Simultaneous multiplexed materials characterization using a high-precision hard X-ray micro-slit array.

The needs both for increased experimental throughput and for in operando characterization of functional materials under increasingly realistic experimental conditions have emerged as major challenges across the whole of crystallography. A novel measurement scheme that allows multiplexed simultaneous measurements from multiple nearby sample volumes is presented. This new approach enables better measurement statistics or direct probing of heterogeneous structure, dynamics or elemental composition.

Probing transverse coherence of x-ray beam with 2-D phase grating interferometer.

Transverse coherence of the x-ray beam from a bending magnet source was studied along multiple directions using a 2-D π/2 phase grating by measuring interferogram visibilities at different distances behind the grating. These measurements suggest that the preferred measuring orientation of a 2-D checkerboard grating is along the diagonal directions of the square blocks, where the interferograms have higher visibility and are not sensitive to the deviation of the duty cycle of the grating period. These observations are verified by thorough wavefront propagation simulations.

Non-equilibrium effects evidenced by vibrational spectra during the coil-to-globule transition in poly(N-isopropylacrylamide) subjected to an ultrafast heating-cooling cycle.

Molecular dynamics simulations in conjunction with finite element calculations are used to explore the conformational dynamics of a thermo-sensitive oligomer, namely poly(N-isopropylacrylamide) (PNIPAM), subjected to an ultra-fast heating-cooling cycle. Finite element (FE) calculations were used to predict the temperature profile resulting from laser-induced heating of the polymer-aqueous system. The heating rate (∼0.

Thermodynamic considerations for solubility and conformational transitions of poly-N-isopropyl-acrylamide.

Thermodynamic considerations based on the free energy of hydration, free energy of solvation and partition coefficient predictions of the monomer N-isopropyl-acrylamide (NIPAM) determined using various intermolecular potentials are used to elucidate the origin of hydrophobicity/hydrophilicity across the lower critical solution temperature (LCST). Thermodynamic properties are predicted for NIPAM using adaptive bias force-molecular dynamics and various popular force-fields (AMBER, OPLS-AA, CHARMM and GROMOS) at four different temperatures: below the LCST (275 K and 300 K) and above the LCST (310 K and 330 K). The effect of changes in the thermodynamic properties of the monomer NIPAM at various temperatures below and above LCST on the kinetics of conformational transition of thermo-sensitive polymers is discussed.

Vibrational spectra of proximal water in a thermo-sensitive polymer undergoing conformational transition across the lower critical solution temperature.

The vibrational spectrum of water near a thermo-sensitive polymer poly(N-isopropylacrylamide) (PNIPAM) undergoing conformational transition through the lower critical solution temperature (LCST) is calculated using molecular dynamics simulations. The characteristic structural features observed at the atomic scale for these proximal water molecules in a solvated polymer chain while undergoing the conformational transition are strongly correlated to their vibrational densities of states. Comparison of the vibrational spectrum below LCST for the proximal water with the vibrational spectrum obtained for bulk water reveals a significant fraction of the hydrogen bonding between the proximal water molecules and the polymer side groups.

Role of solvation dynamics and local ordering of water in inducing conformational transitions in poly(N-isopropylacrylamide) oligomers through the LCST.

Conformational transitions in thermo-sensitive polymers are critical in determining their functional properties. The atomistic origin of polymer collapse at the lower critical solution temperature (LCST) remains a fundamental and challenging problem in polymer science. Here, molecular dynamics simulations are used to establish the role of solvation dynamics and local ordering of water in inducing conformational transitions in isotactic-rich poly(N-isopropylacrylamide) (PNIPAM) oligomers when the temperature is changed through the LCST.

Fabrication of Poly(ethylene glycol) Hydrogel Structures for Pharmaceutical Applications using Electron beam and Optical Lithography.

Soft-polymer based microparticles are currently being applied in many biomedical applications, ranging from bioimaging and bioassays to drug delivery carriers. As one class of soft-polymers, hydrogels are materials, which can be used for delivering drug cargoes and can be fabricated in controlled sizes. Among the various hydrogel-forming polymers, poly(ethylene glycol) (PEG) based hydrogel systems are widely used due to their negligible toxicity and limited immunogenic recognition.

Elucidating chemical and morphological changes in tetrachloroauric solutions induced by X-ray photochemical reaction.

Chemical and morphological changes induced by an X-ray photochemical reaction in tetrachloroauric solutions leading to Au(3+)-to-Au(0) reduction are monitored in real time by X-ray absorption spectroscopy and X-ray small angle scattering. Prior to metal precipitation, the intermediate state, also observed by other techniques, is unambiguously determined for the first time to be the reduction of Au(3+) to Au(1+), whose kinetics is strictly of the zeroth order. The morphological changes occur simultaneously in the solutions, that is, the gold complexes rearrange and aggregate, as unequivocally observed by the correlated changes in the Au L(3) emission and small angle scattering intensities.

Development and Monte Carlo analysis of antiscatter grids for mammography.

Mammography arguably demands the highest fidelity of all x-ray imaging applications, with simultaneous requirements of exceedingly high spatial and contrast resolution. Continuing technical improvements of screen-film and digital mammography systems have led to substantial improvements in image quality, and therefore improvements in the performance of anti-scatter grids are required to keep pace with the improvements in other components of the imaging chain. The development of an air-core honeycomb (cellular) grid using x-ray lithography and electroforming techniques is described, and the production of a 60 mm x 60 mm section of grid is reported.