Abhinay Mishra

Highly efficient polyurethane ionomer corrosion inhibitor: the effect of chain structure

A series of polyurethane (PU) ionomers with different degree of sulfonation (DS) have been synthesized and successfully used as corrosion inhibitor for mild steel (MS) in acidic medium. Nuclear magnetic resonance (NMR) and Fourier transform infra red (FTIR) spectra of the sulfonated PUs confirmed the sulfonation on the >NH group of the urethane linkage and DS increases with the increase in the ratio of the sulfonating agent and PU. More than 90% inhibition efficiency (IE) of sulfonated polyurethanes (SPU) has been reported using only 20 ppm of the ionomers. These ionomers inhibited the corrosion of MS through adsorption following the Langmuir adsorption isotherm. Surface coverage has been scaled using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effect of sulfonation on the electronic and chemical structure of PU molecules has also been investigated. Electronic structure calculations have been performed to predict the adsorption behavior of ionomers on the metal surface, and thereby, the relative inhibition has been quantitatively correlated with DS.

Nanostructure to Microstructure Self-Assembly of Aliphatic Polyurethanes: The Effect on Mechanical Properties

We report the step by step self-assembly from nanostructure to microstructure (bottom-up approach through X-ray diffraction (1.6 nm), small angle neutron scattering (SANS) (11.6 nm), atomic force microscopy (70 nm smaller crystallite from enlarged image and 450 nm greater crystallites), and polarizing optical microscope (2 microm)) of aliphatic polyurethanes (PU) in contrast to aromatic polyurethanes depending on hard segment content (HSC). Polyurethanes of 10 to 80% HSC have been synthesized by using appropriate amount of polyol and chain extender. The effect of self-assembled patterns on mechanical properties both in solid and liquid state has been established exhibiting structure-property relationship of supramolecular polyurethanes. The crystallinity enhances but the degradation temperature decreases with increasing HSC. The characteristic length (measure of gap between lamellar crystallites), as revealed from SANS, gradually decreases with increasing HSC suggesting compactness of the crystallites through extensive hydrogen bonding. The Youngs modulus increases with increasing HSC with a percolation threshold of hard segment (50%) while the toughness improves up to 30% HSC followed by gradual decrease in presence of bigger crystallites which promote brittle fracture. The origin of self-assembly in aliphatic PUs has been demonstrated through electronic structure calculations to form a loop structure with minimum intermolecular distance (2.2 A) while that distance is quite large in aromatic polyurethanes (4.6 A) that cannot form hydrogen bonds. The unique splintering of domain structure and its subsequent reformation under dynamic shear experiment has been established.

Self-assembled aliphatic chain extended polyurethane nanobiohybrids: emerging hemocompatible biomaterials for sustained drug delivery.

Novel polyurethanes (PUs) have been synthesized using an aliphatic diisocyanate and aliphatic chain extenders with varying chain length. Nanocomposites of PUs have been prepared by dispersing 2-D nanoclay in poly-ol followed by prepolymerization and subsequent chain extension using various chain extenders. Systematic improvement in toughness and adequate enhancement in stiffness in the presence of nanoclay has been observed for PUs with longer chain extenders, and these new classes of nanocomposites exhibit no toughness-stiffness trade-off. Bottom-up self-assembly starting from the molecular level to micron-scale crystallite has been revealed through electronic structure calculation, X-ray diffraction, small-angle neutron scattering, atomic force microscopy and optical images. The role of hydrogen bonding has been revealed for this type of supramolecular assembly, and in the presence of organically modified nanoclay hydrogen bonding contributes to the formation of bigger clusters of nanocomposites. Controlled biodegradation of PU and its nanocomposites has been investigated in enzymatic media. Biocompatibility of these novel nanocomposites has been extensively verified through platelet adhesion, aggregation and hemolysis assay. Sustained drug delivery by biocompatible pristine PU and its nanocomposites has been demonstrated either by controlling the crystallite size of the polyurethane through alteration of the aliphatic chain length of the extender or by incorporating disc-like nanoclay, creating a tortuous path that results in delayed diffusion. Hence, the developed nanohybrids are potential biomaterials for tissue engineering and drug delivery.

Aromatic polyurethanes: the effect of hard segment and chain structure on their properties

Abstract Structural variation and its effect on the properties of aromatic polyurethanes (PUs) with different chain structures have been reported. Polarized optical microscopic studies of aromatic PUs demonstrate the development of micro clusters with increasing hard segment content (HSC). Higher crystallinity has also been proven from differential scanning calorimeter (DSC) and X-ray diffraction (XRD) studies. A globular pattern has been observed through atomic force microscopy (AFM) and the pattern depends on the type of diisocyanate used to prepare the PU. The difference in surface morphology is evident for two different PUs. The tensile modulus increases systematically with increasing HSC while toughness decreases, due to the presence of bigger crystallites in higher HSC polymer. Both the modulus and toughness vary on the type of diisocyanate present in PUs.

Mechanical and dielectric behaviors of perovskite (Ba,Sr)TiO 3 borosilicate glass ceramics

Perovskite (Ba,Sr)TiO3 glass ceramics were crystallized in the presence of La2O3 for glass ceramic system [(Ba1−xSrx)TiO3]-[2SiO2-B2O3]-[K2O]-[La2O3] (x = 0.0 and 0.4). The formation of major crystalline phase of BaTiO3 along with secondary phase of Ba2TiSi2O8 was confirmed by X-ray diffraction (XRD) studies. Major crystalline phase was clearly seen in the micrographs of (Ba,Sr)TiO3 borosilicate glass ceramic samples. The prepared glass ceramic samples showed very high values of toughness and elastic modulus. Barium strontium titanate (BST) glass ceramics are used in barrier layer capacitors for storage of high energy due to their very high dielectric constant and low dielectric loss.