Rheological properties and shear-induced structures of ferroelectric nematic liquid crystals.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41837749.
- Also identified by DOI 10.1039/d5sm01207d.
- No licence information is recorded for this record.
- Because redistribution is not established, this page shows the abstract only. Follow the links below for the full text.
Abstract
Recently discovered ferroelectric nematic (N<sub>F</sub>) liquid crystals are fluids with a polar orientational order. The electric polarization vector can be aligned by an electric field and by surface anchoring. Here, we explore how the polarization field and effective viscosity of the N<sub>F</sub> materials are affected by shear flows. We explore three N<sub>F</sub> materials, abbreviated RM734, DIO, and a room-temperature FNLC919, all of which exhibit a paraelectric nematic (N) and an N<sub>F</sub> phase. All materials show an increase in the effective viscosity upon cooling, with Arrhenius behavior in broad temperature ranges except near the phase transitions. In DIO and FNLC919, the antiferroelectric SmZ<sub>A</sub> phase separating the N and N<sub>F</sub> phases shows a strong dependence of the effective viscosity on the shear rate: this viscosity is lower than the viscosity of the N and N<sub>F</sub> phases at high shear rates (<i></i> = 500 s<sup>-1</sup>) but is much higher when the shear rate is low, <i></i> = 2.5 s<sup>-1</sup>. The behavior is associated with the layered structure of the SmZ<sub>A</sub> phase. All mesophases in all three materials exhibit shear-thinning behavior at low shear rates (<100 s<sup>-1</sup>) and a nearly Newtonian behavior at higher shear rates. In terms of alignment, we observe three regimes in the N and N<sub>F</sub> phases: flow-alignment at low shear rates, <i></i> < 10<sup>2</sup> s<sup>-1</sup>, a log-rolling regime with the director and polarization along the vorticity axis at <i></i> > 10<sup>3</sup> s<sup>-1</sup>, and polydomain structures at intermediate rates. In the flow-aligning regime, the N<sub>F</sub> polarization does not tilt away from the shear direction, which is in sharp contrast to the flow-induced tilt of the N director. The effect is attributed to the avoidance of splay deformations and associated space charge in the flowing N<sub>F</sub>. The temperature and shear rate dependencies of the viscosity and the uncovered shear-induced structural effects of N<sub>F</sub> advance our understanding of these materials and potentially facilitate their applications.