1
|
Kovalchuk O, Kovalchuk T, Tomašovičová N, Timko M, Zakutanska K, Miakota D, Kopčanský P, Shevchuk O, Garbovskiy Y. Dielectric and electrical properties of nematic liquid crystals 6CB doped with iron oxide nanoparticles. The combined effect of nanodopant concentration and cell thickness. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.120305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
2
|
Patranabish S, Sinha A, Kanakala MB, Yelamaggad CV. Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helical structure and macroscopic polarization. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:465101. [PMID: 36067787 DOI: 10.1088/1361-648x/ac8fd3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Accepted: 09/06/2022] [Indexed: 06/15/2023]
Abstract
The twist-bend nematic (Ntb) phase is a recent addition to the family of nematic (N) phases of liquid crystals (LCs). A net polar order in the Ntbphase under an external electric field is interesting and it was predicted in several recent theoretical studies. We investigated the field-induced polarization behaviour, dielectric, and electro-optic properties of a bent LC dimer CB7CB in the N and Ntbphases. A threshold-dependent polarization current response was obtained in both the phases under triangular and square-wave input electric fields, existing till frequencies as high as 150 Hz. The polarization switching times were found in ∼1 ms region, especially in the N phase. In the Ntbphase, electric field-induced deformation of the helical structure was observed, like ferroelectric LCs. Dielectric measurements revealed the presence of cybotactic clusters via collective relaxations. The dielectric anisotropy (Δϵ) is negative at the frequencies of polarization measurements. The net polarization resulted from field-induced reorientation of cybotactic clusters and additionally from the field-induced deformation of helical structures in the Ntbphase. We explored the possibility of ionic contributions to the net polarization by synthesizing TiO2nanoparticles (NPs) dispersed CB7CB LC nanocomposite. Incorporation of the NPs resulted in reduction of the collective order, increase in the ionic impurity content and conductivity, but an extinction of the field-induced polarization response. Our results demonstrate that the net polarization has competing contributions from both ferroelectric-like and ionic origin (up to ∼10 Hz) in the LC phases, but it becomes dominantly ferroelectric-like at higher frequencies.
Collapse
Affiliation(s)
- Sourav Patranabish
- Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Aloka Sinha
- Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Madhu B Kanakala
- Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Dasanapura Hobli, Bengaluru 562162, India
| | - C V Yelamaggad
- Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Dasanapura Hobli, Bengaluru 562162, India
| |
Collapse
|
3
|
Patranabish S, Wang Y, Sinha A, Majumdar A. Quantum-dots-dispersed bent-core nematic liquid crystal and cybotactic clusters: Experimental and theoretical insights. Phys Rev E 2021; 103:052703. [PMID: 34134338 DOI: 10.1103/physreve.103.052703] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2020] [Accepted: 04/09/2021] [Indexed: 11/07/2022]
Abstract
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 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.
Collapse
Affiliation(s)
- Sourav Patranabish
- Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Yiwei Wang
- Department of Applied Mathematics, Illinois Institute of Technology, Chicago, Illinois 60616, USA
| | - Aloka Sinha
- Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Apala Majumdar
- Department of Mathematics and Statistics, University of Strathclyde, Glasgow G11XQ, United Kingdom
| |
Collapse
|
4
|
Garbovskiy Y. Conventional and unconventional ionic phenomena in tunable soft materials made of liquid crystals and nanoparticles. NANO EXPRESS 2021. [DOI: 10.1088/2632-959x/abe652] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Abstract
A great variety of tunable multifunctional materials can be produced by combining nanoparticles and liquid crystals. Typically, the tunability of such soft nanocomposites is achieved via external electric fields resulting in the field-induced reorientation of liquid crystals. This reorientation can be altered by ions normally present in liquid crystals in small quantities. In addition, nanomaterials dispersed in liquid crystals can also affect the behavior of ions. Therefore, an understanding of ionic phenomena in liquid crystals doped with nanoparticles is essential for future advances in liquid crystal-aided nanoscience and nanotechnology. This paper provides an overview of the ionic effects observed in liquid crystals doped with nanomaterials. An introduction to liquid crystals is followed by a brief overview of nanomaterials in liquid crystals. After giving a basic description of ions in liquid crystals and experimental methods to measure them, a wide range of ionic phenomena in liquid crystals doped with different types of nanomaterials is discussed. After that, both existing and emerging applications of tunable soft materials made of liquid crystals and nanodopants are presented with an emphasis on the role of ionic effects in such systems. Finally, the discussion of unsolved problems and future research directions completes the review.
Collapse
|
5
|
Lalik S, Deptuch A, Jaworska-Goła B T, Fryń P, Dardas D, Stefańczyk O, Urbańska M, Marzec M. Modification of AFLC Physical Properties by Doping with BaTiO 3 Particles. J Phys Chem B 2020; 124:6055-6073. [PMID: 32569472 DOI: 10.1021/acs.jpcb.0c02401] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In this paper, for the first time, the influence of the BaTiO3 particles on the antiferroelectric liquid crystalline phase was shown. Low concentrations and two different sizes of BaTiO3 particles (nano- and submicroparticles) were used. It was found that admixture of the ferroelectric particles causes a decrease in the concentration of free ions in the liquid crystal matrix. Despite the small amount of admixture, a decrease in spontaneous polarization, switching time and rotational viscosity, was observed, while the tilt angle of molecules and the smectic layer thickness did not change. It turns out that BaTiO3 particles have a very large impact on the dielectric spectra not only in the antiferroelectric phase but also in the ferroelectric and paraelectric phases of the polymorphic mixture studied. The dopants affect also the complex conductivity. In this paper, we explain why some properties are modified by BaTiO3 particles and others are not.
Collapse
Affiliation(s)
- Sebastian Lalik
- Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków, Poland
| | - Aleksandra Deptuch
- Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków, Poland.,Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31-342 Kraków, Poland
| | | | - Patryk Fryń
- Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków, Poland
| | - Dorota Dardas
- Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań, Poland
| | - Olaf Stefańczyk
- Department of Chemistry, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-0033 Tokyo, Japan
| | - Magdalena Urbańska
- Institute of Chemistry, Military University of Technology, Kaliskiego 2, 00-908, Warszawa, Poland
| | - Monika Marzec
- Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków, Poland
| |
Collapse
|
6
|
On the Analogy between Electrolytes and Ion-Generating Nanomaterials in Liquid Crystals. NANOMATERIALS 2020; 10:nano10030403. [PMID: 32106491 PMCID: PMC7152844 DOI: 10.3390/nano10030403] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Revised: 02/18/2020] [Accepted: 02/19/2020] [Indexed: 12/20/2022]
Abstract
Nanomaterials in liquid crystals are a hot topic of contemporary liquid crystal research. An understanding of the possible effects of nanodopants on the properties of liquid crystals is critical for the development of novel mesogenic materials with improved functionalities. This paper focuses on the electrical behavior of contaminated nanoparticles in liquid crystals. More specifically, an analogy between electrolytes and ion-generating nanomaterials in liquid crystals is established. The physical consequences of this analogy are analyzed. Under comparable conditions, the number of ions generated by nanomaterials in liquid crystals can be substantially greater than the number of ions generated by electrolytes of similar concentration.
Collapse
|
7
|
Nanomaterials in Liquid Crystals as Ion-Generating and Ion-Capturing Objects. CRYSTALS 2018. [DOI: 10.3390/cryst8070264] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|