Samoilov O. Manifestations of structural factors in the optical and electrophysical properties of liquid crystal dispersions of carbon nanotubes

Object of the study: mechanisms of interaction of anisometric NP with organic molecules of LC. Purpose: to determine the structural and functional, in particular optical features of liquid crystal suspensions of nanoparticles of different anisometry by optical methods. Methods: optical spectrophotometry (temperature dependences of optical transmission, the effect of dopants on the helical twisting of cholesteric liquid crystals (CLC) and the location of selective reflection maxima), differential scanning calorimetry (determination of the phase transition parameters) and measurement of electrophysical characteristics (electrical conductivity, dielectric constants of the investigated suspensions). Theoretical and practical results, scientific novelty: for the first time, significant differences between the properties of LC dispersions of single–walled and multi–walled carbon nanotubes (SWCNT and MWCNT) were found. It is shown that in the nematic phase at the same concentration the optical density of SWCNT dispersions is much (~ 3 times) higher, and in the isotropic phase the dependences of the optical density on the concentration of both types of CNTs are essentially similar and described by Bouguer–Lambert–Ber law. For the first time, it was revealed that for CNT dispersions in cholesteric liquid crystals the concentration dependence of the optical density is essentially nonmonotonic, with extrema corresponding to changes in the CNT aggregation state. Using optical microscopy, it was found that at low concentrations of CNTs focus on structural defects of cholesterol LC, and with concentration increasing, the formation of CNT aggregates occurs. In this case, the defects (so–called "oily grooves") disappear, and the texture of cholesterol LC becomes more homogeneous. It is shown that for LC dispersions of modified organoclays of laponite type in similar conditions the features characteristic of CNTs are absent, optical properties are determined by the exfoliation process, and additional injection of laponite in CNT dispersion leads to significant improvement of system homogeneity and temporal stability. For LC systems containing components of different dielectric anisotropy, anomalous concentration dependences of optical transmission in the vicinity of dielectric compensation are found out and conditions for the implementation of new photoelectrooptical effects based on the Fredericks transition in the presence of dispersed nanoparticles are determined. Practical significance: the results obtained in the dissertation on the interaction of LC with NP can be used in the development of new composite nanomaterials as a multifunctional basis for electro-optical and optoelectronic devices. The dissertation work shows the possibility of implementing a new photoelectro-optical Fredericks transition for 5CB + ZhK440 systems, opens wide prospects for the use of photosensitive nematic LC with negative dielectric constant in optoelectronics. Scope of application: The results obtained in this work on the interaction of LC with nanoparticles can be used in the development of new composite nanomaterials as a multifunctional basis for electro–optical and optoelectronic devices.