Browsing by Author "Ummer Bashir Khoja"

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Exploring a solid polymorphism and phase transitions in 4-cyano-4′-pentylbiphenyl (5CB) and rGO-doped 5CB using temperature dependent Raman spectroscopy
(Elsevier B.V., 2025) Ummer Bashir Khoja; Chandan Bhai Patel; Pankaj Kumar Tripathi; Rajesh Kumar; Soni Mishra; Sachin Kumar Singh; Ranjan Kumar Singh; Kunwar Vikram
Raman spectroscopy is used to examine the temperature-dependent phase transition behaviour of the liquid crystalline system 4-cyano-4′-pentylbiphenyl (5CB) and its nanocomposite with reduced graphene oxide (5CB@rGO) over the temperature range of −160 °C to 90 °C. First time, such a broad temperature range study of 5CB and 5CB@rGO has been reported. The structural and intermolecular interaction characteristics of the liquid crystal 5CB and its behaviour in the presence of reduced graphene oxide (rGO) are examined in depth by the temperature-induced Raman spectra and DFT calculations. To assess the phase transitions in 5CB and 5CB@rGO, the significant bands associated with the polar C[tbnd]N group and phenyl rings were thoroughly examined. A new crystal-crystal (solid polymorphism) phase transition is investigated first time, occurring between −120 °C and −100 °C. Another significant new crystal-crystal phase transition in 5CB and 5CB@rGO is also exposed, taking place between −20 °C and −10 °C. Differential scanning calorimeter (DSC) measurements confirm this new phase transition in 5CB and temperature sensitivity fairly matches Raman analysis. To evaluate the structural as well as change in intermolecular interactions in each phase, the detailed DFT study is performed on the 5CB molecule to establish the spectra-structure relation. The detailed spectra-structure correlation is discussed in this study. The spectra-structure correlation and change in spectral parameters are used to investigate the structure and intermolecular interaction of each phase. © 2025 Elsevier B.V.
Raman signature of the interaction between functionalized MWCNT and the liquid crystalline system (4DBA)
(American Institute of Physics, 2024) Ummer Bashir Khoja; Chandan Bhai Patel; Rajesh Srivastava; Vijay K. Mishra; Pankaj Tripathi; Amit Raj Singh; Ranjan K. Singh; K. Vikram
Liquid crystalline systems provide the best molecular matrix as a host for carbon nanotubes (CNTs) due to their fluidity character that controls the molecular ordering. The anisotropic shape of the CNTs makes them highly suitable nanoparticles that can be embedded in liquid crystalline systems to achieve uniform tunable dispersion. The uniform and stable dispersion of CNTs in the liquid crystalline host is challenging due to strong Vander Waal forces between CNTs. The functionalization of CNTs is one of the most popular techniques to achieve the dispersion system in an LC host due to the covalent bonding between CNT and LC systems. The COOH functionalized multi-wall carbon nanotubes (F-MWCNT) provide effective sites to interact with LC systems with the carboxylic group at the terminal. Raman spectroscopy is used as a probe to investigate the interaction between 4DBA and F-MWCNT through COOH - -COOH dimer formation. Comparative Raman analysis of 4DBA, 4DBA + bare MWCNT, and 4DBA + F-MWCNT spectra show bands associated with the COOH group giving strong evidence of interaction between 4DBA and F-MWCNT. Raman study reveals the mechanism of dimer formation between F-MWCNT and 4DBA. © 2024 Author(s).