title: Active microrheology and simultaneous visualization of sheared phospholipid monolayers.
abstract: Two-dimensional films of surface-active agents-from phospholipids and proteins to nanoparticles and colloids-stabilize fluid interfaces, which are essential to the science, technology and engineering of everyday life. The 2D nature of interfaces present unique challenges and opportunities: coupling between the 2D films and the bulk fluids complicates the measurement of surface dynamic properties, but allows the interfacial microstructure to be directly visualized during deformation. Here we present a novel technique that combines active microrheology with fluorescence microscopy to visualize fluid interfaces as they deform under applied stress, allowing structure and rheology to be correlated on the micron-scale in monolayer films. We show that even simple, single-component lipid monolayers can exhibit viscoelasticity, history dependence, a yield stress and hours-long time scales for elastic recoil and aging. Simultaneous visualization of the monolayer under stress shows that the rich dynamical response results from the cooperative dynamics and deformation of liquid-crystalline domains and their boundaries.
authors.affiliation: Department of Chemical Engineering, University of California-Santa Barbara, Santa Barbara, California 93106, USA.
authors.forename: S Q
authors.initials: SQ
authors.lastname: Choi
authors.forename: S
authors.initials: S
authors.lastname: Steltenkamp
authors.forename: J A
authors.initials: JA
authors.lastname: Zasadzinski
authors.forename: T M
authors.initials: TM
authors.lastname: Squires
mesh_terms: D008856:Microscopy, Fluorescence / Q000295:instrumentation / Q000379:methods*; D010743:Phospholipids / Q000737:chemistry*; D012212:Rheology / Q000295:instrumentation / Q000379:methods*; D013499:Surface Properties; D014783:Viscosity
chemical_list: D010743:Phospholipids