Delft duo plots polymer stress at molecular level.

What happens at the molecular level when a polymer solidifies from its melt? Delft researchers Georgy Filonenko and Richard Janissen analyzed the mechanochemical response that occurs when a polymer hardens. They published their results on 12 December in JACS.

The researchers used spiropyrene (SP), a mechanophore, or molecule that emits light when you apply force to it. Spiropyrene changes under mechanical stress from colorless to the fluorescent isomer merocyanine (MC). That switch appears to be much easier in solid PMMA. Due to the internal stress in the polymer, the activation energy for this reversible isomerization changes from 140 kJ/mol in a liquid polymer to 70 kJ/mol in the solid form.