Dresden 2009 – wissenschaftliches Programm
CPP 16.8: Poster
Dienstag, 24. März 2009, 14:00–16:30, P3
Two-dimensional Lamellar Phase of Polye(styrene — Jens-Uwe Günther, •Heiko Ahrens, and Christiane A. Helm — Institut für Physik, Uni Greifswald, Felix-Hausdorff-Str. 6, 17487 Greifswald
Polystyrene sulfonate (PSS) adsorbed onto oppositely charged dioctadecyldimethylammonium bromide (DODA) monolayers at the air/water interface is investigated with X-ray reflectivity and grazing incidence diffraction. DODA in the condensed phase is in an oblique lattice. At low PSS bulk concentrations (0.001 * 0.1 mmol/L) the surface pressure corresponding to the fluid/condensed phase transition and the DODA molecular area in the condensed phase are decreased, the latter due to a reduced tilt angle. Both findings are attributed to PSS shielding the electrostatic repulsion between the DODA molecules. Bragg peaks caused by flatly adsorbed, aligned PSS chains are observed, with DODA in the fluid or the condensed phase. The two-dimensional lamellar phase is only found at intermediate PSS bulk concentrations (0.001 * 1 mmol/L). In this phase, the PSS coverage can be varied by a factor three, depending on DODA molecular area and polymer bulk concentration. Charge compensation in the lamellar phase is almost achieved at 1 mmol/L. At larger bulk concentrations, PSS adsorbs flatly yet without chain alignment. Presumably, a necessary condition for a twodimensional lamellar phase is a pronounced electrostatic force which causes a large persistence length as well as repulsion between the aligned chains.