Effects of subphase composition on the monolayer behavior of “core–coronae” type hybrid amphiphiles

Abstract

As described in this paper, the effect of solutes on monolayer properties of a “core–coronae” type amphiphile was studied. The “core–coronae” type hybrid amphiphile comprises double-decker-shaped polyhedral silsesquioxane (DDSQ) as a core and four di(ethylene glycol) (DEG) units as coronae (4DEG-DDSQ). The molecule was spread onto a water subphase containing phosphoric acid, 1,3-bis(hydroxymethyl)urea, or potassium chloride. Then monolayer properties were studied using surface pressure (π)–area (A) isotherm and Brewster angle microscope measurements. Addition of phosphoric acid and 1,3-bis(hydroxymethyl)urea to the water subphase increased the limiting surface area of the 4DEG-DDSQ monolayer compared to that prepared in the pure water surface. The surface area increase is attributed to formation of strong hydrogen bonding between OH groups of DEG units and solutes. Addition of KCl showed a negligible change in the π–A isotherm, even though DEG units coordinate with K+ ions. The monolayer spread on the different subphases was transferred onto a solid substrate and the morphology of the transferred film was observed using atomic force microscopy (AFM). The AFM images show a dot-like structure, irrespective of the subphase composition, whereas the dot size decreases and the dot density increases with addition of solutes.