Exchange Dynamics of Fluoroalkyl Block Copolymers in Selective Solvents

Due to omniphobic nature of fluoropolymers, block copolymers (BCPs) having fluoropolymer block can be an excellent choice for self-assembly of multi-compartmented nanoparticles. However, the strong incompatibility between fluoroblock and solvent could pose high energy barrier for the exchange of BCPs, kinetically trapping the systems. Herein, we investigated the chain exchange dynamics of the self-assembled fluoroalkyl-BCP micelles as well as their structures using contrast-varied small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). Time-resolved SANS revealed the effects of temperature and fluoroblock length on the exchange dynamics within spherical micelles. Despite of high energy barrier for the fluoroblock pullout from the core domain, the exchange is reasonably fast due to significantly small friction within fluoropolymers. However, as the fluoroblock molar mass approaches 100 kDa, the energy barrier becomes tremendous that the fluoroblocks are actually arrested at the core. Therefore, the chain size of fluoroblock should be wisely chosen to drive self-assembly towards equilibrium in such strongly segregated systems.