Design Principles for Fluid Molecular Ferroelectrics.

Fluid molecular ferroelectrics are a new class of organic materials where ferroelectricity is found in conjunction with 3D fluidity whilst still retaining spontaneous polarization values comparable to their traditional solid-state counterparts. One of the major challenges for soft condensed matter physics is predicting whether a fluid molecular material will form ferroelectric phase with nematic or smectic order. Through the synthesis of 45 systematically varied molecules, and by analogy to solid molecular ferroelectrics, it is shown that subtle hydrogen-fluorine (H/F) substitution(s) allows for tuneable syn-parallel pairing motifs resulting in either specific pairings, leading too geometrically constrained lamellar order, or diversified pairings, stabilising nematic ordering. Large-scale, fully atomistic molecular dynamics simulations reveal that smectic ferroelectricity emerges from discrete lateral pairing modes, whereas nematic phases arise from a multiplicity of equivalent polar configurations. Together, these findings establish experimentally validated design principles for fluid molecular ferroelectrics and provide a predictive framework for engineering functional polar fluids.