Browsing by Author "Hamilton, WA"

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    Adsorption at liquid interfaces: a comparison of multiple experimental techniques
    (EDP Sciences, 2009-02) Law, BM; Brown, MD; Marchand, L; Lurio, LB; Hamilton, WA; Kuzmenko, I; Gog, T; Satija, S; Watkins, E; Majewski, J
    It has proven to be a challenging task to quantitatively resolve the interfacial pro. le at diffuse interfaces, such as, the adsorption pro. le near a bulk binary liquid mixture critical point. In this contribution we examine the advantages and disadvantages of a variety of experimental techniques for studying adsorption, including neutron reflectometry, X-ray reflectometry and ellipsometry. Short length scale interfacial features are best resolved using neutron/X-ray reflectometry, whereas, large length scale interfacial features are best resolved using ellipsometry, or in special circumstances, neutron reflectometry. The use of multiple techniques severely limits the shape of the adsorption pro. le that can describe all experimental data sets. Complex interfaces possessing surface features on many different length scales are therefore best studied using a combination of neutron/X-ray reflectometry and ellipsometry. © 2009, EDP Sciences
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    Application of time-resolved small angle neutron scattering to non-equilibrium kinetic studies
    (Springer Nature, 2011-11-15) Mata, JP; Hamilton, WA; Gilbert, EP
    Small-angle neutron scattering (SANS) provides structural information on the length scale from one to several hundred nanometres. Time-resolved SANS measurements (TR-SANS) therefore yield kinetic information on the evolution from one quasi-static structure to another. The technique offers complementary information to neutron spectroscopic methods where the focus is dynamics. Approaches for maximising time resolution in SANS are described, along with the particular advantages of neutrons, and some recent examples are discussed. © 2023 Springer Nature
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    Calmodulin binds a highly extended HIV-1 MA protein that refolds upon its release
    (Cell Press, 2012-08-08) Taylor, JEN; Chow, JYH; Jeffries, CM; Kwan, AH; Duff, AP; Hamilton, WA; Trewhella, J
    Calmodulin (CaM) expression is upregulated upon HIV-1 infection and interacts with proteins involved in viral processing, including the multifunctional HIV-1 MA protein. We present here the results of studies utilizing small-angle neutron scattering with contrast variation that, when considered in the light of earlier fluorescence and NMR data, show CaM binds MA in an extended open-clamp conformation via interactions with two tryptophans that are widely spaced in sequence and space. The interaction requires a disruption of the MA tertiary fold such that MA becomes highly extended in a long snakelike conformation. The CaM-MA interface is extensive, covering ∼70% of the length of the MA such that regions known to be important in MA interactions with critical binding partners would be impacted. The CaM conformation is semiextended and as such is distinct from the classical CaM-collapse about short α-helical targets. NMR data show that upon dissociation of the CaM-MA complex, either by the removal of Ca2+ or increasing ionic strength, MA reforms its native tertiary contacts. Thus, we observe a high level of structural plasticity in MA that may facilitate regulation of its activities via intracellular Ca2+-signaling during viral processing. © 2012 Biophysical Society.
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    (Corrected) Calmodulin binds a highly extended HIV-1 MA protein that refolds upon its release
    (Elsevier, 2023-05-02) Taylor, JEN; Chow, JYH; Jeffries, CM; Kwan, AH; Duff, AP; Hamilton, WA; Trewhella, Jill
    (Biophysical Journal 103, August 2012; 541–549) The authors identified an omission in this article. The figure legend for Figure S2 should include the following: “The model displayed here includes full-length calcium-bound CaM and the matrix protein sequence spanning amino acids 1–113; i.e., it does not include the flexible C-terminal tail (amino acids 114–133).” None of the article's conclusions are affected by this omission. In addition, after publication of the article, the SAXS and SANS data and modeling for this article were deposited in the Small Angle Scattering Biological Data Bank (SASBDB; https://www.sasbdb.org/) under accession code SASDKR3. Finally, the first author's name should appear as “James E. N. Taylor” rather than “James E. Taylor.”
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    Dynamical transition in a large globular protein: macroscopic properties and glass transition
    (Elsevier, 2010-01) Kealley, CS; Sokolova, AV; Kearley, GJ; Kemner, E; Russina, M; Faraone, A; Hamilton, WA; Gilbert, EP
    Hydrated soy-proteins display different macroscopic properties below and above approximately 25% moisture. This is relevant to the food industry in terms of processing and handling. Quasi-elastic neutron spectroscopy of a large globular soy-protein, glycinin, reveals that a similar moisture-content dependence exists for the microscopic dynamics as well. We find evidence of a transition analogous to those found in smaller proteins, when investigated as a function of temperature, at the so-called dynamical transition. In contrast, the glass transition seems to be unrelated. Small proteins are good model systems for the much larger proteins because the relaxation characteristics are rather similar despite the change in scale. For dry samples, which do not show the dynamical transition, the dynamics of the methyl group is probably the most important contribution to the QENS spectra, however a simple rotational model is not able to explain the data. Our results indicate that the dynamics that occurs above the transition temperature is unrelated to that at lower temperatures and that the transition is not simply related to the relaxation rate falling within the spectral window of the spectrometer. © 2010, Elsevier Ltd.
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    Importance of thermodynamic interactions on the dynamics of multicomponent polymer systems revealed by examination of the dynamics of copolymer/homopolymer blends.
    (American Chemical Society, 2008-05-13) Kamath, SY; Arlen, MJ; Hamilton, WA; Dadmun, MD
    The effect of copolymer composition oil their dynamics in a homopolymer matrix has been studied using specular neutron reflectivity (NR). We have monitored the segregation process of random copolymers, containing styrene (S) and methyl niethacrylate (MMA), to the d-PS/d-PMMA interface from a polymer matrix. Four random copolymers containing 50, 54, 67, and 80% MMA were studied at 10 wt % loading in d-PMMA, where the interfacial excess, Z*, growth scaled as t(1/2) as predicted by theory. These results are correlated to the diffusion-limited growth of a copolymer wetting layer at the d-PS/d-PMMA interface. The mutual and tracer diffusion coefficients and the effective friction coefficients for these copolymers were then determined. The results demonstrate that the copolymer composition has a significant impact on its dynamics. Copolymer dynamics are significantly faster than those for a diblock copolymer at the same composition, which indicates that the impact of the change in composition is more than that due to an increase in the MMA content in the copolymer. Analysis of the friction factor using the Lodge-McLeish model indicates that the local composition around a copolymer is richer in styrene than the model predicts. We attribute this to the fact that the model uses only chain connectivity to calculate the self-concentration and does not include contributions due to thermodynamic interactions between the two blend components. The observation that the local environment around a copolymer is richer in styrene is in agreement with our simulation results and indicates that the styrene monomers in the copolymer aggregate together to minimize contact with the PMMA matrix. These results exemplify the importance of thermodynamic interactions on the dynamics of multicomponent polymer systems, particularly miscible homopolymer/copolymer blends. © 2008, American Chemical Society
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    The multipurpose time-of-flight neutron reflectometer "Platypus" at Australia's OPAL reactor
    (Elsevier Science BV, 2011-03-11) James, M; Nelson, A; Holt, SA; Saerbeck, T; Hamilton, WA; Klose, F
    In this manuscript we describe the major components of the Platypus time-of-flight neutron reflectometer at the 20 MW OPAL reactor in Sydney, Australia. Platypus is a multipurpose spectrometer for the characterisation of solid thin films, materials adsorbed at the solid-liquid interface and free-liquid surfaces. It also has the capacity to study magnetic thin films using spin-polarised neutrons. Platypus utilises a white neutron beam (lambda=2-20 angstrom) that is pulsed using boron-coated disc chopper pairs; thus providing the capacity to tailor the wavelength resolution of the pulses to suit the system under investigation. Supermirror optical components are used to focus, deflect or spin-polarise the broad bandwidth neutron beams, and typical incident spectra are presented for each configuration. A series of neutron reflectivity datasets are presented, indicating the quality and flexibility of this spectrometer. Minimum reflectivity values of <10(-7) are observed: while maximum thickness values of 325 nm have been measured for single-component films and 483 nm for a multilayer system. Off-specular measurements have also been made to investigate in-plane features as opposed to those normal to the sample surface. Finally, the first published studies conducted using the Platypus time-of-flight neutron reflectometer are presented. (C) 2011 Elsevier B.V. All rights reserved.
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    Neutron scattering study of a membrane phase miscibility gap: coexistence of L3 "sponge" and La Lamellar phases
    (Insitute of Physics, 2010-12-16) Hamilton, WA; Porcar, L
    We report on a small angle neutron scattering (SANS) study of a temperature driven first order phase transition in a 25wt% solution of the surfactant AOT (Sodium Di-2-ethylhexyl Sulfosuccinate) in 1.5wt% heavy brine between an isotropic L3 "sponge" state at 27°C and a stacked lamellar Lα monophase 55°C. The prominent scattering features of these phases are correlation peaks due to the mean passage size of the L3 sponge and the Lα stacking separation. This ratio of the monophase peak positions Qα/Q31.3, is consistent with previous observations in this and similar systems. In the present study we tracked this system through the intermediate L3 +Lα biphasic miscibility gap. There the initial appearance of the Lα peak at 33.25°C was at a scattering vector some 23% higher than the final high temperature monophase value. During coexistence both L3 and Lα phase peak positions decreased linearly with increasing temperature maintaining a roughly constant ratio Qα/Q3 ~1.6-1.7. Two phase fits to the scattering data and application of scaling law predictions allow us to obtain local L3 phase volume fractions in the biphasic region and make preliminary determinations of the structural accomodations necessitated by phase coexistence in this system's miscibility gap.© 2010, Insitute of Physics
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    New approach to quantification of metamorphism using ultra-small and small angle neutron scattering
    (Elsevier; Cambridge Publications, 2008-07) Anovitz, LM; Lynn, GW; Cole, DR; Rother, G; Allard, LF; Hamilton, WA; Porcar, L; Kim, MH
    Small- and Ultra-Small Angle Neutron Scattering (SANS and USANS) provide powerful tools for analysis of porous rocks because neutrons probe both the surface and the interior of the material providing bulk statistical information over a wide range of length scales. For monomineralic materials scattering contrast arises from the difference between the scattering length density of the rock and the pores (taken to be zero). Pore-grain interfaces are best described by self-similar fractals with non-universal dimensions (2 < D < 3). This leads to a non-integer power-law as a function of the scattering I(Q) = I(1)Q-a + B where B is the incoherent background. For a volume or mass fractal scatterer a = D; if only the surface is a fractal, then a = 6-D. In this manner, surface fractals (a>3) and mass fractals (a<3) are easily distinguished. Non-fractal “fuzzy” interfaces (a>4) may also be observed. We have used SANS and USANS to characterize samples from two transects (contact out to ~1700 m) from the contact metamorphosed Hueco limestone at Marble Canyon, TX. Significant changes in a number of scattering parameters are observed as a function of distance, including regions of the aureole outside the range of classic reaction petrology. Our modeling suggests that changes in surface free energy, pore volume and hydrogen content, among other variables, can be quantified. Both the mass and surface fractals Dm and Ds can be fitted as a function of the surface fractal correlation length as: log10(D/r) = -0.9648 * log10r(Å) + 0.30103 r2 = 0.9999, s = 0.038 although metamorphism does not necessarily proceed linearly along this curve with increasing grade. Nonetheless, the ability to measure these variables shows that these techniques provide a novel approach to the analysis and study of metamorphism.
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    New approach to quantification of metamorphism using ultra-small and small angle neutron scattering
    (Elsevier, 2009-12-15) Anovitz, LM; Lynn, GW; Cole, DR; Rother, G; Allard, LF; Hamilton, WA; Porcar, L; Kim, MH
    In this paper we report the results of a study using small angle and ultra-small angle neutron scattering techniques (SANS and USANS) to examine the evolution of carbonates during contact metamorphism. Data were obtained from samples collected along two transects in the metamorphosed Hueco limestone at the Marble Canyon, Texas, contact aureole. These samples were collected from the igneous contact out to similar to 1700 m. Scattering curves obtained from these samples show mass fractal behavior at low scattering vectors, and surface fractal behavior at high scattering vectors. Significant changes are observed in the surface and mass fractal dimensions as well as the correlation lengths (pore and grain sizes), surface area to volume ratio and surface Gibbs Free energy as a function of distance, including regions of the aureole outside the range of classic metamorphic petrology. A change from mass-fractal to non-fractal behavior is observed at larger scales near the outer boundary of the aureole that implies significant reorganization of pore distributions early in the metamorphic history. Surface fractal results suggest significant smoothing of grain boundaries, coupled with changes in pore sizes. A section of the scattering Curve with a slope less than -4 appears Lit low-Q in metamorphosed samples, which is not present in unmetamorphosed samples. A strong spike in the surface area to volume ratio is observed in rocks near the mapped metamorphic limit, which is associated with reaction of small amounts of organic material to graphite. It may also represent an increase in pore Volume or permeability, suggesting that a high permeability zone forms at the boundary of the aureole and moves outwards as metamorphism progresses. Neutron scattering data also correlate well with transmission electron microscopic (TEM) observations, which show formation of micro- and nanopores and microfractures during metamorphism. The scattering data are, however, quantifiable for a bulk rock in a manner that is difficult to achieve using high-resolution imaging (e.g. TEM). Thus, neutron scattering techniques provide a new approach to the analysis and study of metamorphism. © 2009, Elsevier Ltd.
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    PLATYPUS - the time-of-flight neutron reflectometer at Australia’s New 20 MW OPAL research reactor
    (Australian Institute of Physics, 2006-12-05) James, M; Nelson, A; Brûlé, A; Hamilton, WA
    Neutron reflectometry is used to probe the structure of surfaces, thin-films or buried interfaces as well as nanoscale processes occurring at them. Applications cover nanostructured magnetic thin films, electrochemical and catalytic interfaces, adsorbed surfactant layers, self-assembled monolayers, biological membranes, polymer coatings and photosensitive films. Contrast variation and selective deuteration of hydrogenous materials are important aspects of the neutron-based technique. Neutron reflectometry probes the structure of materials normal to the surface at depths of up to several thousand Å, with a depth resolution of a few Å. A time-of-flight neutron reflectometer (PLATYPUS) is under construction at Australia’s new 20 MW OPAL research reactor at Lucas Heights (due for completion in 2007). PLATYPUS has been designed to study nanoscale films on solid and free-liquid surfaces. Magnetic materials can be examined using a polarized beam option, while in-plane structures can be studied by off-specular scattering using a 2-dimensional helium-3 detector. Kinetic studies will also be possible due to a disc chopper system that offers the possibility of tailoring the resolution of the instrument to suit the lengthscales of interest. In this presentation we report the design, specifications and results of commissioning experiments of the PLATYPUS neutron reflectometer.
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    Quokka: the small-angle neutron scattering instrument at OPAL
    (Australian Institute of Physics, 2006-12-05) Noakes, TJ; Christoforidis, J; Schulz, JC; Hamilton, WA; Gilbert, EP
    A small-angle neutron scattering (SANS) instrument[1] is being designed as part of the initial instrument suite for the new 20-MW Australian Reactor, OPAL. This instrument is designed to study structure on 1-100nm length scales on the wide variety of materials of scientific and technological importance for which neutron scattering has some considerable advantages over its x-ray counterpart, in particular (i) systems for which isotopic (H/D) contrast may be employed to highlight ordering, such as self-assembled polymer, surfactant and bio-molecule mesophases, and (ii) systems which scatter the neutron due to its magnetic moment, such as flux line penetration arrays in type II superconductors. The OPAL SANS instrument, receiving neutrons from a large liquid-D2 cold source, will be in the spirit of the world’s best facilities and will greatly build upon the Australian Nuclear Science and Technology Organisation’s existing expertise and facilities. Scheduled to begin operation in 2007, it will provide Australian and international researchers with opportunities to access state-of-the-art SANS instrumentation. [1] E.P. Gilbert, J.C. Schulz and Terry J. Noakes, Physica B, (2006) in press
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    Small angle neutron scattering (SANS) studies on the structural evolution of pyromellitamide self-assembled gels
    (ACS Publications, 2014-10-31) Jamieson, SA; Tong, KWK; Hamilton, WA; He, L; James, M; Thordarson, P
    The kinetics of aggregation of two pyromellitamide gelators, tetrabutyl- (C4) and tetrahexyl-pyromellitamide (C6), in deuterated cyclohexane has been investigated by small angle neutron scattering (SANS) for up to 6 days. The purpose of this study was to improve our understanding of how self-assembled gels are formed. Short-term (< 3 h) time scales revealed multiple phases with the data for the tetrabutylpyromellitamide C4, indicating one-dimensional stacking and aggregation corresponding to a multifiber braided cluster arrangement that is about 35 Å in diameter. The corresponding tetrahexylpyromellitamide C6 data suggest that the C6 also forms one-dimensional stacks but that these aggregate to a thicker multifiber braided cluster that has a diameter of about 62 Å. Over a longer period of time, the radius, persistence length, and contour length all continue to increase in 6 days after cooling. These data suggest that structural changes in self-assembled gels occur over a period exceeding several days and that fairly subtle changes in the structure (e.g., tail-length) can influence the packing of molecules in self-assembled gels on the single-to-few fiber bundle stage © 2014, American Chemical Society.
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    Structure of [C(4)mpyr][NTf2] room-temperature ionic liquid at charged gold interfaces
    (American Chemical Society, 2012-05-15) Lauw, Y; Horne, MD; Rodopoulos, T; Lockett, V; Akgun, B; Hamilton, WA; Nelson, A
    The structure of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyr][NTf2]) room-temperature ionic liquid at an electrified gold interface was studied using neutron reflectometry, cyclic voltammetry, and differential capacitance measurements. Subtle differences were observed between the reflectivity data collected on a gold electrode at three different applied potentials. Detailed analysis of the fitted reflectivity data reveals an excess of [C4mpyr]+ at the interface, with the amount decreasing at increasingly positive potentials. A cation rich interface was found even at a positively charged electrode, which indicates a nonelectrostatic (specific) adsorption of [C4mpyr]+ onto the gold electrode. © 2012, American Chemical Society
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    Studying electrical double layers in ionic liquids using neutron and x-ray reflectometry
    (Australian Institute of Physics, 2010-02-05) Lauw, Y; Nelson, A; Horne, MD; Rodopoulos, T; Minofar, B; Webster, NAS; Hamilton, WA
    Ionic liquids are typically defined as salts that exist in a liquid state at, or near, room temperature. Due to their favourable properties (e.g., good thermal stability, low volatility, and wide electrochemical window), ionic liquids have potential use in many industrial applications, such as catalysis, lubrication, batteries, and metal electrodeposition. Despite recent advances in the field, ionic liquid research is still in its infancy. Additional fundamental studies are needed to explore the properties of ionic liquids and to allow the full potential of these properties in particular applications to be exploited. Electrical double layers (EDL) are well known in aqueous colloidal systems where the potential field from a charged surface affects many properties of the particle. The structure of the EDL at a conductive surface is of prime importance to electrochemistry because it strongly affects the transport of reactants and products within the region where electrochemical reactions take place. The understanding of the EDL in ionic liquids is not nearly as advanced as aqueous systems and even a description of how it responds to changes in the conductor potential is yet to be agreed. Here we present some recent results from simulation and Neutron/X-ray reflectometry measurements that explore the electrical double layer in ionic liquids at the air-liquid and solid-liquid interfaces. The effect of water impurities within the (EDL) of an ionic liquid is of particular interest since they are known to reduce the electrochemical window of ionic liquids, decrease their density and viscosity, and anomalously decrease their surface tension.
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    Surface force confinement cell for neutron reflectometry studies of complex fluids under nanoconfinement
    (American Institute of Physics, 2008-10) Cho, JHJ; Smith, GS; Hamilton, WA; Mulder, DJ; Kuhl, TL; Mays, J
    In this paper, we describe the construction of a new neutron surface force confinement cell (NSFCC). The NSFCC is equipped with hydraulically powered in situ, temporally stable, force control system for simultaneous neutron reflectometry studies of nanoconfined complex fluid systems. Test measurements with deuterated toluene confined between two opposing diblock copolymer (polystyrene+poly 2-vinylpyridine) coated quartz substrates demonstrate the capabilities of the NSFCC. With increasing hydraulically applied force, a series of well-defined decreasing separations were observed from neutron reflectivity measurements. No noticeable changes in the hydraulic pressure used for controlling the surface separation were observed during the measurements, demonstrating the high stability of the apparatus. This newly designed NSFCC introduces a higher level of control for studies of confinement and consequent finite size effects on nanoscale structure in a variety of complex fluid and soft condensed matter systems. © 2008, American Institute of Physics
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    Water absorption and transport in bis-silane films
    (Royal Society of Chemistry, 2009-01-07) Wang, YM; Wang, P; Kohls, D; Hamilton, WA; Schaefer, DW
    Water (D2O) ingress in bis-amino silane and bis-sulfur silane films was studied by in situ neutron reflectivity. Bis-amino silane film absorbs substantially more D2O (33 vol%) than the bis-sulfur silane film (4.6 vol%) at equilibrium. The volume increase (swelling) of both films, however, is much smaller than the total volume of D2O absorbed in the films. The results suggest that the absorbed water exists in two populations: one is dissolved in the polymer matrix (Henry's mode) while the other occupies unrelaxed free volume existing in the polymer (Langmuir mode). The dominance of Langmuir mode accounts for the small film thickness change during the water absorption. Dual-mode sorption is also consistent with the observed two-stage swelling process whereby an initial rapid increase in film thickness is followed by a slower process extending over 11 h. © 2009, Royal Society of Chemistry
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    X-ray and ellipsometric study of strong critical adsorption
    (American Physical Society, 2007-06) Brown, MD; Law, BM; Marchand, L; Lurio, LB; Kuzmenko, I; Gog, T; Hamilton, WA
    Carpenter [Phys. Rev. E 61, 532 (2000)] succeeded in determining a single universal model, called the P1 model, that could describe the ellipsometric critical adsorption data from the liquid-vapor interface of four different critical binary liquid mixtures near their critical demixing temperatures. The P1 model also recently has been used to describe neutron reflectometry data from a critical liquid mixture/crystalline quartz interface. However, in another recent study, the P1 model failed to simultaneously describe x-ray reflectometry and ellipsometry data from the liquid-vapor surface of the critical mixture n-dodecane + tetrabromoethane (DT). In this paper, we resolve this discrepancy between x-ray and ellipsometric data for the DT system. At large length scales (far from the interface) the local concentration is described by the P1 model in order to correctly reproduce the temperature dependence of the ellipsometric data. Close to the interface, however, the molecular structure must be correctly accounted for in order to quantitatively explain the x-ray data. An important conclusion that arises from this study is that neutron or x-ray reflectometry is most sensitive to short-range interfacial structure, but may provide misleading information about long-range interfacial structure. Ellipsometry provides a more accurate measure of this long-range interfacial structure. Complex interfacial structures, possessing both short- and long-range structure, are therefore best studied using multiple techniques. © 2007, American Physical Society