Van der Waals energy of lecithins in the ripple phase

摘要: The van der Waals energy of a two-dimensional array tilted alkyl chains is evaluated numerically by summing the contributions pairs ${\mathrm{CH}}_{2}$ groups and water molecules. found to be lower for system with spatially oscillating tilt angle theta than flat layer. cost in free these oscillations estimated assuming that where magnitude reduced, there an increase chain area hence fluidity. It free-energy reduction due interaction sufficient compensate increased fluidity at temperatures few degrees below chain-melting temperature. Thus provides plausible physical mechanism occurrence ripple phase. surface profile predicted good agreement observed ${P}_{\ensuremath{\beta}}$ or phase electron microscopy characterized x-ray diffraction. An analytic expression negative term form z'z''', z'=tantheta derived on basis this mechanism.