Eur. Phys. J. E (2006) 20: 387-394
https://doi.org/10.1140/epje/i2006-10027-y

Regular Article

pH-dependent kinetics of MgCl₂ adsorption under a fatty-acid Langmuir film

¹ LPPI, Université de Cergy-Pontoise, 5 mail Gay-Lussac Neuville/Oise, 95031, Cergy-Pontoise Cedex, France
² Campus Boucicaut, Institut des Nanosciences de Paris, 140 rue de Lourmel, 75015, Paris, France
³ Synchrotron Soleil, L'Orme des Merisiers, Saint Aubin, BP 48, 91192, Gif-sur-Yvette Cedex, France
⁴ Service de Chimie Moléculaire/LIONS, CEA-Saclay, bât. 125, 91191, Gif-sur-Yvette, France

^* e-mail: Sophie.Cantin-Riviere@lpms.u-cergy.fr

Received: 22 March 2006
Accepted: 28 July 2006
Published online: 23 August 2006

Abstract

The effect of subphase pH (5.5 and 10.5) on the structure of behenic-acid monolayers was investigated during Mg²⁺ adsorption by means of Grazing Incidence X-ray Diffraction (GIXD) and Brewster Angle Microscopy (BAM). The final phase corresponding to an ion superlattice commensurate to the behenic-acid cell is pH-independent. In contrast, the sequence of phases evidenced from the initial L₂-phase to this final state presents at pH 10.5 an additional stage associated to a film condensation toward the L' ₂-phase. The structures of the intermediate states preceding the superstructure nucleation are slightly different, both with a short-range fatty-acid order. Finally, a laser light effect that could result from visible light absorption by the inorganic complexes is evidenced in the final state as well as in the intermediate phases.