Adsorption of Poly(ethylene oxide)-<i>b</i>-poly(ε-caprolactone)\nCopolymers at the Silica−Water Interface

Abstract

The adsorption of amphiphilic poly(ethylene oxide)-<i>b</i>-poly(ε-caprolactone) and poly(ethylene oxide)-<i>b</i>-poly(γ-methyl-ε-caprolactone) copolymers in aqueous solution on silica and glass surfaces has been\ninvestigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and\ncomplementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of <i>M</i>_n\n= 5000 and a hydrophobic polyester block of poly(ε-caprolactone) (PCL) or poly(γ-methyl-ε-caprolactone)\n(PMCL) of <i>M</i>_n in the 950−2200 range. Compared to homoPEO, the adsorption of the copolymers is\nsignificantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric\nexperiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface\ncoverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to\nthe aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks\noriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering\nusing the contrast matching technique and by tapping mode atomic force microscopy. The experimental\nobservations agree with the coadsorption of micelles and free copolymer chains at the interface.