Jai Prakash

Here, we present the observations on the morphological appearance of multiferroic core-shell CoFe2O4/ZnO nanocrystals (CFZNCs) dispersed into the nematic liquid crystal (NLC, 5CB) matrix. A concentration-dependent patterning of CFZNCs clusters has been found to nucleate during the Fréedericksz transition on the application of sufficient dc bias across the CFZNCs/5CB samples. Well-ordered two-dimensional patterns were seen for intermediate doping concentrations of CFZNCs (0.05 wt. % and 0.1 wt. %), whereas, intense aggregation was observed at higher concentration (0.2 wt. %). It has been found that the size of the planarly aligned patterned domains (PPDs) varied (from 25 to 6 μm) on increasing the dc bias across the CFZNCs/5CB composite during the Fréedericksz transitions. Interestingly, the chain-like clusters of CFZNCs appeared on the circumference of the PPDs embedded within the homeotropically aligned 5CB material. The formation of PPDs could be attributed to the LC-anisotropy-imparted ordering of CFZNCs in the vicinity of Fréedericksz transition. We hope that the present work will add to our understanding of LC-imparted self-assembly of NCs/QDs in an anisotropic medium like LCs for facilitating their applications in the fabrication of photonic devices.

Recently, doping guest materials such as quantum dots (QDs) into liquid crystals (LCs) has been of great interest since their addition substantially enhances the properties of LC and opens new avenues for scientific advancement. Here, we report the induction of homeotropic alignment in cells without alignment layers of the negative dielectric nematic liquid crystal, N-(4-Methoxybenzylidene)-4-butylaniline (MBBA) by doping with carbon dots (CDs ∼2.8 ± 0.72 nm). The CDs-MBBA composites (CDs concentration: 0.002, 0.01, 0.03, 0.1 and 0.3 wt%) were investigated using optical polarising microscopy, electro-optical and dielectric techniques. Polarizing optical micrographs and voltage dependent optical transmission revealed the induced homeotropic alignment for all the composites under investigation. Interestingly, the least concentrated sample, 0.002 wt% exhibited partial homeotropic alignment. However, due to light leakage, the optical transmission value below threshold voltage was relatively higher than the rest of the composites. MBBA is a negative dielectric material, hence the application of a voltage across the cell was able to switch the alignment from a dark to a bright state for all composites. However, above a certain voltage (>threshold voltage), the bright state produced some instabilities. The value of dielectric permittivity was observed to decrease with increasing concentration, confirming the effect of CDs in producing homeotropic alignment in MBBA. Measurements as a function of temperature were conducted to examine the thermal stability of the induced alignment. The alignment was found to be stable throughout the nematic phase of MBBA. The induction of such alignment without conventional alignment (i.e., rubbing of polyimides) technique can be helpful in addressing the evolving display demands by making liquid crystal displays (LCDs) and other display devices cost effective.