Solid-Like Domains in Mixed Lipid Bilayers. Effect of Membrane Lamellarity and Transition Pathway

We present optical observations of phase separation in mixed model membranes in the form of giant unilamellar vesicles. These observations are compared to the phase behavior of lipid mixtures, which we determined by X-ray scattering and differential scanning calorimetry or extracted from the existing literature. The domain properties are affected not only by the bulk phase behavior but also by the membrane lamellarity and phase transition pathways. These observations have important implications for how phase behavior determined by bulk methods using dense, multilamellar lipid bilayers are linked to phase separation in giant, unilamellar lipid bilayers as observed by microscopy.