Tadpole and Mixed Linear/Tadpole Micelles of Diblock Copolymers: Thermodynamics and Chain Exchange Kinetics

Chain architecture is known to control macro molecular self-assembly and furthermore affect in a more complex way nanostructure stability. Equilibrium properties and chain exchange kinetics between micelles formed by tadpole-shaped diblock copolymers containing a loop-shaped hydrophobic block and a linear hydrophilic block are investigated using dissipative particle dynamics simulations. We found that tadpoles form micelles of smaller size and aggregation number than the corresponding linear diblock copolymers and have faster chain exchange kinetics, demonstrating that chain architecture can alter its effective hydrophobicity. Similar observations are made for linear diblock copolymer with a less hydrophobic core block indicating that the more compact conformation of tadpole core forming block makes it "less hydrophobic". We show that tadpole and linear block copolymers form mixed micelles with tadpoles (or less hydrophobic chains) located on the periphery of the micelle core. The chain exchange kinetics between mixed micelles is found to be quicker than in linear diblock copolymer micelles and slower than in tadpole micelles. Tadpole escape or less hydrophobic chain exchange between mixed micelles occurs slower (in part due to the shielding role that these chains play) than in the corresponding pure micelles, while linear more hydrophobic chain exchange only slightly changes, suggesting that the exchange kinetics of the individual components can be affected differently by mixing.