Simulation of self-assembly in solution by triblock copolymers with sticky blocks at their ends


Recent simulations of the self-assembly of ABA triblock copolymers in dilute solution in a selective solvent are reviewed. The medium is a good solvent for the internal block (B) and a poor solvent for the terminal blocks (A). The simulations detect both free chains, which sometimes form intramolecular 'hairpins", and interchain aggregates. Analysis of the equilibrium between the open and intramolecularly aggregated states among the free chains permits a quantitative assessment of the importance of loop entropy in the self-assembly. When the energetic affects are relatively weak, multichain aggregates are loose, with a small number of chains and a preponderance of dangling ends. As the energetic effects become more important, the system forms larger aggregates with a closer approximation to a core-shell model. Most of the chains in these larger aggregates form loops, but a few dangling ends are also present. At sufficiently high concentration, the dangling ends and loops can form bridges that connect micelles (or smaller aggregates) into clusters. Eventually, a concentration is reached at which a single cluster permeates throughout the entire system, resulting in gelation. This gel point can be determined quantitatively in the simulations. The gel is a thermo-reversible network, because the bridges have finite lifetimes. The lifetime distribution of the bridges, which plays an important role in the stress relaxation by the thermo reversible network, can be evaluated in the simulation.

Publication Title

Progress in Colloid and Polymer Science