Opportunity at National Institute of Standards and Technology (NIST)
Small-Angle Neutron Scattering from Polymer Systems, from Complex Fluids, and in Biology
NIST Center for Neutron Research
Please note: This Agency only participates in the February and August reviews.
Our efforts focus on the use of small-angle neutron scattering (SANS) to investigate structures and phase transitions in a wide class of materials: synthetic polymers, complex fluids, and biological macromolecules. When used with deuterated samples, the SANS technique is a good probe for structure determination as well as investigations of phase transitions. The unifying theme for this research is the nanometer size scale. The miscibility of polymers in solution or in the blend state has occupied a part of our research efforts. This included the effect of pressure on phase transitions. We have found that the simplest water-soluble polymer (polyethylene oxide) is a good model for studying the effect of hydrophobic and hydrophilic interactions and their impact on clustering and solvation. Better solvation is found with solvent mixtures than with individual solvents. Various possible causes of clustering were considered and carefully investigated. Similar studies were conducted on a polyelectrolyte system (polyacrylic acid), which shows scattering features similar to well-known biopolymers (such as DNA). The helix-to-coil transition of DNA was mapped out and found to vary substantially depending on the solvent used. The nature of hydrophobic and hydrophilic interactions in ternary complex fluid mixtures that form micelles is an ongoing research interest. Phase transitions between the unimer phase (below the critical micelle condition) and other phases (characterized by spherical, cylindrical, or lamellar micelles morphologies) turns out to be a rich and exciting field of research. The effect of pressure on these phase transition lines was carefully investigated. A new phase was recently identified. These projects and more are described in a 700 page book covering most aspect of SANS available online at http://www.ncnr.nist.gov/staff/hammouda/the_SANS_toolbox.pdf.
Small-angle neutron scattering; Nanoscale polymer structures; Complex fluids; Biopolymer structures; Polymer miscibility;
Open to U.S. citizens
Open to Postdoctoral applicants