Electro-optic switching in iron oxide nanoparticle embedded paramagnetic chiral liquid crystal via magneto-electric coupling

Abstract

The variation in optical texture, electro-optic, and dielectric properties of iron oxide nanoparticles (NPs) embedded ferroelectric liquid crystal (FLC) with respect to change in temperature and electrical bias conditions are demonstrated in the current investigations. Improvement in spontaneous polarization and response time in nanocomposites has been attributed to magneto-electric (ME) coupling resulting from the strong interaction among the ferromagnetic nanoparticle's exchange field (due to unpaired e−) and the field of liquid crystal molecular director. Electron paramagnetic resonance spectrum of FLC material gives a broad resonance signal with superimposed components indicating the presence of a source of spin. This paramagnetic behavior of host FLC material had been a major factor in strengthening the guest host interaction by giving an additional possibility of (a) spin-spin interaction and (b) interactions between magnetic-dipole and electric-dipole moments (ME effects) in the composite materials. Furthermore, the phenomenon of dielectric and static memory effect in these composites are also observed which yet again confirms the coupling of magnetic NP's field with FLC's director orientation. We therefore believe that such advanced soft materials holding the optical and electrical properties of conventional LCs with the magnetic and electronic properties of ferromagnetic nanoparticles are going to play a key role in the development of futuristic multifunctional optical devices.

Modifications of FLC Physical Properties through Doping with Fe2O3 Nanoparticles (Part I)

“…For example, after doping the ZLI-3654 liquid crystalline mixture with Fe 2 O 3 nanoparticles (ca. 24 nm, 0.25 and 1.25 × 10 −5 wt.%), stripe-like domains were observed under crossed polarizers, which were explained by the chain-like alignment of nanoparticles in the LC matrix [ 29 ]. In turn, the increase in spontaneous polarization versus applied voltage after doping was explained based on the magnetoelectric coupling resulting from the strong interaction between the nanoparticles’ exchange field (unpaired electron) and the molecular director field [ 29 ].…”

“…24 nm, 0.25 and 1.25 × 10 −5 wt.%), stripe-like domains were observed under crossed polarizers, which were explained by the chain-like alignment of nanoparticles in the LC matrix [ 29 ]. In turn, the increase in spontaneous polarization versus applied voltage after doping was explained based on the magnetoelectric coupling resulting from the strong interaction between the nanoparticles’ exchange field (unpaired electron) and the molecular director field [ 29 ]. Meanwhile, the rotational viscosity and response time decrease with increasing the voltage in relation to pure ZLI-3654 (modification of the electric field of electric dipoles by a nanoparticle magnetic field).…”

Facet dependent electro‐optical properties of liquid crystals doped with Au nanocrystals

“…The combination of nanoparticles (NPs) and liquid crystals (LCs) has drawn widespread attention in the scientific field [1–3]. In the LC/NP composite systems, because of good compatibility of LCs and excellent properties of NPs, the NPs can improve the electro‐optical properties of LCs [4–14], regulate LC alignment [15–19], and stabilise LC phases [20, 21]. The E‐O properties of chiral nematic LCs (N*LCs) are obviously improved by Cu 2 O with different crystal planes due to the exposure of different properties [8].…”

Orientational order parameter of liquid crystalline nanocomposites by Newton’s rings and image analysis methods

“…Incorporation of metal oxide nanoparticles into liquid crystals makes it easier to obtain better display parameter profiles [3]. The metal oxide nanoparticles embedded in liquid crystal bases have attracted much interest not only in the field of magnetic recording media but also in the area of medical care.…”