Department Of Chemical Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Large scale synthesis of nanoparticles requires their simultaneous synthesis and separation. In this work, we establish a framework for simultaneous synthesis and separation of nanoparticles based on an environmentally benign aqueous two-phase system (ATPS) and illustrate the proof of concept in the synthesis of silver nanoparticles. For this, the ATPS was prepared using polyethylene glycol and trisodium citrate dihydrate. These components act as reducing agents and can be used for nanoparticle synthesis at ambient temperature (∼30 °C). The concentration of the reducing agents in the ATPS is maintained relatively high to ensure the formation of two phases. Nanoparticle synthesis at these high concentrations is achieved using sodium hydroxide as a catalyst. The proclivity of the nanoparticles to adsorb at the liquid-liquid interface is explored and exploited to separate them as they are synthesized. The novel green synthesis and separation technique proposed here is shown to have a significant potential for the synthesis of nanoparticles on a large scale. The unspent reagents in the reaction can be effectively recycled and reused. Copyright © 2020 American Chemical Society.

Department Of Biotechnology

World University root node

ACS Sustainable Chemistry and Engineering

Simultaneous Synthesis and Separation of Nanoparticles Using Aqueous Two-Phase Systems

The kinetics of dissolution of Co in alkaline glycine solution under anodic conditions was investigated. Potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) data of Co dissolving in 0.1 M glycine solution at pH 10 were acquired. At low overpotentials, in the active region, the polarization current increases with potential, whereas at high overpotentials, in the passive region, it decreases with potential. Co surface exposed to the alkaline glycine solution was characterized using scanning electron microscopy and x-ray photoelectron spectroscopy, and based on the binding energies of the deconvoluted peaks, oxides, hydroxides, and Co-glycine complexes were identified as the likely species present on the surface. Impedance data was subjected to electrical equivalent circuit analysis, and a circuit with three Maxwell elements was found to model the faradaic impedance. Polarization and EIS data were also analyzed in the framework of mechanistic analysis, and a mechanism with four adsorbed intermediates is proposed. The proposed model captures the salient features of the polarization and EIS results. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

Journal of Solid State Electrochemistry

Mechanistic analysis of anodic dissolution of cobalt in alkaline glycine solution

Purpose: This paper aims to investigate the role of shapes of containers (nine different containers) on entropy generation minimization involving identical cross-sectional area (1 sq. unit) in the presence of identical heating (isothermal). The nine containers are categorized into three classes based on their geometric similarities (Class 1: square, tilted square and parallelogram; Class 2: trapezoidal type 1, trapezoidal type 2 and triangular; Class 3: convex, concave and curved triangular). Design/methodology/approach: Galerkin finite element method is used to solve the governing equations for a representative fluid (engine oil: Pr = 155) at Ra = 103–105. In addition, finite element method is used to solve the streamfunction equation and evaluate the entropy generation terms (Sψ and Sθ). Average Nusselt number ((Formula presented.)) and average dimensionless spatial temperature ((Formula presented.)) are also evaluated via the finite element basis sets. Findings: Based on larger (Formula presented.), larger (Formula presented.) and optimal Stotal values, containers from each class are preferred as follows: Class 1: parallelogrammic and square, Class 2: trapezoidal type 1 and Class 3: convex (larger (Formula presented.), optimum Stotal) and concave (larger (Formula presented.)). Containers with curved walls lead to enhance the thermal performance or efficiency of convection processes. Practical implications: Comparison of entropy generation, intensity of thermal mixing ((Formula presented.)) and average heat transfer rate give a clear picture for choosing the appropriate containers for processing of fluids at various ranges of Ra. The results based on this study may be useful to select a container (belonging to a specific class or containers with curved or plane walls), which can give optimal thermal performance from the given heat input, thereby leading to energy savings. Originality/value: This study depicts that entropy generation associated with the convection process can be reduced via altering the shapes of containers to improve the thermal performance or efficiency for processing of identical mass with identical heat input. The comparative study of nine containers elucidates that the values of local maxima of Sψ (Sψ,max), Sθ (Sθ,max) and magnitude of Stotal vary with change in shapes of the containers (Classes 1–3) at fixed Pr and Ra. Such a comparative study based on entropy generation minimization on optimal heating during convection of fluid is yet to appear in the literature. The outcome of this study depicts that containers with curved walls are instrumental to optimize entropy generation with reasonable thermal processing rates. © 2020, Emerald Publishing Limited.

International Journal of Numerical Methods for Heat and Fluid Flow

Can the shape influence entropy generation for thermal convection of identical fluid mass with identical heating? A finite element introspection

Supramolecular gels are three-dimensional network structures formed by the hierarchical self-assembly of small molecules through weak noncovalent interactions. On the basis of the various interactions contributed by specific functional groups/moieties, gels with different architectures can be constructed that are smart to the external stimuli such as pH, type of solvent, stress, temperature, etc. In the present work, we explore the oscillatory shear response of supramolecular self-assembled systems formed by the low-molecular-weight (LMW) gelator based on difunctionalized amino acid, florenylmethoxycarbonyl (Fmoc)-lysine(Fmoc), Fm-K(Fm) in aqueous buffer solution, at two different pH (6 and 7.4). Small amplitude oscillatory shear (SAOS) reported weak frequency dependence of moduli indicating a gel-like network structure. Large amplitude oscillatory shear (LAOS) indicated flow regimes dictated by yielding and subsequent network dynamics analogous to cagelike soft glassy events reported for colloidal systems. The three interval thixotropy test (3iTT) indicated recovery of moduli due to regelation contributed by the reversible interactions. A generalized network model framework is utilized to investigate the transient network characteristics of the Fm-K(Fm) gels. The "network creation"and "network loss"rates were chosen as exponential functions of scaled shear stress (= |τ12(t)G|) to effectively describe the complex response. On the basis of the insights, possible mechanisms to explain the differences/similarities in the response at different pH are speculated. It is further illustrated that the modeling strategy can be extended to supramolecular gels of different classes because of the commonality/universality of their response features under oscillatory shear. © 2020 American Chemical Society.

Langmuir

Fibrillar Network Dynamics during Oscillatory Rheology of Supramolecular Gels

Supramolecular gel material built from low-molecular-weight (LMW) gelators finds potential applications in various fields, especially in drug delivery, cell encapsulation and delivery, and tissue engineering. The majority of the LMW gelators in these applications are based on functionalized peptides/amino acids consisting of proteinogenic amino acids which are proteolytically unstable. Herein, we have developed a new LMW gelator containing non-proteinogenic amino acid namely 2,3-diaminopropionic acid (Dap), a key precursor in the synthesis of many antibiotics namely viomycin and capreomycin, by functionalizing with fluorenylmethoxycarbonyl at both amino terminals of Dap [Fm-Dap(Fm)]. Hydrogelation test at different pH indicates that Fm-Dap(Fm) can form a hydrogel in a wide range of pH (4.9 to 9.1) with minimum hydrogelation concentration depends on the pH. The mechanical strength and thermal stability of the Fm-Dap(Fm) hydrogel material are found to decrease with increasing pH (acidic &gt; neural/physiological &gt; basic). The thermal stability of Fm-Dap(Fm) hydrogels is pH-dependent and elicits high stability at acidic pH. Also, Fm-Dap(Fm) hydrogels exhibit strong thixotropic property where regelation (self-healing) occurs upon release of stress. Morphological analysis indicates the formation of fibrils, which are entangled to form three dimensional network structures. Several spectroscopic measurements provided evidence for the self-assembly of Fm-Dap(Fm) molecules through intermolecular aromatic π-π stacking and hydrogen bonding interactions during hydrogelation. Interestingly, Fm-Dap(Fm) not only exhibits hydrogel formation but also shows cell viability and enhanced cell proliferation at physiological pH (7.4). Further, Fm-Dap(Fm) forms a hydrogel upon co-incubation with vitamin B12 and also exhibits release of vitamin B12 over a period. The current study thus demonstrates the development of a new hydrogel material, based on LMW gelator containing the non-proteinogenic amino acid, which can elicit cell viability, enhanced cell proliferation, drug encapsulation, and drug release properties. Hence, Fm-Dap(Fm) hydrogel could be an ideal material for biomedical applications, especially in tissue engineering and drug delivery. © 2019 Elsevier B.V.

Fulltext

Colloids and Surfaces B: Biointerfaces

Non-proteinogenic amino acid based supramolecular hydrogel material for enhanced cell proliferation

Accelerated thermal ageing studies were carried out on poly(3,4ethylenedioxythiophene): poly(styrene sulfonate)(PEDOT:PSS) thin films upto 150 °C to predict its life-time. The effect of thermal ageing on the chemical structure and the electronic structure is investigated. Changes in the conductivity of PEDOT:PSS films with ageing are studied along with UV–Vis, ATR-FTIR, Raman spectroscopy and AFM analysis. Conductivity at different temperatures shows an exponential decrease with time in the case of PEDOT:PSS (1.6PSS). Based on this data, the life-time of PEDOT:1.6PSS thin films at ambient conditions is predicted. The analysis of changes in the chemical structure using FTIR spectroscopy and the corresponding changes in the electronic structure using UV–Vis data shows changes in the polaronic states during ageing. Corresponding changes in the Raman spectroscopy data show oxidized-neutral transitions occurring during ageing which results in the conductivity changes. It is observed that unidirectional shearing of PEDOT:1.6PSS dispersion during film formation improved the thermal ageing characteristics. The ageing resistance of these films became comparable to that of PEDOT:2.5PSS films with higher PSS ratio. AFM studies show the effect of ageing on the surface morphology of films and shearing of films during formation can result in better ageing resistance and stable morphology. © 2019 Elsevier Ltd

Polymer Degradation and Stability

Understanding the mechanism of ageing and a method to improve the ageing resistance of conducting PEDOT:PSS films

A modeling approach based on sequential stages of pressure compression (NPT) and constant volume (NVT) molecular dynamics (MD) simulations was used effectively for generation of models of glassy samples of poly(phenylene oxide) PPO. Starting from a large periodic simulation box the samples were brought down to the desired density using NPT simulations and also NVT simulations for energy and structural relaxation. The GROMOS 45a3 force-field, with appropriate intermolecular potentials for PPO, was used to model the interatomic interactions. The PPO glassy phase was studied by independently generating 9 samples with different numbers of chains (for the chains of repeat units 15, 25 and 40). Structural analysis included dihedral angle distribution, intra-chain and inter-chain radial distribution functions, radius-of-gyration and torsion angle distributions, free volume and the orientation distributions of intra-chain and inter-chain phenylene rings. The simulated solubility parameter was in excellent agreement with experimental data for PPO. This computational study of the glassy phase of PPO is an extension of earlier studies by others on single, unperturbed chains of PPO. © 2020 Taylor & Francis Group, LLC.

Journal of Macromolecular Science, Part B: Physics

Detailed Molecular Structure of Glassy Poly(phenylene oxide) (PPO) Studied by Molecular Dynamics Simulations

In this article, we report the influence of organic modifier structure (alkyl chain length C8-C20, single vs ditallow) and thereby, the effect of hydrophobicity on the structure, thermal and mechanical properties of poly(methyl methacrylate) (PMMA)-clay hybrids. Melt processed PMMA-clay hybrids were characterized using wide-angle X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The organoclays having an alkyl chain length of more than 12 CH2 groups resulted in the formation of nanocomposites. The glass transition temperature (Tg) of PMMA increased in the presence of clay. The mean-field lattice model was used to predict the free energy for nanocomposite formation, which showed a reasonable match with the experimental results and provided a general guideline for the proper selection of polymer and organoclay (ie, organic modifier) to obtain nanocomposite. Tensile modulus showed maximum improvement of 58% for the nanocomposites compared to 9% improvement for the composites. Tensile modulus increased with increases in the alkyl chain length of the organic modifier and clay loading. The level of improvement for the tensile properties of nanocomposites prepared from primary and secondary ammonium-modified clay is the same as that obtained with the commercial organoclays.

The critical organic modifier aliphatic
            tail length
            for the formation of poly(methyl methacrylate)‐montmorillonite nanocomposites

It has been reported in recent literature that interdigitated flow fields exhibit lesser pressure drop than serpentine flow fields for large area cells of vanadium redox flow batteries. In the present work, we report on a comprehensive characterization of the performance of cells using interdigitated flow fields. The study encompasses two cell sizes (nominal active area of 900 and 1500 cm2) and seven variants in terms of shape of the headers or channels and the number and orientation of the channels. Experimental investigations include pressure drop and polarization behavior under different flow conditions. It is shown that intedigitated flow fields suffer from flow mal-distribution when employed in cells of this size range with a correspondingly degraded electrochemical performance compared to cells with serpentine flow field. Improvement in the flow distribution by providing pillars in the headers is shown to improve electrochemical performance, although with a concomitant increase in pressure drop. The best interdigitated configuration among those studied has been found to match the discharge capacity of serpentine at high flow rates; however, the serpentine is found to be superior, in terms of both discharge capacity and pressure drop, at its best operating condition, which occurs at lower flow rates. © 2020 Elsevier B.V.

Journal of Power Sources

Performance characteristics of several variants of interdigitated flow fields for flow battery applications

Active particles encapsulated in a droplet are called active compound particles. In addition to the activity induced fluid flows, these multiphase structures may experience imposed flows in the process of generating and manipulating them in microfluidic devices or in their natural habitats. Therefore, we investigate the deformation dynamics and stability of a drop encapsulating a model microswimmer, a spherical squirmer (shaker) concentrically placed in a drop, when subjected to an imposed shear flow. Using Lamb's general solution, Stokes equations are solved to determine the flow field and consequently the shape of the droplet interface. Shear flow always deforms the drop and the flow induced by the active particle may enhance or impede this deformation based on its orientation. The extent of deformation also depends on (i) the size of the active particle and the droplet, (ii) the viscosity of the droplet fluid and the fluid in which it is dispersed, (iii) the orientation of the active particle, and (iv) the relative strength of activity and imposed shear. Finally we find that the presence of an imposed vorticity field has a stabilizing effect on the active compound particle as it rotates the encapsulated swimmer and the drop undergoes a time periodic deformation. © 2020 IOP Publishing Ltd.