Conferences/Events: WORKSHOP ON MICROSTRUCTURE AND MACROMOLECULAR RESEARCH WITH COLD NEUTRONS National Bureau of Standards, Gaithersburg, MD, April 21–22, 1988

Abstract

On April 21-22, 1988, over 160 scientists, including 25 from industry, 70 from universities and 30 from government laboratories and agencies (not including NBS), gathered at NBS, Gaithersburg, for a Workshop on Microstructure and Macromolecular Research with Cold Neutrons. This workshop was one of a series, each devoted to a major area of research with cold neutrons, that are being held in conjunction with the development of the Cold Neutron Research Facility (CNRF) at the NBS 20 MW research reactor as a national, useroriented research facility. The dual aims of this workshop were to highlight research opportunities in the application of cold neutron techniques to the study of submicron structure in materials and macromolecular systems, and to inform and involve the scientific community in the planning for instrumentation for the CNRF. The long wavelength neutrons that are produced by a cold moderator, such as the 40 K D2 0-ice moderator recently installed in the NBS reactor, are a powerful probe of both the structure and dynamics of materials. The emphasis of this workshop was on the structural applications of cold neutrons. Thus techniques such as small angle neutron scattering (SANS), which probes structure in bulk materials on the 1 to 100 nm scale, and the relatively new technique of neutron reflectometry, which probes near surface structure to depths of tenths of microns, were discussed in detail. For both of these techniques, cold neutrons substantially extend the distance scale probed and improve the spatial resolution beyond what has been possible with thermal neutrons. The first morning session of the workshop on Scientific Opportunities with Cold Neutrons opened with a review by T. Russell (IBM Almaden Research Center) of the impact SANS has had on Polymer Science in general, and on the understanding of the interactions and correlations in polymer mixtures in particular. Russell also discussed recent developments, important to the development of polymer composites, in the use of grazing incidence neutron and x-ray scattering for the evaluation of conformation changes and concentration gradients in polymer mixtures near surfaces and at interfaces. The use of scattering methods to characterize such seemingly dissimilar materials as porous rock and agglomerated colloids was the subject of the talk by S. K. Sinha (Exxon Research and Engineering Co.). Sinha presented a general formalism which unified the concepts of surface and mass fractals and showed how the selfsimilar nature of fractal structures is most directly revealed through scattering measurements. Several examples were presented which underscored the need for scattering instruments which probe a wide range of length scales in order to accurately determine the nature and limits of fractal behavior. The second half of this session was devoted to applications of neutron reflectometry, reviewed by