Ultrasonic degradation of solutions of poly(vinyl acetate) in dioxan: The effects of the temperature and polymer concentration

The ultrasonic degradation of poly(vinyl acetate) (PVAc) solutions was carried out in dioxan at 25, 30, 35, 40, and 45 °C to investigate the effects of the temperature and solution concentration on the rate of degradation. The kinetics of degradation were studied by viscometry. The calculated rate constants indicated that the degradation rate of the PVAc solutions decreased as the temperature and solution concentration increased. The calculated rate constants were correlated in terms of the concentration, temperature, vapor pressure of dioxan, and relative viscosity of the PVAc solutions. This degradation behavior was interpreted in terms of the vapor pressure of dioxan, the viscosity, and the concentration of the polymer solutions. With increasing temperature, the vapor pressure of the solvent increased, and so the vapor entered the cavitation bubbles during their growth. This caused a reduction in collapsing shock because of a cushioning effect; therefore, the rate of degradation decreased. As the solution concentration increased, the viscosity increased and caused a reduction in the cavitation efficiency, and so the rate of degradation decreased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 445–451, 2004     

<Emphasis Type="Italic">Stachys lavandulifolia</Emphasis> and <Emphasis Type="Italic">Lathyrus</Emphasis> sp. Mediated for Green Synthesis of Silver Nanoparticles and Evaluation Its Antifungal Activity Against <Emphasis Type="Italic">Dothiorella sarmentorum</Emphasis>

In this study, silver nanoparticles (AgNPs) were biosynthesized using Stachys lavandulifolia and Lathyrus sp. The first sign of the reduction of silver ions to AgNPs was the change in color of S. lavandulifolia and Lathyrus sp. extracts changed into dark brown and auburn after treating with silver nitrate, respectively. The UV–Vis spectroscopy of reaction mixture (extract+silver nitrate) produced by S. lavandulifolia and Lathyrus sp. showed the strong adsorption peaks at ?440 and 420 nm, respectively. The transmission electron microscope images showed the synthesis of AgNPs using S. lavandulifolia and Lathyrus sp. with an average size of 7 and 11 nm, respectively. The result of X-ray diffraction pattern showed four diffraction peaks at 38°, 44°, 64°, and 77° for both types of biosynthesized AgNPs. Fourier transform infrared spectroscopy showed the possible role of involved proteins and polyhydroxyl functional groups in the synthesis process of AgNPs. Inductively coupled plasma analysis determined the conversion rate (percentage) of silver ions to silver nanoparticles in reaction mixtures of S. lavandulifolia and Lathyrus sp. 99.73 and 99.67 %, respectively. In addition, antifungal effect of AgNPs, synthesized by both extracts, was studied separately on mycelial growth of Dothiorella sarmentorum, in a completely randomized design on potato dextrose agar (PDA) medium. The inhibition rate of mycelial growth was strongly depended on the density of AgNPs and it strongly increased with increasing the density of AgNPs in the PDA medium. AgNPs more than 90 % of them inhibited from the mycelia growth of the fungus at the concentration of 40 µg/mL and higher.     

The effect of modulated electric field on characteristic of SDBD-like plasma jet for surface modification

In this paper, the dynamics and flow behaviour of an atmospheric argon plasma jet was studied in the new nozzle structure similar to the surface dielectric barrier discharge (SDBD) using the Schlieren imaging method. The effect of plasma jet driven by repetitive high-voltage microsecond pulses with low-frequency sinusoidal bias was measured qualitatively in a single mirror Schlieren optical system. The enhancement of plasma jet length and cross-section of plasma jet with surface in this condition is due to highly turbulent flow of argon plasma jet in this structure. This study revealed the important role of SDBD structure and modulated electric field on the behaviour of plasma jet in a high diameter nozzle. In practice, this technique allows us to increase the jet length of the nozzle output to 5 cm and under these conditions, the diameter of the plasma jet cross-section is increased to 8 mm, without increasing the electrical power consumption. Eventually, the hydrophilicity of the surface is also measured by the contact angle of a water droplet that decreases from 78° to 8° after surface treatment, implying we were able to reach a super-hydrophilic surface with this plasma jet structure.     

Numerical solution to the shearing flow of granular materials between two plates

We study the shearing flow of granular materials between two horizontal flat plates where the top plate is moving with a constant speed. The constitutive relation used for the stress is based on the continuum model proposed by Rajagopal and Massoudi (DOE Report, DOE/PETC/TR-90/3, 1990). The material coefficients such as viscosity and normal stress coefficients are based on the model of Boyle and Massoudi (Int. J. Eng. Sci 28 (1990) 1261). The governing equations are non-dimensionalized and the resulting system of non-linear differential equations is solved numerically using finite difference technique.     

Synthesis and characterization of potential multifunctional methacrylate-based dental monomers

Research on Chemical Intermediates - We describe synthesis and characterization of a series of novel multifunctional methacrylate-based dental monomers. Triethanolamine was reacted with glycidyl...     

Stability and torsional vibration analysis of a micro-shaft subjected to an electrostatic parametric excitation using variational iteration method

In this article stability and parametrically excited oscillations of a two stage micro-shaft located in a Newtonian fluid with arrayed electrostatic actuation system is investigated. The static stability of the system is studied and the fixed points of the micro-shaft are determined and the global stability of the fixed points is studied by plotting the micro-shaft phase diagrams for different initial conditions. Subsequently the governing equation of motion is linearized about static equilibrium situation using calculus of variation theory and discretized using the Galerkin’s method. Then the system is modeled as a single-degree-of-freedom model and a Mathieu type equation is obtained. The Variational Iteration Method (VIM) is used as an asymptotic analytical method to obtain approximate solutions for parametric equation and the stable and unstable regions are evaluated. The results show that using a parametric excitation with an appropriate frequency and amplitude the system can be stabilized in the vicinity of the pitch fork bifurcation point. The time history and phase diagrams of the system are plotted for certain values of initial conditions and parameter values. Asymptotic analytically obtained results are verified by using direct numerical integration method.     

Chemical Composition of the Essential Oils of <Emphasis Type="Italic">Bunium elegans</Emphasis> and <Emphasis Type="Italic">Bunium caroides</Emphasis>

Analyses of the essential oils of Bunium elegans (Fenzl) Freyn and B. caroides (Boiss.) Hausskn. ex Bornm., using GC, GC/MS, and¹³ C-NMR spectroscopy resulted in identification of their chemical constituents. The oils of both species contain mainly the sesquiterpene hydrocarbons germacrene-D and E-caryophyllene, which amounted to 24.1% and 38% for B. elegans and 22.1% and 26.6% for B. caroides respectively. The oil of B. caroides contained the monoterpenes α-pinene and Z-β-ocimene in 4.1 and 5.9% respectively, while traces of monoterpenes were detected for B. elegans. On the other hand, in B. caroides the phenylpropanoid derivatives asaricin (7.5%) and dillapiole (10.2%) were among the major constituents. __________ Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 335–336, July–August, 2005.     

PVA-clay nanocomposite hydrogels for wound dressing

Polymer gels as soft biomaterials have found diverse applications in biomedical field, e.g. in management and care of wound as wound dressing.The recent researches on nanocomposite materials have shown that some properties of polymers and gels significantly improve by adding organoclay into polymeric matrix. In this work, in order to obtain wound dressing with better properties, nanocomposite hydrogel wound dressing was prepared using combination of polyvinyl alcohol hydogel and organoclay, i.e. Na-montmorillonite, via the freezing-thawing method. The effect of organoclay quantity on the structural, swelling, physical and mechanical properties of nanocomposite hydrogel wound dressing was investigated. The results showed that the nanocomposite hydrogels could meet the essential requirements for the reasonable wound dressing with some desirable characteristics such as relatively good swelling, appreciated vapour transmission rate, excellent barrierity against microbe penetration and mechanical properties. The results also indicated that the quantity of the clay added to the nanocomposite hydrogel is the key factor in obtaining such suitable properties required for wound dressing.     

On propagation of convergence

We discuss some classical theorems and some recent results in the field of complex approximation from the viewpoint of propagation of convergence. We also prove a theorem on propagation of convergence in C². The research was conducted (in part) while enjoying the hospitality of Jagiellonian University, Gracow, Poland, in 1991; and was supported (in part) by a grant from the Faculty Development Fund of the University of Michigan-Flint.