Browsing by Author "White, JW"

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    Deuterium effects in human serum albumin with nanoparticle silica kinetics
    (Australian Institute of Nuclear Science and Engineering, 2016-11-29) White, JW; Raynes, JK; Mata, JP; Gilbert, EP; Knott, RB; de Campo, L
    Light scattering shows three stages of the interaction of 80Å radius silica nanoparticles with human serum albumin in buffered solutions. The structures formed in the fast stage, twenty minutes after mixing, have been identified in a “stopped flow” neutron small angle scattering experiment. Good scattering functions were obtained at two-minute time resolution for this phase of the interaction in D2O and H2O. pH dependent changes in structure are analysed using standard fitting programs with a minimum number of parameters. This experiment was aimed to find the structural signature of nanoparticle-protein interaction, possibly the “protein corona” supposed to be formed as a means to promote entry of nanoparticles into cells. Here we use small “engineered” nanoparticles where the indications of toxicity are strong. We show with nanometric resolution that for our system, the association is largely a form of protein-induced aggregation distinct from the protein corona hypothesis. The corona might well be the mode of interaction for small proteins and nanoparticles 10-100 times larger than we have studied, but measurements on widely used commercial products may be more relevant.
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    Effects of surfactant transport on high internal phase emulsions under shear: a combined rheological and structural study
    (American Institute of Chemical Engineers, 2021-10-19) Yaron, PN; Reynolds, PJ; Mata, JP; White, JW
    We report the change in rheological behavior of high-internal phase emulsions (HIPEs) under shear of a polyisobutylene-based (PIBSA) oil-soluble surfactant and with and without the addition of a water-soluble polyacrylamide (PAM) co-surfactant. We used a series of contrast-matched small-angle and ultra-small angle neutron scattering (SANS and USANS) coupled with in situ rheological measurements to track the locations of the surfactant and co-surfactant as a function of shear. This work follows a series of papers analyzing the structural variation and stability of emulsions stabilized with PIBSA and various mixtures of PIBSA/PAM under static and shear conditions. The emulsions’ sensitivity to aqueous/oil phase ratios, surfactant concentration, surfactant molecular weight, and polydispersity has been defined. The emulsions consist of almost spherical micron scale, highly polydisperse, aqueous droplets dispersed in a continuous oil phase with aqueous/oil phase ratios of about 9:1. The emulsions are rheologically unexceptional and follow previously established predictions and theory. The emulsions show refinement to higher viscosity after high shear, and shear thinning. The structural basis for its rheological behavior however does not follow theory. Shear dependent changes observed in the SANS data were tracked by SANS model parameters using a convolution of two well-established models. Shear thinning is explained by SANS observed shear disruption of inter-droplet bilayer links, causing deflocculation to more spherical, less linked, aqueous droplets. Refinement to higher viscosity is accompanied by droplet size reduction and loss of surfactant from the oil continuous phase. Refinement occurs because of shear-induced droplet anisotropy, which we have also observed in the SANS experiment. The observed anisotropy and emulsion refinement cannot be reproduced by either isolated molecule or mean-field models and require a more detailed consideration of interdroplet forces in the sheared fluid. Even at concentrations by the stability limit, a large percentage of surfactant(s) is dissolved as small n-mers or as larger reverse micelles that play an important part in stabilization of the emulsion under shear. Steady shear on PIBSA/PAM emulsions reduces the number of reverse surfactant micelles present in the both the continuous oil phase to provide the surfactant needed to cover the newly formed surface area as the emulsion refines to smaller droplet sizes. Surfactant adsorption to droplet interfaces is accomplished by two processes. The first draws soluble surfactant from the oil phase to the interface and lowers the concentration of dissolved n-meric surfactant. In parallel, oil-soluble reverse micelles begin to break up, allowing a shear rate dependent steady state to establish between the surfactant reservoirs and aqueous droplets. The application of low-shear rate recovery intervals allowed the recovery dynamics of the surfactant distribution to be observed. The results showed little reduction of the emulsion interfacial area upon return to its quiescent state, but a large recovery of the reverse micelle volume fraction that indicates the continuous phase acts as the reservoir of surfactant when the emulsion is under shear. Drastic changes in the rheological behavior of emulsions with PAM co-surfactant indicate different kinetics dictate surfactant and co-surfactant droplet adsorption. We report the effect of altering the chain length and concentration of PAM based co-surfactants (C12-PAM, C14-PAM, and C16-PAM) on the properties of the high-internal phase PIBSA emulsions under shear.
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    An energy dispersive time resolved liquid surface reflectometer
    (Elsevier, 2001-07-21) Garrett, RF; White, JW; King, DJ; Dowling, TL; Fullagar, W
    Two designs are presented for an energy dispersive liquid surface reflectometer with time resolution in the milli-second domain. The designs utilise rotating crystal and Laue analyser optics respectively to energy analyse a pink synchrotron X-ray beam after reflection from a liquid surface. Some performance estimates are presented, along with results of a test experiment using a laboratory source and solid state detector. © 2001 Elsevier Science B.V.
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    Extended Q-range small angle neutron scattering from inverse micellar solutions of PIBSA—Micelle and molecular scattering
    (Elsevier Science BV, 2013-02-15) Mata, JP; Reynolds, PA; Gilbert, EP; White, JW
    Inverse micelles play an important role in the stability of high internal phase water in oil (W/O) emulsions. The influence of both solvent and temperature has been investigated on the structure of inverse micelles prepared from the polyisobutylene-based surfactant, PIBSA, using small-angle neutron scattering (SANS). By collecting data over an extended range of scattering vector (Q), combined with the use of solvent deuteration, SANS has highlighted an additional contribution to the anticipated micellar scattering, namely a signal characteristic of rod-like scattering that is consistent with single dissolved molecules of the PIBSA surfactant and its primarily hydrogenated (mainly alkane oil) solvent (both MW ca. 1000 Da). The solvency effect of three different solvents (hexadecane, cyclohexane and toluene) on micellar–monomer (rod) equilibrium has also been evaluated. The volume fractions of rods and micelles in solution are found to agree with the sample compositions, as does the intensity of the observed incoherent background. This consistency across fit parameters not only highlights the sensitivity of the model but also the value of extended Q range, enhanced signal-to-noise studies in such soft matter systems. The data show the extent to which quantitative measurements can be carried at the molecular level using small angle scattering.© 2013, Elsevier Ltd.
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    High internal phase emulsions under Shear. Co-surfactancy and shear stability
    (American Chemical Society, 2011-05-19) Yaron, PN; Scott, AJ; Reynolds, PA; Mata, JP; White, JW
    Large changes in the rheology of high-internal phase aqueous-in-oil emulsions (HIPEs) using an oil-soluble polyisobutylene-based primary surfactant (PIBSA) are provoked by very small quantities of water-soluble polyamide-based cosurfactants (PAM with C-12, C-14, and C-16 tails). The structural origin of this was studied using small-angle neutron scattering (SANS) from sheared emulsions, with simultaneous in situ rheology measurements. The PAM drastically lowers the droplet oil interfacial tension by displacing PIBSA, causing large droplet deformation under shear and much lowered emulsion yield stress. With PAM, the surfactant monolayer at the droplet surface becomes more responsive to droplet shape change and redistributes in response to shear which the PIBSA-only system does not. Although it is oil-insoluble, PAM also reaches the nanoscale PIBSA micelles in the oil phase, changing micelle size and content in ways predictable from the hydrophilicity of the different PAMs. PAM does not, however, strongly affect the viscosities at high shear rates; shear thinning and thickening are unaffected. Droplet size, droplet-droplet flattening, and linkage determine the viscosities observed, more so than, droplet-oil interfacial tension. We infer from this that the droplet motion under shear does not involve much transient droplet deformation as the droplets move by each other. Author: Dikundwar, AG; Venkateswarlu, C; Piltz, RO; Chandrasekaran, S and Row, TNG Year: 2011 Journal: Crystengcomm Title: Crystal structures of fluorinated aryl biscarbonates and a biscarbamate: a counterpoise between weak intermolecular interactions and molecular symmetry Volume: 13 Pages: 1531-1538 Abstract: Conformational features and supramolecular structural organization in three aryl biscarbonates and an aryl biscarbamate with rigid acetylenic unit providing variable spacer lengths have been probed to gain insights into the packing features associated with molecular symmetry and the intermolecular interactions involving 'organic' fluorine. Four structures but-2-yne-1,4-diyl bis(2,3,4,5,6-pentafluorophenylcarbonate), 1; but-2-yne-1,4-diyl bis(4-fluorophenylcarbonate), 2; but-2-yne-1,4-diyl bis(2,3,4,5,6-pentafluorophenylcarbamate), 3 and hexa-2,4-diyne-1,6-diyl bis(2,3,4,5,6-pentafluorophenylcarbonate), 4 have been analyzed in this context. Compound 1 adopts a non-centrosymmetric "twisted'' (syn) conformation, whereas 2, 3 and 4 acquire a centrosymmetric "extended'' (anti) conformation. Weak intermolecular interactions and in particular those involving fluorine are found to dictate this conformational variation in the crystal structure of 1. A single-crystal neutron diffraction study at 90 K was performed on 1 to obtain further insights into these interactions involving 'organic' fluorine.© 2011, American Chemical Society
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    Human serum albumin binding to silica nanoparticles - effect of protein fatty acid ligand
    (Royal Society of Chemistry, 2014-02-19) Ang, JC; Henderson, MJ; Campbell, RA; Lin, JM; Yaron, PN; Nelson, A; White, JW
    Neutron reflectivity shows that fatted (F-HSA) and defatted (DF-HSA) versions of human serum albumin behave differently in their interaction with silica nanoparticles premixed in buffer solutions although these proteins have close to the same surface excess when the silica is absent. In both cases a silica containing film is quickly established at the air-water interface. This film is stable for F-HSA at all relative protein-silica concentrations measured. This behaviour has been verified for two small silica nanoparticle radii (42 Å and 48 Å). Contrast variation and co-refinement have been used to find the film composition for the F-HSA-silica system. The film structure changes with protein concentration only for the DF-HSA-silica system. The different behaviour of the two proteins is interpreted as a combination of three factors: increased structural stability of F-HSA induced by the fatty acid ligand, differences in the electrostatic interactions, and the higher propensity of defatted albumin to self-aggregate. The interfacial structures of the proteins alone in buffer are also reported and discussed. © 2015, Royal Society of Chemistry.
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    Nano- and microstructure of high-internal phase emulsions under shear
    (American Chemical Society, 2010-03-18) Yaron, PN; Reynolds, PA; McGillivray, DJ; Mata, JP; White, JW
    High-internal phase aqueous-in-oil emulsions of two surfactant concentrations were studied using small-angle neutron scattering (SANS) and simultaneous in situ rheology measurements. They contained a continuous oil phase with differing amounts of hexadecane and d-hexadecane (for contrast matching experiments), a deuteroaqueous phase almost saturated with ammonium nitrate, and an oil-soluble stabilizing polyisobutylene-based surfactant. The emulsions’ macroscopic rheological behavior has been related to quantify changes in microscale and nanoscale structures observed in the SANS measurements. The emulsions are rheologically unexceptional and show, inter alia, refinement to higher viscosity after high shear, and shear thinning. These are explained by changes observed in the SANS model parameters. Shear thinning is explained by SANS-observed shear disruption of interdroplet bilayer links, causing deflocculation to more spherical, less linked, aqueous droplets. Refinement to higher viscosity is accompanied by droplet size reduction and loss of surfactant from the oil continuous phase. Refinement occurs because of shear-induced droplet anisotropy, which we have also observed in the SANS experiment. This observed anisotropy and the emulsion refinement cannot be reproduced by either isolated molecule or mean-field models but require a more detailed consideration of interdroplet forces in the sheared fluid. © 2010, American Chemical Society
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    Preliminary SAXS and SANS studies of protein-based adhesive elastomer secreted by the Australian frog Notaden bennetti
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Graham, LD; White, JW; Knott, RB
    When provoked, Notaden bennetti frogs secrete an exudate which rapidly forms a tacky elastic solid (frog glue). This protein-based material acts as a promiscuous pressure-sensitive adhesive that functions even in wet conditions. The adhesive strength and elasticity if the glue make this an attractive material for orthopedic repairs and other surgical procedures, possibly including topical would closure. Protein analysis of the denaturing gel electrophoresis revels a characteristic pattern of bands with apparent molecular masses of 13-500 kDa, with the largest protein also being the most abundant one. This large protein (called Nb-1R) appears to be the major structural component of the glue. Key issues understanding of the function of all proteins are shape and 3D structure. The Small Angle X-Ray and Neutron Scattering (SAXS and SANS) techniques are well suited to explore the shape of proteins in solution and these techniques have been applied to various forms of the frog glue, Scattering results indicated an Rg of 2.0-3,6nm, which is consistent with globular proteins of 30-170kDa. One possible explanation to the difference between the molecular mass ranges deduced from gel electrophoresis and scattering data is the dominant protein is elongated rather than spherical.
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    Stability of high internal phase emulsions at low surfactant concentration studied by small angle neutron scattering
    (Elsevier, 2010-09-15) Reynolds, PA; McGillivray, DJ; Mata, JP; Yaron, PN; White, JW
    The changes in structure of high internal phase emulsions at low concentrations and at elevated temperature are reported for comparison with the same emulsions under conditions well away from instability. Small angle neutron scattering measurements on aqueous ammonium nitrate droplets dispersed in hexadecane and stabilized by very small quantities of a polyisobutylene-based surfactant (PIBSA) as well as related inverse micellar solutions in hexadecane, have been made as a function of temperature and surfactant concentration. Experimental conditions here favour larger and more deformable droplets than in previous studies. Besides the expected micelles and adsorbed surfactant, planar bilayers of micron lateral extent between touching droplets cover 20% of the droplet surface. Another difference from previous experiments is that the oil phase in the emulsions, and corresponding inverse micellar solutions are different in micellar radii and composition. The differences, and changes with surfactant concentration and temperature, are attributed to fractionation of the polydisperse PIBSA in the emulsions, but not the inverse micellar solutions. At low PIBSA concentration and high temperature the SANS shows emulsion decomposing into separate oil and aqueous phases. This occurs when the micelle concentration reaches a very small but measurable value. The inverse micelles may suppress by steric action long wavelength unstable capillary waves in the bilayers. Depletion repulsion forces here have a minor role in the emulsion stabilization. © 2010, Elsevier Ltd.
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    Structure of high internal phase aqueous-in-oil emulsions and related inverse micelle solutions. 3. Variation of surfactant
    (American Chemical Society, 2009-09-10) Reynolds, PA; Gilbert, EP; Henderson, MJ; White, JW
    The small angle neutron scattering from high internal phase water-in-hexadecane and saturated ammonium nitrate-in-hexadecane emulsions is compared with that from related hexadecane-based inverse micellar solutions. Three molecular weights of the monodisperse polyisobutylene acid amide (PIBSA) surfactant 750, 1200, and 1700 were studied over a range of surfactant concentrations. As an additional comparison, emulsions based on sorbitan monooleate and isostearate surfactants were investigated. The scattering from molecular weight 1200 water-based PIBSA emulsions can be fitted at all concentrations to a model with a surfactant coated aqueous droplet-oil interface together with the majority of the surfactant in the oil phase of the emulsion in the form of inverse micelles. Variation of the molecular weight shows a variety of phases of increasing curvature: lamellar, sponge, and, most commonly, the emulsion structure described above. In addition, the molecular weight affects the oil component in the emulsions, which can contain either cylindrical micelles or spherical micelles of varying water but constant hexadecane content. Increased phase curvature is favored by both increased PIBSA molecular weight and ammonium nitrate dissolved in the water. These observations are consistent with "Wedge theory". The structures observed in the emulsions are close to those observed in related inverse micellar solutions made from hexadecane, the surfactant, and water. Lower concentrations of surfactant in the micellar solutions decrease micelle curvature, except where the inverse micelles are spherical and small; here, there is little effect of dilution. Substitution of sorbitan surfactants for PIBSAs produces slightly less organized but similar structures, with smaller spherical micelles containing proportionally more water. The aqueous-oil droplet interface has a relatively invariant monolayer of adsorbed surfactant. For all emulsions, we can infer from the mass balance that micelle concentrations are depressed in the inverse micellar solutions because up to half the added surfactant is present as individually dissolved molecules. © 2009, American Chemical Society
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    Structure of high internal phase aqueous-in-oil emulsions and related inverse micelle solutions. 4.Surfactant mixtures
    (American Chemical Society, 2009-09-10) Reynolds, PA; Gilbert, EP; Henderson, MJ; White, JW
    The effects of combinations of surfactants on the structure and stability of high internal phase water-in-hexadecane and saturated ammonium nitrate-in-hexadecane oil-based emulsions and oil-based inverse micellar solutions are reported, The combinations were 750, 1200, and 1700 molecular weight monodisperse and 450 and 1000 molecular weight polydisperse polyisobutylene acid amides, and sorbitan monooleate. The samples made from mixtures have qualitatively similar nanostructures to emulsions made from single surfactants. Again, for the emulsions, micrometer-scale aqueous droplets are dispersed in a continuous oil phase, which contains inverse spherical micelles composed of surfactant, hexadecane, and water. In quantitative terms, lower average surfactant molecular weight, lower ammonium nitrate content, and lower surfactant content increased the swelling of micelles, their water content, and the tendency of the emulsion to be unstable and form a sponge phase. This instability also allows micelle plasticity such that their geometry and content in mixed surfactant systems are not simply predictable by interpolation from single surfactant systems. An example was found of a mixed micelle 3 times larger than either single component micelle. The observed behavior suggests that mixing surfactant molecules of very different molecular weights destabilizes the emulsions, while mixing surfactants close in molecular weight has the opposite effect. The synergistic effects of surfactant molecular weight polydispersity and binary mixing are most marked for 1:1 molecular mixtures of surfactant. © 2009, American Chemical Society