Ramification and labyrinth instabilities in a ferroelectric nematic fluid exposed to electric fields

• Ferroelectric nematic bridges exposed to electric fields undergo a primary and a secondary interfacial instability. • Experiments and simulations support the requirement of the insulating layers on the electrodes. • Analogies and differences compared to the cases of magnetic and dielectric fluids are presented. • The studied phenomena may give rise to possible new applications in microfluidics, gas sensing and flow control. Recently, an electric field induced interfacial instability of ferroelectric nematic liquid crystals was reported (Sci. Rep. 13:6981 (2023)). It was found that above a threshold, the interface of the fluid with air undergoes a fingering instability or ramification. Here it is shown that by increasing the voltage between the two sides of a ferroelectric liquid bridge, the primary fractal-like ramification is followed by a secondary labyrinthine instability. The instabilities are well distinguishable by their completely different morphologies, and they both emerge sharply at distinct threshold voltages. The critical requirements for the instabilities are presented and the crucial role of the insulating layers on the electrodes is discussed. Experiments and finite element method simulations suggest that the main driving force of the ramification and labyrinthine instabilities is an unexpected electric field component parallel to the electrodes.