Papers by sourav patranabish
Physical review, May 14, 2021
We study a quantum-dots (QDs) dispersed bent-core nematic liquid crystalline system in planar geo... more We study a quantum-dots (QDs) dispersed bent-core nematic liquid crystalline system in planar geometry and present experimental measurements of the birefringence (∆n), order parameter (S), dielectric dispersion and absorption spectra, optical textures, with attention to variations with temperature. A bent-core liquid crystal (LC) 14-2M-CH3 is used as the host material and CdSe/ZnS core-shell type QDs are used as the dopant. The nematic (N) phase of the pristine (undoped) LC 14-2M-CH3 contains cybotactic clusters, which are retained by its QDs incorporated LC nanocomposite. Our experimental findings support (i) reduced orientational order parameter of the QDs dispersed LC system compared to its pristine counterpart, at fixed temperatures, (ii) reduced cybotactic cluster sizes due to the incorporation of QDs and (iii) increased activation energies related to reduced cluster sizes. We complement the experiments with a novel Landau-de Gennes type free energy for a doped bent core LC system, that qualitatively captures the doping-induced reduced order parameter and its dependence on the properties of the QDs, and its variation with temperature.
Physical review, Jan 28, 2019
The bent-core liquid crystals (LCs) are highly regarded as the next-generation materials for elec... more The bent-core liquid crystals (LCs) are highly regarded as the next-generation materials for electro-optic devices. The nematic (N) phase of these LCs possesses highly ordered smecticlike cybotactic clusters which are promising in terms of ferroelectric-like behaviour in the N phase itself. We have studied a one-dimensional (1D) Landau-de Gennes model of spatially inhomogeneous order parameters for the N phase of bent-core LCs. We investigate the effects of spatial confinement and coupling (between these clusters and the surrounding LC molecules) on the order parameters to model cluster formation in recently reported experiments. The coupling is found to increase the cluster order parameter significantly, suggesting an enhancement in the cluster formation and could also predict a possible transition to a phase with weak nematic-like ordering in the vicinity of nematic-isotropic transition upon appreciable increase of the coupling parameter γ.
Journal of Physics: Condensed Matter, Sep 20, 2022
Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helica... more Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helical structure, macroscopic polarization and fast switching speeds The twist-bend nematic (N tb) phase is a recent addition to the nematic (N) phases of liquid crystals (LCs). A net polar order in the N tb phase under an external electric field was predicted in several recent theoretical studies but yet to be experimentally realized. We investigated the polar nature, dielectric properties, electro-optical switching and optical transmission properties of a bent LC dimer CB7CB. The LC showed a relatively high-temperature nematic (N) phase and a lower-temperature nematic (N X) phase (also called N tb in literature). A threshold-dependent polarization current response with large polarization values was obtained in the entire mesophase range. The associated switching times were found in submillisecond region. This ferroelectric-like polarization resulted from collective reorientation of polar cybotactic clusters. In N X phase, electric field-induced deformation of twisted helical structures also contributed to net polarization. Dielectric measurements confirmed the presence of cybotactic clusters via relaxation processes with large activation energies. Deformation of the N X helical structure under external electric field was corroborated by polarized optical microscopy and optical transmission studies. The field-induced deformations, net polar order and fast switching will contribute towards greater understanding of the N X (or N tb) phase dynamics. It may also find applications in next-generation electro-optic devices.
arXiv (Cornell University), Jan 10, 2019
Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helica... more Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helical structure, macroscopic polarization and fast switching speeds The twist-bend nematic (N tb) phase is a recent addition to the nematic (N) phases of liquid crystals (LCs). A net polar order in the N tb phase under an external electric field was predicted in several recent theoretical studies but yet to be experimentally realized. We investigated the polar nature, dielectric properties, electro-optical switching and optical transmission properties of a bent LC dimer CB7CB. The LC showed a relatively high-temperature nematic (N) phase and a lower-temperature nematic (N X) phase (also called N tb in literature). A threshold-dependent polarization current response with large polarization values was obtained in the entire mesophase range. The associated switching times were found in submillisecond region. This ferroelectric-like polarization resulted from collective reorientation of polar cybotactic clusters. In N X phase, electric field-induced deformation of twisted helical structures also contributed to net polarization. Dielectric measurements confirmed the presence of cybotactic clusters via relaxation processes with large activation energies. Deformation of the N X helical structure under external electric field was corroborated by polarized optical microscopy and optical transmission studies. The field-induced deformations, net polar order and fast switching will contribute towards greater understanding of the N X (or N tb) phase dynamics. It may also find applications in next-generation electro-optic devices.
arXiv (Cornell University), Jan 10, 2019
Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helica... more Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helical structure, macroscopic polarization and fast switching speeds The twist-bend nematic (N tb) phase is a recent addition to the nematic (N) phases of liquid crystals (LCs). A net polar order in the N tb phase under an external electric field was predicted in several recent theoretical studies but yet to be experimentally realized. We investigated the polar nature, dielectric properties, electro-optical switching and optical transmission properties of a bent LC dimer CB7CB. The LC showed a relatively high-temperature nematic (N) phase and a lower-temperature nematic (N X) phase (also called N tb in literature). A threshold-dependent polarization current response with large polarization values was obtained in the entire mesophase range. The associated switching times were found in submillisecond region. This ferroelectric-like polarization resulted from collective reorientation of polar cybotactic clusters. In N X phase, electric field-induced deformation of twisted helical structures also contributed to net polarization. Dielectric measurements confirmed the presence of cybotactic clusters via relaxation processes with large activation energies. Deformation of the N X helical structure under external electric field was corroborated by polarized optical microscopy and optical transmission studies. The field-induced deformations, net polar order and fast switching will contribute towards greater understanding of the N X (or N tb) phase dynamics. It may also find applications in next-generation electro-optic devices.
We report possible biaxiality in the nematic phase of a bent-core liquid crystal compound exhibit... more We report possible biaxiality in the nematic phase of a bent-core liquid crystal compound exhibiting cybotactic clustering in entire nematic liquid crystal phase using dielectric spectroscopy with promising application in faster switching displays.
Macromolecular Rapid Communications, Aug 2, 2022
Polymers and peptides have recently been considered as promising materials for piezoelectric ener... more Polymers and peptides have recently been considered as promising materials for piezoelectric energy harvesting because of their biocompatibility and enormous design possibility. However, achieving significant output voltages while meeting environmental safety requirements, low cost, and easy fabrication remains a major challenge. Herein, lipidated pseudopeptide incorporated poly(vinylidene fluoride) (PVDF) composite films are fabricated. Adding lipidated pseudopeptide (BLHA) increases the electroactive phase content, reaching the maximum for the 2 wt% composite film. The composite film containing 2 wt% BLHA manifests the highest dielectric constant and remnant polarization (Pr), among others. A piezoelectric energy harvesting device fabricated with this film generates open‐circuit output voltages up to 23 V, five times amplified output compared to pure PVDF. To the best of our knowledge, this material is superior among the peptide‐based piezoelectric energy harvesters reported in the literature. The device is flexible, durable, low cost, and sensitive to high and low pressures. It can power up multiple liquid crystal display panels when pressed with a finger. The non‐covalent interaction between BLHA and PVDF is the reason behind the composites’ improved piezoelectric response. Density functional theory calculations also support this notion.
Macromolecular Rapid Communications, Jul 22, 2022
The bent-core liquid crystals (LCs) are highly regarded as the next-generation materials for elec... more The bent-core liquid crystals (LCs) are highly regarded as the next-generation materials for electro-optic devices. The nematic (N) phase of these LCs possesses highly ordered smectic-like cybotactic clusters which are promising in terms of ferroelectric-like behaviour in the N phase itself. We have studied a one-dimensional (1D) Landau-deGennes model of spatially inhomogeneous order parameters for the N phase of bent-core LCs. We investigate the effects of spatial confinement and coupling (between these clusters and the surrounding LC molecules) on the order parameters to model cluster formation in recently reported experiments. The coupling is found to increase the cluster order parameter significantly, suggesting an enhancement in the cluster formation and could also predict a possible transition to a phase with weak nematic-like ordering in the vicinity of nematic-isotropic transition upon appreciable increase of the coupling parameter γ.
Journal of Molecular Liquids, 2018
Abstract Nematic phase of bent-core liquid crystals (LCs) exhibiting cybotactic clusters (NCyb) h... more Abstract Nematic phase of bent-core liquid crystals (LCs) exhibiting cybotactic clusters (NCyb) have gained significant importance owing to its promising ability to demonstrate macroscopic biaxiality and the ferronematic phase. In this context, three achiral unsymmetrical four-ring bent-core LC compounds, bearing a long alkyloxy chain and differing only in the terminal substituent moiety (methyl, chloro, nitro), are designed and synthesized followed by their optical, dielectric, electro-optic and structural investigations. The presence of NCyb in the methyl and chloro substituted compounds was confirmed via dielectric spectroscopy and X-ray diffraction observations. The absence of ferroelectric behaviour in any of these compounds, even in the cybotactic nematic phase and in presence of polar substituent moieties (chloro and nitro), is attributed to the increased alkyloxy chain length and antiparallel molecular arrangement. The density functional theory (DFT) optimized molecular structure along with the experimental observations further substantiates these findings. The study establishes that cybotactic clusters and polar end moiety, although being a prerequisite for ferroelectric-like nature, do not necessarily result in a ferronematic phase.
13th International Conference on Fiber Optics and Photonics, 2016
We report possible biaxiality in the nematic phase of a bent-core liquid crystal compound exhibit... more We report possible biaxiality in the nematic phase of a bent-core liquid crystal compound exhibiting cybotactic clustering in entire nematic liquid crystal phase using dielectric spectroscopy with promising application in faster switching displays.
The twist-bend nematic (Ntb) phase is a recent addition to the nematic (N) phases of liquid cryst... more The twist-bend nematic (Ntb) phase is a recent addition to the nematic (N) phases of liquid crystals (LCs). A net polar order in the Ntb phase under an external electric field was predicted in several recent theoretical studies but yet to be experimentally realized. We investigated the polar nature, dielectric properties, electro-optical switching and optical transmission properties of a bent LC dimer CB7CB. The LC showed a relatively high-temperature nematic (N) phase and a lower-temperature nematic (NX) phase (also called Ntb in literature). A threshold-dependent polarization current response with large polarization values was obtained in the entire mesophase range. The associated switching times were found in sub-millisecond region. This ferroelectric-like polarization resulted from collective reorientation of polar cybotactic clusters. In NX phase, electric field-induced deformation of twisted helical structures also contributed to net polarization. Dielectric measurements confi...
arXiv: Soft Condensed Matter, 2019
A fast switching liquid crystal (LC), especially in its nematic (N) phase, can significantly impr... more A fast switching liquid crystal (LC), especially in its nematic (N) phase, can significantly improve the performance and properties of present-day electro-optic devices and displays. We investigated the polar nature and switching behaviour of a bent shaped liquid crystal (LC) CB7CB at different temperatures, subjected to applied voltages of varying amplitude and frequency. A threshold-dependent polarization current response, with large spontaneous polarization, was observed in the nematic (N) and in the twist-bend nematic (Ntb) phases exhibited by the LC compound. The current response was identified as ferroelectric-like in nature, and the corresponding switching time was found to lie in the range of ~ 500 {\mu}s in the N phase, which is fast compared to the usual nematic switching time (in the range of milliseconds). The nematic switching is bi-stable in nature and the nematic polarization arises from the collective reorientation of cybotactic clusters on field-reversal. At larger ...
Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helica... more Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helical structure, macroscopic polarization and fast switching speeds Sourav Patranabish, Aloka Sinha*, Madhu B. Kanakala and C. V. Yelamaggad a Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India; b Centre for Nano and Soft Matter Sciences, P. B. No. 1329, Prof. U. R. Rao Road, Jalahalli, Bengaluru 560013, India;
Physical review. E, 2021
We study a quantum-dots (QDs) dispersed bent-core nematic liquid crystalline system in planar geo... more We study a quantum-dots (QDs) dispersed bent-core nematic liquid crystalline system in planar geometry and present experimental measurements of the birefringence (Δn), order parameter (S), dielectric dispersion, absorption spectra, and optical textures with attention to variations with temperature. A bent-core liquid crystal (LC) 14-2M-CH_{3} is used as the host material and CdSe/ZnS core-shell type QDs are used as the dopant. The nematic (N) phase of the pristine (undoped) LC 14-2M-CH_{3} contains cybotactic clusters, which are retained by its QDs incorporated LC nanocomposite. Our experimental findings support: (i) reduced orientational order parameter of the QDs dispersed LC system compared to its pristine counterpart at fixed temperatures, (ii) reduced cybotactic cluster sizes due to the incorporation of QDs, and (iii) increased activation energies related to reduced cluster sizes. We complement the experiments with a novel Landau-de Gennes-type free energy for a doped bent-core...
Physical Review E
The bent-core liquid crystals (LCs) are highly regarded as the next-generation materials for elec... more The bent-core liquid crystals (LCs) are highly regarded as the next-generation materials for electro-optic devices. The nematic (N) phase of these LCs possesses highly ordered smecticlike cybotactic clusters which are promising for electro-optic applications. We have studied a one-dimensional Landau-de Gennes model of spatially inhomogeneous order parameters for the N phase of bent-core LCs. We investigate the effects of spatial confinement and coupling (between these clusters and the surrounding LC molecules modeled by a coupling parameter γ) on the order parameters. The coupling is found to increase the cluster order parameter significantly, suggesting enhancement in cluster formation, and also predicts a transition to a phase with weak nematiclike ordering above the nematic supercooling temperature.
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Papers by sourav patranabish