The atmosphere is loaded with tiny suspended particles called aerosol, ranging in size from nanometres to micrometres, and consisting of a great variety of materials. The main strand of my research centres on understanding the origins of these particles. Many are formed by condensation of gas phase precursors, by a process called nucleation. Each particle starts out as a cluster of molecules, and the stability of these clusters is key to their rate of formation. However, this stability defies all textbook material properties, since the clusters are so small. Developing theoretical models of clusters is therefore key to making progress.
My theoretical work on the nucleation of phase transitions applies to other areas too, including protein aggregation, biomolecular structural changes, colloidal crystallisation and even stock market dynamics. A particular application here is the behaviour of the nuclear pore complex, a structure that operates as a discriminatory gateway between nucleus and cytoplasm.
I also take an interest in the fundamental nature of irreversible processes, of which nucleation is an example, and in particular the concept of entropy generation. This has included work on stochastic thermodynamics and fluctuation relations that emerge in models described by particle velocities and positions, an example of which is thermal conduction.
A cluster of 67 molecules of nonane, a substance similar to the octane found in petrol, is glimpsed in a computer simulation just after the loss of one of its constituents. The colours are artificial and serve to distinguish the molecules. We can measure the lifetime for such an evaporation event at room temperature to be several tens of nanoseconds. This is very fleeting indeed, but not so short as to make it improbable that a molecule from the surrounding vapour might stick to the cluster first. It is only by such random growth of clusters by condensation, against the natural tendency for the cluster to evaporate, that fresh particles are formed in the atmosphere, in a process known as nucleation.
D. Osmanovic, J. Bailey, A.H. Harker, A. Fassati, B.W. Hoogenboom and I.J. Ford "Bistable collective behavior of polymers tethered in a nanopore", Phys. Rev. E. 85 (2012) 061917.
R.E. Spinney and I.J. Ford "Entropy production in full phase space for continuous stochastic dynamics", Phys. Rev. E. 85 (2012) 051113
R.E. Spinney and I.J. Ford "Nonequilibrium thermodynamics of stochastic systems with odd and even variables", Phys. Rev. Lett. 108 (2012) 170603
C.M. Losert-Valiente Kroon and I.J. Ford, "Becker–Döring rate equations for heterogeneous nucleation, with direct vapour deposition and surface diffusion mechanisms", Atmos. Res. 101 (2011) 553.
J.S. Bhatt and I.J. Ford, "Investigation of MgO as a candidate for the primary nucleating dust species around M-stars'', Monthly Notices of the Royal Astronomical Society 382 (2007) 291-298.
H.Y. Tang and I.J. Ford, "Microscopic simulations of molecular cluster decay: does the carrier gas affect evaporation?'', J. Chem. Phys. 125 (2006) 144316.
I.J. Ford and S.A. Harris, “Molecular cluster decay viewed as escape from a potential of mean force”, J. Chem. Phys. 120 (2004) 4428-4440. download
I.J. Ford, “Statistical mechanics of nucleation: a review”, Proc. Instn Mech. Engrs 218 Part C: J. Mech. Eng. Sci. (2004) 883-899. download
S. Khakshouri and I.J. Ford, “Thermodynamics of attractive hard rods: a test of mean field density functional theory”, J. Chem. Phys. 121 (2004) 5081-5090. download