Effect of molecular weight on the ultrasonic degradation of poly(vinyl-pyrrolidone)

The ultrasonic degradation of poly(vinyl-pyrrolidone) (PVP) of different initial molecular weights was studied at a fixed temperature. The effect of solution concentration on the rate of degradation was investigated. A method of viscometry was used to study the degradation behavior and kinetic model was developed to estimate the degradation rate constant. The results were indicated that the rate of ultrasonic degradation increased with increasing molecular weight. It was found that rate constant decreases as the concentration increases. The calculated rate constants correlated in terms of inverse concentration and relative viscosity of PVP solutions. This behavior in the rate of degradation was interpreted in terms of viscosity and concentration of polymer solution. With increasing solution concentration, viscosity increases and it causes a reduction in the cavitation efficiency thus, the rate of degradation will be decreased. The experimental results show that the viscosity of polymers decreased with ultrasonic irradiation time and approached a limiting value, below which no further degradation took place. This study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to, therefore, become smaller.     

Newtonian viscosity behavior of dilute to moderately concentrated solutions of cellulose acetate butyrate

The Newtonian viscosity behavior of dilute to moderately concentrated solutions of cellulose acetate butyrate in dioxane was investigated at different temperatures. The viscosity data were analyzed in terms of Martin's and Fedor's relationships and also generalized in terms of reduced variables. The rheological behavior of cellulose acetate butyrate solutions in the whole range of concentrations is determined by the parameter (K_MC [n]). The temperature dependence of viscosities was expressed by the Arrhenius-Frenkel-Eyring equation and the activation energy of viscous flow of polymer solutions (ΔGv) was calculated. ΔGv increases with concentration of polymer solution and is independent of temperature. The preexponential factor, A, related to activation entropy, decreases with concentration of polymer solution. The thermodynamic parameter of viscous flow for cellulose acetate butyrate (CAB)-dioxane solutions is indicative of moderately stiff structure for CAB in solutions.     

Preparation of Chitosan/Polyvinyl Alcohol Electrospinning Nano-Membranes Using the Green Solvent,Plasma Acid

Abstract

In this paper, a green solvent for chitosan, plasma acid, was made and chitosan/plasma-acid solutions were prepared. An environmentally friendly chitosan/polyvinyl alcohol (PVA) nano-membrane was prepared via electrospinning due to the difficulty of electrospinning of pure chitosan/plasma-acid solutions. Two blending methods of chitosan with PVA were investigated. One way was to mix a chitosan/plasma-acid solution (1%) and a PVA/water solution (10%) with the volume ratios of 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 and 8:2, respectively. The results showed that fibrous nano-membranes could start to be formed at a chitosan/PVA mixing ratio of 7:3 up to the ratio of 2:8 with increasing PVA. The average fiber diameters increased with increased adding of PVA, ranging from 74.7?nm for the 7:3 ratio to 280.7?nm for the 2:8 ratio. The other way to prepare the chitosan/PVA solutions was to put PVA and chitosan powders into the plasma acid together. Fibrous nano-membranes could also be formed at 6% PVA and 10% PVA solution, both with 1% chitosan compositions. The average diameters of the resulting nano-fibers were 144.67?nm and 300.7?nm, respectively. The Fourier transform infrared (FTIR) spectroscopy results showed that the chitosan was bonded to the PVA by hydrogen bonds in the nano-membranes (6% PVA, 1% chitosan). It is noted that both of the two blending methods permitted obtaining chitosan/PVA nano-membranes. As indicated, the PVA in the solution had a large effect on the diameters of the nano-fibers. The first method permitted obtaining nano-fibers with smaller diameter. The maximum concentration of chitosan in the solution was 0.7% (7:3 ratio). The second method was simpler and permitted increasing the chitosan concentration in the solution to 1% for both the 6% and 10% concentrations of PVA.     

Influence of Synthetic Polymer on Aqueous Anionic Surfactant (SDBS) Micelle Investigated by FT-IR and Ultrasonic Study

The ultrasonic velocity, absorption, density and viscosity measurements were used to study the interaction of PEG, PVP and PVA with anionic surfactant — sodium dodecyl benzene sulfonate (SDBS) in aqueous solutions of different concentrations and temperatures, namely, 303, 313 and 323 K. The properties of SDBS with increasing polymer concentration (0.2–1.2%) were investigated. Interaction of SDBS with polymer was found to involve the binding of surfactant with the polymer molecule followed by the usual micellization; from the observed values the related acoustical parameters are calculated and their variation are discussed. The FT-IR spectrum was also used to characterize these samples.     

Ultrasonic degradation of poly(vinyl alcohol) in aqueous solution

Solution of poly(vinyl alcohol) in water with different concentrations (by weight 1%, 1.5%, 2%) and different volumes (50, 75 and 100 ml) were subjected to ultrasonic degradation. A method of viscometry was used to study the degradation behavior and kinetic model was developed to estimate the degradation rate constant. The degradation rate constant was correlated with the power input due to ultrasonic irradiation and reaction volume. It was found that rate constant decreases as the reaction volume and concentration increases. The proportionality index of the relation between rate constant, power input and reaction volume was found to be nearly equal for all concentrations studied. The proportionality constant was found to be approximately equal for 1% and 1.5% solution and for 2% solution it was approximately half the value for that of 1% and 1.5% solutions. The decrease in rate constant and proportionality constant is attributed to the fact that at higher concentration and at higher volume, the intensity of cavitation phenomenon is depressed and therefore the extent of polymer chain breaking decreases. The difference in the values of limiting viscosities (constant solution viscosity which does not decrease by further ultrasonic irradiation) for 50, 75 and 100 ml solutions for each of 1% and 1.5% concentration was negligible. But 2% solution at 100 ml volume showed slightly higher value of limiting viscosity than that for 50 and 75 ml.     

Study on the Electrospinnability of Polyvinyl Alcohol Solutions by Using Water/N,N-dimethylacetamide or Water/N,N-dimethylformamide as Solvents

The electrospinning of poly(vinyl alcohol) (PVA) (99% hydrolysis degree) aqueous solution with added organic solvents N, N-dimethylacetamide (DMAc) or N, N-Dimethylformamide (DMF) was investigated. After the addition of the organic solvents to the PVA aqueous solutions, the surface tension and conductivity decreased and the viscosity significantly increased, which caused an improved electrospinnability of the PVA solutions. The micro-structures of the three solutions were investigated by dynamic light scattering (DLS), differential scanning calorimetry (DSC) and dynamic viscoelastic measurements. The DLS data revealed that the swelling of the PVA coils was slightly increased but the overlaps of PVA coils decreased greatly after one of the organic solvents was added to the aqueous solution. The DSC data showed both the water-rich phase and PVA-rich phase were destroyed and the solution became more homogenous after the addition due to the interaction between the organic solvent and water. Viscoelastic data showed there was an obvious difference in the storage modulus behavior between the aqueous solutions and the water/solvents solutions. These changes in the micro-structure and properties were the reason for the improved electrospinnability of the PVA solution. According to scanning electron microscopy (SEM), the average diameter of the electrospun PVA nanofibers was about 308 nm for the DMF/water system, and 255 nm for the DMAC/water system, as compared with uneven diameter nanofibers for the water system.     

聚乙烯醇水溶液二维定向凝固的微观组织演化

为了深入探究定向多孔聚合物材料的微观组织形成机理,利用定向凝固原位实时观察手段,研究不同浓度及不同分子量聚乙烯醇(PVA)水溶液在不同抽拉速度下的定向凝固形貌演化.PVA水溶液的定向凝固形态在低浓度(1 wt%,2.5 wt%)和小分子量(M_w=24000)情况下,一次枝晶间距随着抽拉速度的增加而减小.随着PVA浓度和分子量的增加,一次枝晶间距随抽拉速度变化不明显,枝晶主轴尺寸则随速度增加呈现减小的趋势.与传统凝固形态形成机理相比,PVA水溶液的凝固形态由PVA分子的扩散引起的凝固界面不稳定性机理和PVA高分子链交联引起的局部相分离机理竞争决定.     

Multibubble sonoluminescence in aqueous salt solutions

The sonoluminescence from aqueous solutions containing various salts in the concentration range of 0 to 7 M has been examined using 3.5 ms pulses of 515 kHz ultrasound. In almost all cases the sonoluminescence intensity recorded increased with increasing salt level until a critical concentration (in the range of 1-2 M) was reached. At salt levels above the critical concentration the signal intensity decreased sharply with increasing salt concentration. It is not possible to satisfactorily account for the trends in terms of changes in solution viscosity, rate of bubble coalescence, water vapour pressure, air/water interfacial tension or ionic strength. However, a good correlation of the increase in the signal with the extent of gas solubilisation in the solutions with changing salt concentration was observed. Possible reasons for the signal increase with the addition of salts and the marked decrease at high salt concentrations are discussed.     

Ultrasonic degradation of aqueous carboxymethylcellulose: effect of viscosity, molecular mass, and concentration

It is well established that prolonged exposure of solutions of macromolecules to high-energy ultrasonic waves produces a permanent reduction in viscosity. It is generally agreed as well and also this study proved the hydrodynamic forces to have the primary importance in degradation. According to this study the sonolytic degradation of aqueous carboxymethylcellulose polymer or polymer mixtures is mainly depended on the initial dynamic viscosity of the polymer solution when the dynamic viscosity values are in the area range enabling intense cavitation. The higher was the initial dynamic viscosity the faster was the degradation. When the initial dynamic viscosities of the polymer solutions were similar the sonolytic degradation was dependent on the molecular mass and on the concentration of the polymer. The polymers with high molecular mass or high polymer concentration degraded faster than the polymers having low molecular mass or low polymer concentration. The initial dynamic viscosities were adjusted using polyethyleneglycol.     

Ultrasonic degradation of polymers: effect of operating parameters and intensification using additives for carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA)

Use of ultrasound can yield polymer degradation as reflected by a significant reduction in the intrinsic viscosity or the molecular weight. The ultrasonic degradation of two water soluble polymers viz. carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) has been studied in the present work. The effect of different operating parameters such as time of irradiation, immersion depth of horn and solution concentration has been investigated initially using laboratory scale operation followed by intensification studies using different additives such as air, sodium chloride and surfactant. Effect of scale of operation has been investigated with experiments in the available different capacity reactors with an objective of recommending a suitable type of configuration for large scale operation. The experimental results show that the viscosity of polymer solution decreased with an increase in the ultrasonic irradiation time and approached a limiting value. Use of additives such as air, sodium chloride and surfactant helps in increasing the extent of viscosity reduction. At higher frequency operation the viscosity reduction has been found to be negligible possibly attributed to less contribution of the physical effects. The viscosity reduction in the case of ultrasonic horn has been observed to be more as compared to other large capacity reactors. Kinetic analysis of the polymer degradation process has also been performed. The present work has enabled us to understand the role of the different operating parameters in deciding the extent of viscosity reduction in polymer systems and also the controlling effects of low frequency high power ultrasound with experiments on different scales of operation.     

Ultrasound-based treatment approaches for intrinsic viscosity reduction of polyvinyl pyrrolidone (PVP)

The present work deals with achieving viscosity reduction in polymer solutions using ultrasound-based treatment approaches. Use of simple additives such as salts, or surfactants and introduction of air at varying flow rates as process intensifying parameters have been investigated for enhancing the degradation of polyvinyl pyrrolidone (PVP) using ultrasonic irradiation. Sonication is carried out using an ultrasonic horn at 36 kHz frequency at an optimized concentration (1%) of the polymer. The degradation behavior has been characterized in terms of the change in the viscosity of the aqueous solution of PVP. The intrinsic viscosity of the polymer has been shown to decrease to a limiting value, which is dependent on the operating conditions and use of different additives. Similar extent of viscosity reduction has been observed with 1% NaCl or 0.1% TiO₂ at optimized depth of horn and 27 °C, indicating the superiority of titanium dioxide as an additive. The combination of ultrasound and ultraviolet (UV) irradiation results in a significantly faster viscosity reduction as compared to the individual operations. A kinetic analysis for the degradation of PVP has also been carried out. The work provides a detailed understanding of the role of the operating parameters and additives in deciding the extent of reduction in the intrinsic viscosity of PVP solutions.     

Features of the Quenching of the Triplet States of Water-Soluble Porphyrins by Molecular Oxygen

Using the methods of time-resolved absorption spectroscopy, we have investigated the features of quenching, by molecular oxygen, of the excited triplet states of water-soluble 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphyrin (H₂TMPyP) and 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin (H₂TSPP) in water–ethanol solutions. It has been revealed that for both compounds the rate constant of quenching of the triplet states increases with increasing viscosity of the medium. Quenching of the excited triplet states of the dissociated (in water) and undissociated (in ethanol) forms of water-soluble porphyrins occurs with a different efficiency, and the rate constant of quenching the triplet states by molecular oxygen k _T thereby is higher for the dissociated form. It has been shown by means of mathematical modeling that the experimental results obtained can be described in terms of the change in the rate constants of intracomplex transitions in the porphyrin–oxygen collisional complex at varied solution viscosity and their difference for the dissociated and undissociated forms of water-soluble porphyrin.     

Ultrasonic depolymerization of aqueous polyvinyl alcohol.

Ultrasonication has proved to be a highly advantageous method for depolymerizing macromolecules because it reduces their molecular weight simply by splitting the most susceptible chemical bond without causing any changes in the chemical nature of the polymer. Most of the effects involved in controlling molecular weight can be attributed to the large shear gradients and shock waves generated around collapsing cavitation bubbles. In general, for any polymer degradation process to become acceptable to industry, it is necessary to be able to specify the sonication conditions which lead to a particular relative molar mass distribution. This necessitates the identification of the appropriate irradiation power, temperature, concentration and irradiation time. According to the results of this study the reactors constructed worked well in depolymerization and it was possible to degrade aqueous polyvinyl alcohol (PVA) polymer with ultrasound. The most extensive degradation took place at the lowest frequency used in this study, i.e. 23 kHz, when the input power was above the cavitation threshold and at the lowest test concentration of PVA, i.e. 1% (w/w). Thus this study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to therefore become smaller.     

Study on Steady Shear Rheological Behavior of Concentrated Suspensions of Sulfonated Polyacrylamide/Na-Montmorillonite Nanoparticles

Concentrated suspensions of sulfonated polyacrylamide (SPA)/Na⁺-montmorillonite (Na-MMT) were prepared and their stability and steady shear rheological properties were described as a function of nanoparticle and polymer concentration and temperature. The results showed that the Na-MMT nanoparticles suspensions were stable in the absence and presence of SPA and no sedimentation was seen. The Z-average particle sizes for the SPA/Na-MMT suspensions increased in the presence of SPA. Rheological investigations showed that the SPA solutions and SPA/Na-MMT suspensions displayed non-Newtonian behavior in almost the whole range of shear rate. All the suspensions exhibited a shear-thinning flow character as shear rate increased. The flow curves indicated the shear viscosity and stress of the samples were decreased with increasing nanoparticles concentration up to 1.5 wt%, but for Na-MMT loading greater than 1.5 wt% there was an increase in shear viscosity and stress of the suspensions. Increasing of SPA concentration had more effect on increasing the rheological properties of SPA/Na-MMT suspensions than increasing of nanoclay content. Shear viscosity and stress of the suspensions increased with increasing SPA concentration and decreased with increasing temperature from 50°C to 70°C.     

A Rheological Study of Xanthan Polymer for Enhanced Oil Recovery

This study explored the potential application of xanthan gum as a polymer-flooding agent for oil recovery applications in a specific Devonian oil field. Rheological measurements using oscillatory and steady shear were carried out to examine the change in shear viscosity when the polymer was applied under reservoir conditions. The xanthan rheological properties were described by the Herschel–Bulkley and Ostwald models to characterize its non-Newtonian behavior. As expected, the results showed that higher xanthan concentrations raised the polymer viscosity and increased the degree of shear thinning. Addition of alkalis caused the viscosity of the xanthan solutions to decrease, but they maintained their shear-thinning properties. Polymer solutions in typical oil field brine increased in viscosity by ca. 400% for 720 hours storage time. On the other hand, as expected, the solutions lost their viscosity gradually with increasing temperature. However, at reservoir temperature (68°C), the polymer solutions kept more than 60% of their initial viscosity. In oscillatory deformation tests it was observed that all the measured viscoelastic properties were influenced by temperature and confirmed that xanthan solution behaved as a weak-gel. An order-disorder transition exists within the xanthan-brine solutions which responds to changes in solution concentration, temperature and alkalis.     

Radical pair dynamics in anionic micelles with different alkyl chain length as studied by pulse-mode product-yield-detected ESR

Dynamics of the radical pair composed of benzophenone ketyl radical and an alkyl radical of surfactant molecule in the micellar solution were studied by means of the pulse-mode product-yield-detected electron spin resonance (pulse-PYESR) technique. As the surfactants heptyl (C7), nonyl (C9), decyl (C10) and dodecyl (C12) sulfates were employed. Both the escape rate and the recombination rate of the radical pair decreased monotonously with increasing the alkyl-chain length from C7 to C12. A close relation between the escape rate and the critical micellar concentration divided by the aggregation number and also that between the recombination rate and internal viscosity of micelle are pointed out. The pulse-PYESR analysis on the radical pair containing the alkyl radical of surfactant molecule as one of the components is very powerful in extracting the kinetic constants of micelle, since the alkyl sulfate radical is an ideal probe for the micelle molecule.     

Gelation and Swelling Behavior of Semi-Interpenetrating Polymer Network Hydrogels Based on Polyacrylamide and Poly(vinyl alcohol)

Novel semi-Interpenetrating Polymer Network (semi-IPN) hydrogels based on partially Hydrolyzed Polyacrylamide (HPAM) and Poly(Vinyl Alcohol) (PVA) were prepared by solution crosslinking using chromium triacetate. Effects of PVA content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels decreased with increasing PVA content. It was also found that increasing the PVA content increases the loss factor, indicating that the viscous properties of this gelling system increase more strongly than the elastic properties. The swelling ratio of the semi-IPN gels in tap water decreased as the concentration of the PVA increased. However, the semi-IPN gels showed lower salt sensitivity factor in synthetic oil reservoir water as compared with HPAM gels. Therefore, they are potentially good candidates for enhanced oil recovery applications.     

Study of the sonophotocatalytic degradation of basic blue 9 industrial textile dye over slurry titanium dioxide and influencing factors

The sonophotocatalytic degradation of basic blue 9 industrial textile dye has been studied in the presence of ultrasound (20 kHz) over a TiO(2) slurry employing an UV lamp (15 W, 352 nm). It was observed that the color removal efficiency was influenced by the pH of the solution, initial dye concentration and TiO(2) amount. It was found that the dye degradation followed apparent first order kinetics. The rate constant increased by decreasing dye concentration and was affected by the pH of the solution with the highest degradation obtained at pH 7. The first order rate constants obtained with sonophotocatalysis were twofold and tenfold than those obtained under photocatalysis and sonolysis, respectively. The chemical oxygen demand was abated over 80%.     

Ultrasonic degradation of Rhodamine B in the presence of hydrogen peroxide and some metal oxide

In this research, degradation of Rodamine B in the presence of (hydrogen peroxide), (hydrogen peroxide + ultrasound), (hydrogen peroxide + aluminum oxide), (hydrogen peroxide + aluminum oxide + ultrasound with different ultrasound power), (hydrogen peroxide + iron oxide) and (hydrogen peroxide + iron oxide + ultrasound with different ultrasound power) were investigated at 25 °C. The apparent rate constants for the examined systems were calculated by pseudo-first-order kinetics. The results indicate that the rate of degradation was accelerated by ultrasound. The rate of degradation was increased by increasing power ultrasound. The efficiency of the (hydrogen peroxide + iron oxide + ultrasound) system for degradation of Rodamine B was higher than the others examined.     

Vanishing Viscosity Solutions of the Compressible Euler Equations with Spherical Symmetry and Large Initial Data

We are concerned with spherically symmetric solutions of the Euler equations for multidimensional compressible fluids, which are motivated by many important physical situations. Various evidences indicate that spherically symmetric solutions of the compressible Euler equations may blow up near the origin at a certain time under some circumstance. The central feature is the strengthening of waves as they move radially inward. A longstanding open, fundamental problem is whether concentration could be formed at the origin. In this paper, we develop a method of vanishing viscosity and related estimate techniques for viscosity approximate solutions, and establish the convergence of the approximate solutions to a global finite-energy entropy solution of the isentropic Euler equations with spherical symmetry and large initial data. This indicates that concentration is not formed in the vanishing viscosity limit, even though the density may blow up at a certain time. To achieve this, we first construct global smooth solutions of appropriate initial-boundary value problems for the Euler equations with designed viscosity terms, approximate pressure function, and boundary conditions, and then we establish the strong convergence of the viscosity approximate solutions to a finite-energy entropy solution of the Euler equations.