4th International Conference on Advances in Solidification Processes
8-11th July 2014, Beaumont Estates, Old Windsor, UK

Dr Richard Sear - University of Surrey, UK

Richard Sear
I started my scientific career with a PhD (1995) at the University of Sheffield. The PhD was with George Jackson (who is now at Imperial), and was mainly on calculations of liquid phase diagrams. From 1995 to 1997 I was a postdoc at AMOLF, a research institute in Amsterdam. There I worked with Bela Mulder and Daan Frenkel (who is now at Cambridge). Then I spent one year in the sun at UCLA in Los Angeles, working for Bill Gelbart and Jim Heath (now at Caltech). This was on modelling the self-assembly of Jim’s metal nanoparticles at the water/air interface. I was appointed at the Univesity of Surrey as Lecturer in 1998, and I have been there ever since, although I am now a Senior Lecturer, and so get paid a little more and have to go to more meetings. Over my years at Surrey my research moved to focus mainly on nucleation — this is how phase transitions like boiling and freezing start — and is now mostly focused on understanding the nucleation of crystals. I have also worked on a number of areas of biological physics. These have including the evolution of protein interactions, cell signalling, and studies of phase separation in living cells.

Abstract

How to model nucleation when the nucleation rate does not exist?

Richard P. Sear

University of Surrey, UK

Experimental results for the nucleation of crystalline tin [1], aspirin crystals [2] and ice [3], are not consistent with a nucleation rate that is in the thermodynamic limit. A well defined nucleation rate does not exist in these systems. What is happening is that although each crystallising droplet has a well defined nucleation rate, this rate varies by orders of magnitude from one nominally identical droplet to another. Then there is no well defined rate for a set of droplets at a given supercooling. The droplet-to-droplet variation is caused by the fact that nucleation is occurring at an interface (between the crystallising liquid and a solid impurity) and this interface is rough. This roughness varies randomly from one droplet to another, and the extreme sensitivity of nucleation rates to microscopic surface features means that the rate itself varies from one droplet to another.

I will present experimental results showing this behaviour and then show it can be modelled effectively [4]. This uses ideas from a statistics and other fields of engineering. It allows us to make predictions for how typical nucleation times scale with properties such as volume and level of impurities.

[1] G.M. Pound and V.K. La Mer, JACS 74 (1952) 2323.
[2] Y. Diao et al., JACS 133 (2011) 3756.
[3] R.J. Herbert et al., Atmos. Chem. Phys. Disc. 14 (2014) 1 1, 4191.
[4] R.P. Sear, Cryst. Growth Design 13 (2013) 1329.