Research paper: The effects of polydispersity and metastability on crystal growth

I’ve just uploaded a preprint of a new paper me and my supervisor are writing to arXiv. It’s a freely-available repository research in loads of different areas which people use to make research available before and while its in peer review for a journal.

This one is to do with crystal growth in soft condensed matter. That includes colloidal crystals and closely related things such as proteins, which must be crystallised in order to study their structure in biological/medical research. The broad question of ‘What’s the best way to grow a crystal?’ is relevant in a lot of scenarios, especially given that one is often quite free to vary the conditions in the system to optimise growth; for instance the interactions in a e.g. colloidal suspension can be easily tuned by adding other species such as polymer coils into the solution.

The dynamics of phase transitions, i.e. how systems do or do not actually reach their true equilibrium state, is an important consideration in applying thermodynamics to soft matter. In this paper, we simulate crystal growth (as shown in the video here) in the presence of metastable gas-liquid separation, which may be encouraged or avoided by tuning the interaction potential in a system, and polydispersity, which usually cannot be avoided in soft matter. There’s a variety of nice visualisations showing the effects of these two factors on the crystal growth dynamics, and we find that they can interact in a complex and previously unknown way. The simulation findings are related to existing experimental data and to theoretical considerations. Here’s the link:

The effect of metastability and polydispersity on crystal growth kinetics

This work, in early form, was the subject of a recent internal seminar in the Soft Matter Group at Leeds. I’ve uploaded the slides and an audio recording from the seminar.


How to stop the cable on 9-volt adaptors from breaking

Here’s a common problem for people who own small electronic devices, especially power adaptors for effects boxes.

This is an adaptor from my compressor; it outputs a special voltage, has a special plug on the end, and is expensive to replace. I found that out when, as with every other adaptor like this, the extremely thin cable eventually broke at the point where it joins the body of the adaptor. Even if you’re really careful, a few months or years of wear and tear is usually enough to break it because whenever tension is applied to the cable, it is applied to the same place — a join with only very weak stress relief. The cable bends and flexes in all directions, weakens, and after a while either the coating or the wire itself breaks.

When I got the replacement I came up with a nice way of preventing the same thing happening again. I took a cable tie, wrapped it around the body of the adaptor and loosely threaded the power cable in and out of the tie, following it once around the body. Then I tightened the cable tie and snipped it off, as shown in the picture below.

Threading the cable loosely through a tie wrapped round the body to relieve tension at the join.

This means that the join between the cable and body (the bit that always breaks) is never subject to tension and never moves, so it doesn’t break. Instead, pulling on the cable just smoothly induces a little bit of tension and only a slight bending at all the points where it crosses over the cable tie. The stress in any one part of the cable is never enough to break it, so it doesn’t break even if you grab the cable by the end and swing the adaptor around the place. And that’s magic.