Dr. Hugo Christenson - Summit Speaker Series - May 4, 2016

C5MPT Summit Speaker Series Event

Hugo Christenson

School of Physics and Astronomy

University of Leeds, Leeds LS2 9JT, U.K.

Lecture #2: May 4, 2016 2:00 pm

Donadeo ICE 8-207 Patrick D Daniel/Enbridge Conference Room

Towards topographical control of crystal nucleation

  Much anecdotal evidence concerns the ability of surface defects such as scratches to promote crystal nucleation. Investigations of this phenomenon are bedevilled by the difficulty of separating chemical and topographical effects, and there have been few systematic studies. Although both classical nucleation theory and computer simulations predict stabilisation of a critical nucleus in a surface cavity, it is unlikely that features visible to the naked eye would affect phenomena on the scale of a critical nucleus, i.e. 1-10 nm. Our recent work has identified a viable mechanism in crystal nucleation from vapour, whereby condensation of supercooled liquid occurs in surface defects, followed by crystal nucleation in the condensate. However, this mechanism has no clear analogue in crystal nucleation from the melt or from solution.

We have now embarked on a major effort to learn more about how surface defects promote nucleation, and how to use this to control nucleation. In a two-pronged approach we are using state-of-the-art surface fabrication techniques to engineer surfaces with well-defined grooves, pits and trenches, as well as employing induced or spontaneously arisen surface defects in natural or man-made materials. I will present results on freezing of supercooled water droplets, on crystallisation of crystals from solution (the image shows MnCO3 crystals on reactive-ion etched Si) on ice nucleation from vapour and on nucleation of organic crystals from vapour. I will discuss progress that has been made (minor), and outstanding questions (major).