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

Abstract

Chain architecture is known to control macromolecular 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 coreforming 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.

Micelle Self-Assembly and Chain Exchange Kinetics of Tadpole Block Copolymers with a Cyclic Corona Block

“…These results demonstrate that the kinetics of tadpole and linear chain exchanges in mixed micelles influences each other: tadpole copolymer exchange slows down in the presence of linear chains in the micelles, while the exchange of linear chains speeds up. A similar synergistic effect on the exchange of chains of different architecture from mixed micelles has been previously reported by us for micelles containing linear and tadpole block copolymers with cyclic solvophobic block 12,24 and micelles containing linear diblocks with different rigidity/composition. 12,24 On the other hand, chain exchange in mixed micelles of linear diblock copolymers of different core lengths 20 has been experimentally shown to be uncorrelated, i.e., individual chain exchange is exactly the same as in pure micelles.…”

“…The radial monomer density distribution shown in Figure 3b indicates that there is no preferential localization of tadpole copolymer within the core of LT20 micelle in contrast to what is observed for mixed micelles containing tadpole block copolymers with a cyclic solvophobic block. 12 This is not unexpected as in our present study, the solvophobic blocks of linear and tadpole copolymers are identical, but only the solvophilic block architecture is different. As we see from Figure 3b, the cyclic solvophilic block is localized closer to the micelle interface, i.e., does not extend as far into the corona compared to the linear diblock copolymer, as expected based on the cyclic nature of the solvophilic block and behavior of pure tadpole micelles discussed above (Figure 3a).…”

“…In all simulations, the polymer volume fraction is kept constant at φ = 0.05 in a cubic simulation box of size 36r c (except for pure Ls simulation where a slightly smaller box size was used: 30r c based on the previous work). 12…”

“…Our previous study on mixed micelles from linear and tadpole diblock copolymers (the latter with a cyclic hydrophobic block) has demonstrated a synergistic effect in chain exchange kinetics, i.e., exchange of tadpole copolymer slows down and linear chain speeds up in the presence of each other. 12 Thus, it will be of interest to investigate whether there is any analogous synergy in the chain exchange kinetics in mixed micelles formed by linear and tadpole copolymers with the same solvophobic block and differing in the solvophilic block architecture: cyclic vs linear. In addition, we will also consider mixed micelles formed by linear diblock copolymers of different solvophilic block lengths to further elucidate chain architecture effects.…”

Dissipative Particle Dynamics Aided Design of Drug Delivery Systems: A Review

“…The application of DPD simulation in this field is relatively mature. − Here we present a comparison of experimental methods and DPD simulation in studying self-assembly morphology based on the conclusion from Guo and his colleagues Figure.…”