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The local dynamics of lipid molecules (fully hydrated) ordered in multilayers of dipalmitoylphosphatidylcholine (DPPC) and DPPC-d62 are studied by IQENS. In the smectic A(Lα) state the diffusion coefficient of the lipid rotational diffusion is Drot = 2 · 10-9 s-1 and of the lateral Brownian motion Dlat = 2 · 10-7 cm2 s-1. The lipids also exhibit an out-of-plane vibrational motion (= dynamic surface roughness) the frequency of which depends on the amplitude, b (τ-1 = 1 · 108 s-1 for b = 0.2 nm; τ-1 = 2.3 · 107 s-1 for b = 0.6 nm). In the solid state (Lβ) the choline headgroups exhibit rotational motion about an average axis forming an angle of 55 degrees with the normal, while the chain ends (the last 5 CH2-groups) exhibit a hindered rotation (correlation time 2 · 109 s-1).
Pfeiffer et al. (Sun,) studied this question.