Surface rheology of heterogeneous interfaces

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We propose to view quasi two-dimensional monolayer suspensions on a homogeneous subphase as model sys-tems for complex nano/micro-structured membranes [1]-[4] We will measure their effective rheological behavior with a miniaturized magnetic needle surface rheometer. The goal is to enable predictions of surface rheological properties of a complex membraneous structure from the characteristics of the structure and the rheological properties of the subphase and the single component membrane constituents by experimentally unravelling the major parameters and their effect on the effective surface rheological behavior. Four important parameters are studied in particular: a) The area fraction of the more viscous or solid component of the monolayer, b) the strength of static interactions between the components, c) the internal degrees of freedom of the constituents of the monolayer, such as the conformations of macromolecules, and d) the size of the solid or more viscous constituents of the monolayer. The parameters a-c are known to be relevant for the rheological behavior of three-dimensional (3D) complex fluids. The cross-over length scale, defined by the ratio of the surface to bulk viscosity, renders the size of the colloidal particles as compared to the cross-over length into an additional and crucial quantity for the effective rheological behavior of the complex monolayer.