Thermodynamic quantities of adsorption of polyethylene glycol dodecyl ethers to the saturated adsorption surfaces

The equilibrium surface tension of aqueous solutions of C 12 H 25 (OC 2 H 4 ) n OH (n = 2, 3, 4, and 5) was measured with the Wilhelmy plate method. The measurements were carried out at 298 K, 303 K and 308 K for solutions of several different concentrations in the saturated adsorption region. The partial molar area of the surfactant, and the standard chemical potential, entropy and enthalpy of adsorption were estimated. From these thermodynamic data, a model of molecular state in saturated adsorption surface is deduced: this includes the vortical orientation of the hydrophobic dodecyl group, a molecular arrangement similar to that in the solid crystal, and helical conformation of the hydrophilic polyoxyothyiene chains. [1]