Programme

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The talk schedule can be downloaded as a pdf file here.

Debra J. Bernhardt (Searles)	University of Queensland	Nonequilibrium flow in nanopores (keynote)
		Fluids in small nanopores have properties that differ from bulk fluids at the same state point due to the restriction of motion, wall-fluid interactions and layering effects, especially close to the wall. Of particular interest is the change in rheological properties and nonequilibrium flow due to confinement. It has been found that the onset of nonlinear behaviour can occur at lower flow rates when a fluid is confined, and when this occurs linear response theory cannot be applied and the flux will not longer be proportional to the force. We show how nonlinear response theory [1] can be applied to these systems and how it can be used to improve the results obtained from simulations, if nonlinearity sets in at relatively low forcing. Simulations of Poiseuille flow will be used to demonstrate the behaviour. [2] Study of lubrication is an area where changes in behavior due to flow is important. In many cases lubrication occurs at high strain rates and under high confinement. In this work we evaluate the response of a fluid under shear flow in a nanopore. The movement of the boundaries in opposite directions induces the shear. The viscous heat generated inside the pore is removed by a thermostat applied exclusively to the atomic walls, leaving the dynamics of the fluid as realistic as possible. [3,4] We will also discuss the characterization of slip in these small pores. [1] D. J. Evans, D. J. Searles and S. R. Williams, J. Chem. Phys; 128, 014506 (2008). [2] S. J. Brookes, J. C. Reid, D. J. Evans and D. J. Searles, Journal of Physics: Conference Series297, 012017 (2011). [3] S. Bernardi, S. J. Brookes, D. J. Searles and D. J. Evans, Journal of Chemical Physics, 137, 074114 (2012). [4] S. Bernardi and D. J. Searles, Molecular Simulation, doi: 10.1080/08927022.2015.1049174, accepted (May 2015).
Gary Bryant	RMIT University	Synchrotron SAXS and Neutron studies of Structure Factors in Hard Sphere Suspensions
Pierluigi Cesana	Kyushu University (Australia Branch)	Effective response of elastic liquid crystal membranes
		Nematic elastomers (NEs) are polymeric materials with embedded nematic mesogens. Their mechanical response is governed by the coupling of rubber elasticity with the orientational order of a liquid crystalline phase. NEs exhibit large spontaneous deformations, which can be triggered and controlled by many different means (temperature, electric fields, irradiation by UV light). These properties make them interesting as materials for fast soft actuators and justify the considerable attention that they have attracted in recent years. For NEs in the thin membrane limit, an interplay of material and structural non-linearities is observed. These membranes can display fine-scale features both due to wrinkling that one expects in thin elastic membranes and due to oscillations of the local optical axis that one expects in liquid crystal elastomers. In this talk I will present an energy-minimization approach based on homogenization to describe the effective energy density of thin membranes of liquid crystal elastomers by providing a detailed characterization of the fine-scale features. If time allows, I will show how to model the space-time evolution of a microstructure as a Branching Random Walk process. This modeling work is inspired by experimental investigation of the jerky character of martensitic transformations occurring in shape memory alloys. Comparisons are reported for numerical and analytical solutions and experimental observations.
Derek Chan	University of Melbourne and Swinburne University of Technology	Modelling the collision between a rising bubble and a deformable flat interface
		A millimetre size bubble rising in water can reach terminal velocities the corresponds to Reynolds number ~600. The collision of such bubbles with a flat air-water interface that can deform will result in bounces before the bubble coalesces with the surface. The dimension of the interaction zone between the bubble and the air-water interface is in the micrometer range whereas the collision dynamics are controlled by deformations and interfacial separations down to the nanometre range. The almost 6 orders of magnitude variation in the important length scales of the problem poses significant challenge to approaches based on direct numerical computation. A continuum model with no adjustable parameters has been developed that is able to predict collision and bounces observed for such bubble interaction in water and in alcohol. The ability to predict the terminal velocity accurate is an important pre-requisite in obtaining good quantitative agreement between theoretical predictions and experimental results.
Nathan Clisby	University of Melbourne	Monte Carlo simulation of polymers attached to a surface
		We describe recently developed Monte Carlo techniques which allow for extremely accurate estimates of the universal properties of polymers attached to a surface via study of self-avoiding walks. The underlying idea of “scale-free moves” may be usefully applied to other polymer systems.
Peter Daivis	RMIT University	Nonlocal constitutive equations for shear flow in fluids with strongly inhomogeneous density and velocity profiles
		We present new theoretical expressions for the density, strain rate and shear pressure profiles in strongly inhomogeneous fluids undergoing steady shear flow with periodic boundary conditions. The expressions that we obtain take the form of truncated functional expansions, where the independent variables are the spatially varying longitudinal and transverse forces that we apply in non-equilibrium molecular dynamics simulations. The longitudinal force is directed along the y-axis, is composed of one or more sinusoidal components that vary in the y-direction and it produces strong density inhomogeneity. The transverse force is directed along the x-axis and varies sinusoidally in the y-direction and it produces shear flow. The functional expansions define new material properties, the response functions, which characterise the system's non-local response to the longitudinal force and the transverse force. We find that the longitudinal force, which is mainly responsible for the generation of density inhomogeneity, also modulates the strain rate and shear pressure profiles. Likewise, we find that the sinusoidal transverse force, which is mainly responsible for the generation of sinusoidal shear flow, can also modify the density. These couplings between density inhomogeneity and shear flow are also characterised by non-local response functions. We conduct non-equilibrium molecular dynamics simulations to calculate all of the response functions needed to describe the response of the system for weak shear flow in the presence of strong density inhomogeneity up to the third order in the functional expansion. These response functions are then substituted directly into the truncated functional expansions and used to predict the density, velocity and shear pressure profiles. The results are compared to the directly evaluated profiles from molecular dynamics simulations and we find that the predicted profiles from the functional expansions give excellent agreement with the directly computed density, velocity and shear pressure profiles.
Sergio De Luca	UNSW	Studying of the anticancer drugs - Dendrimer interactions: a molecular dynamics approach
		The present study investigates the physical mechanism underlying the interactions of anticancer drugs with peptide dendrimers. Our molecular dynamics results show that the dendrimers used in this work have potential applications in cancer therapy and drug delivery. Peptide dendrimers are macromolecules with the structure composed of branches and a core formed by amino acids linked via peptide/amide bonds. The dendrimers studied here were synthesized and used to understand the solubility, permeability and deposition of anticancer drugs such as 5-Fluorouracil through the skin. The experimental data have demonstrated that the solubility of drugs in water and its permeability across the human epidermis is improved when used in conjunction with peptide dendrimers.
Ian Douglass	University of Sydney	The role of particle softness in amorphous atomic alloys
		A key property of glass forming alloys, the anomalously small volume difference with respect to the crystal, is shown to arise as a direct consequence of the soft repulsive potentials between metals. This feature of the inter-atomic potential is demonstrated to be responsible for a significant component of the glass forming ability of alloys due to the decrease in the enthalpy of fusion and the associated depression of the freezing point arising from the softening of the inter-atomic repulsion.
Denis J Evans	ANU	Dissipation and the Foundations of Classical Statistical Thermodynamics (keynote)
		In this talk I discuss logical inconsistencies concerning the application of Clausius' Inequality to irreversible thermodynamic processes. We then go on to discuss the derivation of the postulates of statistical thermodynamics from the laws of mechanics and the axiom of causality - that cause precedes effect. In order to do this we discuss three main theorems: the Fluctuation Theorem [1] that gives the relative probability that path integrals of the dissipation take on equal but opposite values; the Dissipation Theorem [2] that relates nonequilibrium averages to time integrals of correlation functions involving dissipation function and the Equilibrium Relaxation Theorem [3] that shows how nonequilibrium systems can, under specified circumstances, relax to that quiescent state we call equilibrium. The mathematically defined dissipation function is central to each of these theorems. [4] It enables us, for the first time, to give a mathematical definition of an equilibrium system. Finally we show how the Gibbs equation of classical thermodynamics can be derived easily using our Equilibrium Relaxation Theorem. References 1. Evans DJ and Searles DJ, The fluctuation theorem, Advances in Physics, 2002, 51,1529-1585. 2. Evans DJ, Searles DJ and Williams SR, On the fluctuation theorem for the dissipation function and its connection with response theory J. Chem. Phys. 2008, 128, 014504, ibid, 2008, 128, 249901 3. Evans DJ, Searles DJ and Williams SR, Dissipation and the relaxation to equilibrium, J. Stat. Mech., 2009, P07029 4. Reid JC, Williams SR, Searles DJ, Rondoni L and Evans DJ, Fluctuation relations and the foundations of statistical thermodynamics: A deterministic approach and numerical demonstration, Nonequilibrium Statistical Physics of Small Systems: Fluctuation Relations and Beyond, Editors R. Klages, W. Just, C. Jarzynski, 2013 Wiley-VCH, 57-82.
Kirill Glavatskiy	University of Queensland	Is local equilibrium sufficient for irreversible systems with delayed response?
		Validity of local equilibrium has been questioned for non-equilibrium systems which are characterized by delayed response. In particular, for systems with non-zero thermodynamic inertia, the assumption of local equilibrium leads to negative values of the entropy production, which is in contradiction with the second law of thermodynamics. In this talk we address this question by suggesting a variational formulation of irreversible evolution of a system with non-zero thermodynamic inertia. We introduce the Lagrangian, which depends on the properties of the normal and the so-called "mirror-image" systems. We show that the standard evolution equations, in particular the Maxwell-Cattaneo-Vernotte equation, can be derived from the variational procedure without going beyond the assumption of local equilibrium. We also argue, that the second law of thermodynamics in non-equilibrium should be understood as a consequence of the variational procedure and the property of local equilibrium. For systems with instantaneous response this leads to the standard requirement of the local instantaneous entropy production being always positive. However, if a system is characterized by delayed response, the formulation of the second law of thermodynamics should be altered. In particular, the quantity, which is always positive, is not the instantaneous entropy production, but the entropy production averaged over a proper time interval.
Marsel Gokovi	Griffith University	Mass transport rates in confined spaces
		Theoretical predictions have been developed using statistical mechanics for the zero-density limit transport of gases in regular micropores. These results appear to be valid in some applications under standard laboratory conditions, and match existing data well. These results have been extended, using ad hoc combinations of statistical mechanics and Navier-Stokes, to model density dependence, with reasonable success. We have attempted to use statistical mechanics to develop a density-dependent extension to the theory, valid at low densities, and show how we have successfully used our theory to model density-dependent transport in a simple pore model.
Stephen Hannam	RMIT University	Molecular dynamics calculations of intermediate scattering functions for a model colloidal fluid with explicit solvent.
		Colloidal suspensions are extremely useful model systems for the study of nucleation and vitrification. They show a phase behavior that can be mapped onto a hard-sphere (HS) system, but they also exhibit a glass transition. [1,2] The common methods used to study these systems experimentally are dynamic light scattering (DLS) and x-ray photon correlation spectroscopy (XPCS). As a complement to light scattering experimental results, Molecular Dynamics (MD) simulation was used to study a model colloidal suspension at a range of concentrations from the dilute limit up to the freezing point. We modelled the colloidal particles with a Weeks-Chandler-Anderson (WCA) potential modified to include a hard-core, while the solvent was a simple WCA fluid. The colloid/solvent size ratio was set to 4.03:1 and the mass ratio was 50:1. In order to remove strong depletion effects inherent in binary systems with comparable size ratios, modified colloid-solvent interaction parameters were used. With the modified interaction parameters the liquid structure, phase behavior and crystal structure were shown to match experimental and theoretical HS systems. [2] To study the dynamical behavior of the model, the velocity autocorrelation function was computed and was shown to exhibit behavior which matches experimental results more closely than the single component HS model (i.e. velocity reversals at low concentrations).[2] The intermediate scattering functions were calculated over the same range of concentrations giving results in good agreement with light scattering experiments. [1] P. N. Pusey and W. van Megen, Nature London 320, 340 (1986). [2] W. van Megen and S. M. Underwood, Nature London 362, 616 (1993). [3] S. D. W. Hannam, P. J. Daivis and G. Bryant, Molecular Simulation (2015).
Peter Harrowell	University of Sydney	The Statistical Mechanics of Liquid Structure
		We investigate the connection between the geometry of Favoured Local Structures (FLS) in liquids and the associated liquid and solid properties. We introduce a lattice spin model - the FLS model on a face centered cubic lattice - where this geometry can be arbitrarily chosen among a discrete set of 115 possible FLS [1]. We find crystalline groundstates for all choices of a single FLS. Sampling all possible FLS's, we identify the following trends: (i) low symmetry FLS's produce larger crystal unit cells but not necessarily higher energy groundstates, (ii) chiral FLS's exhibit peculiarly poor packing properties, (iii) accumulation of FLS's in supercooled liquids is linked to large crystal unit cells, and (iv) low symmetry FLS's tend to find metastable crystal structures on cooling. Apart from the depression of the freezing point due to the high energy of their crystals, we find no compelling evidence to suggest that low symmetry FLS's exert any particular influence in stabilizing the supercooled liquid. In contrast, when we extend our model to include multiple degenerate FLS's we find that the stability of the supercooled liquid is systematically enhanced as we increase the multiplicity of the FLS's. 1. P. Ronceray and P. Harrowell, Soft Matt. 11, 3322 (2015)
Emma Hodges	Monash University	Fluctuation theorems to probe equilibrium properties of non-equilibrium work trajectories using simulation
		Numerical simulations of a Langevin equation are used to model the detachment of a particle, using an optical tweezer, from a substrate to which it is bound. The external driving force arises from the combined optical tweezer and substrate potentials, and thermal fluctuations are taken into account by a Brownian force. The Jarzynski and Crooks fluctuation theorems are applied to obtain the equilibrium free energy of binding from non-equilibrium work trajectories for various tweezer pulling rates. Umbrella sampling is used to obtain the equilibrium probability of particle escape for a variety of trap potentials. The model is motivated by tweezer experiments of cell binding to membranes, where the simulated situation corresponds to the limit of weak binding.
David Huang	University of Adelaide	Surface effects in nanofluidic energy harvesting (keynote)
		With an external input of energy, a porous membrane can be used to separate ions from salt water to produce fresh water in the process of desalination. Conversely, the inverse process in which salt and fresh water are mixed across a porous membrane can be used to generate energy. This energy source is potentially significant, with the free energy of mixing of fresh and salt water in estuaries around the world equivalent to about 20% of global energy needs. This presentation examines the theoretical limits to the conversion rate and efficiency of salinity-gradient-driven conversion, focussing in particular on the impact of hydrodynamic slip on the process.
Ahmad Jabbarzadeh	University of Sydney	Surface Induced Crystallization of Polymers
		Crystallization is a ubiquitous phenomenon whose understanding is difficult. For monatomic (e.g. metallic), and molecular systems (small or large) the focus of research has been mainly on bulk crystallization. Surface induced crystallization is an important process in interaction of nucleating agents, colorants, and additives with polymers. In this talk I will presents molecular dynamics simulations of crystallization of a model polymer, in bulk, on smooth surfaces, and on rough surfaces and the results will be compared.
Ravi Jagadeeshan	Monash University	Coil-stretch hysteresis in polymer solutions
		Can a polymer solution have two values of stress at the same value of strain rate? Such a possibility would have significant consequences for many industrial processes that involve polymer solutions, such as ink-jet printing and the spinning of nano-fibres. However, none of the current models for polymer solutions, which are used to solve for the flow of polymer solutions, admits such a possibility. Yet nearly 40 years ago, de Gennes (Nobel prize in Physics, 1991) predicted that polymer solutions could have different states of stress at the same strain rate if their deformation histories were different. It took 30 years for experimental confirmation of de Gennes' prediction to be achieved by Steve Chu (Nobel prize in Physics, 1997) and Eric Shaqfeh at Stanford, using stained DNA molecules. Until recently, the influence of the concentration of the polymer solution on such hysteretic behaviour has been unknown, since de Gennes' early theory was confined to the limit of dilute solutions. I will show in this talk, through experiments and simulations, that the situation becomes more complicated and intriguing as the polymer concentration increases and as the flow type varies from extensional to shear flow. The phenomenon of hysteresis in polymer solutions provides a fascinating insight into the influence of non-linear effects on the molecular scale on macroscopic solution properties.
Matthew King	Griffith University	Chaos and fluctuations in a modified Ehrernfest wind-tree model
		The nonequilibrium Ehrenfest wind-tree model is an interesting model for testing fluctuation relations, because it was believed to be a non-chaotic system that obeyed fluctuation relations. More recently, it was shown that over short times the dynamics is chaotic, but at almost all field strengths trajectories are eventually periodic. We have considered perturbations of the Ehrenfest wind-tree model that do not permit these eventually periodic orbits, and studied the Lyapunov exponents and fluctuation relations in these systems. For some perturbations the system remains chaotic for all times investigated, and the fluctuation relations are obeyed. However, we will also present results on some systems which appear to remain non-trivially non-chaotic at long times. Joint work with Owen Jepps
Naida M. Lacevic	University of Melbourne	Viscoelasticity of glycerol at ultra-high frequencies investigated via molecular dynamics simulations
		The viscoelastic behavior of simple Newtonian liquids, such as glycerol, was shown recently to exert a strong effect on nanomechanical devices. We present a calculation of the shear and longitudinal moduli of glycerol in the gigahertz frequency regime and temperature range between 273 K and 323 K using classical molecular dynamics simulations. The full frequency spectra of shear and longitudinal moduli of glycerol between 0.5 GHz and 100 GHz at room temperature are computed, which was not previously available from experiments or simulations. We also demonstrate that the temperature dependence of the real parts of the shear and longitudinal moduli agree well with available experimental counterparts obtained via time-domain Brillouin scattering (TDBS). This work provides new insights into the response of molecular liquids to ultra-high frequency excitation and opens a new pathway for studying simple liquids at high frequencies and strain rates. This is joint work with John E. Sader.
Daniel R. Ladiges	University of Melbourne	Frequency-domain Monte Carlo method for oscillatory gas flows
		Gas flows generated by resonating nanoscale devices inherently occur in the non-continuum, low Mach number regime. Numerical simulation of such flows presents a considerable challenge, which has motivated the development of several Monte Carlo methods for low Mach number flows. We present a frequency-domain Monte Carlo method for oscillatory low Mach number gas flows, based on the linearized Boltzmann equation. This circumvents the need for temporal simulations, providing direct access to both amplitude and phase information using a pseudo-steady algorithm. The proposed method is demonstrated with several examples, and good agreement is found with both existing time-domain Monte Carlo methods and accurate numerical solutions of the Boltzmann-BGK equation. Analysis of these simulations, using a rigorous statistical approach, shows that this frequency-domain method provides a significant improvement in computational speed compared to existing time-domain Monte Carlo methods. Joint work with John E. Sader
Lang Liu	University of Queensland	Interfacial resistance and size-dependent transport coefficients in nanoporous materials
		Quantitative estimation of interfacial barriers to transport at fluid-crystal interfaces located at the entry and exit boundaries is critical for accurate determination of the permeabilities of adsorptives in nanoporous materials, particularly carbon nanotubes1. Molecular simulation methods such as dual-control volume grand canonical molecular dynamics (DCV-GCMD)2 and equilibrium molecular dynamics (EMD)1,3,4 have previously used to tackle this issue; however, existing approaches have involved approximations or are specific to low loadings or very small driving forces. In particular, it is often assumed that the internal transport coefficient is that obtained from simulations using a periodic system, thereby overlooking any size dependence. Here, we report our novel EMD method, validated by DCV-GCMD simulations, to quantitatively determine interfacial and size-dependent intra-crystalline resistances for carbons without any approximation. This method is also readily to extend to all the ranges of loadings and driving forces and all nanoporous materials. We investigate the internal and external resistances to transport of CH4 in finite length CNTs having the diameter of 1.36nm, at ambient temperature, considering also an external bulk region. It is found that overall transport coefficients of CH4 are 2-3 orders of magnitude lower than the corresponding values for infinitely long CNTs. We determine the interfacial resistance using the one-way flux method4, and extract the size-dependent intra-crystalline resistance from the overall resistance using our novel technique. We find that while the interfacial resistance is independent of CNT length, the intra-crystalline resistance per unit length is a decreasing function of length. Consequently, the internal diffusivity of CH4 increases with increase in CNT length. However, the ratio of interfacial resistance to the overall resistance is an increasing function of pressure, and is close to 25% for CH4 at 15 bar in a 50 nm long (10,10) CNT. Joint work with Suresh Bathia. 1 Newsome, D. A.; Sholl, D. S. Nano Letters 2006, 6, 2150- 2153. 2 Arya, G.; Maginn, E. J.; Chang, H.-C. J. Phys. Chem. B 2001, 105, 2725-2735. 3 Zimmermann, N. E.; Smit, B.; Keil, F. J. J. Phys. Chem. C 2012, 116, 18887-18883. 4 Newsome, D. A.; Sholl, D. S. J. Phys. Chem. B 2005, 109, 7237-7244.
Adrian Menzel	RMIT University	Planar Poiseuille flow of highly confined polymer solutions
		When polymer solutions are confined to small channels of the order of nanometers in width, they exhibit unexpected behaviour. These systems can be difficult to investigate experimentally, but molecular dynamics simulations now have the power and flexibility to allow us to investigate them. In this work, we simulate coarse- grained model polymer solutions in highly confined channels both in equilibrium and undergoing Poiseuille flow, using molecular dynamics. We find that the temperature, velocity, and concentration profiles across the channel vary with flow rate. In particular, increasing the flow rate leads to an increase in the wall-mediated polymer depletion region. We show that for sufficiently large channel-widths a bulk-like flow can be achieved that behaves according to classical continuum equations for velocity and temperature. For narrower channels, we find that the classical Navier-Stokes- Fourier description of fluid flow breaks down. Finally, we have also implemented an algorithm to calculate the local pressure tensor across the channel, and have studied the variation of the first normal stresses with position and compared the results with predictions of the first normal stress coefficients from equilibrium molecular dynamics simulations.
Guy Metcalfe	Swinburne University of Technology and Monash University	Entropy Production, Fluctuations and the Slow Approach to Equilibrium in a Mechanical Analogue to Soft Matter: the Soft Billiard
		Billiard dynamical systems have played a foundational role in statistical mechanics and dynamical systems theory due to their clean definition, rich dynamics and direct application to many problems in physics. In traditional billiard models a point particle moves force-free along a geodesic line and specularly reflects from a boundary. The new wrinkle that I put into this old system is a soft boundary. If the boundary is soft, then the particle will exchange energy with its environment on a scale that fits the definition of a small system, which puts this soft mechanical nonequilibrium system into the same thermodynamic category as molecular motors and large molecules such as DNA or proteins. This talk will discuss results from a driven soft billiard experiment. With a small LED embedded in the particle, superposed light streak photos measure the probability distribution function of particle position, from which one can calculate the information entropy as a function of time, energy input (equivalent to temperature) and softness of the boundary. The approach to equilibrium is very slow, exhibiting a stretched exponential form. As the system is brought to the point of zero particle motion, entropy production is dominated by large and rare fluctuations and the time to attain equilibrium diverges.
Gerald Pereira	CSIRO	Brazil nuts and more
		Understanding segregation in granular materials is important not only scientifically but also in industrial and geophysical applications. Discrete particles which make up a granular material will differ in size, density, shape and frictional properties. When such materials are made to flow (e.g. under a shearing force) they will tend to segregate based on these intrinsic properties. Here we seek to understand the physical mechanisms which underly this segregation. We discuss both numerical and theoretical models which describe the basic physical flows.
Mihail N. Popescu	Max Planck Institute for Intelligent Systems	Effective interaction between active colloids and fluid interfaces
		In the last decade significant attention has been paid to micrometer sized particles capable of self-induced motility by promoting at their surfaces catalytically activated chemical reactions in the surrounding solution. They are seen as promising candidates for the development of novel techniques such as chemical sensing or water treatment. There are many application relevant cases in which the suspension containing active colloids is bounded by a fluid-fluid interface, and thus the colloidal particles may reside in the vicinity of the interface or get near the interface during their motion. Here we present theoretical evidence that, in such a case, chemically active (or locally heated) spherical particles experience a very strong, long-ranged effective force field due to the Marangoni stresses self-induced at the interface. This force of hydrodynamic origin gives rise to a drift of the particle towards or away from the fluid interface (depending only on how the tensioactive agent affects the interface) on time scales which can be orders of magnitude shorter than those associated with Brownian diffusion. In particular, this can facilitate significantly the process of particle adsorption towards the interface and therefore has potentially important implications for, e.g., the subsequent self-assembly of particles at fluid--fluid interfaces.
Andrey Pototsky	Swinburne University of Technology	Instability modes and regular density patterns in a colony of self-propelled surfactant particles covering a thin liquid layer
		We consider a colony of point-like non-interacting self-propelled surfactant particles (swimmers) that covers a thin liquid layer on a solid support. Although the particles predominantly swim orthogonally to the free film surface, their motion also has a component parallel to the film surface. The coupled dynamics of the swimmer density and film height profile is captured in a long-wave model allowing for diffusive and convective transport of the swimmers (including rotational diffusion). The dynamics of the film height profile is determined by the upward pushing force of the swimmers onto the liquid-gas interface that always acts destabilising, by the solutal Marangoni force due to gradients in the swimmer concentration that always acts stabilising, and finally by the rotational diffusion of the swimmers that can act stabilising or destabilising. After reviewing and extending the analysis of the linear stability of the flat film with homogeneous swimmer density, we analyse the nonlinear behaviour and show that non-interacting point-like swimmers self-organise in highly regular (standing, travelling and modulated waves) and various irregular density patterns.
Prabhakar Ranganathan	Monash University	The mechanobiology of construction and operation of traffic networks in interstitial swarms of bacteria
		Many pathogenic bacteria such as Pseudomonas aeruginosa colonise interstitial spaces between tissue surfaces. When cells reach a sufficient density, they appear to use a range of collective strategies to spread quickly as a monolayer to lay the foundations for a mature biofilm. It has been recently shown (Gloag et al., PNAS, 110, 11541-11546, 2013) that, in P. aeruginosa colonies growing at an agar-glass interface, cells at the edge of advancing colonies self-organize into distinctive networks of trenches as they plough through the soft agar. Cells behind these bulldozer rafts secrete extracellular DNA (eDNA) that through an as-yet-unknown mechanism appears to regulate traffic to ensure a smooth supply of cells from the colony interior to the advancing edge. Incorporating DNA-degrading enzymes in the substrate results in traffic grid-lock and considerably slows down the speed of surface colonisation. A generic moving interface model is proposed to explore the interplay between cell motility, active forcing, and mechanical interfacial interactions with a passive medium. The model accounts for the dynamics of nematic orientation of the rod-shaped active particles at the interface. A fingering instability of the edge of the active monolayer as it ploughs its way through the soft substrate could explain the emergence of cell rafts. The merging of rafts and the prevention of cells from aligning perpendicular to trench walls in the colony interior leads to colony morphologies similar to those observed in the experiments. The moving interface model may also be applied to other biological systems such as cytoskeletal-membrane interactions.
Shibu Saw	University of Sydney	Rigidity of matter as a consequence of configurational constraint
Qiang Sun	University of Melbourne	Boundary regularised integral equation formulation of the Debye-Hückel model
		In this talk, I will present a recently developed boundary integral formulation, boundary regularised integral equation formulation (BRIEF). It is an ideal tool to investigate the Debye-Hückel model which is a popular and effective implicit model to describe the electrostatic phenomena in liquids. Compared to the conventional boundary integral method (CBIM), all traditional singular behaviour in the boundary integrals is removed analytically in BRIEF. As a result, BRIEF is able to facilitate the use of higher order surface elements to represent the surface. Also, it can handle near singular behaviour, such as multi-scale problems with extreme geometric aspect ratios and field value calculations near the boundary, without diminished precision.
Andrew Tarzia	University of Adelaide and CSIRO	Design Principles for the Self-Assembly of Porous Materials
		Throughout biology and materials science the process of self-assembly is taken advantage of to build complicated structures that are ubiquitous to life and industry. Commonly this process is non-equilibrium and results in the formation of a functional, complex structure from specific, simple building blocks. Porous materials (examples: MOFs, COFs, PAFs, PCPs, zeolites) are prevalent in the literature due to their immense diversity and potential use in a vast array of applications (examples: sorption and separation, catalysis, electronic devices). General synthetic approaches for porous materials rely upon the use of self-assembly. A coarse-graining procedures is being developed to be used in molecular dynamics simulations that capture the process of self-assembly in porous materials. The coarse-grained model can be applied to a variety of porous materials through simple parameter changes allowing a general understanding of factors affecting self-assembly of porous materials. The model uses rigid-bodies and anisotropic interactions to represent real physical systems. The model is still under development but offers a method to study the self-assembly of a vast array of porous materials with the ability to add or reduce complexity as needed due to the generalised design approach.
Maryna Vlasiuk	Swinburne University of Technology	Molecular simulation of the thermodynamic properties of liquid neon
		Liquid neon is an interesting but difficult system to study. The temperatures of liquid state for neon are low, namely 25K to 44K. From the first principle point of view, much effort has been made to design very accurate intermolecular potentials. On the other hand, discussions [1, 2] about neon being distantly associated with the corresponding state family allow the use of simple models for describing properties of neon. In our study we use intermolecular potentials of different origins and quality. These are two accurate ab initio potentials [3,4], an empirical potential derived for noble gases [5] but not specifically for neon, and a simple Lennard-Jones model, which we use as a reference. To account for quantum effects we follow the approach introduced by Feynman and Hibbs [6] and employ the quantum effective potentials. We run a number of Monte Carlo simulations in the canonical ensemble [7] for generating our results. For calculating thermodynamic properties (heat capacities, compressibilities, speed of sound, etc.) we use Lustig's formalism [8]. Our study demonstrates that the empirical BFW potential [5] with quantum cor- rection achieves the best agreement with experimental data, surpassing the accuracy of `tailor-made' ab initio potentials. [1] J. D. Boer. Physica, 14:139, 1948. [2] P. D. Neufeld and R. A. Aziz. J. Chem. Phys., 59:2234, 1973. [3] R. Eggenberger, S. Gerber, et al. Mol. Phys., 82:689, 1994. [4] K. Leonhard and U. K. Deiters. Mol. Phys., 98(20):1603-1616, 2000. [5] J. A. Barker, R. A. Fisher, et al. Mol. Phys., 21:657, 1971. [6] R. P. Feynman and A. R. Hibbs. Quantum Mechanics and Path Integrals. McGraw- Hill: New York, 1965. [7] R. J. Sadus. Molecular Simulation of Fluids: Theory, Algorithms, and Object- orientation. Elsevier, Amsterdam, 1999. [8] R. Lustig. Mol. Sim., 37(6):457-465, 2011.
Brad Wells	CSIRO	Towards developing structure-property relationships for tactic methacrylic ester polymers
		Directly simulating the bulk properties of polymers presents a significant computational challenge. Polymers are generally amorphous, and thus able to adopt a wide range of configurations which are sampled in a typical simulation. Despite this complexity however, the bulk properties of polymers can be seen as being effectively encoded within a relatively small number parameters. These parameters include structural features of the polymer chains, internal chain flexibility and non-bonding interactions between chain segments. These are the parameters that are specified in a typical molecular dynamics simulation. Understanding how each of these factors influences the bulk properties of the polymer may lead to the ability to create polymers tailored to specific applications. In this paper some preliminary results in attempting to determine structure-property relationships for the methacrylate ester polymers are presented. A particular focus of this work is in determining how the tacticity of the polymer chains can be included in the descriptive model. To investigate the structure property-relationships of the polymers a multi-scale simulation approach is employed, utilising simulations based both on density functional theory and empirical potentials. Some factors that influence bulk properties of the polymers, such as the glass transition temperature are discussed.
David Williams	ANU	The Physics of Threading Rotaxanes and Nanotubes
		Rotaxanes are mechanically linked molecules which consist of rings threaded on a molecular axle with the ends stoppered to prevent the rings from falling off. These have been synthesised for about 50 years, but their physics is only just beginning to be elucidated. They are examples of soft matter in that their behaviour can be dominated by entropy and they can self-organise under the action of weak internal forces. Here we will examine one of the more fundamental problems: How does a rod thread a ring or tube? We will show that event, which is governed by translational and orientational entropy, is in almost all cases of practical interest very rare. The probability obeys simple power laws based on the geometry of the rod/ring/tube system. This work has applications to other areas (polymer translocation, threading of nanotubes), where threading is of importance.
Stephen R. Williams	ANU	Beyond Thermodynamics: Totally Nonequilibrium Relaxation towards Equilibrium
		Equilibrium thermodynamics concludes that a system, which is relaxing towards equilibrium, will feature a monotonic relaxation of the free energy, which will thus be at a minimum when equilibrium is reached. Here we present a detailed study of a fluid relaxing from an initial nonequilibrium state, prepared in the presences of an external field, which causes the density to be inhomogeneous. Unlike the more typical relaxation processes that are studied in science, such as a chemical reaction which obeys transition state theory, the process we consider here is a totally nonequilibrium relaxation. We show how the relaxation can even be non-monotonic for the dissipation function. While this system is at odds with the traditional second law; it does obey the modified second law for the dissipation theorem which may be derived from the fluctuation theorem. In contrast to the traditional one this modified second law explicitly requires an ensemble average, does not require the thermodynamic limit to be taken, and explicitly involves the prior history of the system.
William van Megen	RMIT University	Exposing a dynamical signature of the freezing transition through the sound propagation gap
		The conventional view of freezing holds that nuclei of the crystal phase form in the metastable fluid through purely stochastic thermal density fluctuations. The possibility of a change in the character of the fluctuations as the freezing point is traversed is beyond the scope of this perspective. Here we show that this perspective may be incomplete by examination of the time autocorrelation function of the longitudinal current, computed by molecular dynamics for the hard-sphere fluid around its freezing point. In the spatial window where sound is overdamped, we identify a change in the long-time decay of the correlation function at the known freezing points of monodisperse and moderately polydisperse systems. The fact that these findings agree with previous experimental studies of colloidal systems in which particle are subject to diffusive dynamics, suggests that the dynamical signature we identify with the freezing transition is a consequence of packing effects alone.