Table (5) Characteristic rotation times and amplitudes derived from curve fitting to rotational ACFs using two exponential functions. τ 1 = fast rotations, τ 2 = slow rotations, a i = corresponding amplitude. The characteristic times indicate the existence of two main rotational modes (fast and slow) for the glycerol moieties. Based on the amplitudes, the short time scale rotations contribute more to the overall ACF rot in the single bilayer systems, whereas other systems display similar amplitudes between both rotational modes (Table ). The MMG-1 glycerol moieties display a trend of slower short time scale rotations and faster long time scale rotations (Table ). However, when both short and long time scale rotations are considered, the overall rotations of MMG-1 headgroups are likely faster in comparison to MMG-6. The differences between MMG-1 and MMG-6 in this regard are less pronounced in the non-interdigitated double bilayer systems. No clear indication of distinct ACF rot could be observed for different clusters based on g 3 analysis (Figure ). These results imply that the headgroup rotational dynamics are unrelated to the tail conformations or packing; it is probable that this is more closely related to the extent of headgroup hydration.