The driving forces are the hydrophobic interaction and van der Waals interaction between tails. Membranes thus form non-covalent cooperative structures. 7.4 shows that membranes form essentially two-dimensional systems. The physics of membranes, still in its infancy, displays many phenomena similar to those in fluids and solids. The basic structure of a membrane is shown in Fig.
Real membranes are obviously far more complex.
The detailed arrangement of the lipids and proteins depends very much on characteristics of all components and the phase diagram of a membrane system can be complicated. As one example we mention the existence of periodic structures in lipid monolayers. Not enough is known, however, to give details. In one s, a lipid can travel about 2 m m. All lipid bilayers show a first order phase transition associated with the melting of the hydrocarbon chains.