Liquid mixtures research

You would have thought we should know pretty much all there is to know about simple mixtures of alcohols and water by now: these are 'simple' systems, miscible across the whole concentration range. But it turns out that their behaviour on a microscopic level is anything but simple. One of the 'simplest' systems to exhibit some rather odd behaviour is a mixture of methanol and water. Methanol is the smallest alcohol and also an amphiphile: it has both water-loving and water-hating bits to it.

It was found that although perfectly miscible in all proportions on a macroscopic scale, this system exhibits microimmiscibility, with each component clustering with its own kind more than you would expect.

2. Current investigations

One of the motivations for looking at a system like aqueous methanol is that is a very simple prototype for more complex amphiphiles such as proteins. But structurally it is still a long way from a protein, so more recent work looked at N-methylacetamide (NMA, shown above). It's a simple NH-CO protein linkage capped by methyl groups. One of the most surprising things that this work discovered was that the addition of water to liquid NMA does not break the chains of hydorgenpbonded peptide fragments, but instead water inserts itself between chains, acting as bridging molecule. From here, we've moved on to look at more complicated molecular peptides in solution, such as glutamic acid or glycine-l-alanine. Both these systems have multiple sites for hydrogen bonding with water or other solute molecules to occur and we are finding that the solution structure and dynamics is anything but simple.

3. Future plans

Away from liquids of biological relevance, the same computational techniques methodolgies can be used to investigate mixtures with very different purposes. The production of alcohols to act as fuel additives to petroleum offers the potential for both enhancing the octane-rating of the fuel, whilst at the same time being produced from renewable sources. But there are real problems; not just with the production of the alcohols from biomass, but also because hydrocarbons and alcohols don't mix particularly well. And the presence of even a small amount of water makes matters even worse, causing the two phases to separate.

A detailed understanding of the structure and dynamics of the alcohol-hydrocarbon-water three-component system is still far from complete, but this project will attempt to elucidate this and also identify how this may influence the liquid-phase separations on a macroscopic level.