Research

The expertise of Phil Attard is in the field of classical equilibrium statistical mechanics. His research encompasses applications, techniques, and the foundations of the subject. The properties of liquids are explored at the molecular level using various computational and mathematical techniques, and by collaborative experiments. The emphasis is on the development of new methods for the treatment of more complex systems, and on specific calculations aimed at rationalising measured data and unexplained phenomena. Work has mainly focused on inhomogeneous and confined liquids, and on the interactions of colloidal particles and surfaces in such liquids. This has resulted in an increased understanding of fundamental phenomena, and in direct comparison of calculated and measured surface forces. Knowledge of how the cooperative behavior of molecules determines macroscopic processes can be used to unravel a multitude of scientific and industrial problems.

Research Interests

• Statistical Mechanics
  • Integral Equations (Inhomogeneous, Singlet, Triplet Correlations , Bridge Functions, Three Body Potentials, Molecular, Polymer)
  • Simulations (Extended Ensemble, Grand Canonical, Inhomogeneous, Phase Transitions)
  • Applications (hard-sphere, Lennard-Jones, primitive model electrolyte)
  • Foundations (Thermodynamics, Entropy, Probability and Statistics)
• Surface Forces
  • Surface Force Measurement (Elastic Deformation, Dynamic Force Measurement)
  • Electric Double Layer
  • Electrostatic Correlations (Double Layer, Dipolar, van der Waals)
  • Hydration Repulsion
  • Hydrophobic Attraction, Nanobubbles
  • Entropic and Structural Forces (Oscillatory, Packing, Depletion)
• Colloid Science
  • Aggregation
  • Bubbles
  • Electrokinetics

  Reviews
  

  1. P. Attard, Electrolytes and the Electric Double Layer, Adv. Chem. Phys. 92, 1-159 (1996).
  2. P. Attard, Recent Advances in the Electric Double Layer in Colloid Science, Curr. Opin. Coll. Int. Sci. (scheduled for publication in May, 2001).
  3. P. Attard Friction, Adhesion, and Deformation: Dynamic Measurements with the Atomic Force Microscope, J. Adhesion Sci. Technol. (in press).
  4. P. Attard and G. Gillies, Deformation and Adhesion of Viscoelastic Particles: Theory and Atomic Force Microscopy, Aust. J. Chem. (in press).

  Top Ten Papers
  

  1. P. Attard, Spherically Inhomogeneous Fluids. I. Percus-Yevick Hard-Spheres: Osmotic Coefficients and Triplet Correlations, J. Chem. Phys. 91, 3072-3082 (1989).
     First algorithm and solution of the spherical Ornstein-Zernike equation, with accurate results for the hard-sphere triplet correlation function.
  2. P. Attard, D. R. Berard, C. P. Ursenbach, and G. N. Patey, The Interaction Free Energy between Planar Walls in Dense Fluids. An Ornstein-Zernike Approach with Results for Hard-Sphere, Lennard-Jones, and Dipolar Systems, Phys. Rev. A 44, 8224-8234 (1991).
     The original derivation of the wall-wall Ornstein-Zernike equation, and, in passing, the Derjaguin approximation in statistical mechanics.
  3. P. Attard, Asymptotic Analysis of Primitive Model Electrolytes and the Electrical Double Layer, Phys. Rev. E 48, 3604-3621 (1993).
     Exact asymptote for Coulomb systems, with direct correlation function expressions for the effective charge and decay length.
  4. J. L. Parker, P. M. Claesson, and P. Attard, Bubbles, Cavities, and the Long-Ranged Attraction between Hydrophobic Surfaces, J. Phys. Chem. 98, 8468-8480 (1994).
     First evidence for nanobubbles and identification of them as the source the long range hydrophobic attraction.
  5. P. Attard, Polymer Born-Green-Yvon Equation with Proper Triplet Superposition Approximation. Results for Hard-Sphere Chains, J. Chem. Phys. 102 5411-5426 (1995).
     Building on the work of Taylor and Lipson, gives the correct superposition approximation for the polymer BGY equation and obtains the first self-consistent results for the inter- and intra-site pair correlation functions.
  6. P. Attard, J. Schulz, and M. W. Rutland, Dynamic Surface Force Measurement. I. van der Waals Collision, Rev. Sci. Instrum. 69, 3852-3866 (1998).
     Analyses previously overlooked dynamic effects in computer controlled force measuring devices, and measures the collision process with molecular resolution.
  7. A. Carambassis, L. C. Jonker, P. Attard, and M. W. Rutland, Forces Measured Between Hydrophobic Surfaces due to a Sub-microscopic Bridging Bubble, Phys. Rev. Lett. 80, 5357-5360 (1998).
     First measurement of the force due to a single bridging nanobubble.
  8. A. Feiler, P. Attard, I. Larson, Calibration of the Torsional Spring Constant and the Lateral Photodiode Response of Friction Force Microscopes, Rev. Sci. Instrum. 71, 2746-2750 (2000).
     First quantitative technique for calibrating the atomic force microscope in friction mode.
  9. P. Attard, The Explicit Density Functional and its Connection with Entropy Maximisation, J. Stat. Phys. 100, 445-473 (2000).
     Contains a generalisation of Boltzmann's entropy to unequal microstates, and a physical interpretation of thermodynamics and statistical mechanics that is based upon entropy.
  10. P. Attard, Interaction and Deformation of Viscoelastic Particles. I. Non-adhesive Particles, Phys. Rev. E 63, 061604 (2001).
      First soft contact theory for viscoelastic particles.

  Vita
  I graduated from the University of New South Wales in 1984 with a BSc, majoring in mathematical physics. My PhD was at the Australian National University (1985-1988). Under the supervision of John Mitchell, I worked on the electric double layer, calculating the force between two charged surfaces in the presence of electrolyte. Mainly analytic techniques were used, based essentially upon density functional theory. The effects of electrostatic correlations and dielectric images were explored within the restricted primitive model, as a perturbation to the Poisson-Boltzmann approach to the electric double layer. The forces due to correlations between dipolar surfaces was also examined. The motivation for the topic of the PhD came from the force measurements carried out in the department (Applied Mathematics), which interest in colloid science continues to this day. Although my work is fundamentally theoretical, my preference is for projects that have measurable consequences, and that have some application in the real world.

  My first post-doctoral appointment was in France ( Centre Recherche Paul Pascal, in Bordeaux, May-December, 1988), where I developed a method for solving the spherically inhomogeneous Ornstein-Zernike equation. This geometry enables a variety of systems to be modelled, such as fluids in spherical pores, or a vapor bubble in a liquid, or the fluid about a colloidal sphere. I in fact used the method to obtain triplet distribution functions for hard-sphere and for Lennard-Jones fluids. (According to M\"uller and Gubbins, `Of the available theories only [Attard's] PY3 theory is able to reproduce very accurately the simulation data over a wide range of conditions' [ Mol. Phys. 80, 91 (1993)].)

  I went on to work for two and a half years with Gren Patey in Canada, (University of British Columbia), where I learnt integral equation methods for molecular fluids, and applied this to study the interaction between two charged macrospheres in a molecular aqueous solvent. In addition we developed a singlet hypernetted chain method for treating the interaction between planar surfaces, which reflects my interest in inhomogeneous fluids and in applications in colloid science. We later did some little work on surface forces in near-critical fluids, including a grand canonical Monte Carlo simulation (with Dan Berard) on separation-induced cavitation and the consequent solvation force in slit pores.

  I returned to Australia in September of 1991, for an Australian Research Council postdoctoral fellowship (in the Department of Applied Mathematics, RSPhysSE, ANU), for which I studied fluids that interacted with three-body potentials (integral equation and Monte Carlo simulation). I also worked with John Parker on a quantitative comparison of theory and experiment for oscillatory solvation forces, and also on a method for accounting for elastic deformation in surface force measurements.

  I took up a Queen Elizabeth II research fellowship in the Department of Physics, ANU, in December of 1992. In the four years there I worked on Monte Carlo simulation methods for inhomogeneous fluids, theories for the measured long-ranged attractions between inert surfaces in water, and integral equation techniques for treating uniform molecular and polymeric fluids. I then returned to the electric double layer and the forces between charged surfaces in electrolyte, (with Stan Miklavcic), and I have written a comprehensive review of primitive models of that field. My final work at ANU was on the fundamental formulation of the isobaric ensemble, and on linear aggregation.

  Toward the end of 1996 I moved my QEII to the School of Chemistry at the University of Sydney, where I initially worked on a grand canonical simulation method that avoided particle insertions. Concurrently I was involved in collaborative efforts aimed at comparing integral equation, simulation, and experimental estimations of the entropic potential in athermal fluids, and in calculating the information entropy of signals.

  A major motivation for moving to Sydney was to work with Mark Rutland and his surface force measuring group. We started out measuring van der Waals forces in air, and ended up pinpointing several artifacts in the MASIF surface forces apparatus, as well as demonstrating a novel method for measuring the the collision of two bodies in real time with molecular resolution. The analaysis and measurements were extended to the atomic force microscope, where it was shown that friction rather than inertia had the major dynamic effect.

  For a number of years I had been interested in the long-ranged attractions measured between hydrophobic surfaces, and while I was at Sydney I carried out with Rutland atomic force measurements that showed a sub-microscopic bubble bridging the surfaces [A. Carambassis, L. C. Jonker, P. Attard, and M. W. Rutland, Forces Measured Between Hydrophobic Surfaces due to a Sub-microscopic Bridging Bubble, Phys. Rev. Lett. 80, 5357-5360 (1998)]. This confirmed in a very direct fashion the proposal by me that such bubbles were the origin of this puzzling phenomenon [J.L. Parker, P.M. Claesson, and P. Attard, Bubbles, Cavities, and the Long-Ranged Attraction between Hydrophobic Surfaces, J. Phys. Chem. 98, 8468-8480 (1994)]. A popular account of this mysterious force is given here.
  

  In March of 1998 I moved my senior research fellowship to the Ian Wark Research Institute at the University of South Australia. The direction of my own research at this time is moving increasingly toward understanding entropy and its role in the formulation of statistical mechanics and of thermodynamics. To this end I initially explored the philosophical basis of randomness and probability in the context of Bayesian statistics. More recently I have abandoned this subjective approach, and with the fervour typical of any convert, I now espouse the objective interpretation of entropy, and have founded a derivation of thermodynamics and statistical mechanics upon it.

  At the Ian Wark I have also had the opportunity to work with experimentalists, notably Ian Larson. With Larson and Adam Feiler, I developed a method for calibrating friction measurements made with the atomic force microscope (friction force microscopy), [A. Feiler, P. Attard, I. Larson, Calibration of the Torsional Spring Constant and the Lateral Photodiode Response of Friction Force Microscopes, Rev. Sci. Instrum. 71, 2746-2750 (2000)]. I believe that our method will eventually become the standard calibration technique for this device. Quantitative measurements of friction on the molecular scale are currently being performed, and I am attempting to relate them to the adhesion and elastic deformation of the surfaces, calculated using the techniques described above.

  At the beginning of 2000, the Australian Research Council named the Ian Wark Research Institute The Special Research Centre for Material and Particle Interfaces. I lead one of the six themes of the SRC, namely 'Microscopic Particles, Bubbles, and Droplets'. A significant part of the research of the SRC deals with soft matter, and the focus of this theme is to quantitatively account for the effects of surface deformation during particle interaction, and to delineate the consequences for measurement and for applications. Work has commenced initially with emulsion droplet stability, with elastic particle adhesion, and with bubble interactions.

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