Relationship between monolayer structure and dynamic surface properties ofalkyl dimethyl phosphine oxides. BAM studies

A conventional LB trough combined with a Brewster angle microscope (BAM) ar e used for the study of monolayers of the non-ionic surfactants alkyl dimet hyl phosphine oxide, eikosyl dimethyl phosphine oxide (EDPO) and octadecyl dimethyl phosphine oxide (ODPO). The monolayers were spread from benzene, h exane or chloroform at c = 10(-3) M on an aqueous subphase. The two homolog ues show significantly different monolayer behaviour although the alkyl cha in of EDPO and ODPO differ by only two -CH2- groups. While EDPO forms well- visible domains, ODPO does not form any domains. Experiments on the relaxat ion behaviour have been performed using an oscillating barrier technique. T he discussion of the viscoelasticity of the monolayers is based on the exis tence of domains. A comparison of the viscoelastic behaviour of the monolay er of the two surfactants can be used to understand the contribution of dom ains to the non-equilibrium monolayer properties. (C) 1999 Elsevier Science B.V. All rights reserved.