Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session V1: Recent Advances in Soft Complex Materials Using Neutron Scattering |
Hide Abstracts |
Sponsoring Units: DMP Chair: Alan J. Hurd, Los Alamos National Laboratory Room: Morial Convention Center LaLouisiane AB |
Thursday, March 13, 2008 11:15AM - 11:51AM |
V1.00001: Neutron and X-ray Characterization of Nanostructured Polymeric Materials Invited Speaker: Controlling the orientation and lateral ordering of the block copolymer microdomains is key to their use as templates and scaffolds for the fabrication of nanostructured materials. Processes must be robust, rapid and simple to implement and should not introduce disruptive processing steps that would impede their use. Grazing incidence small angle x-ray scattering (GISAXS) and neutron neutron scattering have proven to be critical for the characterization of the static and real time development of structure in thin films of block copolymers. Here, studies on poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) diblock copolymers prepared from mixed solvents will be discussed that show highly oriented, cylindrical microdomains with a high degree of lateral order on a wide range of substrates, including silicon oxide, polystyrene, germanium, polyimide, and poly(butylene terephthalate). The preferential solvation of the P4VP block with an alcohol was used to induce a reconstruction that left a nanoporous film upon drying. The evaporation of gold onto the reconstructed films produced thermally stable films that are resistant to reactive ion etching. GISAXS was used to quantitatively examine the structure of these composite films and the transfer of the patterns to the underlying substrate. (research done in collaboration with Soojin Park, Jia-Yu Wang, Bokyung Kim University of Massachusetts), Benjamin Ocko (Brookhaven National Laboratory) and Jin Wang (Argonne National Laboratory). [Preview Abstract] |
Thursday, March 13, 2008 11:51AM - 12:27PM |
V1.00002: Beyond Wrinkles: Stress and Fold Localization in Thin Elastic Membranes Invited Speaker: Thin elastic membranes supported on fluid or elastic foundations deviate from their flat geometries upon compression. We demonstrate that the periodic and much studied wrinkled state is but one possible solution for such strained membranes. Folds, sharply localized solutions, appear whenever the membrane is compressed beyond a third of its initial wrinkle wavelength. Eventually the surface transforms into a symmetry broken state with flat regions of membrane coexisting with locally folded points, reminiscent of a crumpled unsupported membrane. We study this transition in many systems including lipid monolayers on liquid subphases of differing viscosity and use neutron and x-ray reflectivity to elucidate the role of the subphase in setting the wrinkle and fold size. [Preview Abstract] |
Thursday, March 13, 2008 12:27PM - 1:03PM |
V1.00003: Complex Protein Structures by Neutron Scattering Invited Speaker: Neutron scattering by an atom, unlike X-ray scattering, does not depend on the atomic number of that atom. Deuterium atoms scatter neutrons to the same extent as carbon or oxygen atoms and give positive peaks in a nuclear density map, while its isotope, hydrogen, gives a negative peak. Therefore neutron diffraction provides two results that are difficult to obtain from macromolecular X-ray diffraction studies: (1) the locations of hydrogen atoms, including the more mobile ones, and (2) the extent to which a hydrogen atom can be replaced by deuterium. The method shows whether an amino acid side chain (at a given pH value) is ionized or not. For example, one can ascertain whether histidine residues are singly or doubly protonated at the pH of study. Neutron diffraction studies can also be used to determine the absolute configuration of the course of a biochemical reaction by anomalous scattering and enzymatic deuteration of the substrate. Neutron diffraction experiments, however, require large crystals and these are often impossible to obtain for many macromolecules. Examples of reports of the use of neutron diffraction to provide information on enzymatic mechanism will be presented. This includes descriptions of our work on the enzyme D-xylose isomerase for which the orientation of a metal ion-bound water molecule in the active site was found. This water, thought to be involved in the isomerization step, was shown to be water (rather than hydroxyl) at pH 8.0. This analysis also revealed that one lysine has two rather than three attached hydrogen atoms and therefore lacks a positive charge. High-resolution X-ray studies (at 0.94 {\AA}) indicate how some side chains might move during catalysis. This combination of neutron and X-ray diffraction can contribute greatly to the elucidation of enzyme mechanisms. I thank Amy Katz, Xinmin Li, H. L. Carrell, Leighton Coates, Leif Hanson, Joel Harp, Paul Langan, and Benno Schoenborn who were involved in many of the described studies, and particularly Gerard Bunick. We honor his contributions and regret that he is no longer with us. [Preview Abstract] |
Thursday, March 13, 2008 1:03PM - 1:39PM |
V1.00004: Observation of a Fragile-to-Strong Dynamic Crossover Phenomenon in Confined Water and Its Relation to the Existence of a Liquid-Liquid Critical Point in Supercooled Water Invited Speaker: We have observed a fragile-to-strong dynamic crossover phenomenon of $\alpha $ relaxation time and self-diffusion constant in deeply supercooled 1-d confined water. The $\alpha $ relaxation time is measured by quasi-elastic neutron scattering and the self-diffusion constant by nuclear magnetic resonance. Water is confined in 1-d geometry in cylindrical pores of porous silica material, MCM-41 and in double-wall carbon nanotubes. The crossover phenomena can also be observed from appearance of a Boson peak in an incoherent inelastic neutron scattering. We observe a pronounced violation of the Stokes-Einstein relation at and below the crossover temperature at ambient pressure. Upon applying pressure to the confined water, the crossover temperature is shown to track closely the Widom line emanating from the existence of a liquid-liquid critical point buried in an unattainable deeply supercooled state of bulk water. Relation of the dynamic crossover phenomena to the existence of a density minimum in supercooled confined water will be discussed. The crossover temperature is shown to be sensitively dependent on the degree of hydrophilicity of the confining substrate. [Preview Abstract] |
Thursday, March 13, 2008 1:39PM - 2:15PM |
V1.00005: Phase Behavior of Block Copolymer/Inorganic Nanoparticle Composites Invited Speaker: Block copolymers offer as versatile platforms for the fabrication of hybrid nanocomposites with ordered phases useful for various nanotechnology applications. Although the phase behavior of block copolymers is well established the effects of inorganic nanoparticle loading on their phase behavior are not well understood. We carried out a systematic study on the phase behavior of block copolymers with well dispersed nanoparticles. To achieve excellent dispersion of nanoparticles in the polymer phase we used grafted nanoparticles with small polymer chains compatible to a preferred domain of the block copolymer. The nanoparticles sequestered in a preferred domain have profound effects on the thermodynamically induced microphase separation of the block copolymers. To characterize the phase behavior of these systems in a selective solvent we used small angle neutron scattering and that in their bulk and thin film architectures was studied using synchrotron based small angle x-ray scattering and grazing incidence small angle scattering techniques. A number of molecular properties such as the molecular weight of the polymer, segment volume fraction, Flory-Huggins $\chi$ parameter and the nanoparticle concentration influence the state of dispersion of nanoparticles and the nanocomposite morphology in bulk and thin film architectures. The addition of homopolymers provides as yet another variable to alter the interfacial tension and to slow the order-disorder transition. We also probed the nanoscale dynamics at the polymer/nanoparticle interfaces in these systems by using x-ray photon correlation spectroscopy. The dynamics of nanoparticles in the composites is strongly dependent on the dimensionality of the morphology of the block copolymer. Furthermore, the interfacial interaction at the polymer/particle interface plays significant role in the stress relaxation in the composites. \newline \newline $^1$This work was done in collaboration with Chieh-Tsung Lo, Byeongdu Lee, Randall E. Winans, Alec Sandy, XSD Division, Advanced Photon Source and Vilas Pol, David Bohnsack, IPNS, Argonne National Laboratory. \newline $^2$Work benefited from the use of facilities at Argonne National Laboratory funded by DOE, BES under contract DE-AC02-06CH11357 to the UChicago Argonne, LLC. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700