Broadening the Ambit of Raman Solvation Shell Spectroscopy on Small Particle Dispersions

We apply Raman solvation shell spectroscopy (or Raman multivariate curve resolution, i.e., Raman-MCR) on aqueous dispersions of various small particles to distinguish the bulk and the solute-correlated spectra. We previously reported the successful application of the technique on a nanoparticle system. Extending that effort, we sought to answer some questions regarding the applicability of the technique to a wider range of particle dispersions. These questions dictate the choice of materials in this work. Using aqueous dispersions of pulsed laser ablated silver and gold nanoparticles, we find that the energy proximity of the surface plasmonic peak of the particle and the laser emission wavelength used for Raman measurements has no qualitative effect on the Raman-MCR spectral outcome. However, it can assist the detection of bulk to interfacial differences by magnifying them. Furthermore, we report successful implementation of the technique on nonmetallic particles (zinc oxide and titanium dioxide) in aqueous dispersions, which alleviates potential concerns if the metallic nature of the dispersed particles was a prerequisite for applicability of the method. A common trend in the results is also observed for the systems we examined. On moving from the bulk to the solute-correlated component, the relative spectral intensities change at the ∼3250, ∼3400, and ∼3610 cm–1 regions in the water O–H stretching band, observable as a blue shift. This suggests a disruption in the aqueous hydrogen-bonding network within the solvation shell water. Overall, this work demonstrates Raman solvation shell spectroscopy to be a reliable and robust tool to study solvation shells around diverse systems of small particles in dispersions.