BITS Faculty Publications

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    High-performance, high energy density symmetric supercapacitors based on δ-MnO2 nanoflower electrodes incorporated with an ion-conducting polymer
    (RSC, 2024-11) Dalvi, Anshuman
    The present work investigates liquid-based and liquid-free supercapacitors assembled using δ-MnO2-nanoflower-based electrodes. An optimized electrode composition was prepared using acetylene black (AB), a polymer (PEO), a salt (LiClO4), and δ-MnO2 and used for device fabrication. The composite electrode was tested against a liquid electrolyte and a ‘liquid-free’ composite solid polymer electrolyte (CSPE) membrane. In a three electrode geometry, with 1 M solution of LiClO4 as an electrolyte, the specific capacitance of the electrode was found to be ∼385 F g−1, with a specific energy of ∼23 W h kg−1 and specific power of ∼341 W kg−1 (at 1 mA, 1 V). Dunn's method confirmed that the charge storage process was predominantly pseudocapacitive. When the device was assembled in a two-electrode Swagelok cell, a stable specific capacitance of ∼216 F g−1 was observed with a specific energy of 30 W h kg−1 and a specific power of 417 W kg−1. The supercapacitors exhibited stable performance up to ∼7000 cycles with ∼90% capacitance retention and ∼97% coulombic efficiency. A combination of these cells could light two white light-emitting diodes (LEDs, 3 V) for at least ∼10 minutes. Further, all-solid-state supercapacitors (ASSCs) were fabricated using a Li+ ion (CSPE) membrane. The ASSCs exhibited a specific capacitance of ∼496 F g−1 after ∼500 cycles, with a specific energy and power of ∼19 W h kg−1 and ∼367 W kg−1, respectively. The investigation reveals that the electrodes are versatile and show compatibility with liquid and solid electrolytes. The polymer in the electrode matrix plays an important role in enhancing device performance.
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    Antibacterial and antiviral materials based on biodegradable polymers
    (ACS, 2023-12) Jain, Ankit
    Antibacterial and antiviral materials based on biodegradable polymers have become a key area of research in recent years due to the increasing concern over bacterial and viral infections. Biodegradable polymers are attractive for medical applications due to their biocompatibility, biodegradability, and low toxicity. They can be used to produce various antibacterial and antiviral materials such as films, coatings, and nanoparticles. These materials can be used for medical implants, wound dressings, drug delivery systems, and personal protective equipment. Several strategies have been employed to develop antibacterial and antiviral materials based on biodegradable polymers. One approach is to incorporate antimicrobial agents into the polymer matrix, such as nanoparticles, and antibiotics. This chapter focuses on the different antibacterial and antiviral materials based on biodegradable polymers and the application of NPs developed from such materials. The mechanisms of action and performance of these materials against bacteria and viruses are discussed. The challenges and prospects of using these materials are also discussed. The potential of these materials to provide effective and sustainable solutions to combat bacterial and viral infections makes them a promising area of research for the development of new antimicrobial materials.
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    Magnetic nanoparticles–polymer composites for multifeatured drug delivery
    (Elsevier, 2024) Jain, Ankit
    The magnetic nanocomposite is considered to be a hybrid nanocomposite showing a potential application in multifaceted areas of healthcare and medicine such as targeted drug delivery, experimental diagnostics, the genesis of the better biocompatible compound, coating, and separation. Magnetic nanomaterials are incorporated in matrix-like hydrogels, polymers, carbon, ceramic metal frameworks, etc., which produce aggregated systems forming a magnetic nanocomposite. One such material is the ferrites, such as hematite and magnetite, which have shown beneficial holdings such as favorable chemical durability and evidenced low toxicity, and the ratio of surface to volume promises high functionality. Polymer-modified nanoparticles fabricated with magnetic particles also show a great response in targeting anticancer drugs such as doxorubicin, which improves the efficacy. Variegated external factors also influence the targeting of drugs to a specified site. This chapter includes the classification of magnetic nanocomposites such as polymer matrix nanocomposites, mesoporous magnetic nanocomposites, self-assembled colloidal nanocomposites, and multifunctional magnetic nanocomposites. It also summarizes synthesis techniques of magnetic polymer nanocomposites.
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    Electronic Structures and Optical Absorption of N-Type Conducting Polymers at Different Doping Levels
    (ACS, 2019-06) Ghosh, Sarbani
    Theoretical understanding of the electronic structure and optical transitions in n-doped conducting polymers is still controversial for polaronic and bipolaronic states and is completely missing for the case of a high doping level. In the present paper, the electronic structure and optical properties of the archetypical n-doped conducting polymer, double-stranded benzimidazo-benzophenanthroline ladder (BBL), are studied using the density functional theory (DFT) and the time-dependent DFT method. We find that a polaronic state in the BBL chain is a spin-resolved doublet where the spin degeneracy is lifted. The ground state of two electrons corresponds to a triplet polaron pair, which is in stark contrast to a commonly accepted picture where two electrons are postulated to form a spinless bipolaron. The total spin gradually increases until the reduction level reaches cred = 100% (i.e., one electron per monomer unit). With further increase of the reduction level, the total spin decreases until it becomes 0 for the reduction level cred = 200%. The calculated results reproduce the experimentally observed spin signal without any phenomenological parameters. A detailed analysis of the evolution of the electronic structure of BBL and its absorption spectra with increase in reduction level is presented. The calculated UV–vis–NIR spectra are compared with the available experimental results. The electronic structure and optical absorption for different reduction levels presented here are generic to a wide class of conducting polymers, which is illustrated by the corresponding calculations for another archetypical conducting polymer, poly(3,4-ethylenedioxythiophene) (best known as PEDOT).
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    Electronic Structures and Optical Properties of p-Type/n-Type Polymer Blends: Density Functional Theory Study
    (ACS, 2020-04) Ghosh, Sarbani
    A blend made of p-type and n-type polymers can act as bipolar/ambipolar material composites that transport both electrons and holes. Although several experimental efforts are currently devoted to p-/n-type blends of conducting polymers, theoretical studies of these systems are missing to a large extent. In the current paper, using the density functional theory (DFT) and the time-dependent DFT, we calculate electronic and optical properties of a p-type/n-type polymeric blend, where we have chosen the poly(3,4-ethylenedioxythiophene)/benzimidazo-benzophenanthroline ladder (PEDOT/BBL) as a model composite system. We demonstrate that in the blend, PEDOT acts as an electron donor and BBL acts as an electron acceptor under doped conditions. However, no charge transfer between the chains takes place for an undoped composite system. Due to a significant difference in the electron affinities and the ionization energies of PEDOT and BBL, the electronic properties of a negatively (positively) doped PEDOT/BBL blend are primarily governed by the chains where negative (positive) charges are localized, i.e., the BBL chains (the PEDOT chains). However, this is no longer valid for the optical absorption where the electronic transition occurs between the two chains and, therefore, the calculated UV–vis–near-infrared (NIR) absorption spectra of the negatively (positively) doped PEDOT/BBL blend are rather different compared to the corresponding spectra of the single BBL chains (PEDOT chains). The electronic coupling between the photoexcited state and the final charge-transfer state of the blend was calculated to be ∼0.08 eV. The results presented here are generic to a wide class of p-type/n-type combinations, which was further confirmed by calculations performed on the polythiophene (PT)/BBL blend
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    Ordered and disordered microstructures of nanoconfined conducting polymers
    (RSC, 2023) Ghosh, Sarbani
    We probe the microstructural differences of conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives under geometrical nanoconfinement using a high-resolution electron microscopy (HRTEM) technique. Highly ordered domains of poly(3,4-ethylenedioxythiophene):tosylate PEDOT:Tos, which is polymerized within alumina nanochannels, are observed. These features are in contrast to those of the polymer blend poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) PEDOT:PSS inserted into the nanopores. The extent of the order–disorder parameter in terms of surface crystallization and the number of ordered domains of the long-chain polymers strongly depends on the dopant environment, processing conditions and structural confinement. Atomic force spectroscopy of individual PEDOT nanochannels highlights counterion-dependent surface adhesive factors. The molecular dynamics (MD) simulation of these systems reveals similar polymer chain configurations and the resulting morphology.
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    Dynamics and Rheology of Polymer Melts via Hierarchical Atomistic, Coarse-Grained, and Slip-Spring Simulations
    (ACS, 2021-02) Jana, Pritam Kumar
    A hierarchical (triple scale) simulation methodology is presented for the prediction of the dynamical and rheological properties of high molecular-weight entangled polymer melts. The methodology consists of atomistic, moderately coarse-grained (mCG), and highly coarse-grained slip-spring (SLSP) simulations. At the mCG level, a few chemically bonded atoms are lumped into one coarse-grained bead. At this level, the chemical identity of the underlying atomistic system and the interchain topological constraints (entanglements) are preserved. The mCG interaction potentials are derived by matching local structural distributions of the mCG model to those of the atomistic model through iterative Boltzmann inversion. For matching mCG and atomistic dynamics, the mCG time is scaled by a time scaling factor, which compensates for the lower monomeric friction coefficient of the mCG model than that of the atomistic one. At the SLSP level, multiple Kuhn segments of a polymer chain are represented by one coarse-grained bead. The very soft nonbonded interactions between beads do not prevent chain crossing and, hence, can not capture entanglements. The topological constraints are represented by slip-springs, restricting the lateral motion of polymer chains. A compensating pair potential is used in the SLSP model to keep the static macromolecular properties unaltered upon the introduction of slip-springs. The static and kinetic parameters of the SLSP model are determined based on the lower-level simulation models. Particularly, matching the orientational autocorrelation of the end-to-end vector, we determine the number of slip-springs and calibrate the timescale of the SLSP model. As a test case, the hierarchical methodology is applied to cis-1,4-polybutadiene (cPB) at 413 K. Dynamical single-chain and linear viscoelastic properties of cPB melts are calculated for a broad range of molecular weights, ranging from unentangled to well-entangled chains. The calculations are compared, and found in good agreement, with experimental data from the literature.
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    Dynamics of Long Entangled Polyisoprene Melts via Multiscale Modeling
    (ACS, 2021-09) Jana, Pritam Kumar
    A recently proposed hierarchical triple-scale simulation methodology (Behbahani et al., Macromolecules, 2021,54, 2740–2762) is applied to cis-1,4 polyisoprene melts of a broad range of molecular weights, from oligomers to commercial-grade entangled materials. Dynamics are systematically probed over 12 orders of magnitude in time using a combination of atomistic and bottom-up parameterized coarse-grained and slip-spring simulations. Following calibration of the slip-spring simulations using the end-to-end autocorrelation function, generated data are contrasted to dielectric relaxation spectroscopy experiments and rheological measurements in the literature. A good agreement is found, particularly for highly entangled polymer melts, supporting the ability of the scheme to provide bottom-up parameter-free predictions on the dynamics of polymeric materials. Finally, we systematically examine the application of theoretical models to our strictly monodisperse cis-1,4 polyisoprene melts and provide estimates of the phenomenological parameters employed.
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    Wall-Spring Thermostat: A Novel Approach for Controlling the Dynamics of Soft Coarse-Grained Polymer Fluids at Surfaces
    (ACS, 2022-06) Jana, Pritam Kumar
    The rheological properties of polymer composites depend on the interfacial interactions between solid fillers and a polymer fluid. In highly coarse-grained (hCG) models, where one coarse-grained segment represents multiple monomeric repeat units, the solid surface of a filler appears smooth on the hCG scale. Thus, special simulation techniques are required to control the single-chain dynamics and friction at the solid–fluid contact. We devise a simulation strategy─the wall-spring (WASP) thermostat─where transient bonds are formed between the solid surface and the polymer segments, based on a grand canonical Monte Carlo (MC) algorithm. These transient bonds mimic strong, specific interactions of the polymer segments with the solid. The attraction, induced by the transient bonds, can be compensated with a permanent, analytically known potential such that static properties do not differ from the system without WASPs. The single-chain and collective dynamics of the polymer fluid at the surface can be tailored by the areal density of transient bonds and their lifetime. The WASP thermostat allows us to capture dynamic heterogeneities at surfaces, such as those quantified by the non-Gaussian behavior of the van Hove self-correlation of polybutadiene at silica surfaces, obtained by atomistic simulations. The parametrized hCG model enables us to explore the dynamics of polymers at solid surfaces for a wide range of molecular weights. We study the Navier-slip boundary condition and demonstrate that both the slip length and the position of the hydrodynamic boundary increase like the polymer’s end-to-end distance, Re. Since both lengths are approximately equal, the velocity profile vanishes close to the narrow interface between polymer melt and solid.
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    Bundle formation in parallel aligned polymers with competing interactions
    (IOP, 2016) Dutta, Sandipan
    Aggregation of like-charged polymers is widely observed in biological- and soft-matter systems. In many systems, bundles are formed when a short-range attraction of diverse physical origin like charge bridging, hydrogen bonding or hydrophobic interaction, overcomes the longer-range charge repulsion. In this letter, we present a general mechanism of bundle formation in these systems as the breaking of the translational invariance in parallel aligned polymers with competing interactions of this type. We derive a criterion for finite-sized bundle formation as well as for macroscopic phase separation