(369c) Interfacial Rheology of Coexisting Solid and Fluid Monolayers

Authors: 
Zasadzinski, J. A., University of Minnesota
Sachan, A. K., University of Minnesota
Choi, S., KAIST
Kim, K., Univerisity of California, Santa Barbara
Lee, K. Y., University of Chicago
Hwang, L., University of Chicago
Squires, T. M., University of California, Santa Barbara
Biologically relevant monolayer and bilayer films often consist of micron-scale high viscosity domains in a continuous low viscosity matrix. Here we show that this morphology can cause the overall monolayer fluidity to vary by orders of magnitude over a limited range of monolayer composition. Modeling the system as a two-dimensional suspension in analogy to classic three-dimensional suspensions of hard spheres in a liquid solvent explains the rheological data with no adjustable parameters. In monolayers with ordered, highly viscous domains dispersed in a continuous low viscosity matrix, the surface viscosity increases as a power law with the area fraction of viscous domains. Changing the phase of the continuous matrix from a disordered fluid phase to a more ordered, condensed phase dramatically changes the overall monolayer viscosity. Small changes in the domain density and/or continuous matrix composition can alter the monolayer viscosity by orders of magnitude.