title: Lipid monolayers and adsorbed polyelectrolytes with different degrees of polymerization.
abstract: Polystyrene sulfonate (PSS) of different molecular weight M(w) is adsorbed to oppositely charged DODAB monolayers from dilute solutions (0.01 mmol/L). PSS adsorbs flatly in a lamellar manner, as is shown by X-ray reflectivity and grazing incidence diffraction (exception: PSS with M(w) below 7 kDa adsorbs flatly disordered to the liquid expanded phase). The surface coverage and the separation of the PSS chains are independent of PSS M(w). On monolayer compression, the surface charge density increases by a factor of 2, and the separation of the PSS chains decreases by the same factor. Isotherms show that on increase of PSS M(w) the transition pressure of the LE/LC (liquid expanded/liquid condensed) phase transition decreases. When the contour length exceeds the persistence length (21 nm), the transition pressure is low and constant. For low-M(w) PSS (<7 kDa) the LE/LC transition of the lipids and the disordered/ordered transition of adsorbed PSS occur simultaneously, leading to a maximum in the contour length dependence of the transition enthalpy. These findings show that lipid monolayers at the air/water interface are a suitable model substrate with adjustable surface charge density to study the equilibrium conformation of adsorbed polyelectrolytes as well as their interactions with a model membrane.
authors.affiliation: Institut für Physik, Ernst-Moritz-Arndt Universität , Felix-Hausdorff-Straße 6, D-17487 Greifswald, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ortmann
authors.forename: Heiko
authors.initials: H
authors.lastname: Ahrens
authors.forename: Frank
authors.initials: F
authors.lastname: Lawrenz
authors.forename: Andreas
authors.initials: A
authors.lastname: Gröning
authors.forename: Peter
authors.initials: P
authors.lastname: Nestler
authors.forename: Jens-Uwe
authors.initials: JU
authors.lastname: Günther
authors.forename: Christiane A
authors.initials: CA
authors.lastname: Helm
mesh_terms: D008055:Lipids / Q000737:chemistry*; D058105:Polymerization; D011108:Polymers / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D008055:Lipids; D011108:Polymers; D011137:Polystyrenes; D000644:Quaternary Ammonium Compounds; C015831:dimethyldioctadecylammonium; C003321:polystyrene sulfonic acid