A transient polymorph transition of 4-cyano-4′-octyloxybiphenyl (8OCB) revealed by ultrafast differential scanning calorimetry (UFDSC)

Abstract

In this work, ultrafast differential scanning calorimetry (UFDSC) with heating and cooling rates up to 20 000 K s⁻¹ is used to study the transient polymorph transition of the liquid crystal 8OCB. The square plate form (SP), which was reported to grow only from the solution in binary solvent mixtures at low temperature, is found to be the only form growing from a deeply quenched smectic glass during very rapid heating. If the heating rate is slower than 8000 K s⁻¹, reorganization to the parallelepiped form will start, and if the heating rate is slower than 1000 K s⁻¹, the square plate form will reorganize to the parallelepiped form completely, and only melting of the parallelepiped form is observed. The capacity of the UFDSC to capture the unstable polymorphs of low molar mass organic molecules and to follow their rapid transition is demonstrated in this work.