Molecular orientation of monododecyl pentaethylene glycol (C12E5) surfactants at infinite dilution at the air/water interface. A molecular dynamics computer simulation study

Physical Chemistry Chemical Physics Pub Date: 2000-02-21 DOI: 10.1039/A906992E

Abstract

In this publication we used a molecular dynamics computer simulation in order to get more detailed insights into the adsorption process of monododecyl pentaethylene glycol (C12E5) surfactants. We investigated the surface between water and air at infinite small surfactant concentrations. Measured in respect to the surface normal vector the average tilt angle of the C12 chain was found to be of the order of 67.4°±18.3°. For the polar pentaethylene glycol chains we observed tilt angles of 78.0°±8.5°. These results indicate that the molecules are lying nearly flat on the water surface. This observation is in fairly good agreement with neutron reflection experiments of C12E3 and also with a previously performed simulation of sodium dodecylsulfate. Additionally, it turned out that the conformations of C12E5 surfactant molecules adsorbed at the air/water interface are similar to the molecular arrangements of C12E5 in the vacuum phase. This holds, at least, for the regime of infinitely small surfactant concentrations.

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