Adsorption of 1-butanol and 1-pentanoic acid from the aqueous solution on polymers. Analysis of the solid—liquid interfacial activity

Abstract

In order to evaluate the solid—liquid interfacial activity of surfactant, contact angles of aqueous solutions of 1—butanol and 1—pentanoic acid on polypropylene (PP), polystyrene (PSt), polyvinyl chloride (PVC), and polymethyl methacrylate (PMMA) were measured. In many cases, discontinuities in slope of the contact angle θ vs concentration x (mole fraction) curves were observed, which was attributed to the change of the adsorption state from the horizontal to the vertical one. From these data, the decrease of the solid—liquid interfacial tension Δ γSL due to adsorption of surfactant was calculated. A parameter α, defined as lim ( ΔγSL x ), was introduced which was determined by extrapolation of Δγ- x plot. x → 0 The free energy of adsorption ΔG ads 0 was calculated from α value, and ΔG ads ∗ was calculated by: ΔG ads ∗ = ΔG ads 0 - NA 0γLV 0 cos θ 0 , where the last term represents the work of immersion of polymer into water per the area NA 0 of one mole of solute. The α values (and also − ΔG ads 0) are large for PP and small for PMMA. However, −ΔG ads ∗ values are small for PP and large for PMMA, which corresponds to the stronger interaction of PMMA with surfactant than of PP due to the larger polarity of PMMA.