Trace water in stored solvents behind seemingly spontaneous surface polymorphism

Millimolar concentrations of water inadvertently absorbed from the air into a solvent were enough to tip the thermodynamic balance between two polymorphs of a supramolecular monolayer, new research shows. By tracing apparently spontaneous structural differences back to a solvent’s history, the work is a reminder that trace impurities can have outsized effects and shows how solvent handling can create reproducibility issues.