The proposed research will develop a novel, general purpose and widely applicable method to use light scattering to non-evasively measure the elastic properties of 'soft' materials. This new technique will extend significantly the range over which elastic properties an be measured and will directly relate the response of the medium to its internal dynamics. The technique will be exploited to obtain new insight into the origin of the elasticity in a variety of disordered, or glassy, 'soft' materials, including colloidal suspensions near their glass transition, polymer solutions and polymer melts, compressed emulsions, networks of bio-polymers such as DNA and actin, and slowly aging systems. %%% The proposed research will develop a novel, laser-based method to non-invasively probe essential properties of a wide class of materials, including gels, and biomolecules such as DNA and actin, a fibrous molecule that imparts strength to cells. The technique will measure the mechanical properties of the materials, thus determining whether their behavior is more 'solid- like' (as in gelatin) or fluid-like (as in honey), and will significantly extend the range of applicability of traditional methods. The knowledge gained by these studies will provide new insight into underlying origins of the mechanical properties of the materials investigated.. It will also facilitate the application of the materials in commercial or medical areas. ***
