Research Projects

In 2017, two compounds with rod-like molecules (RM230 by Mandle, Chem. Eur. J and DIO by H. Nishikawa et al., Adv. Mater.), having large longitudinal dipole moments (~10D), were reported to show a nematic to nematic (N-N) phase transition. Later, the lower nematic phase was confirmed as a polar nematic, called as the ferroelectric nematic phase (NF). These are known as Ferroelectric Nematic Liquid Crystals (FNLC). Subsequently, many novel FNLCs have been synthesized. The characteristic difference between N and NF is the absence of n ̂≡-n ̂ symmetry in NF phase. This asymmetry along with large dipole moment results in large spontaneous polarisation ((P_s ) ⃗~μC/cm2). This is much larger than that of ferroelectric smectic (~nC/cm2) and of same order with that of solid ferroelectric materials. High (P_s ) ⃗ along with the inherent fluidity make FNLCs extremely desirable candidates for technological applications such ultra-fast and more power-efficient displays, micro-generators, microrobots etc. Research Gap: Despite extensive studies, many aspects of FNLCs still remain unsettled. E.g., almost all the existing FNLCs can be categorised as RM734-type or DIO-type. Most variations to molecular structures of these archetypical FNLCs suppress the NF phase. Madhusudana (PRE, 2021) argues that a sinusoidal modulation in charge density along the molecular length helps in stabilising NF. Very few experimental studies have been reported in the light of Madhusudana’s theory. A concrete correlation between molecular design and the stability of NF phase still remains an open topic and also stands as major hurdle in the path of wide-spread technological applications of FNLCs. Apart from the topic of structure-stability correlation of FNLCs, there are aspects of physical properties of FNLCs which are open for further studies. The N-NF nematic transition has been reported to be associated with interesting pre-transitional behaviour. For example, the splay elastic constant of RM734 decreases to near zero values close to the N-NF transition (Alenka et al., PRX, 2018). The relation between such unusual behaviour and the emergence of NF phase needs further exploration. Moreover, the large dielectric permittivity (~10000) of NF phase is debated in the light of two theoretical models, viz. – the PCG model (Clark, PRR. 2024) and the CPM model (Vaupotic et al. PRR. 2024) describing it to be of interfacial and material origins respectively. More dielectric studies are required for a better understanding of the origin large dielectric permittivity of FNLCs. Due to large molecular dipole moment of FNLCs, large flexoelectric response in the nematic phase, close to N-NF transition, can be expected. Very few studies have measured the flexoelectric response of FNLCs in the N phase. Our study will be focused on both synthesis and physical characterisation of FNLCs. This would give us a broader controllability to lead our study along a holistic as well as efficient way.