Academic staff : Peter Harrowell

Professor Address: School of Chemistry, Building F11 The University of Sydney, NSW, 2006 Australia Email address: p.harrowell@chem.usyd.edu.au Telephone: +61 (2)9351-4102 Fax: +61 (2) 9351-3329

Career Profile:

B.Sc. (University of Sydney)
Ph.D. (University of Chicago)

Areas of interest:

• statistical mechanics
  

• nucleation
  

• crystal growth
  

• rheology of ordered materials
  

• transitions in nonequilibrium systems
  

• computer simulation methods
  

• liquid crystals
  

• glass transitions
  

• theory of highly cooperative dynamics
  

• the physics of biological processes
  

• history of science

Research:

Glass Transition: We are carrying out detailed analysis of the nature of slow relaxation in some simple models of glass forming liquids using computer simulations and theoretical treatments.
In studies of a facilitated kinetic Ising model [Harrowell, Phys.Rev.E, 48, 4359 (1993)] we concluded that the glassy dynamics was the result of an increasing inhomogeneity in the spatial distribution of relaxation kinetics.

This insight has proved a valuable approach to the analysis of structural relaxation in simple liquids [Hurley and Harrowell, Phys.Rev.E, 52, 1694 (1995), J.Chem.Phys., to be published (1996)]. It also provides a valuable general framework with which to relate the range of glass behaviour [Perera and Harrowell, Phys.Rev.E, 54, 1652 (1996)]. We are currently undertaking a detailed study of nature of relaxation and structural fluctuations in supercooled biinary liquid mixtures in 2D using molecular dynamic simulations and theoretical descriptions of the collective processes.

Shear Induced Transitions in Colloidal Suspensions: Extensive nonequilibrium simulations of dilute suspensions of charged colloidal particles have been undertaken with the aim of establishing the correct physical picture of the order/disorder transitions observed experimentally under the influence of shear. We have reproduced the shear induced disordering transition observed in colloidal crystals [Butler and Harrowell, J.Chem.Phys. 103, 4653 (1995)] and established that long wavelength fluctuations play a central role in the transition, unlike its equilibrium analogue. We have also demonstrated that the frequently reported observation of shear induced ordering in simulated liquids CAN arise as an artefact of shearing a liquid through periodic boundary conditions [Butler and Harrowell, J.Chem.Phys. 105, 605 (1996)]. The kinetics of crystallization in a shearing suspension has also been examined [Butler and Harrowell, Phys.Rev.E, 52, 6424 (1996)].

Current work focuses on developing a clearer insight into the coupling of shear flow with structural fluctuations.

The Stabilization of Layered Liquid Crystal Phases: We have just completed a Monte Carlo simulation study of the role of flexible end chains on stabilizing Smectic A and Smectic C phases of liquid crystals. We have demonstrated for the first time that both phases can be stabilized from purely entropic effects [Casey and Harrowell, in preparation]. Ongoing work involves the study of phase transitions in small clusters of mesogens.

Crystal Growth: Our current work involves looking at two questions. The first is the description of crystallization involving density change under conditions of constant N and V (as is often the case). Under these conditions the supercooling is, itself, varying with time [Wild and Harrowell, in preparation]. The second problem considers the relationship between a crystal surface's ability to organize the adjacent liquid and the kinetics of the growth process. Our current work builds on earlier results [Williams, Moss and Harrowell, J.Chem.Phys. 99, 3998 (1993); Moss and Harrowell, J.Chem.Phys. 100, 7630 (1994)] in which we showed that close packed surfaces with short range interactions were unable to fully break the symmetry of the adjacent liquid and hence the growth of these surfaces was impeded.