Adsorption of oligooxypropylenated amines at the aqueous solution—air interface: Homologous series of piperidine and morpholine derivatives

Abstract

The surface tension isotherms for pure oligooxypropylenated piperidine and morpholine at the aqueous solution—air interface were determined and interpreted. The surface excess concentration, Γ, the surface area per molecule, A, and the standard free energy of adsorption, Δ G°, were calculated according to a new empirical adsorption equation. The standard free energy contribution for the oxypropylene group (PO) in morpholine derivatives,Δ G° (PO) = −3.34 kJ mol −1, is substantially lower than that for the PO group located in the piperidine derivatives, i.e. Δ G° (PO)= −3.12 kJ mol −1.