Thermodynamically stable ‘plumber’s nightmare’ structure self-assembles from block copolymers

A thermodynamically stable example of the notorious ‘plumber’s nightmare’ structure has been created using a diblock copolymer by adjusting the interactions of the chain ends. The stability of the plumber’s nightmare structure – so called because the structure is so convoluted, an intricate tangle of tubes – is attributed to the interplay between the strength of the end–end interactions and the initial shape of the curvature. This work holds out the possibility of new ways to make other challenging materials.

Diblock copolymers consist of two types of monomers and can chemically self-assemble into nanostructures with different symmetries. As with any thermodynamic system there is competition between enthalpy and entropy which can be expressed as the minimisation of free energy. Phase diagrams of diblock copolymers have been established based on block polymer fraction, degree of polymerisation and the Flory–Huggins interaction parameter between the two blocks – a measure of the strength of interaction between the polymers. There are certain phases that are co-continuous in the equilibrium phase diagram; gyroid, double diamond and the plumber’s nightmare. And these are only stable over a narrow window on the phase diagram. These phases are interesting because they provide pathways in three dimensions without considering orientation, which is important for many types of applications including energy storage and soft electronics.