High-resolution adiabatic scanning calorimetry of novel ferroelectric nematic liquid crystals with triple bonds

The groundbreaking discovery in 2017 of ferroelectric nematic phases in RM734 and DIO has triggered extensive explorations for new molecules and resulted already in a rich library of polar liquid crystals (LCs). To elucidate the nature of the phase transitions in these novel LCs, high-resolution experimental techniques are necessary. High-resolution adiabatic scanning calorimetry (ASC), providing the temperature dependence of the specific heat capacity, cp(T), and the specific enthalpy, h(T), have proven to be an adequate method. For two novel molecules with triple bonds (SCUT22b and SCUT22c), cp(T) and h(T) behaviour was assessed for the transitions between the ferroelectric nematic phase (NF) to the intermediate phase (Nx) and from the Nx to the nematic (N) phase. For both compounds, the NF-Nx transitions are weakly first order with substantially larger pretransitional behaviour in the Nx than in the NF phase. A broader temperature range around the Nx-N transitions exhibited substantial pretransitional cp(T) background increases in addition to a small narrow cp(T) peak corresponding with a very small true latent heat of less than 0.05 J/g. These observations, seen also in DIO, seem common to the Nx-N phase transitions.