Department of Chemistry
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Item Dynamics and Rheology of Polymer Melts via Hierarchical Atomistic, Coarse-Grained, and Slip-Spring Simulations(ACS, 2021-02) Jana, Pritam KumarA 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.Item Dynamics of Long Entangled Polyisoprene Melts via Multiscale Modeling(ACS, 2021-09) Jana, Pritam KumarA 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.Item Wall-Spring Thermostat: A Novel Approach for Controlling the Dynamics of Soft Coarse-Grained Polymer Fluids at Surfaces(ACS, 2022-06) Jana, Pritam KumarThe 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.Item Coordination polymers of Ag(i) with di-Schiff base and diaminoalkanes: double helix, ladder, CdSO4 and zigzag-chain networks(RSC, 2004) Sarkar, MadhushreeA new di-Schiff base ligand has been prepared from 3-acetylpyridine and 1,2-diaminoethane and its structure has also been characterized by single crystal X-ray diffraction. Furthermore, the ligand was found to form a 1 : 1 complex with Ag(NO3) in CH3CN. The crystal structure of the complex exhibits a 1D-double helix with the pitch length of 10 Å. In these reactions, the ligand was found to disintegrate into the individual components to form a crystal of a 3D-network which comprised of Ag(NO3) and 1,2-diamino ethane. Nitrate ions occupied the channels and form several N–H⋯O hydrogen bonds with the walls of the channels. Interestingly, the topology of the 3D-network was found to be similar to that of the CdSO4. This structure prompted us to study the reactions of Ag(NO3) with 1,2-diaminoethane, 1,2-diaminopropane and 1,3-diaminopropane. The crystal structures of these complexes reveal that 1,2-diaminoethane forms the 3D-network similar to the above reaction, whereas 1,2-diaminopropane and 1,3-diaminopropane form a ladder and 1D-zigzag chain, respectively.Item Crystal engineering of coordination polymers using 4,4'-bipyridine as a bond between transition metal atoms(RSC, 2006) Sarkar, MadhushreeCoordination polymers have attracted an enormous interest among chemists due to their novel physical and chemical properties. This review describes the role of 4,4′-bipyridine in discovering various coordination polymers with novel topologies that range from one-dimensional to three dimensional. The geometries of coordination polymers of bipy include linear, zigzag, four-fold helices, molecular antenna, ladder, railroad, double, triple and quadruple chains, bilayer, square and rectangular grid, honeycomb layers, Lincoln Logs, 3D frames, diamondoid, 42·82 and cubic networks.Item Coordination Polymers Comprised of an Exo Bifunctional Schiff Base Ligand and Succinate Dianion: Critical Analysis of Factors Affecting the Structures and Framework Dimensionality(Wiley, 2017-12-18) Sarkar, MadhushreeThe chemistry of Coordination Polymers (CPs) of an exo bidentate Schiff base ligand, L1b, 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene, where two pyridyl moieties are separated by imine groups, is discussed. The reaction of ligand L1b and disodium succinate with Cd(ClO4)2 resulted in CP1, which is a 2D bilayer structure. Previously, it was reported elsewhere that the reaction of L1b with Cd(NO3)2 followed by the addition of disodium succinate resulted in a 3D network, while the similar reaction with Cd(ClO4)2 resulted in a different 3D network. The result from the current study establishes that reaction conditions and the anion in the metal salt can be crucial in obtaining diversified networks for the same combination of metal center and ligand. The effect of reaction conditions on network geometry is critically analyzed by comparing their single crystal structures and various other parameters.