title: Dynamic mechanical properties of a polyelectrolyte adsorbed insoluble lipid monolayer at the air-water interface.
abstract: Polymers have been used to stabilize interfaces or to tune the mechanical properties of interfaces in various contexts, such as in oil emulsions or biological membranes. Although the structural properties of these systems are relatively well-studied, instrumental limitations continue to make it difficult to understand how the addition of polymer affects the dynamic mechanical properties of thin and soft films. We have solved this challenge by developing a new instrument, an optical-tweezer-based interface shear microrheometer (ISMR). With this technique, we observed that the interface shear modulus, G*, of a dioctadecyldimethylammonium chloride (DODAC) monolayer at the air-water interface significantly increased with adsorption of polystyrenesulfonate (PSS). In addition, the viscous film (DODAC monolayer) became a viscoelastic film with PSS adsorption. At a low salt concentration, 10 mM of NaCl in the subphase, the viscoelasticity of the DODAC/PSS composite was predominantly determined by a particular property of PSS, that is, it behaves as a Gaussian chain in a θ-solvent. At a high salt concentration, 316 mM of NaCl, the thin film behaved as a polymer melt excluding water molecules.
authors.affiliation: †Department of Physics, KAIST, Daejeon 305-701, South Korea.|‡Material Research Laboratory, University of California Santa Barbara, Santa Barbara, California 93106, United States.
authors.forename: Chang Young
authors.initials: CY
authors.lastname: Park
authors.affiliation: †Department of Physics, KAIST, Daejeon 305-701, South Korea.|‡Material Research Laboratory, University of California Santa Barbara, Santa Barbara, California 93106, United States.|¶Gwangju College, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea.
authors.forename: Mahn Won
authors.initials: MW
authors.lastname: Kim
mesh_terms: D000327:Adsorption; D000388:Air; D004573:Electrolytes / Q000737:chemistry*; D055595:Mechanical Phenomena; D011137:Polystyrenes / Q000737:chemistry*; D011312:Pressure; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry; D012995:Solubility; D013499:Surface Properties; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D004573:Electrolytes; D011137:Polystyrenes; D000644:Quaternary Ammonium Compounds; D014867:Water; C015831:dimethyldioctadecylammonium; D012965:Sodium Chloride; C003321:polystyrene sulfonic acid