STABILITY OF DIALKYLDIMETHYLAMMONIUM BROMIDES MONOLAYERS SPREAD AT THE WATER AIR INTERFACE/

The pressure/area (pi/A) isotherms of Langmuir monolayers of a series of the dialkyldimethylammonium bromides with alkyl chain lengths of 12 , 14, 16 and 18 have been studied in terms of their stability at the w ater/air interface. Only dihexadecyldimethylammonium bromide (DHAB) an d dioctadecyldimethylammonium bromide (DOAB) form stable Langmuir mono layers whereas the other compounds investigated desorb from the interf ace. The change of the area available for one molecule in the monolaye r with time at different temperatures of the subphase (water and 0.1 M KBr aqueous solution) was investigated. The process of desorption was found to be controlled by the mechanism of diffusion. Applying the Te r Minassian-Saraga model [L. Ter Minassian-Saraga, J. Chim. Phys. 52 ( 1955) 181], the kinetics parameters corresponding to the desorption an d diffusion, for DDAB and DTAB, were estimated. (C) 1998 Elsevier Scie nce B.V.