Critical demixing in fluid bilayers of phospholipid mixtures. A neutron diffraction study

Critical lateral demixing in fluid bilayers of lecithins differing in chain length by four CH₂ groups is established for the first time by small angle neutron scattering, exploiting the high scattering contrast between deuterated and protonated lipids. Good agreement with the Ornstein-Zernicke theory allows one the estimation of the correlation length of concentration fluctuations. The interesting aspect of critical demixing phenomena is their possible role in membrane processes such as facilitated trans-membrane transport, long range protein-protein interaction, and the control of enzyme activity.