Engineering topics
Madsen, A
Publications and source records attributed to Madsen, A.
Microscopic Dynamics in Nanocomposite Photosensitive Films Studies by X-ray Photon Correlation Spectroscopy
X-ray photon correlation spectroscopy measurements are reported of microscale dynamics in Langmuir-Schaeffer deposited multilayers of a photosensitive azopolymer with a low concentration of gold nanoparticles embedded. Correlation functions were measured as a function of exchanged momentum and illumination conditions (dark and UV light) and fitted with the Kohlrausch-Williams-Watts (KWW) exponential form. The microscopic dynamic of the nanoparticles was quantified, evidencing a non-Brownian superdiffusive behavior with relaxation times {tau} {approx} q{sup -1}, a result analogous to what previously had been observed in the pure azopolymer. Such behavior has been related to intermittent rearrangements or random dipolar interactions within an elastic medium. Photoperturbation with UV light makes the dynamics faster, in accordance with the reduction of the viscosity of the polymer found by shear rheology, but the KWW form of the correlation functions persists. At constant temperature, the dynamics of the nanoparticles embedded in the polymeric matrix is sensibly faster than the slow microscopic dynamic of the polymer. At the same time, the Vogel-Fulcher-Tammann law for the relaxation times indicates a less pronounced temperature dependence than for the pure polymer, resulting in a slightly lower activation temperature T{sub A}.
Cryogenic X-ray Diffraction Microscopy for Biological Samples
X-ray diffraction microscopy (XDM) is well suited for nondestructive, high-resolution biological imaging, especially for thick samples, with the high penetration power of x rays and without limitations imposed by a lens. We developed nonvacuum, cryogenic (cryo-) XDM with hard x rays at 8 keV and report the first frozen-hydrated imaging by XDM. By preserving samples in amorphous ice, the risk of artifacts associated with dehydration or chemical fixation is avoided, ensuring the imaging condition closest to their natural state. The reconstruction shows internal structures of intact D. radiodurans bacteria in their natural contrast.