Electrospun fibers with axially polarized ferroelectric nematic core

The recent discovery of ferroelectric nematic liquid crystals (FNLCs) has led to exciting ferroelectric materials which combine polar long-range orientational order and giant spontaneous electric polarization Ps with 3D fluidity. While this fluidity opens completely new perspectives for the directional control of Ps in space and time, it also requires the confinement of FNLC materials. In this context, we investigate whether and how ferroelectric nematics might be confined as a cylindrical core in a hollow polymer fiber by coaxial electrospinning and whether the ferroelectric order is preserved in this process. We find that it is, in fact, exceptionally easy to spin fibers with a continuous FNLC core, because the polarization stiffening effect counteracts the Plateau-Rayleigh instability which breaks up many simpler core liquids into droplets. Polarization-resolved second-harmonic generation (SHG) measurements reveal that the polar order is preserved in the cylindrical fiber core. While in thin fibers with a core diameter on the order of 1 μm, Ps is uniformly aligned along the fiber axis, we find a twist of Ps along the diameter in thicker fibers. The latter observation is analyzed in light of the current debate on the twisted ground states of ferroelectric nematics. Our study shows that the quasi-1D confinement of FNLCs by coaxial electrospinning leads to novel macroscopically polar fibers, which offer new research opportunities and might be an important step toward application in, e.g., actuators or energy harvesting devices.