Differential thermal and thermogravimetric analyses of bound water content in cellulosic substrates and its significance during cellulose hydrolysis by alkaline active fungal cellulases

Various cellulosic substrates were examined for bound water content by differential thermal analysis (DTA) and thermogravimetry (TG). Samples were heated in the range of 30-100 degrees C at a rate of 3 degrees C/min. DTA vaporization curves for different cellulose samples indicated that the bound water (Wf) was vaporized at higher temperature than free water (Wf) at the surface. Weight loss was observed in two stages, corresponding to Wf and Wb in TG curves. The bound water content was dependent on the degree of crystallinity of cellulose. Among different cellulosic substrates, Walseth cellulose showed the highest bound water content, and it also was found to be the least crystalline. The alkaline-active, alkali-stable cellulase was obtained from the alkalotolerant Fusarium sp. The substrate specificity and viscometric characteristics confirmed the enzyme to be an endoglucanase. The Wb content of Walseth cellulose was lowered during the enzymatic hydrolysis. The possible application of bound water analysis in understanding the hydrolysis of cellulosic substrates of different crystallinity is discussed.     

Steady vortical flow around a finite plate

An explicit solution for a layer of fluid with constant vorticitysurrounding a thin plate of finite length is obtained usingelementary conformal mapping methods. In the limit of largeplate length the behaviour of the solution near the ends ofthe plate tends to that of the previously known solution fora semi-infinite plate. Contour dynamics is used to investigatethe stability of the steady solutions.     

Effect of charge asymmetry and charge screening on structure of superlattices formed by oppositely charged colloidal particles

Colloidal suspensions made up of oppositely charged particles have been shown to self-assemble into substitutionally ordered superlattices. For a given colloidal suspension, the structure of the superlattice formed from self-assembly depends on its composition, charges on the particles, and charge screening. In this study we have computed the pressure-composition phase diagrams of colloidal suspensions made up of binary mixtures of equal sized and oppositely charged particles interacting via hard core Yukawa potential for varying values of charge screening and charge asymmetry. The systems are studied under conditions where the thermal energy is equal or greater in magnitude to the contact energy of the particles and the Debye screening length is smaller than the size of the particles. Our studies show that charge asymmetry has a significant effect on the ability of colloidal suspensions to form substitutionally ordered superlattices. Slight deviations of the charges from the stoichiometric ratio are found to drastically reduce the thermodynamic stability of substitutionally ordered superlattices. These studies also show that for equal-sized particles, there is an optimum amount of charge screening that favors the formation of substitutionally ordered superlattices.     

A low-temperature, soft chemistry method for the synthesis of zirconia nanoparticles in thermally evaporated fatty amine thin films

We demonstrate the synthesis of zirconia nanoparticles in a lipid matrix by a simple, low temperature beaker-based process. This is accomplished by electrostatic entrapment of ZrF6(2-) ions within thermally evaporated octadecylamine (ODA) thin films followed by the low-temperature in situ hydrolysis of the entrapped metal ion complexes. The zirconia particles thus formed were of the monoclinic phase and were fairly monodisperse with particles of average size 40 nm. The zirconia crystallites appeared to exhibit preferred orientation indicating epitaxial growth of the crystals within the lipid matrix. The formation of zirconia nanoparticles in the lipid matrix was investigated using quartz crystal microgravimetry (QCM), optical absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques.