NSLS-II Seminar

Soft condensed matter comprises systems such as liquid crystals, colloids, polymers, surfactant monolayer and gels. A common feature of such systems is the ease by which they can be deformed –for instance by thermal fluctuations- and their tendency for self-organization on a mesoscopic scale. The organization process is often driven by relatively weak interactions such as van der Waals forces, which compete with the thermal fluctuations. Therefore, changes of the dynamics of the sample are often mirrored by conformal changes in the self-assembled structures.
It is shown how the viscoelastic properties of model membranes, consisting of surfactant monolayers at the liquid/air interface, can be probed by X-ray Photon Correlation Spectroscopy (XPCS) under grazing incidence conditions. In combination with grazing incidence diffraction measurements (GIXD) the transitions in the dynamic response of the membranes to surface capillary waves can be related to conformal changes within the monolayers. Systems studied comprise phospholipids monolayers in interaction with charged crystallites and sugars as well as fatty acids at the rotator-crystalline phase transition.
Future developments for the characterization of soft condensed matter systems by XPCS and in-situ x-ray diffraction and scattering methods will be discussed.