On the modeling of quiescent crystallization of polymer melts

In this paper we present a way of modeling crystallization in polymers within the confines of a new general framework that has been developed to describe materials undergoing dissipative processes. Crystallization in polymers is in general an irreversible process, and a characteristic of all such processes is the production of entropy. In addition to postulating constitutive forms for the internal energy and entropy, we prescribe a constitutive relation for the entropy production. This in turn aids in deriving the crystallization rate equation from the second law, under the constraint that all real processes tend to maximize the rate of entropy production. After developing the general framework we derive specific models and compare the predictions of the model against experimental data available for quiescent crystallization in the literature. The predictions of the theory compare very well with the available experimental data for Nylon‐6 obtained by Patel and Spruiell (1).     

HEAT-TRANSFER AND GAS-HOLDUP STUDIES IN A BUBBLE COLUMN: AIR-WATER-GLASS BEAD SYSTEM

Air-holdup and heat-transfer coefficient values are measured in a 0.305 m diameter bubble column equipped with a seven-tube bundle for the air-water and air-water-glass bead system. The dependence of these two properties on air velocity (up to 0.28 m/s), temperature (297-343 K), glass bead powder average size (50-143.3 μm), solids concentration in the slurry (up to 20 weight percent) and bubble column diameter (0.108 and 0.305 m), is experimentally investigated. The effect of internals, as simulated by a single probe and a seven-tube bundle, in the two bubble columns is also examined. The models and correlations commonly employed to estimate these properties are assessed on the basis of generated data.     

A case study of long-term RO plant operation without chemical pretreatment

Described herein is a case study of long-term reverse osmosis (RO) plant operation without applying chemical pretreatments to the feed water. This project was undertaken with the financial support from the Department of Bio-Technology, New Delhi, and the work was carried out by a research team from Central Salt and Marine Chemicals Research Institute (CSMCRI), Bhavnagar (Gujarat), India. A prototype plant with a 30,000 L/d capacity was designed, manufactured, installed and operated at the village of Mocha-Gorsar, located in the Porbandar district, to provide drinking water. The village was to be developed as a model Bio-Village where other projects related to village problems are also operated by other research institutes. Thin-film composite (TFC) membrane-based RO technology was indigenously developed by the institute for treatment of brackish water and waste water for the first time in India; it was used successfully in this plant, which gave a typical NaCl rejection of about 95%. This is a typical case study of RO plant installation where physical methods of pretreatment such as sand and micron cartridge filters were used; no chemical pretreatment of feed was employed for long-term brackish water desalination study. The idea was to avoid the usage of chemicals, which concentrate in the effluent water, might affect the environment and may not suit the village community. Plant performance during 24 months of continuous operation with respect to variable feed salinity, membrane cleaning and regenerations is discussed.     

Effective photopolymerization of C60 films under simultaneous deposition and UV light irradiation: Spectroscopy and morphology study

An effective method for uniform photopolymerization of C₆₀ films using simultaneous deposition and irradiation with ultraviolet (UV) light is described. The photopolymerization process was monitored as a function of irradiation time using Raman and infrared (IR) spectroscopy. New features appeared in the Raman (near the pentagonal pinch A_g(2) mode) and IR spectra (400-1500 cm⁻¹) after more than 20 h of UV irradiation testifying to the transformation of pristine C₆₀ to polymerized C₆₀ phases. Band shape analysis of the vibrational data revealed: (i) the degree of photopolymerization to be ∼90% after 20 h of irradiation, and (ii) the presence of orthorhombic, tetragonal, and rhombohedral phases in the photopolymerized films. Electron microscopy and diffraction studies revealed the amorphous nature of the photopolymerized films which comprised of crystals with a linear dimension of ∼40-60 nm. No evidence for cracks in the surface of the polymerized film was found. The proposed route for photopolymerization provides an opportunity to prepare extended polymeric C₆₀ films suitable for technological applications.     

An Experimental Charge Density Study of the N-H+…O− Bonds in a Proton-Transfer System in Comparison with Regular N-H…O and O-H…N Hydrogen Bonds

An experimental charge density study has been carried out on N-H⁺…O⁻ bonds in the proton-transfer compound piperazinium oxalate as well as on the normal O-H…N bonds in the thiodiglycolic acid-4,4′-bipyridine complex, based on X-ray diffraction measurements at 130 K. The results are compared with those of the normal N-H…O bonds in 5-nitrouracil. In spite of the different crystal geometries, the N-H⁺…O⁻ and the N-H…O bonds exhibit similar values of electron density and the associated curvatures at the hydrogen-acceptor bond critical points (BCPs). Surprisingly, the polarization parameters of the two BCPs are comparable (˜20%). The pseudoatomic charge on the protonated N atom (in N-H⁺…O⁻) is, however, much smaller (-0.05 e) in comparison to the unprotonated case (˜ -0.2 e). The O-H…N hydrogen bonds exhibit shorter H…N distances compared to the charged and the uncharged H…O bonds. Accordingly, the electron densities and the curvatures evaluated at the H…N critical points are also much higher.     

Polyaniline Salts and Complexes as Catalyst in Bisindole Synthesis

Polyaniline salts are prepared by doping of polyaniline base with different Bronsted acids (H₂SO₄, HNO₃ and H₃PO₄), organic acid — p-toluene sulfonic acid (PTSA) and Iodine (I₂). Polyaniline complexes are also prepared using Lewis acids (BF₃, AlCl₃ and SnCl₂). Polyaniline salts and polyaniline complexes are characterized by physical, electrical and spectral methods. Polyaniline salts and polyaniline complexes are used as catalyst for the first time in bisindole synthesis. Bisindole (3,3′-bis(indolyl)phenylmethane) is obtained in excellent yields with simple and more environmental benign procedure. The use of polyaniline catalysts are feasible because of their easy preparation, easy handling, stability, easy recovery, reusability, good activity and eco-friendly.     

Solid state reactions of cordierite precursor oxides and effect of CaO doping on the thermal expansion behaviour of cordierite honeycomb structures

The extruded cordierite honeycomb structure from a stoichiometric formulation of talc, kaolinite, and alumina was subjected to TGA-DSC, dilatometric and XRD investigations. The experimental observations were made to identify the phase transformation sequence in order to understand the solid state reactions involved in the cordierite formation. A maximum cordierite content of 90% was achieved for the samples sintered at 1693 K with a soaking time of 4 h, corresponding to a lowest coefficient of thermal expansion (CTE) of 0.74 × 10^–6/K (along the direction of extrusion) was observed. Attempts were made to establish correlations with cordierite content, processing temperature and CTE of the samples. A few mechanisms are proposed to explain our observations. Attempts are also made to rationalize the low CTE observed along the direction of extrusion on the basis of orientation of anisotropic cordierite crystals as revealed by the transverse I-ratio calculated from the XRD patterns. Effect of CaO doping on CTE of cordierite has been studied in the present work. It was observed that though there is an increase in bulk thermal expansion of cordierite honeycombs on CaO doping due to the absence of micro-cracks as reveled by thermal cycling hysteresis, axial anisotropy was found to be reduced significantly.     

Bandwidth-efficient WDM channel allocation for four-wave mixing-effect minimization

A novel channel-allocation method that allows reduction of the four-wave mixing (FWM) effect while maintaining bandwidth efficiency is presented. It is composed of a fractional bandwidth-allocation algorithm, taking into consideration the use of parameters with distinct differences. This proposed technique allows the computation of an optimal channel-allocation set, where degradation caused by interchannel interference and FWM is minimal. Simulation is carried out to show significant performance improvement, such as an average bit-error rate improvement factor of 1.336 for an eight-channel wavelength-division multiplexing system, without the requirement of increased bandwidth, unlike existing channel-allocation methods.     

Design and synthesis of amphipathic antimicrobial peptides

A large proportion of antimicrobial peptides share a common structural feature that is critical to their antimicrobial activity, i.e. amphipathic alpha-helices. The amphipathy of a polypeptide chain can be quantitated through the value of the hydrophobic moment. Generally, antimicrobial peptides are characterized by high hydrophobic moment and low hydrophobicity values. Using these criteria we have identified two short segments that possess hydrophobic moment properties associated with known antimicrobial peptides. Using in vitro assays the segment derived from the protein perforin displays no antifungal or antibacterial activity and, while showing no alpha-helicity in buffer or liposomes, exhibits a modest degree of alpha-helical structure in the presence of the alpha-helical inducer, 2,2,2-trifluoroethanol. However, rational modifications result in a derivative which assumes an alpha-helical conformation in the presence of liposomes, exhibits potent antifungal activity against plant fungal pathogens, has significant antibacterial activity, effects leakage of a fluorescent dye from acidic liposomes and is devoid of hemolytic activity. Results are also presented for a segment derived from the human immunodeficiency virus envelope protein. We suggest that the identification of putative amphipathic structures in proteins may provide a useful starting strategy in the design and synthesis of antimicrobial peptides.     

High-field stressing of LPCVD gate oxides

We have investigated gate oxide degradation as a function of high-field constant current stress for two types of oxides, viz. standard dry and LPCVD oxides. Charge injection was done from both electrodes, the gate and the substrate. Our results indicate that compared to dry oxides, LPCVD oxides show reduced charge trapping and interface state generation for inversion stress. The degradation in LPCVD oxides with constant current stress has been explained by the hydrogen model