Articles written in Bulletin of Materials Science

• Influence of zinc oxide nanorods on an orientationally ordered fluid comprising soft-bent dimers

Bent-core liquid crystals (LCs) introduced a whole new dimension to the science of LCs. Besides re-emphasizing the importance of the shape of the molecule, they brought in phases with symmetry, not known earlier.Another sub-class of systems that is emerging is that of soft-bent molecules. In contrast with the bent-core molecules, here the bend is achieved through the parity of the aliphatic linker that connects two monomers. They hold the unique advantage that a simple variation of temperature can favour different conformer states and thus govern the self-assembled structure. A highlight of the power of this route is seen in terms of the discovery of a new type of nematic, viz., twist–bend nematic. Investigations on not only this phase but also the regular nematic that often precedes it have received significant attention in the last few years. Here we present results on the regular nematic phase of a binary mixture comprising such a soft-ben dimer, known in the literature as CB7CB, by incorporating zinc oxide nanorods (NRs) into the system. The NRs with anaspect ratio of $\sim$7.2, not very different from that of LCs, further accentuate the importance of shape and shape anisotropy of the entities. Specifically, we observe that the nematic–isotropic transition temperature increases by $\sim$1.9K even for a low concentration of 4% NRs.While the dielectric anisotropy decreases, birefringence shows a substantial increase, adding to thecomplexity of the influence. Upon addition of minute amount of NRs (1%), while the splay elastic constant gets enhanced, its bend counterpart not only gets reduced but retains the convex-shaped thermal profile seen for the parent mixture.

• Confinement of an antiferroelectric liquid crystal in a polymer nanonetwork: thermal and dielectric behaviour

We report the thermal and dielectric investigations on a liquid crystal exhibiting an antiferroelectric phase and confined in a polymer network of sub-micron dimensions. Two different photo-polymerizable monomers have beenemployed for the purpose: one of them (HDDA) is bereft of any aromatic parts, while the other (RM82) contains aromatic as well as aliphatic units and, in fact, forms a liquid crystalline phase in its monomeric state. The polymerization, whichis carried out in the presence of the liquid crystalline host, is expected to yield a nanosegregated structure for HDDA and blended structure for the RM82 case, the difference reflecting the morphologies of the networks, as evidenced by SEMimages. Surprisingly, even a small concentration of the latter polymer added to the former variety has substantial influence on the morphology. The main work focusses on calorimetry and dielectric relaxation spectroscopy of the host liquid crystal confined in these nanonetworks created by the polymers, which can be considered to form virtual surfaces with a finite anchoring energy.We have investigated the in-phase and antiphase modes in the antiferroelectric phase, and the soft mode in the paraelectric phase preceding the antiferroelectric phase. The relaxation frequencies of all these modes are substantiallyinfluenced by the network, with the results showing certain surprises in cases containing both HDDA and RM82.

• The fascinating world of Soft Materials

• # Bulletin of Materials Science

Volume 44, 2021
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Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020