Temperature-dependent adsorption of Pluronic F127 block copolymers onto carbon black particles dispersed in aqueous media

The adsorption properties of Pluronic F127 poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) PEO-PPO-PEO block copolymer onto carbon black (CB) particles dispersed in water have been investigated. The CB particles have fractal structure according to small-angle neutron scattering (SANS) measurements. The Langmuir isotherm could describe the adsorption behavior of Pluronic F127 onto CB particles below the block copolymer critical micellization concentration (CMC). Temperature plays an important role in determining the thickness and structure of the adsorbed layer. Below the temperature where micelles start forming (CMT), the added Pluronic F127 block copolymer molecules contribute to an increase of the adsorbed layer thickness (determined by dynamic light scattering) by forming a monolayer. Above the CMT, SANS experiments, performed under contrast matching conditions where either the block copolymer or the CB particles were rendered "invisible", confirmed that the adsorbed layer had structure and dimensions similar to these of Pluronic F127 block copolymer micelles that form in aqueous solution in the absence of CB. One of the aims of this work is to provide information on how to control the adsorbed layer thickness and structure (and correspondingly, colloidal stability) by tuning variables such as temperature, block copolymer concentration, and/or solvent quality.