Self-aggregation of triblock copolymers at the solid silica-water interface

We report on the adsorption and surface aggregation behavior of triblock co poly(ethylene oxide-tetrahydrofuran-ethylene oxide) copolymers, EOn/2THFmEO n/2, at the silica-water interface. In this work, we have used both time-re solved fluorescence spectroscopy and atomic force microscopy to study the m orphology of the adsorbed layers. We confirm previous suggestions that the copolymers self-assemble at the silica surface to form discrete micelle-lik e structures. The surface aggregation, however, starts at a much lower copo lymer concentration than the corresponding micellization process in solutio n. The time-resolved fluorescence measurements reveal that the copolymer ag gregates are smaller at the surface than those in bulk solution. The AFM me asurements that were performed clearly confirm the existence of discrete mi celle-like copolymer aggregates at the silica surface. An interesting resul t seen in the AFM surface topography images is that, for the high molecular weight copolymer, we observe no surface aggregates at some parts of surfac e. We believe this is related to the polydispersity of the copolymer. Singl e high molecular weight copolymers may effectively compete for surface area with surface aggregates formed by a copolymer fraction of lower molecular weight.