Abstract
The surface acoustic waves (SAWs) were used to study the effect of magnetic nanoparticles on nematic liquid crystal (NLC) behavior in weak magnetic and electric fields. The measurement of the attenuation of SAW propagating along the interface between piezoelectric substrate and liquid crystal is showed as an effective tool to study processes of structural changes. The magnetic nanoparticles Fe3O4 of nanorod shape and different low volume concentration were added to the NLC (4-(trans-4′-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT)) during its isotropic phase. In contrast to undoped liquid crystals the distinctive different SAW attenuation responses induced by both magnetic and also electric fields in studied NLC samples were observed suggesting both structural changes and the orientational coupling between both magnetic and electric moments of nanoparticles and the director of the NLC molecules. Experimental measurements including the investigation under linearly increasing and/or jumped magnetic and electrical fields, respectively, as well as the investigation of temperature and time influences on structural changes were done. The investigation of the SAW anisotropy gives supplemental information about the internal structure of nanoparticles in investigated NLCs. In addition, some magneto-optical investigations were performed to support SAW results and study their stability and switching time. The analysis of observed SAW attenuation characteristics confirmed the role of concentration of magnetic nanoparticles on the resultant behavior of investigated NLC compounds. Obtained results are discussed within the context of previous ones. The theoretical background of the presented SAW investigation is introduced, too.
Highlights
Liquid crystalline materials have been of particular interest for several decades because of their anisotropic structural properties that can induce unique electric, magnetic or thermal responding behaviors [1,2]
We report results of investigation of nematic liquid crystal (NLC) doped with magnetic particles of nanorod shape and different concentrations to determine their effect on structural changes under external weak magnetic and/or electrical fields as well as the temperature influence on structural changes using surface acoustic wave (SAW)
Structural changes in investigated NLCs under both magnetic and electric fields were monitored taking use of the measurements of the attenuation of SAW propagating along the interface between the
Summary
Liquid crystalline materials have been of particular interest for several decades because of their anisotropic structural properties that can induce unique electric, magnetic or thermal responding behaviors [1,2]. The surface acoustic wave (SAW) technique can be very useful tool for the investigation of structural changes in NLCs doped with various kinds of nanoparticles [20,21,22] The advantage of this SAW technique is that, compared to the case when the longitudinal wave is used, only a very thin layer of NLC is required. The response of SAW attenuation can reflect sufficiently on any changes in NLC orientational properties initiated by applied fields and/or by changed other external conditions In this contribution, we report results of investigation of NLCs doped with magnetic particles of nanorod shape and different concentrations to determine their effect on structural changes under external weak magnetic and/or electrical fields as well as the temperature influence on structural changes using SAW. The theoretical background of the utilized SAW investigation is presented
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