What's the mechanism of the phospholipid bilayer of the cell membrane ?

The lipid bilayer has been firmly established as the universal basis for cell-membrane structure. It is easily seen by electron microscopy, although specialized techniques, such as x-ray diffraction and freeze-fracture electron microscopy, are needed to reveal the details of its organization. The bilayer structure is attributable to the special properties of the lipid molecules, which cause them to assemble spontaneously into bilayers even under simple artificial conditions