Internal structures in membranes: Ripples, hats, saddles, and egg cartons

Membranes such as bilayers that form spontaneously in lipid-water systems can show surprising variety in their phase behavior, shapes, and textures. Many of these phases and textures seem to be the result of subtle effects of either competing interactions between the constituent molecules or the expression of internal degrees of freedom within these essentially two-dimensional systems. The richness of their behavior has made membranes fascinating model systems for both experimental and theoretical research. There have been recent developments in the study of such structures as ʹripple phasesʹ and other textures, primarily in bilayer membranes.