Talks

Nanoparticle and colloidal gels, flocculated suspensions, and attractive driven glasses are of fundamental scientific interest and pose challenges to industrial formulation and application because of the hierarchy of structures that connect particle properties to bulk material properties. In many cases the processing of these materials relies on the fact that the underlying structure may be reversibly broken down by flow. As a result their rheological behavior is of technological relevance to process design optimization, and can exhibit complex behaviors such as solid-like linear viscoelasticity, thixotropy, aging, yielding, hysteresis, and shear localization. Much is known about the fractal and fractal-like microstructure of low density gels under static conditions and the dissolution of the network as a result of flow, but less is known about concentrated systems. In this work, we explore the shear induced structural reordering of a nanoparticle dispersions with tunable attractions using small-angle neutron scattering (SANS) in combination with a rheometer (rheo-SANS) and a novel 1-2 plane shear cell (flow-SANS). The model system is composed of silica spheres which have a relatively thin grafted oligomeric surface layer that provides steric stability in a good solvent, but contributes to a reversible, short range attraction in poor solvents (Eberle et al., Langmuir, 2010). When suspended in tetradecane (C14) the solvent quality can be "tuned" with temperature such that, upon quenching, the system transitions from a fluid to a stable physical gel that occurs without competition for macroscopic phase separation for concentrations, ≥ 0.05 (Eberle et al., PRL, 2011). Rheo-SANS and flow-SANS scattering profiles are analyzed in combination with the steady shear rheology. The strength of attraction is found to have a profound impact on both the rheology and local nanostructure. The goals of this study are to identify the hierarchical structures that quantitatively relate the state or phase of the system, interparticle potential, and particle properties to the bulk rheology.

Residual stress measurement on a submarine hull structure using Deep Hole Drilling technique

Xavier Ficquet, VEQTER, xavier.ficquet@veqter.co.uk
Ed J. Kingston, VEQTER, ed.kingston@veqter.co.uk

The importance of accurately accounting for residual stresses in component integrity assessments is well-known, and universally accepted. Equally, the need to validate numerical predictions of residual stress against high quality residual stress experimental data is now viewed as a necessity.

There are several measurement techniques available to measure residual stresses. They are often classified by their level of destructiveness and their penetration. In order to compare the different measurement techniques an elastic-plastic bent beam sample has been chosen as it is very comparable to the residual stress field induced during the sheet bending process used in the submarine structure. The bent beam has been measured using five different techniques: Incremental centre hole drilling, ring core, slitting, neutron diffraction and deep hole drilling technique. The results from measurement techniques show an excellent agreement when compared with the FEA.

A critical quality of architectural coatings is hiding performance. A primary factor which impacts hiding is the  dispersion of the pigment: both before incorporation into the coating and after full formulation.  This presentation will be divided into two parts.  The first will demonstrate the degree of dispersion of TiO₂ produced by different commercial dispersants as a function of shear rate by ultra small angle neutron scattering (USANS).  In the second part, the dispersion characteristics of  binary colloid mixtures of  polymeric latex and TiO₂ pigment as a function of shear rate will be demonstrated  by USANS. A standard acrylic latex with moderate hiding performance was compared with a modified acrylic latex giving improved hiding performance. Structural parameters for the latices and pigment were extracted using a fractal scattering model. We demonstrate the quality of dispersion of the TiO₂ was better in the modified acrylic latex formulation. The improved dispersion level of pigment leads to the improved hiding performance. The structural parameters are applied to a viscosity model for fractal aggregates and good agreement is obtained between the measured viscosity and predicted values based on the structural measurements.

Rechargeable all-solid-state Li-ion batteries are attractive as safe electrochemical energy-storage devices.  The biggest challenge in the realization of these batteries is the need for a fast Li-ion conductor as the solid electrolyte, which significantly improves battery safety and stability relative to conventional liquid electrolyte containing batteries. Both Sulfur and oxide based compounds are of interest.

Recently, we synthesized the analogous cubic Li⁺ Argyrodites, Li₆PS₅X (X = Cl, Br, I).  Among the these compounds Li₆PS₅Br exhibit highest room temperature conductivity of  1.03×10^-3 S/cm which is close to the Li-mobility in liquid electrolytes that are composed of LiPF₆ salt dissolved in various carbonates. With such high lithium mobilities, these materials may be ideal for use as solid electrolytes in Li-ion batteries.  We try to understand the structural variation of these compounds using X-ray and Neutron and bond valence approach.

Optimisation of biomedical titanium alloys focuses on tailoring alloy elastic properties to biological materials by adjusting alloying concentration in the metastable β (bcc) phase. The common aim is to achieve minimum Young's modulus, ideally approaching that of bone (20-40 GPa).

We propose to measure the phonon dispersion of Ti-24Nb-4Zr-8Sn (weight %) by inelastic X-ray scattering. This work will back up the science of designing low modulus β (bcc) titanium alloys for biomedical applications with experiment-based fundamental understanding.

In this seminar I will use my PhD work to give some background to the beta-Ti system and then explain why I think measuring the phonon dispersion of a representative alloy will be both interesting and worthwhile.

This is the first of a series of short presentations; typically on the last Thursday of the month as part of the regular seminar program. The purpose of these presentations is for us to become more familiar with each other and the science that we do (at the Bragg Institute and elsewhere).  Each month will have a mix of researchers from different parts of the Institute and different research disciplines.

Hyaluronic acid (HA) is a high molecular weight polysaccharide. HA is involved in a wide range of processes in the human body, such as wound healing, tumor progression and joint lubrication [1, 2, 3]. In this contribution we show, that HA also stabilizes lipid multilayer systems at physiological conditions. Neutron reflectometry measurements were carried out at V6 and the new BioRef neutron reflectometer at Helmholtz-Zentrum Berlin [4]. Measurements against excess D2O verified, that an oligolamellar DMPC lipid bilayer coating remains stable on a silicon substrate at 21°C in its ordered state (Lß', Pβ') with a d-spacing of 66 Å, but detaches almost completely from the solid support at 38°C in its chain-disordered state (Lα) [5]. By contrast oligolamellar lipid bilayers remain stable on a substrate at 38°C when incubated with a solution of HA in D₂O [6]. Lamella transformations occur over time, resulting in a new lamella phase with a d-spacing of 247 Å. This effect has to our knowledge not been reported before. We will discuss a possible mechanism of the transformation of the oligolamellar lipid system with incubation time. Also potential consequences of the "new" lamella phase with respect to further insight in natural processes like joint lubrication will be under consideration.

[1] M.T. Longaker et al, Ann. Surg., 1991, 213, 292

[2] B.P. Toole et al.,Glycobiology, 2002,12, 37

[3] T. Kawano et al., Arthritis & Rheumatism, 2003, 48, 1923

[4] M. Strobl et al. J. Phys. (Conf. Ser.), 2010, 251

[5] M. Kreuzer et al., Rev. Sci. Instrum., 2011, 82, 023902

[6] M. Kreuzer et al., submitted to Biophysical Journal, 2011

It is now well appreciated that the combination of antiferromagnetic interactions and lattice symmetries based on triangles lead to phenomena known broadly as geometrical frustration. The spin system under question cannot simultaneously satisfy all of its near neighbour pair-wise exchange interactions and the resulting ground state can have a large degeneracy, or under constrained.

Over the past 15 years I have studied many 3D pyrochlore magnets, here I will review the work on Heisenberg systems before discussing recent work looking for exotic quantum spin systems.

Quantum spin liquid (QSL) in which magnetic spins remain disordered in the limit of zero Kelvin, underpins much of modern condensed matter theory. Previous studies have shown that QSL ground states tend to emerge in the geometrically frustrated materials and the organic salts K-BEDT-TTF)₂Cu₂(CN)₃, Et_nMe_4-nSb[Pd(DMIT)₂]₂ and ZnCu₃(OH)₆Cl₂. [1-3] may be good candidates. Two different experimental programs have begun to look for other systems where spin ½ ions ccupy a triangular motif. One family under investigation is the intercalated derivatives of Znsubstituted copperhydroxynitrate (CHN) [4], Cu_2(1-x)Zn_2x(OH)₃NO₃, the other is the inorganic compound Ba₃CuSb₂O₉.

To date the bulk properties of polycrystalline samples have been performed and small single crystals have been grown. These data will be presented along with some preliminary neutron scattering work that is currently underway.

This work is done in collaboration with Chris Wiebe (Winnipeg, Canada), Haidong Zhou (FSU), Jian Wu, Fletcher Werner, Julia S. Wildeboer, Alexander Seidel, Zohar Nussinov and Stuart A. Solin (Wahsington University in St Louis).

References
S. Yamashita et al., Nature Phys. 4, 459 (2008).
M. Yamashita et al., Science 328, 1246 (2010).
J. S. Helton et al., Phys. Rev. Lett. 98, 107204 (2007).
G. G. Linder et al., J. Solid State Chem. 116 1 (1995)

Tethered membranes are planar lipid bilayers tied to a gold electrode by a series of hydrophilic polyethylene glycol (PEG) chains anchored to the gold surface by organodisulfide groups. They are exceptionally robust and suitable for measuring the effects of purified ion channel proteins on membrane conductivity. We have shown that the presence of the tethering PEG chains does not interfere, with the incorporation of a wide range of ion channel proteins with molecular weights up to 200 kDa. Membrane conductance is reliably determined using an AC impedance technique (using frequencies between 0.1 Hz to 1 kHz). Membrane capacitance is also simultaneously determined, and is an indicator of membrane thickness. Conductance (and capacitance) can be plotted versus time, during the addition of various pharmaceuticals being tested as channel blockers or actuators, enabling dose/response relationships to be routinely evaluated. It is also possible to use tethered membrane preparations in pulse amperometry (analogous to classic voltage clamp experiments on single cells). This technique permits determination of ion selectivity, voltage dependence, and rectification of ion channel currents. For channels that spontaneously insert into membranes, eg some bacterial toxins, the voltage and compositional dependence of the insertion can be measured. Case studies to be discussed include bacterial sodium channels, bacterial potassium channels, voltage dependent mechanosensitive channels and the chloride intracellular channel CLIC, and the synergistic behaviour of PGLa with magainin‐2.

About the Speaker

Bruce studied model and biological membranes using solid state nuclear magnetic resonance during his career at CSIRO. He was director of the Cooperative Research Centre for Molecular Engineering, pursuing applications of devices based on molecular ion channels in membranes, and then Chief Scientist of AMBRI Ltd. He and colleagues formed Surgical Diagnostics Pty Ltd, and later Tethered Membrane Pty Ltd., to pursue research applications for tethered membrane technologies. Prof. Cornell’s recent work has focussed on developing novel tethered membrane constructs and techniques to study ligand and voltage gated ion channels and antimicrobial peptides. He is Adjunct Professor at the University of Western Sydney and Board Member at the Griffith University Microelectronics and Nanotechnology Centre.

In this presentation, the background related to thermoelectrics, including thermoelectric effects, thermoelectric conversion efficiency and applications of thermoelectric devices will be briefly introduced first. Some important research progress in thermoelectric field including new concepts and new material systems during the last decade will be followed secondly. Finally, the research in my group at Tongji University, including recently type-I Ge-based single crystals, single crystalline Zintl compounds, PbTe based materials, CoSb3 based skutterudites, chelcogenides, and polymer-inorganic nanocomposite thermoelectric materials will be introduced.

About the speaker:

Prof. Kefeng CAI received his B.S. and Ph.D. from Wuhan University of Technology (PR China) in 1987 and 1998, respectively. He worked on Materials Synthesis and Processing at the State Key Laboratory of Advanced Technology, Wuhan University of Technology from 1987 to 2001 (as an associate professor since 1995). He did a Postdoctoral fellow from February 1999 to January 2001at Physics Department,  University of the Witwatersrand, South Africa, and worked as an Alexander von Humboldt Research Fellow from August 2001 to December 2002 at Materials Research Institute, German Aerospace Center. He  joined  Tongji University as a professor since 2003. He is interested in thermoelectrics and synthesis and characterization of nanomaterials. Currently he is a member of International thermoelectric society and Senior member of American Nanosociety, and he is also an Editorial Board member of The Open Crystallography Journal, Global Journal of Physical Chemistry, and World Journal of Nano Science and Engineering. He has published more than 60 research papers in peer reviewed journals, two review papers and 10 patents.

We shall discuss uniqueness of neutron reflectivity techniques in determining chemical and magnetic structures in multilayered materials by taking Langmuir-Blodgett films as examples. In particular we shall discuss results of a sub-Kelvin polarized neutron scattering study carried out at ADAM beamline of ILL. Spin-vortices are most appealing characteristics of two-dimensional (2D) easy-plane spin systems, which are receiving recent interest for their fundamental properties and possible technological application involving nano-structured magnetic materials. Spin-vortices are in-plane circular spin arrangement, which may have core spins directing out-of-plane to reduce exchange energy. A spin vortex exists with its counterpart, an anti-vortex, as a pair below a characteristic temperature, T_BKT, defined by essential scaling of spin-spin correlation and susceptibility. The unbinding of vortex-pairs above T_BKT is known as Berezinskii-Kosterlitz-Thouless (BKT) transition. A sufficiently strong in-plane magnetic field, below T_BKT, may cause the core of a vortex to move towards the core of an anti-vortex so that the cross-tie domain-walls become annihilated, resulting in a homogeneous magnetization. Above T_BKT, the vortices are free and may also be generated but no field can annihilate such individual topological defects. The branching of zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves are explained by reconfiguration of the vortex structure. The low-field magnetization data was found to follow power-law behaviour as predicted by Berezinskii-Kosterlitz-Thouless (BKT) transition for a finite-size system. We have also observed that a field of 15 kOe annihilates vortex-antivortex pairs completely to produce a homogeneous phase with saturation moment ~ 7u_B per Gd-ion below BKT transition temperature (~ 600 mK).

References:

1. S. Gayen, M. K. Sanyal, A. Sarma, M. Wolff, K. Zhernenkov and H. Zabel, Phys. Rev. B 82, 174429 (2010).

2. M. K. Sanyal, J. Mater. Chem., 19, 4300 (2009)

To better understand the issues and promises associated with bioactive papers, 3 examples will be analyzed. The first is paper assay for direct blood typing. Antibodies and blood are sequentially added/printed on paper. Paper is used to separate antibody agglutinated (specific) from non-agglutinated (non-specific) red blood cells (RBC) and communicate blood typing. The second example aims at developing a Gold-nanoparticle (AuNp) paper bioassay for antibody detection for blood/urine analysis. By controlling the AuNp aggregate size and surface coverage, the sensitivity of the Surface Enhanced Raman Scattering SERS was enhanced by 3 to 6 orders of magnitude. The effects of polyelectrolyte solution concentration, molecular weight and charge density on the SERS enhancement factor are presented. In the third example, an enzyme is retained on paper, with and without polyelectrolyte used as a retention aid. The effects of polyelectrolyte chemistry (CPAM, PEO, PAA) on enzyme retention, aging and reaction kinetics are quantified using image analysis. The concept is to engineer paper-bioassay for telemedicine. A drop of biofluid is deposited on enzyme-paper; the reaction kinetics producing a colour product is captured and transmitted/analyzed with the camera of a cell phone.

The presentation will initiate a discussion on the relationship between immobilized biomolecule morphology and functionality.

Neutron is an important probe to find out the location of hydrogen atoms in biological macromolecules.  We have been working on investigation of the drug interaction with the target protein by neutron crystallography.  We have been determined several drug target proteins such as HIV-protease, pancreatic elastase, and beta-lactamase with the use of both neutron and X-ray diffraction data.  In this seminar, we would like to introduce the contributions of hydrogen atoms on the function and recognition of the drug candidates.