Abstract
This Ph.D Thesis is dedicated to the study of the ultra-slow and non stationary dynamics of a multilamellar vesicles gel. We have developed an experiment based on the observation of the system by optical microscopy and we have adopted a set of image analysis techniques to determine the “coarse–grained“ field of displacements inside the sample. With the displacements fields obtained during experiments with fixed temperature, we have shown that the system shows some elongations and contractions of the whole sample, which are stationary and induced by the small temperature fluctuations which are always present experimentally. The system also shows an internal dynamics which is heterogeneous both spatially and temporally.<br />We have shown that the internal dynamics follow a exponential law of aging and that temperature, and more precisely its fluctuations, seems to play a crucial role as the driven force of rearrangements in the system, because of mechanical solicitations imposed by the elongations/contraction. By looking at both spatial and temporal structure of the displacement fields, we have seen that two kinds of events take place in the system. First reversible shearing along the longitudinal axis of the capillary are induced by temperature fluctuations, in an intermittent way. Simultaneously, other events take place and we have been able to show that they are irreversible and correspond to a ballistic time evolution of the displacement. For the two kinds of events, we have shown that rearrangements are correlated other long length scales, which are about 1000 times larger than typical vesicles size.<br />_________________________________________________________________________