Soft discotic matrix with 0-D silver nanoparticles: Impact on molecular ordering and conductivity

Magnified charge carrier conduction, permittivity, and mesomorphic properties of columnar structure of a room temperature discotic liquid crystalline material due to the dispersion of low concentration ferroelectric nanoparticles

Liquid crystal nanocomposites have been a hot topic of research due to optimization of physical properties with such blending. There are several reports on enhancement of physical properties of nematic liquid crystals due to the blending of the nanomaterials. L. M. Lopatina and J. V. Selinger [Phys. Rev. Lett. 102, 197802 (2009)]10.1103/PhysRevLett.102.197802 have even proposed a theory based on experimental results for the enhancement of the properties of the nematic mesophase in the presence of ferroelectric nanoparticles. However, discotic liquid crystal nanocomposites are less studied. In the present experimental work, we have studied the effect of ferroelectric (BaTiO_{3}) nanoparticles on a room temperature discotic liquid crystalline material, namely 1,5-dihydroxy-2,3,6,7-tetrakis(3,7-dimethyloctyloxy)-9,10-anthraquinone. We investigated the physical properties of low concentration ferroelectric nanoparticle dispersed discotic columnar structure, using calorimetric, optical, x-ray diffraction, and dielectric spectroscopy tools. Results show that inclusion of ferroelectric nanoparticles in the discotic matrix consolidates the stability of the columnar matrix of the Col_{h} phase by virtue of their ferroic nature. An enhancement in charge carrier conductivity by several orders of magnitude at ambient conditions has been observed which makes such systems highly appropriate for one-dimensional conductors. Low concentration of BaTiO_{3} nanoparticles substantially enhanced permittivity of the system also. A molecular relaxation mode has been observed in the middle frequency range of the dielectric spectra. Enhancement of these important parameters could be possible due to the ferroelectric nature of the dispersed nanoparticles.

Facile ultrathin film of silver nanoparticles for bacteria sensing

Silver nanoparticles (AgNPs) exhibit excellent anti-microbial and bactericidal properties. Due to bacterial abhorrence for AgNPs, it is difficult to develop a label-free, sensitive and low-cost bacteria sensor using them. In the present article, we report that an ultrathin and uniform Langmuir-Schaefer (LS) film of AgNPs can be employed for bacteria sensing effectively as compared to that of non-uniform and randomly distributed AgNPs in spin coated film. The uniformly distributed AgNPs in the LS film offer a relatively larger contact surface for bacteria as compared to that of spin coated film. Due to higher contact surface, adsorption of the bacteria on LS film is strongly preferable as compared to that of spin coated film leading to an enhanced sensing performance of the LS film than that of spin coated film. Soil bacteria was grown by the standard protocol and were utilized as model system for bacteria sensing application. The soil bacteria sensing was done by monitoring the piezoresponse and dissipation parameters using a quartz crystal microbalance, simultaneously. Our study indicates that the LS film of AgNPs not only facilitates the adsorption of the soil bacteria but also kills them.

Morphological transformation in the supramolecular assembly of discotic liquid crystal molecules using silver nanoparticles and its sensing application

Triphenylene based discotic liquid crystal (TP) molecules are rich in π-electrons which facilitate π-stacking interaction of the molcules leading to formation of one dimensional nanowires. These nanowires can assemble to form nanoribbons due to a lateral cohesive force among the nanowires. The flat nanoribons undergo a morphological transformation due to incorporation of silver nanoparticles (SNP) into the matrix of TP molecules. The presence of SNP induces a chiral twisting to the nanoribbons and therefore the flat nanoribbons transform into a helical nanoribbon structure. The global chiral structure exhibited by the composition of achiral constituents is due to the creation of topological defects like disclination and dislocation. These defects can lead to a geometrical frustration in the nanoribbons which relaxes with the formation of twisted helical nanoribbons. A minor change in morphology of the supramolecular assembly can have a remarkable effect on the physicochemical properties of the nanoribbons. In this article, we demonstrate that even a minor change in the geometry of aliphatic chains on the surface of nanoribbons can be employed for sensing organic solvents such as acetone and ethanol. The sensing was performed at room temperature. Relative humidity has no effect on the sensing response.

Defect-mediated colloidal interactions in a nematic-phase discotic solvent

Interactions between colloidal inclusions dispersed in a nematic discotic liquid-crystalline solvent were investigated for different solute-solvent coupling conditions. The solvent was treated at the level of Gay-Berne discogens. Colloidal inclusions were coupled to the solvent with a generalized sphere-ellipsoid interaction potential. Energy strengths were varied to promote either homeotropic or planar mesogenic anchoring. Colloid-colloid interactions were modeled using a soft, excluded-volume contribution. Single-colloid and colloid-pair samples were evolved with Molecular Dynamics simulations. Equilibrium trajectories were used to characterize structural and dynamical properties of topological defects arising in the mesomorphic phase due to colloidal inclusions. Boojums were observed with planar anchoring, whereas Saturn rings were obtained with homeotropic anchoring. The manner in which these topological defects drive colloidal interactions was assessed through a free energy analysis, taking into account the relative orientation between a colloidal dyad and the nematic-field director. The dynamical behavior of defects was qualitatively surveyed from equilibrium trajectories borne from computer simulations.

Recent Advances in Discotic Liquid Crystal-Assisted Nanoparticles

This article primarily summarizes recent advancement in the field of discotic liquid crystal (DLC) nanocomposites. Discotic liquid crystals are nanostructured materials, usually 2 to 6 nm size and have been recognized as organic semiconducting materials. Recently, it has been observed that the dispersion of small concentration of various functionalized zero-, one- and two-dimensional nanomaterials in the supramolecular order of mesophases of DLCs imparts negligible impact on liquid crystalline properties but enhances their thermal, supramolecular and electronic properties. Synthesis, characterization and dispersion of various nanoparticles in different discotics are presented.