Adsorption of Pluronic block copolymers on silica nanoparticles

Polymers on the surface of nanoparticles are of great scientific and technological importance since they dictate many important properties and functions of dispersed systems. We investigate here the organization of a representative poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer on silica nanoparticles dispersed in water. Pluronic P105 (EO₃₆PO₅₆EO₃₆) adsorbs on protonated silica and starts forming hydrophobic domains above a certain bulk polymer concentration, called critical surface micelle concentration (csmc), which is lower than the critical micelle concentration (cmc) of Pluronic P105 in plain water. The csmc decreases with increasing particle concentration and decreasing particle size. Below its csmc, the PEO-PPO-PEO block copolymer adsorption on protonated silica nanoparticles is similar to the adsorption of PEO homopolymers. Above the csmc, the block copolymers form micelle-like aggregates on protonated silica nanoparticles, as suggested by the adsorbed layer thickness, adsorbed polymer amount, and presence of hydrophobic domains.