Surface acoustic wave investigation of magnetic nanoparticle size and concentration effect on liquid crystal behavior.

The effect of spherical magnetic nanoparticles with different size (5, 10, 15, and 20 nm) and volume concentration (10-3, 5 × 10-4, and 10-4) on liquid crystal 4-cyano-4'-hexylbiphenyl (6CB) behavior was investigated using surface acoustic wave (SAW). The attenuation response of SAW propagating along with the substrate/liquid crystal interface was used to study the structural changes induced by an applied magnetic field. The obtained results showed the shift of the threshold magnetic field with an increase in the volume concentration of nanoparticles toward lower fields and also the decrease in the isotropic-nematic phase transition temperature depending on the nanoparticle size and the nanoparticle volume fraction. Results confirmed again that the bulk viscosity coefficients should dominate the SAW attenuation and that the SAW investigation in the presented configuration is applicable to monitoring of the role of magnetic dopants in structural changes under external fields. Some theoretical background of the presented SAW investigation is introduced as well. Obtained results are discussed within the context of previous ones.