Structural Changes in Liquid Crystals Doped with Rod-Like Magnetic Particles Studied by Surface Acoustic Waves

Abstract

The effect of rod-like magnetic particles on liquid crystal (6CHBT) structural changes in electric and weak magnetic fields were studied by means of the attenuation of surface acoustic wave of frequency 30 MHz propagating along ferronematic liquid crystals. Three low volume concentrations (Φ = 1 × 10 −5 , 1 × 10 −4 and 1 × 10 −3 ) of rod-like magnetic particles were added to liquid crystal during its isotropic phase. Several measurements including the investigation of the effects of electrical and magnetic fields applied both separately and in conjunction as well as the influence of temperature on the surface acoustic wave attenuation were performed. The distinctive surface acoustic wave attenuation responses induced by both electric and magnetic fields in studied ferronematic liquid crystals have been observed suggesting both structural changes and the orientational coupling between magnetic moments of magnetic particles and the director of the liquid crystal. Obtained results confirmed the significant influence of the presence of magnetic particles on the structural properties and resulting behavior of 6CHBT liquid crystal.

Study of Structural Changes in Nematic Liquid Crystals Doped with Magnetic Nanoparticles Using Surface Acoustic Waves

“…As for the memory effect observed in the decreasing regime, in the case of samples with lower concentrations (10 −5 and 5 × 10 −5 ), except the hysteretic development, no remainder attenuation was registered at zero magnetic field, however, in the case of higher concentration (10 −4 and 5.2 × 10 −4 ) it represents about 10% and 20%, respectively. Similar effect of concentration on function of ∆α (B) dependences was already observed in the case of 6CHBT doped with other dopants [20,21,44,45]. Comparing presented structural changes with those obtained on 6CHBT doped with rod-like [44], chain-like [45] or spherical [20] magnetic nanoparticles, these changes belong to less marked, they are close to that doped with chain-like nanoparticles, where the length was comparable with investigated nanorods.…”

Effect of Spherical, Rod-Like and Chain-Like Magnetic Nanoparticles on Magneto-Optical Response of Nematics

“…It is evident that the stronger anchoring in the case of rod-like particles (rigid anchoring) ensures stable magneto-optical responses. It should be noted that while capacitance measurements [23] showed weak anchoring only in the case of spherical magnetic particles and in the case of both chainlike and rod-like particles rigid anchoring, our SAW [19][20][21] and presented magneto-optical measurements indicated similar behaviour for spherical and chain-like particles but different behaviour in the case of rod-like particles. This fact supports rather the conclusion that the rigid anchoring is above all the characteristic property of only rod-like magnetic particles in LC suspension.…”

“…The intensity of transmitted light was recorded by means of a photodetector connected to a multimeter and subsequently to the computer that monitored the light intensity as a function of magnetic field. The magnetic field that was controlled also by computer could be increased/decreased continuously (80 mT/min) or altered by a jump (pulsed change) with the relaxation time of the increase/decrease shorter than 0.3 s. The pulse width (duration) 120 s was chosen on the basis of our previous results obtained investigating structural changes in these LCs using surface acoustic waves [19,20,21] when SAW changes could reach the saturated state during such long time. No bias magnetic field was applied before starting the measurement so that suspensions could appear to be compensated ferronematics.…”

“…Recently, we have studied the effect of magnetic particles on LC structural changes in electric and magnetic fields using the measurement of attenuation of the surface acoustic wave (SAW) propagating along ferronematic liquid crystal. The magnetic nanoparticles in low volume concentration (Φ = 10 −4 -10 −5 ) and a different arrangement, including spherical, rod-like, and chainlike shape, as a dopant in the LC (6CHTB), were investigated [19][20][21]. The structural changes of these ferronematics were studied also by capacitance measurements [22][23][24].…”

Magnetic Liquid Switching Using Rodlike Ferronematic 6CHBT Liquid Crystal Mixture Depending on the Diffraction Patterns

“…The diffraction methods were utilized a useful tool for the characterization of LCs doped with rodlike magnetic particles induced by weak magnetic fields [28].…”