Biomedical subjects

Glenn A Waychunas

Publications and source records attributed to Glenn A Waychunas.

3 recordsLinked to original sources

PubMed2005

New information on water interfacial structure revealed by phase-sensitive surface spectroscopy.

A phase-sensitive sum-frequency vibrational spectroscopic technique is developed to study interfacial water structure of water/quartz interfaces. Measurements allow deduction of both real and imaginary parts of the surface nonlinear spectral response, revealing an unprecedentedly detailed picture of the net polar orientations of the water species at the interface. The orientations of the icelike and liquidlike species appear to respond very differently to the bulk pH change indicating the existence of different surface sites on quartz with different deprotonation pK values.

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PubMed2004

Nanoparticles: strained and stiff.

Nanoparticles may contain unusual forms of structural disorder that can substantially modify materials properties and thus cannot solely be considered as small pieces of bulk material. We have developed a method to quantify intermediate-range order in 3.4-nanometer-diameter zinc sulfide nanoparticles and show that structural coherence is lost over distances beyond 2 nanometers. The zinc-sulfur Einstein vibration frequency in the nanoparticles is substantially higher than that in the bulk zinc sulfide, implying structural stiffening. This cannot be explained by the observed 1% radial compression and must be primarily due to inhomogeneous internal strain caused by competing relaxations from an irregular surface. The methods developed here are generally applicable to the characterization of nanoscale solids, many of which may exhibit complex disorder and strain.

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PubMed2004

Analysis and simulation of the structure of nanoparticles that undergo a surface-driven structural transformation.

A room temperature solid-state structural transformation was observed in 3 nm ZnS nanoparticles in methanol following the addition of water (Zhang et al., Nature 424, 1025, 2003). Experimental wide angle x-ray scattering (WAXS), x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopy measurements show a large increase in crystallinity associated with water addition, in agreement with molecular dynamics (MD) predictions. Here we perform first-shell EXAFS and pair distribution function analysis and whole-nanoparticle calculations of WAXS, EXAFS and XANES to compare structural data with the MD predictions. The predicted WAXS patterns give excellent agreement with data, while the predicted EXAFS and XANES spectra give poor agreement. Relative to WAXS, XANES and EXAFS spectra contain additional structural information related to the distribution of disorder. The discrepancy between the x-ray diffraction and x-ray absorption results indicates that structural disorder is partitioned between interior and surface regions more strongly than predicted in the MD simulations.

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