6. Conclusion
We have made temperature-dependent measurements of THz-TDS
and DLS for an AOT reverse micelle with a Stokes radius of ~12 nm.
Two relaxation processes of water with ~12 ps and ~3 ps at room temperature
have been found; the slow component is due to the collective
motion of bulk-like water, whereas the fast one is due to the local
motion of the interfacial water at the surfactant. The slowing down of
the slow component with decreasing temperature is more pronounced
than that in liquid water above Tc (=286 K). This is due to the confinement
effect of reverse micelles. Furthermore, the time constant of the
slow component abruptly drops at Tc, and its temperature behavior
below Tc is similar to that of liquid water. On the other hand, the reverse
micelle dramatically shrinks at Tc. These results are explained in terms
of the water shedding from the reverse micelle at Tc. That is, the motion
of the water extracted from the reverse micelle speeds up owing to the
reduction in the confinement, and is roughly the same as that of liquid
water. The time constant of the fast component also decreases suddenly
at Tc, which is ascribed to the size reduction of the reverse micelle