UNEXPECTED DYNAMICS IN SHAPE FLUCTUATIONS OF BILAYER VESICLES

Fluid lipid bilayers are composed of two mono-molecular sheets held to gether by weak van der Waals forces. Except for viscous resistance, th e monolayers are Gee to slide relative to one another - giving rise to a ''hidden'' degree of freedom within the composite structure. In thi s paper, important effects of interlayer coupling are demonstrated thr ough their influence on the static and dynamic features of undulating bilayer vesicles. In particular, it is shown that the non-local bendin g elasticity can modulate mean square undulatory amplitudes with a lon g wavelength suppression similar to that of membrane tension; the two effects are indistinguishable on the basis of spectral analysis. With regard to conformational dynamics, we show that the two dissipative me chanisms - namely interlayer drag and conventional hydrodynamics - are important on different length scales. With the crossover length being a fraction of a mu m, it is concluded that viscous resistance to conf ormational changes is dominated by interlayer dissipation in the mesos copic regime.