Arnab Chakrabarty

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  Available from: Arnab Chakrabarty

  Article: Coarse grain modeling of polyimide copolymers

  A. Chakrabarty, T. Cagin
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  ABSTRACT: Addressing the wide span of timescales, where various important phenomena takes place in a polymer system, is inconceivable through a typical molecular dynamics simulation. Coarsening of simpler polymer systems has demonstrated significant potential in computationally characterizing and simulating systems at larger timescales. Addressing the need to extend existing coarsening methodologies on multifunctional materials to help design future generation materials is both promising and challenging. In this paper we present development of an atomistically informed coarse grain bead model of piezoelectric polyimide copolymers for large-scale simulations of thermal, mechanical and especially electrical properties. The coarsening approach generated a gain of two and a half orders of magnitude in terms of computational time and an order of magnitude gain in system size (equivalent to similar to 360,000 atomistic model) while retaining the physical characteristics specific to the piezoelectric polymer. Reasonable agreement was observed between simulation results of the coarse grained and the atomistic model. Specifically mechanical moduli, density, dielectric constant, yield behavior, work hardening, response under dynamic loading and glass transition behavior were analyzed and compared. (c) 2010 Elsevier Ltd. All rights reserved.
  Polymer. 01/2010; 51:2786-2794.
• Article: CARBON NANOTUBE POLYMER NANOCOMPOSITES FOR ELECTROMECHANICAL SYSTEM APPLICATIONS

  Arnab Chakrabarty
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  ABSTRACT: Polymer nanocomposites refer to a broad range of composite materials with polymer acting as the matrix and any material which has at least one dimension in the order of 1 ~ 100 nanometer acting as the filler. Due to unprecedented improvement observed in properties of the nanocomposites, research interest in this area has grown exponentially in recent years. In designing better nano-composites for advanced technological applications some of the major challenges are: understanding the structure-property relationships, interaction and integrity of the two components at the interface, the role of nanofillers in enhancing the properties of the resulting material. In our work, we have utilized first principle calculations, atomistic simulations, coarse-grained modeling and constitutive equations to develop structureproperty relationships for an amorphous aromatic piezoelectric polyimide substituted with nitrile dipole, carbon nanotubes and resulting nanocomposites. We have studied in detail structure-property relationships for carbon nanotubes and (? ?CN)APB/ODPA polyimide. We have developed chemically sound coarse-grained model based on atomic level simulations of the piezoelectric polyimide to address the larger length and time scale phenomena. The challenge of coarse grain model for these polymers is to reproduce electrical properties in addition to the structure and energetics; our model is the first to successfully achieve this goal. We have compared and analyzed atomistic scale simulation results on the nanocomposite with those predicted from micromechanics analysis. Notably, we have investigated the time dependent response of these highly complex polymers, to our best knowledge this is the first of its kind. In particular we have studied the thermal, mechanical and dielectric properties of the polyimide, nanotube and their nanocomposites through multi-scale modeling technique. We expect the results obtained and understanding gained through modeling and simulations may be used in guiding development of new nanocomposites for various advanced future applications. In conclusion we have developed a computational paradigm to rationally develop next generation nano-materials.
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  Available from: Arnab Chakrabarty

  Article: Computational studies on mechanical and thermal properties of carbon nanotube based nanostructures

  A. Chakrabarty, T. Cagin
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  ABSTRACT: The excellent set of properties of carbon nanotube and carbon nanotube-based nanostructures has been established by various studies. However the claimed property values and trends have not been unanimously agreed upon. Using state of the art molecular dynamics and ab initio methods, we have extensively studied the mechanical, thermal and structural properties of carbon nanotubes and carbon nanotube based nanostructures. Additionally this study aims to address the approaches used in various studies to assess the validity and influence of various definitions used for determining the physical properties as reported in earlier experiments and theoretical calculations. We have come up with equations, which quantitatively address the wide differences in trend and values of nanotube axial modulus available across the literature. Applying a novel bond rearrangement scheme, we have found similar values in twist modulus of zigzag and armchair nanotubes. This opposes the claim of difference that was shown to be valid only at finite limit in our study. We have shown that the contribution of van der Waals energy in a multi-wall nanotube is powerful enough to make it hexagonal in shape but negligible in affecting the axial modulus. These insights will also help in designing micromechanics model of materials made from carbon nanotube or nanotube like structures. In particular, we have calculated the mechanical properties (young modulus, bending modulus and twist modulus) of isolated and bundled nanotubes, single and multi-wall nanotubes and sin-le and multi-wall carbon nanotube based tort. We also report studies on thermal variation of moduli and thermal expansion of nanotubes. The result obtained by first principles calculation based interatomic potential agrees well with the experimental results.
  Cmc-Computers Materials & Continua. 01/2008; 7:167-189.
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  Available from: Arnab Chakrabarty

  Article: Development of dynamic models of reactive distillation columns for simulation and determination of control

  Arnab Chakrabarty
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  ABSTRACT: Dynamic models of a reactive distillation column have been developed and implemented in this work. A model describing the steady state behavior of the system has been built in a first step. The results from this steady state model have been compared to data provided from an industrial collaborator and the reconciled model formed the basis for the development of a dynamic model. Four controlled and four manipulated variables have been determined in a subsequent step and step tests for the manipulated variables were simulated. The data generated by the step responses was used for fitting transfer functions between the manipulated and the controlled variables. RGA analysis was performed to find the optimal pairing for controller design. Feedback controllers of PID type were designed between the paired variables found from RGA and the controllers were implemented on the column model. Both servo and regulatory problems have been considered and tested.