Phase diagram of a lipid monolayer on the surface of water

The monolayer isotherms of heneicosanoic acid show a variety of features in the range 1-8°C; such features are often assumed to be solid-fluid or fluid-fluid transitions. Using x-ray diffraction (and searching for in-plane and off-plane peaks) we find (a) two distinct distorted-hexagonal (DH) solids at high pressures, both with essentially vertical chains; (b) two distinct tilted-DH solids at intermediate pressures; and (c) an expanded solid at the lowest pressures. All "plateaus" in these isotherms are in-plane structural transitions; all "kinks" are solid-solid tilting transitions.link_to_subscribed_fulltex

Determination of lattice structure and calculation of molecular tilt in lipid monolayers on water using x-ray diffraction

We report the first determination of lattice structure for classical (fatty acid and alcohol) monolayer systems on the surface of water, based on our observation of first- and second-order x-ray diffraction peaks. Monolayers of both heneicosanoic acid and heneicosanol in the highest-pressure phase pack into a distorted hexagonal lattice with orthorhombic cell dimensions of a7.5 t/rA, b5.0 i/rA. From the observed peak intensities, we have calculated the molecular tilt directions and magnitudes, using the assumption (reasonable given the dense packing) that the chains are parallel to each other and in the all-trans configuration. the temperature range 05°C, the molecules tilt towards the b axis, but at higher temperatures the tilt direction changes to the a axis. © 1990 The American Physical Society.link_to_subscribed_fulltex

At the limit of polychromatic microdiffraction

With a high-energy 3rd generation source like the Advanced Photon Source (APS), it is possible to push the performance of polychromatic microdiffraction far beyond current levels and to approach the intrinsic limit of the technique based on sample damage and the diffraction limit of X-rays. We describe ongoing efforts to improve the spatial, temporal and momentum transfer resolution of polychromatic microdiffraction on beamline 34-ID-E at the APS. The goal of this effort is to provide high-resolution images of 3D crystal structures over sufficient volumes and with sufficient detail to clarify the underlying physics of inhomogeneous structure and evolution on mesoscopic length scales. The performance of a high-speed amorphous Si area detector system and the ongoing development of advanced focusing optics will be described and discussed in light of the ultimate limits set by the physics of X-rays and materials, and in light of opportunities to field specialized insertion devices and optics for polychromatic microdiffraction. (C) 2009 Elsevier B.V. All rights reserved.

Boundary migration in a 3D deformed microstructure inside an opaque sample

How boundaries surrounding recrystallization grains migrate through the 3D network of dislocation boundaries in deformed crystalline materials is unknown and critical for the resulting recrystallized crystalline materials. Using X-ray Laue diffraction microscopy, we show for the first time the migration pattern of a typical recrystallization boundary through a well-characterized deformation matrix. The data provide a unique possibility to investigate effects of both boundary misorientation and plane normal on the migration, information which cannot be accessed with any other techniques. The results show that neither of these two parameters can explain the observed migration behavior. Instead we suggest that the subdivision of the deformed microstructure ahead of the boundary plays the dominant role. The present experimental observations challenge the assumptions of existing recrystallization theories, and set the stage for determination of mobilities of recrystallization boundaries