Lyotropic Liquid Crystals

These liquid crystals form the basic fabric of all biomembranes in living cells, and are found in all manner of consumer products, from shampoos and fabric softeners to ice cream stabilisers and cake mixes. The molecules involved, membrane lipids, detergents and surfactants, all share the common feature that they are amphiphilic.

This typical amphiphile, DOPC, has two major molecular elements: a polar headgroup and two oily hydrocarbon chains.

Because the headgroup wants to be in contact with water, whereas the hydrocarbon chains hate water, when we mix an amphiphile with water, structures form spontaneously which hide the oily chains from the water, but allow the headgroups to be hydrated. These are the lyotropic liquid crystalline phases. Some have rather simple structures, such as the lamellar phase:

The amphiphiles, represented as two-tailed tadpoles, form bilayers, which stack periodically. The amphiphiles are free to diffuse around in each monolayer, making this a two dimensional liquid and a one dimensional crystal.

Other phases have interfaces which bend, sometimes in a simple manner, as in the inverse hexagonal (HII) phase:

Here the interface has curved into cylinders with water on the inside. The cylinders pack onto a two dimensional hexagonal lattice, so now we have a two dimensional liquid and a two dimensional crystal.

Sometimes the interface may bend in an extremely complex way, as the gyroid cubic phase:

In this tortured structure, the interface has been bent into convoluted saddles which are arranged on a cubic lattice. This is a two dimensional liquid and a three dimensional crystal.

Nature has devised many other beautiful structures which allow the headgroups to hydrate, yet hide the chains from water. We spend our time searching for new structures, trying to understand the energetics of why they form, the geometrical route ,by which one structure grows from another, and developing new instrumentation for probing this fascinating and delicate phase of matter.