When exposed to an external electric field higher than the critical Fréedericksz transition threshold the molecules orient themselves parallel to the field. The experiments were performed on a 0.1% volumetric fraction of single-walled carbon nanotubes (SWCNTs) in 4-cyano-4’-pentylbiphenyl (5CB) liquid crystal (LC).
, was used to calculate the relaxation times when the field is switched on or off, and the values were in good agreement with experimental data. A theoretical model based on elastic continuum theory, in which the interaction between carbon nanotubes and LC molecules is similar to the one described by Burylov et al. Experimentally it can be determined by measuring the intensity of a light beam traversing the sample as a function of the time. This is called the Fréedericksz transition and the molecular movement is characterized by the relaxation time. Under the action of an external magnetic or electric field above a critical threshold, nematic molecules collectively change their orientation. Experimental studies revealed that carbon nanotubes have a strong interaction with liquid crystal molecules and align themselves parallel with the long axis of the nematic. When nanoparticles are inserted in liquid crystals, nematic molecules are attached to the particle surface due to anchoring forces. Hence, new measurement methods and theoretical models have to be developed for their characterization. In many cases, the chemical or physical properties of microparticles or nanoparticles are different from those of the corresponding bulk materials. This might be the reason why there are so many research papers presenting new materials and new experiments regarding their behavior in different external electric, magnetic or laser fields. The increased interest for nanomaterials in different domains such as chemistry, medicine or engineering, makes their characterization quite necessary.
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