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.
Bibliographical noteFunding Information:
We thank Drs Mati Meron and Binhua Lin for GIXD data analysis help. The National Institutes of Health (HL-51177) partially or wholly supported AKS, SQC, KHK, QT, TMS, and JAZ. The Basic Science Research Program through 2012R1A6A3A04040395 provided additional support for SQC and KHK. HLH and KYCL were supported by the National Science Foundation (MCB-1413613 and the MRSEC program at the University of Chicago, DMR-1420709). ChemMatCARS was supported by NSF/DOE (CHE-0822838) and the Advanced Photon Source was supported by the Department of Energy, BES (W-31-109-Eng-38).
© The Royal Society of Chemistry.