Gopalakrishna Pillai Harikrishnan

This article presents a generalized machine learning pathway to compute the elastic response of cross-linked, rubber like polymers.

We experimentally probe the microscopic variations in a model polymer–nanoparticle (NP) binary mixture (mixture of polybutadiene and clay nanoplatelets) across a thermal evolution path for which T_evolution > T_g(polymer). The evolution of the NP dispersion, NP crystallinity, polymer chain–NP interface, and nature of polymer chain–NP interaction are mapped for a spectrum of temperatures and NP concentrations constrained by experiments. Multiple pieces of evidence indicate that thermal evolution does not influence the nature of interparticle dispersion and is also independent of NP concentration in the binary mixture. However, the NP crystalline order significantly reduces across the thermal evolution path. Thermal evolution induces a transition of a sharp polymer chain–NP interface to a diffuse interfacial layer. In contrast, an already diffuse polymer–NP interface existing in the binary mixture due to particle crowding at high NP concentrations undergoes no significant change in its nature across the evolution path. At all particle concentrations, thermal evolution changes the dominant interaction from polymer chain–polymer chain to polymer chain–NP. These insights aid in explaining the molecular origins of unique and anomalous behaviors shown by polymer–nanoparticle binary mixtures while undergoing thermal evolution.

We ask, do nanoparticles influence topological defects during a molecularly controlled elastomeric synthesis? If so, how?

We elucidate the influences of hydration on the morphological heterogeneity of the broad class of segmented copolymers.

Confinement of graphene and its functional derivatives in synthetic and biomacromolecules has been widely demonstrated recently to manifest in several multiscale phenomena in their mixtures. However, the intricate adsorbed interfacial region formed between polymer chains and a single layer of atomistically thin carbon sheet hitherto evaded an understanding of its nature and characteristics. Here, we reveal the structure of this constrained region and estimate the thickness of the adsorbed polymer layer on a single layer of atomistically thin graphene oxide sheet using both direct experiments and molecular dynamics simulations. We use small angle neutron scattering (SANS) on a model multicomponent mixture formed by an adsorbing polymer, graphene oxide and solvent for revealing the structure of the constrained interfacial region. We quantify the intricate adsorbed polymer layer thickness on a single layer of atomistically thin graphene oxide sheet by Euclidean approximation of the experimentally observed self similar interfacial structure. The state of polymer chain random walk and influence of unadsorbed chains under experimental conditions are investigated and juxtaposed against the accuracy of this quantification. For long chain polymers, the adsorbed layer thickness increases with increasing polymer molecular weight and shows a scaling relationship with polymer radius of gyration. For short chains, the thickness is nearly independent of molecular weight and shows a scaling relationship . Coarse grained molecular dynamics simulations performed on a model system similar to experiments qualitatively ratify the experimentally observed molecular weight-thickness relationship. Simulations show no discernible scaling relationship between radius of gyration and adsorbed layer thickness for low molecular weight polymers but show a consistent scaling for high molecular weight polymers. A comparison between results from experiments and simulation indicate a discerning pathway in deciphering interface governed multiscale phenomena in mixtures of adsorbing macromolecules with graphene and its functional derivatives.

Several interfacial phenomena are active during polymeric foaming, the dynamics of which significantly influence terminal stability, cell structure and in turn the thermo-mechanical properties of temporally evolved foam. Understanding these dynamics is important in achieving desired foam properties. Here, we introduce a method to simultaneously portray the time evolution of bubble growth, lamella thinning and Plateau border drainage, occurring during reactive polymeric foaming. In this method, we initially conduct bulk and surface shear rheology under polymerizing and non-foaming conditions. In a subsequent step, foaming experiments were conducted in a rheometer. The microscopic structural dimensions pertaining to the terminal values of the dynamics of each interfacial phenomena are then measured using a combination of scanning electron microscopy, optical microscopy and imaging ellipsometry, after the foaming is over. The measured surface and bulk rheological parameters are incorporated in time evolution equations that are derived from mass and momentum transport occurring when a model viscoelastic fluid is foamed by gas dispersion. Analytical and numerical solutions to these equations portray the dynamics. We demonstrate this method for a series of reactive polyurethane foams generated from different chemical sources. The effectiveness of our method is in simultaneously obtaining these dynamics that are difficult to directly monitor due to short active durations over multiple length scales.

We report a simple, serendipitous, two step mediation that overcomes the polyaddition threshold of castor oil during polyurethane formation. The mediation facilitates formation of polyurethane systems directly from castor oil without triricinolein chain extension or the use of supplementary hydroxyl compounds. The mediation involves refluxing castor oil with n‐Butyl lithium in the presence of a solvent followed by water addition. We demonstrate the effectiveness of this mediation by successfully generating two important polyurethane systems (foam and coating) from castor oil. We identify that the mediation introduces two new compounds in castor oil namely, a lithiated diglyceride and a lithium salt of fatty acid. We characterize the new polyurethane synthesized for their hard‐soft segmented morphology, glass transition temperature, and thermomechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43964.