Grafting density induced reentrant disorder-order-disorder transition in planar di-block copolymer brushes

By means of multiscale molecular simulation, we show that solvophilic-solvophobic AB diblock copolymer brushes in the semi-dilute regime present a re-entrant disorder/order/disorder transition. The latter is fully controllable through two parameters: the grafting density and the solvophobic to solvophilic ratio of the tethered macromolecules. Upon increasing density, chains first aggregate into patches, then further order into a crystalline phase and finally melt into a disordered phase. We demonstrate that the order/disorder transition can be explained through the peculiar properties of the aggregates: upon increasing density, the aggregation number grows as expected. On the contrary, their projection on the plane shrinks, thus melting the emergent ordered phase. Such a density dependent shrinkage, seen for the first time as the cause to an order/disorder phase transition, is as a consequence of the entropic/enthalpic competition that characterises the hierarchical self-assembly of the brush.

Automated summary

Through multiscale molecular simulation, it is shown that solvophilic-solvophobic AB diblock copolymer brushes exhibit a re-entrant disorder/order/disorder transition in the semi-dilute regime. This transition is fully controllable through adjustments to the grafting density and the solvophobic to solvophilic ratio of the tethered macromolecules. The transition from order to disorder is explained by the density dependent shrinkage of aggregates, which is caused by entropic/enthalpic competition during hierarchical self-assembly of the brush.