Browsing by Author "Sandhya, S"

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    Nucleation kinetics of the formation of low dimensional calcium sulfate dihydrate crystals in isopropyl alcohol medium
    (CRYSTAL RESEARCH AND TECHNOLOGY, 2012) Sandhya, S; Sureshbabu, S; Varma, HK; Komath, M
    Calcium sulfate dihydrate, constituted as uniform crystals of low dimensions, is a potential biomaterial for clinical applications like bone graft substitution and drug delivery. In this work, isopropyl alcohol has been used as a solvent to obtain low dimensional calcium sulfate dihydrate crystals from calcium nitrate - sulfuric acid system. Reactants in 0.5 molar concentration at ambient conditions generated uniform rod-shaped crystals of length 35 mu m. Analysis using X-ray Diffractometry and Fourier Transform Infrared Spectrometry showed the material to be well crystallized, phase-pure calcium sulfate dihydrate. The nucleation kinetics has been studied by observing the induction time of phase formation in solutions of millimolar concentrations through turbidimetry at 300 K. The data have been analysed using classical nucleation theory to deduce parameters like interfacial tension (or surface free energy), nucleation rate and critical radius. The surface free energy obtained (5.6 mJ/m2) is comparatively lower than that reported for aqueous precipitation, which could be attributed to the presence of isopropyl alcohol. On escalating the supersaturation ratio, the nucleation rate drastically increased and the critical radius decreased exponentially. Particles formed at supersaturation 1.39 showed a monomodal distribution centered at 8.2 nm in Dynamic Light Scattering analysis. Comparable particle sizes were obtained in Transmission Electron Microscopy.
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    Studies on polyurethane potting compound based on HDI-TMP adduct for fabrication of haemodialyzer
    (JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 2001)
    Polyurethane potting compounds based on hexamethylene diisocyanate-trimethylol propane (HDI-TMP) adduct (Component "A") and polypropylene glycol, polyethylene glycol and castor oil (Component "B") were prepared as potential compounds for the fabrication of haemodialyzer. The setting characteristics of the potting compounds having isocyanate index 2.0 are better than those compounds having 1.35. The aging stability of PEG and PPG based potting compounds are poorer than those of castor oil based potting compounds. Appreciable hydrolytic, oxidative and chemical stability could be observed with castor oil based potting compounds of HDI-TMP adduct. (C) 2001 Kluwer Academic Publishers.
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    Studies on polyurethane potting compound based on isocyanurate of aliphatic diisocyanate for fabrication of a haemodialyser
    (JOURNAL OF BIOMATERIALS APPLICATIONS, 2000)
    Polyurethane potting compounds based on multifunctional isocyanurate of aliphatic diisocyanate, hexamethylene diisocyanate (HDI-IC) as Component A and polypropylene glycol, polyethylene glycol and castor oil (Component B) were prepared as potential potting compounds for the fabrication of a haemodialyser. The setting characteristics of the potting compounds having isocyanate index 2.54 are better than those of the compounds having 1.77. The ageing stability of castor oil and PPG-based potting compounds having isocyanate index 2.54 is better than that of PEG oil-based potting compounds. Appreciable hydrolytic, oxidative and chemical stability could be observed with HDI-IC/PPG/2.54 potting compounds for development of haemodialyser, oxygenator, etc.