Relaxation studies of surfactant adsorption layers at the liquid/air interface by a funnel method

The funnel method presented as a technique for investigating dynamic surfac e properties at the liquid/air interface consists of a hydrophobic funnel w hich is moved through a liquid interface in order to compress or expand its area isotropically. A counter-body compensates the displaced liquid by mov ing in the direction opposite to the funnel movement allowing for a constan t liquid phase boundary level. Relaxation processes induced by the funnel m ovement are monitored by means of the surface tension response measured by a Wilhelmy plate right after expansion/compression of the interface. Studie s are preformed with the non-ionic surfactant dodecyl dimethyl phosphine ox ide. The relaxation curves depend on the direction and amount of the interf acial deformation. The experimental data are interpreted by a diffusion rel axation theory. Differences between experiment and theory are explained by changes in the effective area during compression or expansion. (C) 1998 Els evier Science B.V. All rights reserved.