Franz Grieser

University of Melbourne, Melbourne, Victoria, Australia

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Publications (366)1250.35 Total impact

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    ABSTRACT: Structural forces play an important role in the rheology, processing and stability of colloidal systems and complex fluids, with polyelectrolytes representing a key class of structuring colloids. Here, we explore the interactions between soft colloids, in the form of air bubbles, in solutions of monodisperse sodium poly(styrene sulfonate) as a model polyelectrolyte. It is found that by self-consistently modelling the force oscillations due to structuring of the polymer chains along with deformation of the bubbles, it is possible to precisely predict the interaction potential between approaching bubbles. In line with polyelectrolyte scaling theory, two distinct regimes of behaviour are seen, corresponding to dilute and semi-dilute polymer solutions. It is also seen that by blending monodisperse systems to give a bidisperse sample, the interaction forces between soft colloids can be controlled with a high degree of precision. At increasing bubble collision velocity, it is revealed that hydrodynamic flow overwhelms oscillatory structural interactions, showing the important disparity between equilibrium behaviour and dynamic interactions. Copyright © 2015 Elsevier Inc. All rights reserved.
    Journal of Colloid and Interface Science 08/2015; 451. DOI:10.1016/j.jcis.2015.03.050 · 3.55 Impact Factor
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    ABSTRACT: Interactions between colliding air bubbles in aqueous solutions of polydisperse sodium poly(styrene sulfonate) (NaPSS) using direct force measurements were studied. The forces measured with deformable interfaces were shown to be more sensitive to the presence of the polyelectrolytes when compared to similar measurements using rigid interfaces. The experimental factors that were examined were NaPSS concentration, bubble collision velocity and polyelectrolyte molar mass. These measurements were then compared with an analytical model based on polyelectrolyte scaling theory in order to explain the effects of concentration and bubble deformation on the interaction between bubbles. Typically structural forces from the presence of monodisperse polyelectrolyte between interacting surfaces may be expected, however, it was found that the polydispersity in molar mass resulted in the structural forces to be smoothed and only a depletion interaction was able to be measured between interacting bubbles. It was found that an increase in number density of NaPSS molecules resulted in an increase in the magnitude of the depletion interaction. Conversely this interaction was overwhelmed by an increase in the fluid flow in the system at higher bubble collision velocities. Polymer molar mass dispersity plays a significant role in the interactions present between the bubbles and has implications that also affect the polyelectrolyte overlap concentration of the solution. Further understanding of these implications can be expected to play a role in the improvement in operations in such fields as water treatment and mineral processing where polyelectrolytes are used extensively. Copyright © 2015 Elsevier Inc. All rights reserved.
    Journal of Colloid and Interface Science 12/2014; DOI:10.1016/j.jcis.2014.12.076 · 3.55 Impact Factor
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    ABSTRACT: In complex fluids, soft or deformable components, such as drops, bubbles, or capsules, respond to their surrounds in a far more complicated manner than rigid particle dispersions. This creates challenges in the processing and the characterization of these systems for a diverse set of applications. These applications range from the purification of minerals or pharmaceuticals using solvent extraction processes, to the formulation of emulsions and foams in food and personal care products. Through a combination of novel experimental methods, mainly using Atomic Force Microscopy (AFM) to visualize the collisions between micro-drops or micro-bubbles on the nanoscale, coupled with theoretical models, we have been able to quantitatively link the dynamic coupling of shape changes with external forces that control their behavior for a range of systems involving drops and bubbles. This talk will focus on how oil-water and air-water deformable interfaces are mediated by the presence of highly concentrated surfactant systems or non-adsorbing poly-electrolytes. We observe significant differences between the structural forces between these deformable interfaces compared to the periodic oscillatory structural forces commonly observed between rigid interfaces. In addition, quantitative comparison between these system types indicates that the deformable nature of droplets allows them to act as far more sensitive probes than solid spheres. Furthermore, the responsive nature of soft surfaces can give rise to unexpected behavior not encountered in rigid systems including reversible aggregation/flocculation for emulsion droplets and, potentially, spatial ordering within concentrated emulsion phases. The impact of hydrodynamic drainage effects on the resulting force behavior as well as changes associated with the aspect ratio of the nano-colloid will also be discussed.
    14 AIChE Annual Meeting; 11/2014
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    ABSTRACT: Pt-Pd bimetallic nanoparticles supported on graphene oxide (GO) nanosheets were prepared by a sonochemical reduction method in the presence of polyethylene glycol as a stabilizing agent. The synthetic method allowed for a fine tuning of the particle composition without significant changes in their size and degree of aggregation. Detailed characterization of GO-supported Pt-Pd catalysts was carried out by transmission electron microscopy (TEM), AFM, XPS, and electrochemical techniques. Uniform deposition of Pt-Pd nanoparticles with an average diameter of 3 nm was achieved on graphene nanosheets using a novel dual-frequency sonication approach. GO-supported bimetallic catalyst showed significant electrocatalytic activity for methanol oxidation. The influence of different molar compositions of Pt and Pd (1:1, 2:1, and 3:1) on the methanol oxidation efficiency was also evaluated. Among the different Pt/Pd ratios, the 1:1 ratio material showed the lowest onset potential and generated the highest peak current density. The effect of catalyst loading on carbon paper (working electrode) was also studied. Increasing the catalyst loading beyond a certain amount lowered the catalytic activity due to the aggregation of metal particle-loaded GO nanosheets.
    Journal of Solid State Electrochemistry 11/2014; 18(11):3163-3171. DOI:10.1007/s10008-014-2562-4 · 2.23 Impact Factor
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    ABSTRACT: The hydrophobic force describes the attraction between water-hating molecules (and surfaces) that draws them together, causing aggregation, phase separation, protein folding and many other inherent physical phenomena. Attempts have been made to isolate the range and magnitude of this interaction between extended surfaces for more than four decades, with wildly varying results. In this perspective, we critically analyse the application of common force-measuring techniques to the hydrophobic force conundrum. In doing so, we highlight possible interferences to these measurements and provide physical rationalisation where possible. By analysing the most recent measurements, new approaches to establishing the form of this force become apparent, and we suggest potential future directions to further refine our understanding of this vital, physical force.
    Physical Chemistry Chemical Physics 07/2014; 16(34). DOI:10.1039/c4cp01410c · 4.20 Impact Factor
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    ABSTRACT: The multibubble sonoluminescence (MBSL) signals generated by 3.5 ms pulses of 515 kHz ultrasound in air-saturated ethylene glycol, water and ethylene glycol/water mixtures were examined in the absence and presence of a range of solutes; including aliphatic alcohols of various chain lengths (C3 - C6), and ionic and zwitterionic surfactants. In general, the alcohols quenched the SL in most solvent mixtures and the surfactants enhanced the SL signal. However, in some solvent mixtures complex effects were observed in the presence of the solutes. The discussion presented rationalises the varied behaviour of the solutes on the MBSL observed in terms of their influence on inter- and intra- bubble effects experienced by bubbles in an ultrasound field.
    The Journal of Physical Chemistry B 12/2013; 118(1). DOI:10.1021/jp409075n · 3.38 Impact Factor
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    ABSTRACT: The hydrophobic attraction describes the well-known tendency for nonpolar molecules and surfaces to agglomerate in water, controlled by the reorganization of intervening water molecules to minimize disruption to their hydrogen bonding network. Measurements of the attraction between chemically hydrophobised solid surfaces have reported ranges varying from tens to hundreds of nanometers, all attributed to hydrophobic forces. Here, by studying the interaction between two hydrophobic oil drops in water under well-controlled conditions where all known surface forces are suppressed, we observe only a strong, short-ranged attraction with an exponential decay length of 0.30 ± 0.03 nm—comparable to molecular correlations of water molecules. This attraction is implicated in a range of fundamental phenomena from self-assembled monolayer formation to the action of membrane proteins and nonstick surface coatings.
    Journal of Physical Chemistry Letters 11/2013; 4(22):3872–3877. DOI:10.1021/jz402068k · 6.69 Impact Factor
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    ABSTRACT: The hydrophobic force is a fundamental interaction in nature, and is central to many processes ranging widely from dispersing oil spills to forming cell membranes. Yet, many studies by different groups over the past 30 years to directly measure the hydrophobic force have led to the observations of extra attractions that have varied in range from tens to hundreds of nanometers. Perhaps most surprisingly, the hydrophobic effect is often invoked to explain results using solid (mainly mica) surfaces in contact with water, but rarely in the study of drops and bubbles, arguable some of the most hydrophobic interfaces in nature. For solid surfaces many secondary phenomena, surface chemical heterogeneity and roughness, and the presence of nano-bubbles, have been uncovered without a clear picture of how to describe the hydrophobic effect on a microscopic scale. We employ molecular smooth and inert oil droplets in aqueous solutions to isolate the intrinsic hydrophobic attraction, showing it to be far a shorter range and stronger attraction than the conflicting results in the literature suggest. This is also more consistent with an expected molecular origin. We have measured this force directly by suppressing any extraneous forces leaving only a “hydrophobic force” between two drops in aqueous solution. We also introduce separately different mild repulsive forces of quantum electrodynamic, electrical and hydrodynamic origin between the drops, and in each case the same attraction is observed.
    13 AIChE Annual Meeting; 11/2013
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    ABSTRACT: The formation of the hydrated electron through the secondary reaction, H + OH- → H2O + eaq, has been examined in the sonolysis of argon-saturated aqueous solutions at an ultrasound frequency of 355 kHz. The detection of the hydrated electron was achieved by measuring its reaction with the one-electron acceptors Fe(CN) and methyl viologen. The results obtained indicate that hydrated electrons are produced predominately at the bubble/aqueous solution interface at comparatively high local concentrations, estimated to be > 1.5 x 10-3 M. The half-life of the hydrated electron under such conditions is estimated to be < 60 ns.
    The Journal of Physical Chemistry A 02/2013; 117(12). DOI:10.1021/jp312389n · 2.78 Impact Factor
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    ABSTRACT: The degradation of paracetamol was studied by sonolysis, photocatalysis and sonophotocatalysis in the presence of homogeneous (Fe3+) and heterogeneous (TiO2) photocatalysts using 213 kHz ultrasound (US). The degradation rates obtained for sonolysis, photocatalysis and sonophotocatalysis using TiO2 (1 g/L) were about 8.3, 30.2 and 40.2 × 10−7 M min−1, respectively. In the case of reactions involving Fe3+, the degradation rates obtained were 26.1, 18.6 and 46.7 × 10−7 M min−1 for US + Fe3+, UV + Fe3+ and US + UV + Fe3+, respectively. The above results indicate that the combination of sonolysis with photocatalysis (TiO2 or Fe3+) results in an additive effect from combining the two processes, with a synergy index value of ∼1.0. There was no synergistic effect in total organic carbon (TOC) removal in sonophotocatalysis with TiO2, whereas the mineralization process was synergistic when sonophotolysis was carried out in the presence of Fe3+. Further studies with electrospray mass spectrometry analysis revealed the formation of a hydroxylated derivative of paracetamol during sonolysis.
    Separation and Purification Technology 01/2013; 103:114–118. DOI:10.1016/j.seppur.2012.10.003 · 3.07 Impact Factor
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    ABSTRACT: Understanding the mechanics and outcome of droplet and bubble collisions is central to a range of processes from emulsion stability to mineral flotation. The atomic force microscope has been shown to be sensitive and accurate in measuring the forces during such interactions; in combination with a suitable model framework, a powerful tool is obtained for understanding surface forces and droplet stability in dynamic systems. Here we demonstrate for the first time that this process is not limited to linear motion, and that accelerating, decelerating and cyclical droplet velocities can be used to explore the collisions between droplets and bubbles in ways that much more closely mimic real systems. In particular, the motion of droplets experiencing oscillating pumping pressures is explored, providing insight into fluid handling for microfluidics. By modelling a range of processes in which drops collide and deform, and sometimes coalesce, the validity of the theoretical model - which accounts for deformation, surface forces and dynamic lubrication - is demonstrated. Further, it is shown how this model can be used as a predictive tool to determine whether a given droplet collision will be stable or colaescent.
    Soft Matter 01/2013; 9(8):2426. DOI:10.1039/C2SM27463A · 4.15 Impact Factor
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    ABSTRACT: The effects of the water-soluble polymer polyvinylpyrrolidone (PVP) on the multi-bubble sonoluminescence (MBSL) intensity generated in aqueous solutions exposed to ultrasound at the two ultrasound frequencies of 20 kHz and 363 kHz, have been examined. In both cases the presence of PVP, at concentrations of up to 2 g/100 mL, was found to enhance the MBSL intensity emitted from the solutions. Based on the intensity behaviour of the SL observed from aqueous solutions containing PVP/surfactant and PVP/alcohol mixtures it is suggested that PVP enhances MBSL by increasing the number of active bubbles in the system by hindering bubble-bubble coalescence processes and probably also by changing the structure of the bubble "clouds" formed at the acoustic antinodes in solution. The influence of PVP on bubble-bubble coalescence rates was also measured to support the interpretation of the MBSL emission experiments.
    The Journal of Physical Chemistry B 10/2012; 116(46). DOI:10.1021/jp308897c · 3.38 Impact Factor
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    ABSTRACT: Few-layered reduced graphene oxide–Pt composites are prepared using a combination of two ultrasound frequencies at 20 kHz and 211 kHz. Such a unique dual frequency arrangement operating in tandem, yields large exfoliated graphene sheets with platinum nanoparticles dispersed on them. The extent of reduction achieved by the use of this dual frequency sonication arrangement is evaluated by XPS, IR, and Raman spectroscopies. Transmission electron and atomic force microscopies confirm the morphology of resulting assemblies to be bi- and single layered sheets. These composites show good electrocatalytic activity towards methanol oxidation.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 09/2012; 409:81–87. DOI:10.1016/j.colsurfa.2012.06.006 · 2.35 Impact Factor
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    ABSTRACT: The redox reactions of organic radicals, with Fe(CN) and methyl viologen, generated from the sonochemical decomposition of aliphatic alcohols in aqueous solutions, have been studied. The number of radicals produced was found to relate to the amount of adsorbed alcohol molecules (Gibbs surface excess) at the gas-aqueous solution interface for any bulk solution concentration of the alcohol. The majority of the radicals produced are from the thermal degradation of the alcohol molecules that have entered imploding cavitation bubbles. The maximum rate of reduction at 355 kHz, of Fe(CN) , was 2.6±0.3 μM min-1 whereas for methyl viologen it was 1.2 ±0.3 μM min-1 under the conditions used. The difference in the rates is attributed to the reaction of various pyrolytically produced organic radicals with the methyl viologen radical cation. The possible reactions occurring in the sonolysis of alcohol/water systems are discussed in detail.
    The Journal of Physical Chemistry A 07/2012; 116(30). DOI:10.1021/jp3037507 · 2.78 Impact Factor
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    ABSTRACT: A comparison between the temperatures within imploding acoustic cavitation bubbles and the extent of sonoluminescence (SL) quenching by C(1)-C(5) aliphatic alcohols in 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][EtSO(4)], a well known imidazolium based room temperature ionic liquid (RTIL)), has been made at an ultrasound frequency of 213kHz. The temperatures obtained ranged from 3500±200K, in neat [EMIM][EtSO(4)], to about 3200±200K in RTIL-alcohol containing solutions. It was also found that the SL intensity decreased with increasing concentration (up to 1M) of the alcohols to a greater extent compared with the relative changes to the bubble temperatures. Both the extent of the reduction in the bubble temperatures and the SL quenching were much smaller than those obtained in comparable aqueous solutions containing aliphatic alcohols. Possible reasons for the differences in the observed trends between water/alcohol and [EMIM][EtSO(4)]/alcohol systems under sonication at 213kHz are discussed.
    Ultrasonics Sonochemistry 06/2012; 20(1):47-51. DOI:10.1016/j.ultsonch.2012.05.011 · 3.82 Impact Factor
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    ABSTRACT: The use of atomic force microscopy to measure and understand the interactions between deformable colloids - particularly bubbles and drops - has grown to prominence over the last decade. Insight into surface and structural forces, hydrodynamic drainage and coalescence events has been obtained, aiding in the understanding of emulsions, foams and other soft matter systems. This article provides information on experimental techniques and considerations unique to performing such measurements. The theoretical modelling frameworks which have proven crucial to quantitative analysis are presented briefly, along with a summary of the most significant results from drop and bubble AFM measurements. The advantages and limitations of such measurements are noted in the context of other experimental force measurement techniques.
    Journal of Colloid and Interface Science 04/2012; 371(1):1-14. DOI:10.1016/j.jcis.2011.12.047 · 3.55 Impact Factor
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    ABSTRACT: A systematic study of collisions between surfactant-free organic drops in aqueous electrolyte solutions reveals the threshold at which continuum models provide a complete description of thin-film interactions. For collision velocities above ~1 μm/s, continuum models of hydrodynamics and surface forces provide a complete description of the interaction, despite the absence of surfactant. This includes accurate prediction of coalescence at high salt concentration (500 mM). In electrolyte solutions at intermediate salt concentration (50 mM), drop-drop collisions at lower velocity (<1 μm) or extended time of forced drop-drop interaction exhibit a strong pull-off force of systematically varying magnitude. The observations have implications on the effects of ion-specificity and time-dependence in drop-drop interactions where kinetic stability is marginal.
    Langmuir 03/2012; 28(9):4259-66. DOI:10.1021/la204753y · 4.38 Impact Factor
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    ABSTRACT: Polymeric stabilizers are used in a broad range of processes and products, from pharmaceuticals and engine lubricants to formulated foods and shampoos. In rigid particulate systems, the stabilization mechanism is attributed to the repulsive force that arises from the compression of the polymer coating or "steric brush" on the interacting particles. This mechanism has dictated polymer design and selection for more than thirty years. Here we show, through direct measurement of the repulsive interactions between immobilized drops with adsorbed polymers layers in aqueous electrolyte solutions, that the interaction is a result of both steric stabilization and drop deformation. Drops driven together at slow collision speeds, where hydrodynamic drainage effects are negligible, show a strong dependence on drop deformation instead of brush compression. When drops are driven together at higher collision speeds where hydrodynamic drainage affects the interaction force, simple continuum modeling suggests that the film drainage is sensitive to flow through the polymer brush. These data suggest, for drop sizes where drop deformation is appreciable, that the stability of emulsion drops is less sensitive to the molecular weight or size of the adsorbed polymer layer than for rigid particulate systems.
    Langmuir 02/2012; 28(10):4599-604. DOI:10.1021/la204272u · 4.38 Impact Factor
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    ABSTRACT: Compound drops arise from the contact of three immiscible fluids and can assume various geometric forms based on the interfacial chemistry of the phases involved. Here we present a study of a new class of compound drops that is sessile on a solid surface. The possible geometries are demonstrated experimentally with appropriate fluid combinations and accounted for with a quantitative theoretical description. Although such systems are broadly controlled by relative interfacial energies, subtleties such as the van der Waals force and effects of micro-gravity, despite drop sizes being well below the capillary length, come into play in determining the equilibrium state that is achieved. The drying of a compound sessile drop was measured experimentally, and the process revealed a novel transition between different characteristic configurations of compound sessile drops. Such drops may prove to be useful as the first step towards development of functional surfaces in applications such as soft optics, photonics and surface encapsulation.
    Soft Matter 01/2012; 8(43):11042. DOI:10.1039/C2SM26637G · 4.15 Impact Factor
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    ABSTRACT: Acoustically generated sonoluminescence (SL) and sonochemiluminescence (SCL) have been used to produce molecular hydrogen in a photocatalytic process using Ru(bipy)32+ as a photosensitizer, methyl viologen as an electron relay agent, and colloidal platinum as the catalyst. SL and SCL and various radicals were generated in water using 355 kHz ultrasound. The efficacy of the photocatalytic hydrogen production was to some extent limited by sonochemical side reactions, however, the in situ photon generation was sufficiently intense for pronounced H2 generation above the background sonochemical processes.
    The Journal of Physical Chemistry C 12/2011; 116(1):1056–1060. DOI:10.1021/jp209946s · 4.84 Impact Factor

Publication Stats

8k Citations
1,250.35 Total Impact Points

Institutions

  • 1984–2014
    • University of Melbourne
      • • The Particulate Fluids Processing Centre (PFPC)
      • • School of Chemistry
      Melbourne, Victoria, Australia
  • 1984–2008
    • Victoria University Melbourne
      Melbourne, Victoria, Australia
  • 2005
    • Osaka Prefecture University
      Sakai, Ōsaka, Japan
    • Max Planck Institute of Colloids and Interfaces
      Potsdam, Brandenburg, Germany
  • 2004–2005
    • University of Bath
      • Department of Chemistry
      Bath, ENG, United Kingdom
  • 1977–2002
    • University of Notre Dame
      • Department of Chemistry and Biochemistry
      South Bend, Indiana, United States
  • 1993
    • The Commonwealth Scientific and Industrial Research Organisation
      Canberra, Australian Capital Territory, Australia
  • 1987
    • Argonne National Laboratory
      Lemont, Illinois, United States