title: Interfacial rheology of coexisting solid and fluid monolayers.
abstract: 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 compositions. Modeling the system as a two-dimensional suspension in analogy with 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.
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA. zasad008@umn.edu.
authors.forename: A K
authors.initials: AK
authors.lastname: Sachan
authors.affiliation: Departments of Chemical and Biomolecular Engineering and KINC, KAIST, Daejeon, 305-701, Korea.
authors.forename: S Q
authors.initials: SQ
authors.lastname: Choi
authors.affiliation: Departments of Chemical and Biomolecular Engineering and KINC, KAIST, Daejeon, 305-701, Korea.
authors.forename: K H
authors.initials: KH
authors.lastname: Kim
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA. zasad008@umn.edu.
authors.forename: Q
authors.initials: Q
authors.lastname: Tang
authors.affiliation: Department of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: L
authors.initials: L
authors.lastname: Hwang
authors.affiliation: Department of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: K Y C
authors.initials: KY
authors.lastname: Lee
authors.affiliation: Department of Chemical Engineering, University of California, Santa Barbara, CA 93106, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: Squires
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA. zasad008@umn.edu.
authors.forename: J A
authors.identifier: http://orcid.org/0000-0001-5663-6989
authors.initials: JA
authors.lastname: Zasadzinski