Effect of CdSe/ZnS quantum dots doping on the ion transport behavior in nematic liquid crystal

The tunability of ion transport behavior in the liquid crystal (LC) system doped with nanomaterials offers a stable and potential technology for designing the next generation application devices. Earlier research efforts, including theoretical and experimental approaches, explore ion density and the effect on mesomorphic properties of several LC nanocomposite system using different variables such as doping concentration, ionic contamination and type of material. In the present work, considering the simplest nematic 5CB LC and core–shell type CdSe/ZnS quantum dots (QDs), the temperature-dependent ion transport behavior and electrical properties have been experimentally measured with varying QD concentration by dielectric spectroscopy technique. The mobile ion concentration and diffusion constant are effectively analyzed using two different approaches: modified Sawada model and Uemura formalism. Utilizing the experimental dielectric data in the pure and doped nematic LC systems, we described the ion trapping and releasing nature of QDs with respect to concentration level and observed the significant contribution of the two types of mobile ions differing in size and mobility. The study also demonstrates that the doping of QDs effectively traps two kinds of ions while the ion releasing phenomenon occurs only for one type of ion with high doping concentration. The effective interaction between QD ligands and molecules creates a tactoid-like ellipsoidal shape of the nanoparticles which in turn enhances the mobile ion density in the higher doped samples. Additionally, the diffusive motion of ions varies linearly with temperature. We have investigated the two plateau regions in the frequency-dependent real part of conductivity with Jonscher power law and observed the significant contribution of the first type of ion to the conduction process in all the studied samples. These experimental findings in this studied system will facilitate the advanced understanding of ion interaction for nanomaterials in other complex LC matrix.