Dresden 2014 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 16: Interfaces and Thin Films II

CPP 16.1: Talk

Tuesday, April 1, 2014, 09:30–09:45, ZEU 114

Lipid Monolayers and Adsorbed PSS with Different Degrees of Polymerization: Evidence of Lipid/PSS Complexes — •Thomas Ortmann, Heiko Ahrens, Andreas Gröning, Frank Lawrenz, and Christiane A. Helm — Inst. f. Physik, Uni Greifswald, 17487 Greifswald, Germany

To gain insight into the equilibrium conformation of adsorbed polyelectrolytes and into their interactions with the supporting surface, lipid monolayers at the air/water interface serve as model substrate with adjustable surface charge.

Monolayers of cationic lipid DODA with adsorbed anionic Polystyrene sulfonate (PSS) are studied by isotherms and X-ray techniques. From salt-free solutions, PSS adsorbs flatly. The lipid monolayer shows a fluid/ordered phase transition. For polymer lengths exceeding 8 nm, PSS adsorbs in a lamellar manner to the lipid monolayer, for both lipid phases. On monolayer compression, the area per lipid molecule and the intermolecular separation of the PSS chains are reduced by a factor of two. On increase of PSS molecular weight, the phase transition pressure of the lipids decreases until the polymer length exceeds the persistence length (27 nm), then it levels off. However, the phase transition enthalpy of the lipids is almost independent of PSS molecular weight. These observations suggest complexes consisting of stiff PSS chains and lipids. If the PSS chains are shorter than 8 nm, the lamellar arranged PSS chains are only found when the lipids are in the ordered phase.