Adsorption of 1,3-dioxane derivatives at mercury and free interfaces

Adsorption of various 2-alkyl-5-hydroxy-1,3-dioxanes at mercury/liquid and free (liquid/air) interfaces was studied using the high-precision tensammetric and surface tension experimental methods. It was found that for most of these compounds adsorption can well be described by the Frumkin model. The values of the lateral interaction parameter b were determined from the experimental isotherms using linear and nonlinear fitting procedures. They were found to be positive, indicating an attractive interaction among adsorbed species. For the trans isomers at mercury, the lateral interaction parameter b assumed values close to zero; hence the Langmuir model became adequate. The standard free energy of adsorption Delta G degrees for all these compounds was also determined from the equilibrium adsorption data. Based on these values the extension of the energy minimum driving adsorption was estimated. The calculated Delta G degrees values were found to be lower at mercury (more negative) than at the free interface. The monotonic correlation between the alkyl chain length and Delta G degrees was determined for the surfactants studied. (C) 1996 Academic Press, Inc.