DSpace Collection:
http://hdl.handle.net/2289/150
2024-03-25T23:14:32ZEffect of doping of organo-soluble carbon dots on ionic relaxation and conductivity of planar anchored cyanobiphenyl based nematic liquid crystal
http://hdl.handle.net/2289/8241
Title: Effect of doping of organo-soluble carbon dots on ionic relaxation and conductivity of planar anchored cyanobiphenyl based nematic liquid crystal
Authors: P, Priscilla; Singh, Ashwani Kumar; Malik, Praveen; Kumar, Sandeep; Supreet; Gathania, Arvind K.; Prakash, Jai; Castagna, Riccardo; Lucchetta, Daniele Eugenio; Malik, Poonma; Singh, Gautam
Abstract: We demonstrate here the striking effect of organo-soluble carbon dots (CDs, diameter ~7- 8 nm) on the tunability of ionic relaxation and conductivity of the host, planar anchored thermotropic nematic liquid crystal (5CB, 4- Cyano-4′-pentylbiphenyl). The optical texture, frequency, temperature, and concentration dependent dielectric studies of pristine 5CB and CDs-5CB composites have been performed using the polarising optical microscope and high-resolution dielectric spectroscopy, respectively. The doping of 0.5 wt% CDs into planar anchored 5CB is resulted into the vertical alignment confirmed through the cross-polarised optical microscope. The doping of CDs in 5CB liquid crystal is resulted into an unprecedented faster ionic relaxation with an abatement of the ionic amplitude at room temperature. The shift in the relaxation frequency for 0.5 wt% CDs-5CB composite (induced vertical alignment) as compared to pristine 5CB (planar aligned) at 28 ◦C (nematic) is found to be ~13 folds which is further increased to ~18 folds at 38 ◦C (isotropic). A similar trend in the conductivity curve is also observed which further confirms the significant enhancement in conductivity value with increase in temperature and concentration of dopant CDs. The observation of enhanced ionic conductivity and faster ionic relaxation in CDs-5CB composites as compared to pristine 5CB are attributed to the complete change of planar to vertical alignment by doping of CDs on planar anchored liquid crystal sample cells. It appears that the plausible strong interaction between hydrocarbon chains of CDs and 5CB molecules through anchored substrate surfaces with increasing concentration of CDs and decrease in rotational viscosity of host 5CB with increasing temperature certainly plays a pivotal role in the tuning of ionic relaxation and conductivity in the liquid crystal sample cells. We certainly believe that our results would catalyze the cognizance of the ionic relaxation and conductivity in CDs-5CB composites and other related systems. Moreover, such composites with tunable ionic relaxation/conductivity would be certainly helpful in the fabrication of various tuneable devices such as wave front corrector, low frequency oscillation generators, dynamic light scattering, and so on.
Description: Restricted Access.2024-04-05T00:00:00ZLeaning induced layer undulated tilted smectic phase of asymmetric bent-core liquid crystals
http://hdl.handle.net/2289/8236
Title: Leaning induced layer undulated tilted smectic phase of asymmetric bent-core liquid crystals
Authors: Mishra, Vishnu Deo; Srinivasa, H.T.; Roy, Arun
Abstract: We report the synthesis and experimental studies on the liquid crystalline phase of a homologous series of compounds comprised of strongly asymmetric bent-core banana shaped molecules. Our x-ray diffraction studies clearly indicate that the compounds exhibit a frustrated tilted smectic phase with layer undulated structure. The low value of the dielectric constant as well as switching current measurements indicate
the absence of polarization in this layer undulated phase. In spite of the absence of polarization, a planar aligned sample can be transformed irreversibly to a higher birefringent texture on the application of a high electric field. The zero field texture can only be retrieved by heating the sample to the isotropic phase and cooling it subsequently to the mesophase. We propose a double tilted smectic structure having layer undulation to account for the experimental observations with the layer undulation arising due to the leaning of the molecules in the layer.
Description: Restricted Access.2023-02-21T00:00:00ZInterfacial instabilities in confined displacements involving non-Newtonian fluids
http://hdl.handle.net/2289/8235
Title: Interfacial instabilities in confined displacements involving non-Newtonian fluids
Authors: Parmar, Vaibhav Raj Singh; Bandyopadhyay, Ranjini
Abstract: The growth of interfacial instabilities during fluid displacements can be driven by gradients in pressure, viscosity and surface tension, and by applying external fields. Since displacements of non-Newtonian fluids such as polymer solutions, colloidal and granular slurries are ubiquitous in natural and industrial processes, understanding the growth mechanisms and fully-developed morphologies of interfacial patterns involving non-Newtonian fluids is extremely important. In this perspective, we focus on {displacement experiments} wherein competition{s} between capillary, viscous, elastic and frictional forces drive the onset and growth of interfacial instabilities in confined geometries. We conclude by highlighting several exciting open problems in this research area.
Description: Restricted Access.2024-03-14T00:00:00ZGlassy relaxation in a de Vries smectic liquid crystal consisting of bent-core molecules
http://hdl.handle.net/2289/8233
Title: Glassy relaxation in a de Vries smectic liquid crystal consisting of bent-core molecules
Authors: Mishra, Vishnu Deo; Pratap, G.; Roy, Arun
Description: Restricted Access.2024-02-26T00:00:00Z