title: Linear and nonlinear microrheology of lysozyme layers forming at the air-water interface.
abstract: We report experiments studying the mechanical evolution of layers of the protein lysozyme adsorbing at the air-water interface using passive and active microrheology techniques to investigate the linear and nonlinear rheological response, respectively. Following formation of a new interface, the linear shear rheology, which we interrogate through the Brownian motion of spherical colloids at the interface, becomes viscoelastic with a complex modulus that has approximately power-law frequency dependence. The power-law exponent characterizing this frequency dependence decreases steadily with increasing layer age. Meanwhile, the nonlinear microrheology, probed via the rotational motion of magnetic nanowires at the interface, reveals a layer response characteristic of a shear-thinning power-law fluid with a flow index that decreases with age. We discuss two possible frameworks for understanding this mechanical evolution: gelation and the formation of a soft glass phase.
authors: Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA. leheny@pha.jhu.edu.
authors: Daniel B
authors: DB
authors: Allan
authors: Daniel M
authors: DM
authors: Firester
authors: Victor P
authors: VP
authors: Allard
authors: Daniel H
authors: DH
authors: Reich
authors: Kathleen J
authors: KJ
authors: Stebe
authors: Robert L
authors: RL
authors: Leheny
mesh_terms: D000388:Air; D000818:Animals; D002645:Chickens; D003102:Colloids / Q000737:chemistry*; D004548:Elasticity; D005782:Gels; D005898:Glass; D016014:Linear Models; D008280:Magnetics; D009113:Muramidase / Q000737:chemistry*; D053770:Nanowires; D012212:Rheology / Q000379:methods*; D033081:Shear Strength; D013499:Surface Properties; D014783:Viscosity; D014867:Water / Q000737:chemistry*
chemical_list: D003102:Colloids; D005782:Gels; D014867:Water; C421864:hen egg lysozyme; D009113:Muramidase