Ca2+ and Mg2+ induced molecular interactions in a dehydrocholic acid: didodecyldimethylammonium bromide mixed monolayer

PAULA V. MESSINA; JUAN M. RUSO; GERARDO PRIETO; MARCOS D. FERNANDEZ LEYES; PABLO C. SCHULZ; FELIX SARMIENTO

COLLOID AND POLYMER SCIENCE

SPRINGER

Lugar: Berlin; Año: 2010 vol. 288 p. 449 - 459

0303-402X

The aim of this article is the evaluation of Ca2+ and Mg2+ subphases presence effect on mixed monolayers composed by dehydrocholic acid (HDHC) and didodecyl- dimethylammonium bromide (DDAB). The monolayer stability was analyzed by the evaluation of thermodynamic parameters, DeltaG^E_(mix) and alfa. At all calcium ion-tested concentration, the mixed systems XHDHC =0.6 and 0.8 at Pi=30 mJ m-2 were always the most favored proportions. The XHDHC =0.6 system was also stable in magnesium presence, and the XHDHC =0.2-mixed monolayer went through a stable to an unstable state as the content of Ca2+ or Mg2+ augment. Finally, the XHDHC =0.4 monolayer showed a particular behavior, i.e., remained stable at low cation concentration, unstable at intermediate concentration and stable again at high concentration. The effect was similar at Mg2+ presence.