Kinetics of the Initial Stage of Gelation in Chitosan Solutions Containing Glutaric Aldehyde: Viscometric Study

The effects of glutaric aldehyde concentration C _GA(in the range from 0.07 to 0.2 wt %) and temperature T(from 20 to 65°C) on the kinetics of an increase in the effective viscosity _effof aqueous solutions of chitosans (C _CH= 2.4 wt %, pH 3.6, and ionic strength I= 0.05) with molecular masses equal to 33 × 10⁴and 55 × 10⁴and the degrees of substitution at N-acetyl and amino groups of 0.08 and 0.90, respectively were studied. The kinetic curves _eff(t) exhibited the induction periods of a relatively slight increase in the viscosity of chitosan–glutaric aldehyde mixed solutions with time followed by the periods of a drastic increase in the viscosity. The former periods correspond to the formation of gel clusters; the latter periods, to the gelation over the whole volume of a solution. Optimal ranges of the parameters C _GAand Twere determined for the preparation of spherical gel particles of slightly cross-linked chitosan, which are used for the sorption of heavy metals from low-concentrated solutions.     

Microporous polyethersulfone membranes prepared under the combined precipitation conditions with non‐solvent additives

Using diethylene glycol (DegOH) as non‐solvent additive (NSA) and N, N‐dimethylacetamide (DMAc) as solvent (S), polyethersulfone (PES) flat sheet membranes were prepared via immersion precipitation combined with the vapor induced phase separation (VIPS) process. Light transmittance was used to follow the precipitation rate during the immersion process as well as during the VIPS stage. As the addition of the NSA, the viscosity of casting solutions increased, which led to a slow precipitation rate. Though the precipitation rate decreased, the instantaneous demixing type was maintained. High flux membranes were obtained only at a high mass ratio of NSA/S; producing membranes had cellular pores on the top surface and sponge‐like structure on cross section. The VIPS process prior to immersion precipitation was important for the formation of cellular pore on the surface. With the increase in exposure time, the liquid–liquid phase separation took place on the surface of casting solution; nucleation and growth induced the formation of cellular pore on the top surface. Coagulation bath temperature also had large effect on the precipitation rate; high temperature on coagulation bath mainly accelerated the transfer of solvent and non‐solvent. Higher flux membrane with a porous skin layer could be obtained at a high coagulation bath temperature, but at the same time the mechanism properties were weakened. Copyright © 2007 John Wiley & Sons, Ltd.     

The cellulose solvent system N,N-dimethylacetamide/lithium chloride revisited: the effect of water on physicochemical properties and chemical stability

The water content in the binary systemN,N-dimethylacetamide/lithium chloride (DMAc/LiCl), acommon cellulose solvent, has been proven to be a crucial parameter. A quickdetermination of water content in DMAc based on the solvatochromism of aUV-active betain probe dye has been developed and validated. An analogousmethod, based on the solvatochromic fluorescence shift ofZelinskij's dye, which strongly depends on thesolventpolarity, was established for water determination in DMAc containing LiCl.Precise physicochemical data of the system DMAc/LiCl, such as density,viscosity, and conductivity, have been obtained. The limiting solubility forLiCl in absolute DMAc is 8.46 wt%. As shown by lightscattering experiments, water in DMAc/LiCl induces aggregation upon standingforlonger periods of time, which is even more prominent for diluted solutions andthose having a poor state of dissolution.     

Synthesis of associating poly(acrylic acid) in supercritical carbon dioxide and its solution properties

Hydrophobically associating polymers have been synthesized in supercritical carbon dioxide by copolymerization of acrylic acid with different amounts of acrylate with hydrocarbon or fluorocarbon groups. It was found that conversion of hydrocarbon comonomers was above 95% whereas that for fluorocarbon comonomers was only about 50%. In addition, large amounts of hydrophobic groups could be easily introduced to poly(acrylic acid) by reaction in supercritical carbon dioxide. The solution properties were investigated by rheology. The results indicated that intermolecular association of the copolymer was strong and viscosity was maximum under acidic conditions. In aqueous solutions fluorocarbon hydrophobes associated much more strongly than the hydrocarbon variety, but the viscosifying effect of PAAC-18 series copolymers in 2% (w/w) solution was more pronounced than that of the PAAF series, results which did not agree with the conclusions of Ravey and Stébé. It was also found that the thixotropy behavior of copolymer solution at pH 3.2 was more complex than that at pH 5.0, at which pseudoplasticity only was observed for solutions of all copolymers. Contact angles of copolymer solutions on a glass sheet were measured. The data indicated that contact angles of hydrocarbon-modified polymers were smaller than those of fluorocarbon analogues. As time passed the contact angle became smaller and smaller. Fluorocarbon analogues were better than hydrocarbon analogues, and longer hydrophobic chains were better than shorter chains, at maintaining the hydrophobic character of the surface.     

Friedel-Crafts Polymers. 10. Polycondensation of 4-4′-Dichloromethlydiphenyl Ether with Phenol and Isomeric Cresols

Friedel-Crafts polycondensations of 4, 4′-dichloromethyldiphenyl ether (DDE) with phenol and isomeric cresols were carried out under different experimental conditions. The molecular weight of the polymer products was estimated by end group analysis, that of soluble products by VPO, and they were characterized by TGA and solution viscosity. DMF solutions of samples prepared from phenol and p- and m-cresols, but not those from o-cresol, showed abnormal viscosity behavior. However, the viscosity behavior of DMF-water solutions was normal. Abnormal vis-cisoty data of DMF solutions were correlated by an empirical relation. Curing of one fusible and soluble DDE-phenol polymer sample with hexamine was studied by measuring the percentage of cured material as a function of time at selected temperatures.     

Effect of coagulating agent viscosity on the kinetics of formation,morphology, and transport properties of cellulose nanofiltration membranes

Low-viscous coagulating agents are tradionally used to precipitate polymers from their solutions and obtain films and fibers from them; they represent, as a rule, the combinations of solvent and nonsolvent of the polymer used. At the same time, since the structure of the precipitated polymer is formed under non-equilibrium conditions, the influence of the coagulant viscosity can be quite substantial. The influence of the viscosity of the medium on the formation of structure, morphology, and transport characteristics of the precipitated polymer is studied by example of forming of the cellulose membranes from solution in N-methyl-morpholine N-oxide using some proton-donor coagulants. In this regard, the interdiffusion processes proceeding at the contact of cellulose solutions and coagulating agents (water, propylene glycol, glycerin) are explored using the laser interferometry method. Varying the precipitator viscosity allows one to change the rate of formation and correspondingly the morphology of the cellulose films. In turn, the membrane structure determines its transport characteristics, which were assessed by the filtration of aprotic media with anionic dyes—Orange II and Remazol Brilliant Blue R. The application of the low-viscous precipitator provides the formation of a uniform film structure in the bulk, but leads to development of defects close to the surface, while a viscous medium promotes the formation of a relatively thin dense shell on the films.     

Capillary Flow of Cationic Polyelectrolyte Solutions

The flow rates and the dynamic contact angles of aqueous solutions of cationic polyelectrolyte (CPE) in quartz capillaries with radius of 3–4 m are measured. It is shown that the surface tension and viscosity of CPE solutions with concentrations from 10^–1 to 10^–5 g/l are the same as for water. Surface inactivity of CPE leads to the substantial difference between the capillary properties of their solutions and those of surfactant solutions. It is established that, as the solution concentration increases, the advancing contact angles are reduced from 83° to 75°; the receding contact angles lie between 10° and 20°. Large hysteresis of contact angle can probably be related to the formation of metastable wetting film behind the receding meniscus. Surface hydrophobization occurs as a result of the adsorption of CPE molecules on the negatively charged quartz surface. The specific features of the application of CPE solutions in the deposition technology of hydrophobic coatings, the capillary imbibition and displacement of oils from hydrophobic pores are discussed.     

Pulsed Photoacoustic Study of the Diffusion of Chromophores in Human Skin

The technique of pulsed photoacoustic spectroscopy was used to investigate the diffusion of chromophores in human skin. The kinetic of diffusion has been studied for five solutions at different concentrations in a mixture of chromophores, as used in commercial sunscreens. In addition to the classical macroscopic interpretation of the diffusion process, a new method is shown to give more detailed information on chromophore presence at different depths in skin. For the first time, results are expressed in the frequency domain by means of the Fourier transform applied to the photoacoustic signal. The spectra are discussed versus the depth in skin samples and the time of diffusion kinetics. This new method of data analysis is shown to be very useful for understanding the influence of the internal structure of a medium on the penetration rate of chromophores into skin.     

Viscoelastic studies of some phenols from dielectric measurements

The variation of dielectric relaxation time with the viscosity of the medium is being exploited in drawing certain quantitative conclusions regarding molecular motion and intermolecular forces in liquids, liquid mixtures, dilute solutions and multi-component polar solutes in dilute solution. With no perfect empirical or theoretical equation in place for the variation of dielectric relaxation time with viscosity, the experimental investigations on different systems only can give an insight. In the present study the results of dielectric measurements carried out on pure samples of o-ethyl phenol, 2-n-butylphenol, 4-n-butylphenol, and 2,6-butylphenol in dilute solutions in different mixed solvents (benzene?+?paraffin) and on binary mixtures (1?:?1) of p-2-n-butylphenol?+?4-n-butylphenol and p-bromonitrobenzene?+?2,6-butylphenol, are reported. For comparison, the results on p-bromonitrobenzene?+?m-bromonitrobenzene as an example of mixture of non-associative liquids was also carried out and the results are presented. Different parameters determined using these dielectric measurements are also presented using different models and these studies indicate that the dielectric behavior at microwave frequencies favor the concept of dynamic viscosity and a single viscoelastic relaxation time for the system under study.     

The kinetics of chitosan depolymerisation at different temperatures

The stability (in terms of molar mass) of chitosan potentially plays an important role in its behaviour and functional properties in a wide range of applications and therefore any changes over time must be understood.The weight-average molar masses and intrinsic viscosities of chitosan solutions at different temperatures (4, 25 and 40 °C) have been investigated using size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALLS) and a “rolling ball” viscometer respectively. The weight-average molar mass (M_w) and the intrinsic viscosity ([η]) both decrease with increased storage time, although this phenomenon is more pronounced at elevated temperatures.Good correlation was found between the changes in molar mass and intrinsic viscosity with time and these parameters were used to determine the depolymerisation constant (k) and the activation energy (E_a).Knowledge of the effect of storage conditions (e.g. temperature) is important in the understanding the stability of chitosan solutions, but whether or not chitosan depolymerisation will be detrimental to its intended application will depend on the functional significance of the changes that occur.     

Rheological properties of anisotropic poly(para-benzamide) solutions

A study has been made of the viscous properties of poly(para-benzamide) (PBA) solutions in dimethyl acetamide, which undergo a transition from an isotopic to an anisotropic (liquid-crystal) state at a definite concentration C^*. The polymer solutions behave in many respects (as regards the concentration and temperature dependence of viscosity, etc.) like solutions of low molecular weight compounds forming a liquid crystal phase, although the transitions are less pronounced in the polymer solutions owing to their polydispersity. It is shown that the viscometric method, being extremely sensitive to C^*, is convenient for determining phase diagrams of anisotropic polymer solutions. The values of C^* as related to the molecular weight of PBA have been determined, and a general criterion for transition from isotropic to anisotropic solutions established; the latter has the form (CM?)^* ≈ 1.3 × 10⁵ at 20°C. This criterion is in line with the condition for the formation of the liquid-crystal structure in a dispersion of rodlike particles as proposed by Flory. Generalized concentration dependences of viscosity have been plotted by reducing concentration to C^* and viscosity, to the maximum viscosity at the phase transition point. In investigating the flow properties of PBA solutions we revealed the existence of a yield point in the range of low shear stresses, and an intersection of the flow curves of solutions of different concentration at high shear stresses, which excludes a generalized representation of the flow curves in reduced ordinary-type coordinates.     

Rheology of hydroxypropylcellulose solutions

The rheology of hydroxypropylcellulose (HPC)—acetic acid solutions was investigated by using a cone-and-plate rheometer and a capillary rheometer, for polymer concentrations ranging from 10 to 80%. Isotropic solutions exhibit a Newtonian plateau followed at higher shear rates by a pseudoplastic zone. The apparent viscosity varies as C^5.2 if concentration C is less than 27% and as C¹³ for 27% < C < 30%. A biphasic interval (isotropic and cholesteric phases) exists between 30 and 35%. A maximum in viscosity is observed at C = 30%, the height of the viscosity peak being a decreasing function of shear rate. Anisotropic solutions are strongly viscoelastic. Both isotropic and anisotropic solutions give results (apparent viscosity, first normal-stress difference, relaxation time, etc.) which are not in good agreement with Doi's theory. This is understandable since the HPC chain cannot be modeled by a rigid rod. Upon heating, anisotropic HPC—acetic acid solutions undergo an anisotropic to isotropic phase transition which is easily detected by a maximum in the temperature dependence of the first normal-stress difference and of the apparent viscosity.     

制膜液黏度对单皮层PVDF中空纤维膜纺制的影响

以二甲基乙酰胺(DMAc)为溶剂,制备聚偏氟乙烯(PVDF)浓度为15%的制膜液,考察了DMAc同时作为内凝胶浴时膜结构的变化.为保持纺膜过程中的稳定性,分别考察了添加剂LiCl、水以及表面活性剂对制膜液黏度的影响.实验发现添加LiCl可以大大提高制膜液的黏度,而水作为添加剂时对黏度的影响与制膜液本身的浓度有关.在不提高制膜液浓度的基础上,通过提高制膜液黏度克服了膜在纺制过程中的不稳定问题,得到阻力较小的,指状孔贯穿的单外皮层中空纤维膜.     

Rheological study and thermodynamic analysis of the binary system (water/ethanol): Influence of concentration

Water is the most widely used solvent in the chemical and pharmaceutical industry, since it is the most physiological and best tolerated excipient. However, in some cases water cannot be used as a solvent because the active substance or solute is insoluble or only slightly soluble in water. For this and other reasons, nonwater solvents may be used possessing the common characteristic of being soluble or mixable in water; as a result, such solvents can be used to prepare binary or tertiary mixtures, etc., with different purposes such as increasing water solubility, or modifying the viscosity or absorption of the dissolved substance, for example.

Ethanol, along with other alcohols either alone or in water–alcohol solutions involving different proportions, are widely used in the pharmaceutical industry as excipients in different formulations, or as solvents.

Ethanol–water systems are characterized by the so-called volume contraction phenomenon, which is in turn accompanied by a considerable increase in the viscosity of the system. This is attributed to the increase in size of the molecular package secondary to solvation or the formation of hydrogen bonds between the alcohol and water – a phenomenon referred to as viscous synergy.

The formation of hydrogen bonds between alcohol and water modifies with temperature, thus leading to variations in the viscosity of the system.

The present study investigates the viscous synergy of systems comprising pure alcohol in water at different concentrations, determining the proportion of alcohol–water at which maximum viscous synergy occurs, along with the correlation between the viscosity increments and density. The ratio between the maximum viscosity reached by the mixture and the viscosity of pure alcohol is expressed by the enhancement index defined as: E _η ?=?η_max/η _o . Likewise, and since the viscosity of these systems varies with temperature, a thermodynamic study has been made to determine the activation energy of the ethanol–water mixture as a function of concentration.     

Aqueous polysaccharide blends based on hydroxypropyl guar gum and carboxymethyl cellulose: synergistic viscosity and thixotropic properties

Aqueous polysaccharide blends, formed from 2.5% (w/v) solution of hydroxypropyl guar gum (HPG) and 2.5% (w/v) solution of carboxymethyl cellulose (CMC) according to different blending ratios, were investigated at 20 °C in terms of their shear-dependent viscosity and thixotropic properties. The Cross viscosity equation was found to fit the shear-dependent viscosity data with reasonable accuracy. When the HPG solution with the mass fraction (f _HPG) of 0.87 was mixed, the zero shear viscosity (η _o) of the corresponding blend was found to be 168.5753 Pa s, while the η _o values of component HPG and CMC solutions were found to be 3.3859 and 98.6525 Pa s, respectively. For the aqueous HPG/CMC blends investigated, the resulting zero shear viscosity was observed to be much greater than the combined zero shear viscosity of the component polysaccharide solutions, showing a synergistic viscosity property. The quantitative determination of the hysteresis loop area, developed during viscometer tests on shear rate–shear stress reverse paths, was used to describe the thixotropic behavior. When compared with aqueous solutions of the component polysaccharides, these polysaccharide blends could afford enhanced thixotropic property. Maximum thixotropy synergism was observed for the HPG/CMC blend with the f _HPG of 0.67.     

Volumetric,Viscosity and Self-Diffusion Coefficient Studies of [18-Crown-6:M]A Complexed Species in Water at 298.15 K

Density and viscosity measurements were made for aqueous solutions of electrolytes containing 18-crown-6 (18C6) at 298.15 K. A method is proposed to extract the volumetric and viscosity data of the [18C6:M]A complexed species in aqueous solutions from ternary mixtures using the thermodynamic equilibrium constant values at 298.15 K. The apparent molar volume of the [18C6:M]A complexed species have been estimated for these binary solutions. Further, the viscosity data thus obtained were subjected to analysis using the Jones-Dole equation to get viscosity A- and B-coefficients of complexed ions in water. The hydration number and molecular radius of the hydrated complexes in water have been estimated. It was observed that hydration of the complexed ion is strongly influenced by the charge density of the metal ions in the complexed state. The self-diffusion coefficient and correlation time values for the complexes in water were calculated using viscosity data, which indicated that diffusion of complexed species was faster than that of the host ligand 18C6 (D_3d structural entity) in water at 298.15 K. It was suggested that the ionic radii estimated in this work for large hydrophobic cations can be of use in studying electrostatic and hydrophobic interactions especially in aqueous solutions.     

A “Distorted‐BODIPY”‐Based Fluorescent Probe for Imaging of Cellular Viscosity in Live Cells

Cellular viscosity is a critical factor in governing diffusion‐mediated cellular processes and is linked to a number of diseases and pathologies. Fluorescent molecular rotors (FMRs) have recently been developed to determine viscosity in solutions or biological fluid. Herein, we report a “distorted‐BODIPY”‐based probe BV‐1 for cellular viscosity, which is different from the conventional “pure rotors”. In BV‐1 , the internal steric hindrance between the meso‐CHO group and the 1,7‐dimethyl group forced the boron–dipyrrin framework to be distorted, which mainly caused nonradiative deactivation in low‐viscosity environment. BV‐1 gave high sensitivity (x=0.62) together with stringent selectivity to viscosity, thus enabling viscosity mapping in live cells. Significantly, the increase of cytoplasmic viscosity during apoptosis was observed by BV‐1 in real time.     

Sorption of uranium by non-living water hyacinth roots

Summary Many studies have shown that water hyacinth (Eichhornia crassipes) roots can be used to accumulate high concentrations of organic as well as inorganic pollutants. They are currently used to remediate aquatic environments and aqueous solutions. In the present study, sorption of uranium from aqueous solutions by using dried roots of water hyacinth has been investigated. The sorption of uranium was examined as a function of initial concentration, pH, weight of roots and contact time. Five different concentrations 20, 40, 60, 80, and 100 μg ^. ml^-1 were used. Sorption proves to be very rapid and depend on pH, weight of roots and concentration of uranium. Maximum sorption capacity of water hyacinth roots was 64,000 U⁶⁺ μg/g. The sorption of uranium by water hyacinth roots follows a Langmuir isotherm.     

CRITICAL CONCENTRATIONS OF α(1→3)-D-GLUCAN FROM LENTINUS EDODES IN NaOH AQUEOUS SOLUTION

Critical concentrations of α-(1→3)-D-glucan L-FV-Ⅱ from Lentinus edodes were studied by viscometry andfluorescence probe techniques. The dependence of the reduced viscosity on concentration of the glucan in 0.5 mol/L NaOHaqueous solutions with or without urea showed two turning points corresponding to the dynamic contact concentration c_s andthe overlap concentration c~* of the polymer. The values of c_s and c~* were found to be 1×10~(-3) g cm~(-3) and 1.1×10~(-2) g cm~(-3),respectively, for L-FV-Ⅱ in 0.5 mol/L NaOH aqueous solutions. The two critical concentrations of L-FV-Ⅱ in 0.5 mol/LNaOH aqueous solutions were also found to be 1.2×10~(-3) g cm~(-3) fbr c_s and 9.2×10~(-3) g cm~(-3) for c~* from the concentrationdependence of phenanthrene fluorescence intensities. The overlap concentration c~* of L-FV-Ⅱ in 0.5 mol/L NaOH aqueoussolutions was lower than that of polystyrene with same molecular weight in benzene, owing to the fact that polysaccharidetends to undergo aggregation caused by intermolecular hydrogen bonding. A normal viscosity behavior of L-FV-Ⅱ in 0.5 mol/L urea/0.5 mol/L NaOH aqueous solutions can still be observed in an extremely low concentration range at 25℃.     

Densities,Apparent Molar Volumes and Viscosities of Concentrated Aqueous NaNO<Subscript>3</Subscript> Solutions at Temperatures from 298 to 607 K and at Pressures up to 30 MPa

Densities of four (2.124, 2.953, 5.015 and 6.271 mol-kg⁻¹) and viscosities of eight (0.265, 0.503, 0.665, 1.412, 2.106, 2.977, 5.015 and 6.271 mol-kg⁻¹) NaNO₃(aq) solutions have been measured with a constant-volume piezometer immersed in a precision liquid thermostat and using capillary flow techniques, respectively. Measurements were made at pressures up to 30 MPa. The temperature range was 298–607 K for the density measurements and 298–576 K for the viscosity measurements. The total uncertainty of density, viscosity, pressure, temperature and composition measurements were estimated to be less than 0.06%, 1.6%, 0.05%, 15 mK and 0.02%, respectively. The temperature, pressure and concentration dependence of density and viscosity of NaNO₃(aq) solutions were studied. The measured values of density and viscosity of NaNO₃(aq) were compared with data and correlations reported in the literature. Apparent molar volumes were derived using the measured density values. The viscosity data have been interpreted in terms of the extended Jones–Dole equation for strong electrolytes. The values of the viscosity A-, B-, D- and F-coefficients of the extended Jones–Dole equation for the relative viscosity (η/η₀) of NaNO₃(aq) solutions were evaluated as a function of temperature. The derived values of the viscosity A- and B-coefficients were compared with the results predicted by Falkenhagen–Dole theory of electrolyte solutions and calculated with the ionic B-coefficient data.