The NIST/NSF Center for High Resolution Neutron Scattering

at NIST’s Center for Neutron Research

Gaithersburg, Maryland

2003 Highlights of Activities Supported by:

DMR-9986442, Charles Glinka, PI

DMR-0086210, Dan Neumann, PI

Depletion Interactions in Colloid-Polymer Mixtures

S. A. Shah, Y. L. Chen, K. S. Schweizer and C. F. Zukoski, J. Chem. Phys. 118, 3350 (2003); Langmuir 19(12), 5128 (2003); J. Phys. Condensed Matter 15(27), 4751 (2003).

Small-Angle Neutron Scattering (SANS) is exquisitely sensitive to the influence of polymer induced depletion interactions on the solution thermodynamics and phase behavior of colloidal suspensions. Shown here are CHRNS SANS data (by C.F. Zukoski’s group at U. Illinois) showing the development of clustering as the polymer concentration is increased in a suspension of silica particles.

When non-adsorbing polymers are added to stable colloidal suspensions the particles experience an induced “depletion” attraction due to an unbalanced osmotic pressure arising from the exclusion of polymer molecules from the region between colloids. Understanding these interactions is key to controlling the microstructure and properties colloidal suspensions for applications ranging from paints to environmentally responsive ‘smart’ gels.

Particles far apart - no depletion interactionParticles close - depletion interactioncompetes with hard sphere repulsion

The NIST Center for Neutron Research (NCNR) invites high school science classes to tour its facilities on the NIST campus in Gaithersburg, Maryland, and learn about some of the ways beams of neutrons are used in research on the microscopic structure of advanced materials. The tour of the Center is preceded by a lecture, with demonstrations developed specifically for upper level high school students, that introduces some of the basic concepts of neutron physics through analogous optical and wave phenomena. Up to 40 students and accompanying teachers may be accommodated for a lecture and tour that typically take about two hours to complete. Information about the NCNR is available on its web site at http://www.ncnr.nist.gov.

Tours of the National Institute of Standards and Technology’s Center Tours of the National Institute of Standards and Technology’s Center for Neutron Research for High School Science Classesfor Neutron Research for High School Science Classes

NIST Center for Neutron Research

Charles Glinka, NIST, DMR-9986442

Neutron Guide Hall

A Multicritical Point in Superconducting Niobium3.75 kG 4.6 K4.4 K4.1 K

X.S. Ling, S.R. Park et al. Phys. Rev. Lett. 86, 712 (2001);Submitted to Phys. Rev.Lett. (2003).

An applied magnetic field will penetrate a type-II superconductor and form an ordered magnetic vortex lattice at low temperatures. Small-Angle Neutron Scattering (SANS) is the technique of choice for probing the phase behavior of vortex lattices in bulk superconductors.In 2001, scientists at Brown U. discovered a solid-to-liquid-like transition, in which vortices become disordered, in niobium via SANS measurements at CHRNS.By carrying out in situ ac magnetic susceptibility measurements, this same group has now found that the degree of hysteresis associated with the melting transition is strongly field dependent, and disappears at low fields. Detailed SANS and susceptibility data have led to the phase diagram on the right which shows the location of a multicritical point. New theory is needed to explain this phenomenon in type-II superconductors.

SANS patterns showing the disordering (‘melting’) of the hexagonal magnetic vortex lattice in niobium.

GroES

GroEL

Trappedpolypeptide

A Piece of the Protein Folding Puzzle

S. Krueger, S.K. Gregurick, J. Zondlo, E. Eisenstein, J. Struct. Biol. 141, 240 (2003).

Proteins are ubiquitous in biological processes – including the folding of proteins! Proteins that mediate this essential function are called chaperonins and their role in catalyzing the proper folding of proteins has been a subject of intense study for years.

Through the use of deuterium labeling to vary scattering contrast, Small-Angle Neutron Scattering (SANS), combined with results from x ray crystallography and nmr, has provided key insights into the organization of polypeptide chains complexed with chaperonins.

For example, scientists at NIST and the Center for Advanced Research in Biotechnology (CARB) have constructed the model shown of the tertiary structure of a polypeptide (the nonnative subtilisin variant, PJ9) that forms a metastable complex with the chaperonins GroEL and GroES. SANS data collected at CHRNS directly provides the relative location, size and approximate shape of the trapped polypeptide. Subsequent modeling using the known crystallographic coordinates of the individual chaperonins yields the model of the complex shown in the figure.

GroES

GroEL

Trappedpolypeptide

SURF Students - 2003

Jamaal SandersU.C. Irvine

Matt PaolettiBucknell U.

Ramsey Zeitoun U. Maryland

Andrew Rockwell Johns Hopkins

CHRNS participates in the NIST/NSF REU Summer Undergraduate Research Fellowship (SURF) program by hosting four SURF students each year.

In 2003, CHRNS staff mentored student projects in:

•characterizing bioencapsu-lated proteins;

•analyzing small-angle neutron scattering from peptides in cell membranes;

•optimizing the metallurgical characteristics of a bismuth filter for neutron vibration spectroscopy

•investigating factors causing aggregation of polymers in aqueous solutions.

Summer School on Methods and Applications of Neutron Spectroscopy

June 9-13, 2003

CHRNS holds a week long course on neutron scattering each summer - usually in June. These courses are aimed at potential new users of the neutron instruments at the NCNR and emphasize hands-on training at the instruments where

participants carry out experiments and analyze data

In 2003, 32 graduate students and postdocs from 23 institutions attended the 9th CHRNS summer school which emphasized cold neutron techniques for probing the motions of molecules in materials using 4 CHRNS spectrometers that together probe time scales from 10-7s to 10-12 s.

CHRNS Summer School Class of 2003

No matter how strong the nearest neighbor antiferromagnetic interactions, quantum fluctuations prevent static long-range order within an infinite line of spin-1/2 quantum moments. What at first blush appears to be the simplest possible antiferromagnet, thus turns out to be a unique correlated spin liquid in which the elementary excitations are spinons carrying fractionalized spin.

Using inelastic neutron scattering, researchers from Johns Hopkins University and NIST have revealed that spinons get confined under the influence of staggered fields into particles with finite mass – the equivalent of solitons and breathers in the framework of the quantum sine-Gordon model. This enabled the quantitative confirmation of predictions for this exactly solvable model which were made more than 20 years ago.M. Kenzelmann, Y. Chen, C. Broholm, D.H. Reich, and Y. Qiu, Phys. Rev. Lett., in press.

Elementary excitations in a 1-D spin chain

Polar nanoregions in relaxor ferroelectrics

G. Xu, G. Shirane, J.R.D. Copley and P.M. Gehring, Phys. Rev. B (in press).

Relaxor ferroelectrics, such as Pb(Mg1/3Nb2/3)O3 (PMN), exhibit record piezoelectric properties, which make them ideal materials for transducers and actuators. Researchers from Brookhaven National Laboratory and NIST have used diffuse elastic neutron scattering to characterize the formation of the polar nanoregions that are responsible for their remarkable properties.

The figure shows the neutron diffuse scattering around a (100) peak in the (hk0) plane at four different temperatures for PMN. Compared with x-ray measurements, almost all phonon contributions can be removed by integrating the scattering over an appropriate energy range.

Vibrational enhancement at the nanoscale in glassesDisordered materials ranging from common silica glasses to metallic glasses, to polymers and even to proteins, display an enhancement of the vibrations in the low frequency (10’s of cm-1) range. Researchers from Arizona State University and their collaborators have utilized the unique ability of inelastic neutron scattering to simultaneously probe frequency and length scales, to show that this enhancement is greatest on the nanoscale.

The top figure shows the measured vibrational density of states for three different glassy states of rockwool and the ordered crystalline state averaged over a wide range of length scales. Note the low frequency enhancement in the glassy systems. The bottom panel shows the same thing for a length scale of ~ 1 nm.

C.A. Angell, Y.-Z. Yue, L.-M. Wang, J.R.D. Copley, S. Borick and S. Mossa, J. Phys.: Condens. Matter 15, S1051 (2003).

Unilamellar vesicles(~ 50 - 200 nm)

1.4

1.2

1.0

0.8

0.6

0.4

0.2

D/T

454035302520t/ ºC

vesicles cholesterol salt

Vesicles, one of the many phases that phospholipids form in solution, provide a nearly ideal model system for the cell walls of living tissue. Neutron spin echo spectroscopy has shown that the stiffness of these vesicles increases substantially (by ~2) when cholesterol is incorporated into the vesicle wall.

Effective diffusion coefficient of DMPC vesicles, scaled by the solvent viscosity and temperature and normalized to that at 35 C. This quantitiy is inversely related to the wall stiffness. The red symbols indicate the results for the vesicle walls in the absence of cholesterol while the blue symbols show the effect of adding cholesterol.

(D. Bossev and N. Rosov, unpublished)

Cholesterol stiffens phopholipid vesicles: A model system for cell walls

• Flexible, easy-to-use tools for data reduction, visualization, and analysis.

• Advanced data reduction and visualization methods for single-crystal and diffuse scattering time-of-flight data.

• Over 2500 downloads of DAVE software since August 2002.

• New data visualization tools available allowing rapid manipulation and rendering of 3-dimensional representations of data.

• Interactive manipulation of data surfaces

• Advanced data manipulation functionality encapsulated in simple interfaces such as combining inelastic neutron scattering data at different temperatures into a single new data set thus facilitating parametric data analysis.

DAVE

Data Analysis and Visualization Environment