temperatures from 293 to 333 K for four popular hydrophilic deep eutectic solvents (DESs) containing choline chloride (i.e., reline, ethaline, glyceline, and maline), plus several representative decanoic acid?based (i.e., hydrophobic) DESs. The temperature-dependent speeds of sound were used alongside the corresponding experimental densities to calculate the bulk modulus for these illustrative DESs. Interestingly, the bulk modulus was in the 4000?5000 MPa range for choline chloride-derived DESs, essentially twice the value of a hydrophobic DES (typi?ed by 1:2 tetraoctylammonium bromide/decanoic acid), suggesting unique potential for hydraulic applications, for example. The modest volume requirements of FPL-LISP make it suitable for determining the speed of sound in scarce, precious, or hazardous liquids, and the speed of analysis enables integration into a continuous-?ow platform for real-time analytics (e.g., beverage quality control).
关键词： bulk modulus,speed of sound,laser-induced sound pinging,photoacoustic technique,deep eutectic solvents
更新于2025-09-12 10:27:22
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The Effects of Hydrostatic Pressure on the Surface Plasmon Resonance of Gold Nanocrystals
摘要： The surface plasmon resonances of gold nanospheres and nanorods have been measured as a function of hydrostatic pressure up to 17 GPa in methanol-ethanol 4:1 solvent and up to 10 GPa in paraffin. Both the sphere resonance and the longitudinal rod resonance exhibit redshifts while the transverse rod mode shows an extremely weak redshift or blueshift depending on the nanorod aspect ratio. Solidification of the solvent around 11 GPa causes some aggregation of the particles, readily identified through broadening of the SP band and further redshifting. Loading and unloading cycles show only minimal hysteresis in the spectra if the pressure remains below 11 GPa. The surface plasmon shifts are the result of two competing effects. Compression of the conduction electrons in the metals increases the bulk plasma frequency, which causes a blueshift. However, the increase in the solvent density under hydrostatic load leads to an increase in the solvent refractive index, which in turn leads to a redshift. We find that after accounting for the solvent contribution, we can spectroscopically determine the bulk modulus of the gold nanoparticles with a precision of 10%. The value obtained of K0 = 190 GPa is significantly higher than the value for bulk gold (167 GPa). Furthermore, we show that pressure-induced solidification causes a significant broadening and anomalous shift of the surface plasmon band that we attribute to aggregation and nanorod deformation.
关键词： optical absorption,refractive index,hydrostatic pressure,surface plasmon resonance,bulk modulus,gold nanoparticles
更新于2025-09-04 15:30:14