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Electrical Properties and Relaxation Behavior of TOPO Monolayers Formed at the Air/Water Interface

Wydro P., Hąc-Wydro K.

Polish Journal of Chemistry

2007

Vol. 81, nr 1

115-127

The properties of the Langmuir monolayer formed by tri-n-octylphosphine oxide (TOPO) have been analyzed. The investigations were based both on traditional (surface potential measurements) and more advanced (the relative reflectivity using Brewster angle microscopy BAM) experimental techniques and, for better analysis, the semiempirical computation using HyperChem programme has been done. Moreover, detailed characteristics of the relaxation behaviour of TOPO monolayers have been performed. It has been found that with the increase of the surface pressure () the film thickness increases, and TOPO monolayer becomes denser; however its state does not change. Upon film compression, the reorientation of TOPO molecules occurs in this way that they become progressively more perpendicular to the surface until the collapse of the monolayer. The relaxation of TOPO monolayers formed both on water subphase as well as on NaCl solution of various concentrations were analyzed according to two-steps desorption mechanism. As it turned out, the stability of TOPO monolayer decreases with the surface pressure. At lower the loss of the monolayer material is controlled both by dissolution and diffusion mechanism, while at higher surface pressure the monolayer relaxation is controlled by two dissolution steps of different rates and the monolayer does not achieve a steady-state. Moreover, the monolayer stability increases with ionic strength.

Insoluble Amphiphiles at the Air/Water Interface. The Characteristics of Alcohols Monolayers

Wydro P., Hąc-Wydro K., Paluch M.

Polish Journal of Chemistry

2006

Vol. 80, nr 12

2041-2054

In this paper thorough characteristics of monolayers formed at the air/water interface by two alcohols namely hexadecanol and octadecanol has been presented. The experiments were based on surface pressure/area and surface potential measurements. The visualization of monolayers has been performed using Brewster Angle Microscopy. It has been found that both alcohols form at the air/water interface condensed monolayers with transition between liquid condensed (LC) and solid (S) state. From the experimental results the thickness of monolayers has been calculated and compared with theoretical value. These calculations allow drawing conclusion of the slope of the hydrocarbon tails of investigated alcohols in monolayers. From the surface potential measurements the conformation of the O–H bond and the orientation of dipolemoments of both alcohols have been proposed. Moreover, the stability of monolayers formed by investigated alcohols has been studied and it has been found lower stability of hexadecanol monolayers in comparison with those formed by octadecanol.