IUCAA: genesis of a unique research centre

The European Physical Journal H - The Inter-University Centre for Astronomy and Astrophysics (IUCAA) is the second Inter-University Centre established by the Government of India for promotion of...     

Investigation of the curing kinetics of polyurethane/nitrocellulose blends through FT-IR measurements

Polyester (HTPS) based polyurethane (PU) elastomers were currently established to be effective binders for high-energy composites with improved performances. Conventional PU binders are mostly non-energetic materials, and consequently reduce the energy performance significantly. Nitrocellulose (NC), is an energetic polymer widely used as an ingredient in propellants, explosives, fireworks, and gas generators, it may be introduced in PU-based compositions to overcome their performance drawback. Kinetic parameters must be specified in order to build PU binders with the most convenient and appropriate features. Therefore, the cure kinetics of polyester based polyurethane binder systems were investigated by Fourier transform infrared spectroscopy (FT-IR) isothermal method. The polyester prepolymer (Desmophen^® 1200) was cured with hexamethylene diisocyanate (HDI: Desmodur^® N100) at various molar ratios (R_[NCO]/[OH] = 0.6, 1, 1.25, and 1.5) and under different isothermal conditions (T = 60°C, 80°C, 100°C, and 120°C). In addition, the effect of the addition of nitrocellulose on the kinetics of polymerization of PU was investigated. The progression of the reaction was followed based on the decrease of the peak intensity of –NCO group at 2271 cm⁻¹ as a function of the reaction time. The curing kinetic model and the apparent activation energy (E_α) were determined by the use of Kamal autocatalytic model and Friedman isoconversional method, respectively.     

High-order ADI method for stream-function vorticity equations

Many recent works have demonstrated the efficiency of high-order compact (HOC) difference schemes on the stream-function and vorticity formulation of 2-D incompressible Navier-Stokes equations. HOC discretizations induce cross spatial derivatives which are treated explicitly in most ADI schemes. Recently, Karaa and Zhang proposed a fourth-order ADImethod for solving convection-diffusion problems efficiently. In this work, we extend this method to the solution of incompressible Navier-Stokes equations. The driven flow in a square cavity is used as a model problem and numerical results are compared with other results. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Kinetics of styrene uptake by a polyurethane network during the formation of interpenetrating polymer networks

Due to insolubility of the components, formation of interpenetrating polymer networks (IPNs) requires particular ways of synthesis. Among others, IPNs can be prepared by the sequential technique where a network is swollen in a monomer and its crosslinker, which are then polymerized in situ. The simplest case is to swell at equilibrium; however this leads to IPNs of a given composition. For obtaining other compositions, swelling has to be stopped before equilibrium, or the swollen network (gel) has to be deswollen to a certain extent. Therefore, diffusivity of the monomer within the gel has to be known. The kinetics of monomer uptake was studied for a polyether urethane/styrene-divinylbenzene system which gives transparent materials despite the difference in refractive indexes. This allows direct visual observations of the monomer progress within the network. The results are not fully in agreement with the theories of Tanaka and of Candau which both predict the progression of a solvent in a polymeric gel. Two regimes of swelling depending on the concentration distribution of the monomer within the gel were found.     

ChemInform Abstract: Rhodium‐Rich Germanides RERh4Ge2 (RE: Y,Gd—Lu): Structure and Bonding.

The title compounds are prepared by arc‐melting of the elements and subsequent annealing (evacuated silica tube, 970 K, 5d).