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Dhara P, Mukherjee R. Phase separation and dewetting of polymer dispersed liquid crystal (PDLC) thin films on flat and patterned substrates. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.117360] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Shinohara E, Watanabe C, Yanagisawa M. Perpendicular alignment of the phase-separated boundary in adhered polymer droplets. SOFT MATTER 2021; 17:9499-9506. [PMID: 34617089 DOI: 10.1039/d1sm01180d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
We investigated the effect of the adhered interface on the phase separation pattern using two or three adhered droplets containing a binary solution of poly(ethylene glycol) and gelatin. Under the experimental conditions, single domains of the gelatin-rich phase exhibited partial wetting to the droplet adhered interface (DAI) and nonadhered droplet surface. In the case of isolated spherical droplets, the location of the phase separation interface (PSI) of the domains was completely random owing to spatial symmetry. In the adhered droplets, the random orientation of the PSI was observed when the PSI did not contact the DAI. On the other hand, when the PSI contacted the DAI, the PSI was aligned perpendicular to the DAI. Frequency analysis showed that whether the PSI contacts the DAI is purely stochastic. However, the PSI alignment perpendicular to the DAI increases significantly with three adhered droplets, suggesting that the probability increases with increasing DAI area ratio. We explain this perpendicular pattern by the minimization of the interfacial energy and kinetics with a change in the wetting contact angle. These findings will facilitate the research on the phase separation of polymer solutions inside nonspherical micrometric spaces.
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Affiliation(s)
- Eriko Shinohara
- Komaba Institute for Science, The University of Tokyo, Komaba 3-8-1, Meguro, Tokyo 153-8902, Japan.
- Department of Applied Physics, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Koganei, Tokyo 184-8588, Japan
| | - Chiho Watanabe
- Komaba Institute for Science, The University of Tokyo, Komaba 3-8-1, Meguro, Tokyo 153-8902, Japan.
- Graduate School of Integrated Sciences for Life, School of Integrated Arts and Sciences, Hiroshima University, Kagamiyama 1-7-1, Higashi-Hiroshima, Hiroshima 739-8521, Japan
| | - Miho Yanagisawa
- Komaba Institute for Science, The University of Tokyo, Komaba 3-8-1, Meguro, Tokyo 153-8902, Japan.
- Department of Basic Science, The University of Tokyo, Komaba 3-8-1, Meguro, Tokyo 153-8902, Japan
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Pandey A, Maity S, Murmu K, Middya S, Bandyopadhyay D, Gooh Pattader PS. Self-organization of random copolymers to nanopatterns by localized e-beam dosing. NANOTECHNOLOGY 2021; 32:285302. [PMID: 33761481 DOI: 10.1088/1361-6528/abf197] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2020] [Accepted: 03/23/2021] [Indexed: 06/12/2023]
Abstract
Strategic electron beam (e-beam) irradiation on the surface of an ultrathin (<100 nm) film of polystyrene-poly(methyl methacrylate) (PS-PMMA) random copolymer followed by solvent annealing stimulates a special variety of dewetting, leading to large-area hierarchical nanoscale patterns. For this purpose, initially, a negative (positive) tone of resist PS (PMMA) under weak e-beam exposure is exploited to produce an array of sites composed of cross-linked PS (chain-scissioned PMMA). Subsequently, annealing with the help of a developer solvent engenders dewetted patterns in the exposed zones where PMMA blocks are confined by the blocks of cross-linked PS. The e-beam dosage was systematically varied from 180μC cm-2to 10 000μC cm-2to explore the tone reversal behavior of PMMA on the dewetted patterns. Remarkably, at relatively higher e-beam dosing, both PMMA and PS blocks act as negative tones in the exposed zone. In contrast, the chain scission of PMMA in the periphery of the exposed regions due to scattered secondary electrons caused confined dewetting upon solvent annealing. Such occurrences eventually lead to pattern miniaturization an order of magnitude greater than with conventional thermal or solvent vapor annealed dewetting. Selective removal of PMMA blocks of RCP using a suitable solvent provided an additional 50% reduction in the size of the dewetted features.
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Affiliation(s)
- Ankur Pandey
- Department of Chemical Engineering, Indian Institute of Technology Guwahati, Assam 781039, India
| | - Surjendu Maity
- Center for Nanotechnology, Indian Institute of Technology Guwahati, Assam 781039, India
| | - Kaniska Murmu
- Department of Chemical Engineering, Indian Institute of Technology Guwahati, Assam 781039, India
| | - Sagnik Middya
- Center for Nanotechnology, Indian Institute of Technology Guwahati, Assam 781039, India
| | - Dipankar Bandyopadhyay
- Department of Chemical Engineering, Indian Institute of Technology Guwahati, Assam 781039, India
- Center for Nanotechnology, Indian Institute of Technology Guwahati, Assam 781039, India
| | - Partho Sarathi Gooh Pattader
- Department of Chemical Engineering, Indian Institute of Technology Guwahati, Assam 781039, India
- Center for Nanotechnology, Indian Institute of Technology Guwahati, Assam 781039, India
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Das A, Dey AB, Chattopadhyay S, De G, Sanyal MK, Mukherjee R. Nanoparticle Induced Morphology Modulation in Spin Coated PS/PMMA Blend Thin Films. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:15270-15282. [PMID: 33296208 DOI: 10.1021/acs.langmuir.0c02584] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The influence of adding nanoparticles on the ascast morphology of spin coated immiscible polystyrene/poly(methyl methacrylate) (PS/PMMA) thin films of different thickness (hE) and composition (RB, volume ratio of PS to PMMA) has been explored in this article. To understand the precise effect of nanoparticle addition, the morphology of PS/PMMA thin blend films spin cast from toluene on a native oxide covered silicon wafer substrate was first investigated. It is seen that in particle free films, the generic morphology of the films remains nearly unaltered with increase in hE, for RB = 3:1 and 1:3. In contrast, strong hE dependent morphology transformation is observed in films with RB = 1:1. Subsequently, thiol-capped gold nanoparticles (AuNP) containing films with different particle concentrations (CNP) were cast from the same solvent along with the polymer mixture. We observe that addition of AuNPs barely alters the generic morphology of the films with RB = 3:1. In contrast, the presence of the particles significantly influences the morphology of the films with RB = 1:1 and 1:3, particularly at higher CNP (≈10.0%). X-ray photoelectron spectroscopy and X-ray reflectivity of some samples reveal that the AuNPs tend to migrate to the free surface through the PS phase, thereby stabilizing this layer partially or fully (depending on CNP) against dewetting over a surface of adsorbed PMMA layer and influencing the ascast morphology as a function of CNP. The work is fundamentally important in understanding largely overlooked implications of nanoparticle addition on the morphology of PS/PMMA blend thin films which forms the fundamental basis for future interesting studies involving dynamics of nanoparticles within the blend thin films.
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Affiliation(s)
- Anuja Das
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
| | - Arka Bikash Dey
- Saha Institute of Nuclear Physics, Sector 1, AF Block, Bidhan Nagar, Kolkata, West Bengal 700064, India
| | - Shreyasi Chattopadhyay
- CSIR-Central Glass and Ceramic Research Institute, 196, Raja Subodh Chandra Mallick Rd, Jadavpur, Kolkata, West Bengal 700032, India
| | - Goutam De
- S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India
| | - Milan K Sanyal
- Saha Institute of Nuclear Physics, Sector 1, AF Block, Bidhan Nagar, Kolkata, West Bengal 700064, India
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
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Basu N, Mukherjee R. Evaporative Drying of Sodium Chloride Solution Droplet on a Thermally Controlled Substrate. J Phys Chem B 2020; 124:1266-1274. [DOI: 10.1021/acs.jpcb.9b08809] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Nandita Basu
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering,Indian Institute of Technology Kharagpur, Kharagpur 721 302, West Bengal, India
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering,Indian Institute of Technology Kharagpur, Kharagpur 721 302, West Bengal, India
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Zhang Y, D'Ambra CA, Katsumata R, Burns RL, Somervell MH, Segalman RA, Hawker CJ, Bates CM. Rapid and Selective Deposition of Patterned Thin Films on Heterogeneous Substrates via Spin Coating. ACS APPLIED MATERIALS & INTERFACES 2019; 11:21177-21183. [PMID: 31117458 DOI: 10.1021/acsami.9b05190] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The selective deposition of polymer thin films can be achieved via spin coating by manipulating interfacial interactions. While this "spin dewetting" approach sometimes generates spatial localization on topographic and chemical patterns, the connection between material selection, process parameters, and resulting film characteristics remains poorly understood. Here, we demonstrate that accurate control over these parameters allows incomplete trichlorosilane self-assembled monolayers (SAMs) to induce spin dewetting on both homogeneous (SiO2) and heterogeneous (Cu/SiO2 or TiN/SiO2) surfaces. Glassy polymers undergo a sharp transition from uniform wetting to complete dewetting depending on spin speed, solution concentration, polymer molecular weight, and SAM chemistry. Under optimal conditions, spin dewetting on line-space patterns results in the selective deposition of polymer over regions not functionalized with SAM. The insights described herein clarify the importance of different variables involved in spin dewetting and provide access to a versatile strategy for patterning polymeric thin films.
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Affiliation(s)
| | | | | | - Ryan L Burns
- Tokyo Electron U.S. Holdings, Inc. , Austin , Texas 78741 , United States
| | - Mark H Somervell
- Tokyo Electron U.S. Holdings, Inc. , Austin , Texas 78741 , United States
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Sahoo S, Bhandaru N, Mukherjee R. Reversible morphological switching and deformation hysteresis in electric field mediated instability of thin elastic films. SOFT MATTER 2019; 15:3828-3834. [PMID: 30993267 DOI: 10.1039/c8sm02622j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Reversible morphology switching in a soft elastic film sandwiched between two parallel electrodes when subject to an externally applied electric field is reported herein. In contrast to electric field mediated instability of a thin liquid film, where the instability patterns remain permanent, in the present case the patterns debond completely or partially when the electric field is switched off, depending on whether the gap spacing (dG) between the film and the top electrode is >100 nm or not. The onset of instability is marked with the appearance of isotropic columns when the applied field strength (U) exceeds a critical value (Uc). The subsequent increase in U leads to the gradual transition of the instability patterns from pillars to bi-continuous labyrinths to an array of holes. Complete conformal contact is established between the film and the top electrode at U = UF. When U is reduced, the morphology changes in a reverse sequence. There is a significant level of hysteresis between the bonding and debonding stages, including persistence of the features at much lower voltages due to pinning of the patterns to the top electrode. Complete detachment occurs at a lower voltage UD when dG > 100 nm. The holes fluctuate before complete contact between the film and the top electrode due to competition between the destabilizing electric field and restoring forces due to stretching of the crosslinked polymer matrix.
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Affiliation(s)
- Sumita Sahoo
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal 721302, India.
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Dhara P, Mukherjee R. Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate. RSC Adv 2019; 9:21685-21694. [PMID: 35518868 PMCID: PMC9066433 DOI: 10.1039/c9ra02552a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Accepted: 07/02/2019] [Indexed: 11/21/2022] Open
Abstract
Thermally induced nematic to isotropic (N–I) phase transition and dewetting of 5CB liquid crystal thin films on flat and topographically patterned substrates.
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Affiliation(s)
- Palash Dhara
- Instability and Soft Patterning Laboratory
- Department of Chemical Engineering
- Indian Institute of Technology Kharagpur
- Kharagpur
- India
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory
- Department of Chemical Engineering
- Indian Institute of Technology Kharagpur
- Kharagpur
- India
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Basu N, Mukherjee R. Morphology modulation in evaporative drying mediated crystallization of sodium chloride solution droplet with surfactant. SOFT MATTER 2018; 14:7883-7893. [PMID: 30229795 DOI: 10.1039/c8sm01370e] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We report the evaporative drying of an aqueous droplet containing a dilute solution of sodium chloride (NaCl) on a hydrophobic substrate made of cross-linked poly-dimethyl siloxane (PDMS). The salt concentration Cn was varied between 0.08 molar (M) and 2.0 M. The contact line of the evaporating droplets shows significant initial retraction for all Cn, before they get pinned. While the final morphology comprises a few small NaCl crystals deposited around the pinned contact line, in droplets with a low Cn (<0.5 M), it transforms to a single large salt crystal when Cn > 0.7 M with no peripheral deposition. We further show that the deposition morphology drastically changes when an anionic surfactant, sodium dodecyl sulfate (SDS), is added into the salt-solutions. Even in the surfactant-laden droplets, the final deposition morphology changes significantly as a function of Cn. It transforms from a thick SDS ring surrounding a fractal-like deposit of NaCl crystallites at lower Cn to a peripheral deposit of NaCl crystals at higher Cn due to competition between micelle formation and crystallization. However, the crystallographic orientation of the deposited NaCl crystals remains unaltered irrespective of the presence of surfactant.
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Affiliation(s)
- Nandita Basu
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Pin 721 302, West Bengal, India.
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Khalesi Moghaddam R, Goharpey F, Khademzadeh Yeganeh J. Interplay between phase separation and dewetting in PS/PVME thin films: effect of temperature. SOFT MATTER 2018; 14:6684-6695. [PMID: 30062346 DOI: 10.1039/c8sm00445e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We studied the effects of temperature on the interplay between dewetting and phase separation at shallow and deep depths at two-phase temperatures in PS/PVME polymer blend thin films. Optical microscopy, AFM measurements, and ellipsometry analysis were performed to investigate the dewetting behavior of the films. At the deep quench depth (phase separation temperature of 115 °C), a two-layer film formed, consisting of a thin PVME layer directly on the surface of a silicon wafer (as the wetting layer) and a bulk layer which was the upper layer. In the bulk layer, the phase separation mechanism was controlled by an apparent nucleation and growth mechanism, which was driven by entropic and anisotropic limitations rather than thermodynamic preferences. After about 106 min of annealing, liquid-liquid dewetting occurred in the interface of the formed layers, triggered by Laplace pressure differences. However, at the shallow quench depth (phase separation temperature of 95 °C), a tri-layered structure formed in the thin films and concentration fluctuations at the interfaces of the formed layers triggered surface fluctuations and instabilities (dewetting phenomenon).
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Dhara P, Bhandaru N, Das A, Mukherjee R. Transition from Spin Dewetting to continuous film in spin coating of Liquid Crystal 5CB. Sci Rep 2018; 8:7169. [PMID: 29740096 PMCID: PMC5940909 DOI: 10.1038/s41598-018-25504-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Accepted: 04/13/2018] [Indexed: 12/03/2022] Open
Abstract
Spin dewetting refers to spontaneous rupture of the dispensed solution layer during spin coating, resulting in isolated but periodic, regular sized domains of the solute and is pre-dominant when the solute concentration (Cn) is very low. In this article we report how the morphology of liquid crystal (LC) 5CB thin films coated on flat and patterned PMMA substrate transform from spin dewetted droplets to continuous films with increase in Cn. We further show that within the spin dewetted regime, with gradual increase in the solute concentration, periodicity of the isotropic droplets (λD) as well as their mean diameter (dD), gradually decreases, till the film becomes continuous at a critical concentration (Cn*). Interestingly, the trend that λD reduces with increase in Cn is exact opposite to what is observed in thermal/solvent vapor induced dewetting of a thin film. The spin dewetted droplets exhibit transient Radial texture, in contrast to Schlieren texture observed in elongated threads and continuous films of 5CB, which remains in the Nematic phase at room temperature. Finally we show that by casting the film on a grating patterned substrate it becomes possible to align the spin dewetted droplets along the contours substrate patterns.
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Affiliation(s)
- Palash Dhara
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, Pin-721302, India
| | - Nandini Bhandaru
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, Pin-721302, India
| | - Anuja Das
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, Pin-721302, India
| | - Rabibrata Mukherjee
- Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, Pin-721302, India.
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Liu X, Bhandaru N, Banik M, Wang X, Al-Enizi AM, Karim A, Mukherjee R. Capillary Force Lithography Pattern-Directed Self-Assembly (CFL-PDSA) of Phase-Separating Polymer Blend Thin Films. ACS OMEGA 2018; 3:2161-2168. [PMID: 31458520 PMCID: PMC6641379 DOI: 10.1021/acsomega.7b02078] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Accepted: 02/09/2018] [Indexed: 06/10/2023]
Abstract
We report capillary force lithography pattern-directed self-assembly (CFL-PDSA), a facile technique for patterning immiscible polymer blend films of polystyrene (PS)/poly(methyl methacrylate) (PMMA), resulting in a highly ordered phase-separated morphology. The pattern replication is achieved by capillary force lithography (CFL), by annealing the film beyond the glass transition temperature of both the constituent polymers, while confining it between a patterned cross-linked poly(dimethyl siloxane) (PDMS) stamp and the silicon substrate. As the pattern replication takes place because of rise of the polymer meniscus along the confining stamp walls, higher affinity of PMMA toward the oxide-coated silicon substrate and of PS toward cross-linked PDMS leads to well-controlled vertically patterned phase separation of the two constituent polymers during thermal annealing. Although a perfect negative replica of the stamp pattern is obtained in all cases, the phase-separated morphology of the films under pattern confinement is strongly influenced by the blend composition and annealing time. The phase-separated domains coarsen with time because of migration of the two components into specific areas, PS into an elevated mesa region and PMMA toward the substrate, because of preferential wetting. We show that a well-controlled, phase-separated morphology is achieved when the blend ratio matches the volume ratio of the elevated region to the base region in the patterned films. The proposed top-down imprint patterning of blends can be easily made roll-to-roll-compatible for industrial adoption.
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Affiliation(s)
- Xiangyu Liu
- Department
of Polymer Engineering, University
of Akron, Akron, Ohio 44325, United
States
| | - Nandini Bhandaru
- Instability
and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India
| | - Meneka Banik
- Instability
and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India
| | - Xiaoteng Wang
- Department
of Polymer Engineering, University
of Akron, Akron, Ohio 44325, United
States
| | - Abdullah M. Al-Enizi
- Chemistry
Department, Faculty of Science, King Saud
University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
| | - Alamgir Karim
- Department
of Polymer Engineering, University
of Akron, Akron, Ohio 44325, United
States
| | - Rabibrata Mukherjee
- Instability
and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India
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