The conformation of Pluronic{\textregistered} block copolymers adsorbed on carbon nanotubes and their interaction with water studied by small-angle neutron scattering

Amphiphilic block copolymers are particularly useful in dispersing single-walled carbon nanotubes (SWCNT) in water. Small-angle neutron scattering measurements conducted at different D$_{2}$O/H$_{2}$O content of the dispersing medium provide quantitative information on the adsorption density and conformation of the polymer interacting with the nanotube surface. Data is presented on Pluronic{\textregistered} F108 - (EO)$_{132}$(PO)$_{50}$(EO)$_{132}$ and F127 (EO)$_{100}$(PO)$_{65}$(EO)$_{100}$, where EO-ethylene oxide and PO-propylene oxide, well below the critical micellization temperature of the polymer. A dense coating of the PPO blocks on the nanotube surface is determined with the PEO chains extended from the cylindrical core-shell structure. The data from the two Pluronic systems show minimal scattering at about 70{\%} D$_{2}$O in the dispersing water, which exhibit a $q ^{-1}$ power law of the scattering vector ($q )$. This indicates near matching of the polymer chains at a surprisingly high scattering length density. The model fit required considerations of tight association of water molecules around PEO chains and slight isotopic selectivity.