聚丙烯腈溶液的凝胶化研究

聚丙烯腈是用途最广泛的聚合物之一,其溶于适当溶剂中形成的聚丙烯腈溶液是制备聚丙烯腈纤维、渗透膜等高分子材料的原料。聚丙烯腈溶液的物理化学性质对所制备材料的性能有很大的影响。本文对高分子溶液的凝胶化和高分子凝胶的特点做了简要介绍,并介绍了聚丙烯腈及其凝胶的特点。根据高分子浓溶液体系的特点提出用于表征聚丙烯腈溶液凝胶化的主要方法。从浓度和温度对聚丙烯腈溶液凝胶化行为的影响、熟化和非溶剂对聚丙烯腈溶液凝胶化行为的影响、聚丙烯腈溶液凝胶化的热可逆性、聚丙烯腈溶液凝胶化的分形特征以及聚丙烯腈凝胶的交联机理这几个方面对已有聚丙烯腈溶液的凝胶化研究成果和最新进展进行了综述。最后对聚丙烯腈溶液凝胶化和聚丙烯腈凝胶的研究前景做了展望。     

A rheological investigation of aqueous solutions of poly (vinyl alcohol) during aging. Part IV: Repeated aging of concentrated solutions

Aging of aqueous solutions of poly (vinyl alcohol) obtained by melting of gels, formed in the aging process from solutions prepared by the dissolution of the polymer in hot water, was investigated using non-Newtonian viscometry and normal stress measurement. It was shown that, if the gels undergo melting at the same temperature at which the original solutions were prepared, aging of such solutions proceeds in the same way as in the case of the original solutions. If melting occurred due to heating at lower temperature, the resulting solutions aged more quickly.     

Shear and extensional rheology of polyacrylonitrile solution: effect of ultrahigh molecular weight polyacrylonitrile

The effect of ultrahigh molecular weight polyacrylonitrile (UHMWPAN) on the shear and extensional rheological behavior of PAN solutions were studied. The PAN solutions were prepared by dissolving medium molecular weight polyacrylonitrile in dilute UHMWPAN/dimethyl sulfoxide solutions. The results of shear rheological measurements indicated that the existence of UHMWPAN reduced the shear-thinning but increased the characteristic relaxation time and the elasticity of PAN solutions. Moreover, the PAN solutions containing UHMWPAN exhibited much more evident strain-hardening behavior than the solution without UHMWPAN. It was found from the results of extensional rheological measurements that the strain hardening and elasticity of PAN solutions increased greatly with the increase of molecular weight or content of UHMWPAN in the solutions. PAN solutions containing a small amount of UHMWPAN have better drawability and favor the increase of jet stretch ratio in dry-jet wet spinning of PAN precursor fibers.     

Preparation and investigation of solutions of chitosan derivatives with long-chain hydrophilic substituents

The preparation of aqueous solutions of chitosan oligo(ethylene oxide) sulfonate and special features of their viscosity and foam-stabilizing properties are described. It is shown that the complete dissolution of the chitosan derivative takes place at a degree of substitution of at least 0.75. An increase in the degree of substitution to 1 leads to a decrease in the viscosity of solutions; however, the viscosity of solutions of chitosan oligo(ethylene oxide) sulfonate in all cases greatly exceeds that of solutions of chitosan acetate of the same concentration. Unlike chitosan acetate solutions, the solutions of chitosan oligo(ethylene oxide) sulfonate have a higher stability and more pronounced foam-stabilizing properties.     

Coordination of ions in aqueous solutions of erbium chloride from X-ray diffraction data

Aqueous solutions of erbium chloride were studied by X-ray diffraction over a broad range of concentrations under standard conditions. The prepeaks observed in the experimental scattering intensity curves were interpreted. The solutions were found to possess two types of structures. Saturated and concentrated solutions down to molar ratio of 1 : 20 have a quasi-crystalline structure defined by inter-ion interactions. Dilute solutions form a water-like structure characterized by a tetrahedral network of hydrogen bonds between water molecules. It was found that prepeaks can also be seen in the intensity curves of dilute solutions, which implies that these solutions retain the so-called long-range order.     

Rheological properties of hexadecyl dimethyl amine modified carboxymethyl hydroxyethyl cellulose solutions and its gelling process

To obtain a new fracturing fluid viscosifier, hexadecyl dimethyl amine was used to modify carboxymethyl hydroxyethyl cellulose (CMHEC) to obtain a product called HD-CMHEC with high viscosity. The rheological properties of HD-CMHEC solutions and CMHEC solutions were studied. For the concentration of 0.3%, the viscosity of CMHEC and HD-CMHEC solutions is, respectively, 19.0?mPa?·?s and 73.6?mPa?·?s, respectively. The viscosity of HD-CMHEC solution increases 2.8 times than before. The thixotropy and viscoelasticity of HD-CMHEC solutions become stronger. As a typical viscoelastic fluid, HD-CMHEC solutions show better rheological performance than that of CMHEC solutions. The gelling process of HD-CMHEC solutions under steady shear was studied in detail. The concentrations of HD-CMHEC solutions, shear rates, and crosslinking agent were investigated. Viscosity versus time curves during the crosslinking process were obtained. The four-parameter crosslinking rheokinetics equation can describe the gelling process of HD-CMHEC solutions under different conditions well. Study on the gelling process of HD-CMHEC solutions under steady shear contributes to the understanding of gel formation, and provides theoretical guidance for exploration and exploitation of the system.     

The properties of water in solutions of hydrophilic polymers

The properties of water in solutions of hydrophilic polymers were compared with those in solutions of their monomeric analogues. The properties of polar groups grafted to polymeric molecules were known to remain unchanged. A comparison of the properties of water in solutions of polymers and the corresponding monomers under equal conditions therefore allowed us to obtain information about the influence of polymeric bonds on the properties of water in solutions of polymers. Proceeding from this, we analyzed the influence of polymeric chains and three-dimensional polymeric network on the activity and concentration of water in solutions of polymers.     

Loss of iridium,osmium and ruthenium from aqueous solutions during storage

Aqueous solutions of iridium are stable (within 3 %) over a four-month storage period in a variety of container types and over a range of acid concentrations. Standard solutions of water-soluble iridium compounds at pH 7 can be employed reliably. Rapid loss of osmium and ruthenium from aqueous solutions at pH 7 means that standard solutions must be used within 1 day of preparation. Nitric acid solutions of osmium and ruthenium should also be avoided. The six plastics studied are unacceptable containers for 0.1 M hydrochloric acid solutions of osmium; 1 M hydrochloric acid is an adequate preservative for osmium solutions for up to two months and for ruthenium solutions for up to four months in glass, quartz or polyethylene containers.     

Phase equilibria in solutions of cellulose derivatives and the rheological properties of solutions in various phase states

Phase equilibria in solutions of hydroxypropyl cellulose in such solvents as water, propylene glycol, poly(ethylene glycols) of various molecular masses, triethyl citrate, and DMSO are analyzed. The phasetransition lines are constructed with the use of microinterference and polarization microscopy methods. In a certain temperature-concentration range, all solutions undergo a sequence of transitions typical for solutions of stiff-chain crystallizable polymers: isotropic and LC states separated by the two-phase corridor and, in some cases, the crystalline state. Of special interest are systems in which the superposition of amorphous (with the LCST or UCST), LC, and crystalline equilibria is realized. The features of the phase states of solutions are compared with the physicochemical characteristics of solvents and the intensity of their interaction with hydroxypropyl cellulose macromolecules. Solutions occurring in various phase states are tested by rheological methods. These solutions demonstrate the typical rheological behavior of anisotropic solutions: the presence of yield stress and the extremum concentration dependence of viscosity with a maximum, when the LC phase appears, and a minimum, when it transforms into the 100% phase. In the case of single-phase solutions, viscosity increases with concentration, while for two-phase solutions, viscosity decreases with an increase in the fraction of the LC phase. The rheological data are found to be sensitive to phase transitions observed in solutions.     

Radiation chemistry of aqueous poly(ethylene oxide) solutions. I

The γ radiolysis of aqueous high molecular weight poly(ethylene oxide) solutions has been studied. The crosslinking and eventual gelation of these solutions appears to occur via an indirect effect. Solubility measurements on the gelled solutions showed that the ratio of crosslinking to degradation is about four. G(H₂) increased from 1.3 in neutral solutions to 3.5 in 0.1N HCl solutions. In heavy water solutions, HD is the major gaseous product. Solvated electrons are not important precursors to hydrogen at neutral pH. Intramolecular crosslinking appears to be an important phenomenon in solutions of high molecular weight polymers.     

Correlation Equations for Predicting the Temperature Depression in Boiling of Aqueous Solutions of Nonvolatile Substances

Three-constant correlation equations describing the boiling point of aqueous solutions of non-volatile substances and temperature depression in boiling of the solutions under normal and arbitrary pressures are considered. The three constants appearing in the correlation equations are tabulated for aqueous solutions of 19 nonvolatile substances, and formulas for determining these constants for other aqueous solutions of nonvolatile substances from experimental data are presented.     

Effect of the solvent nature on the rheological properties of concentrated solutions of various polymers

The paper compares the viscous, high-elastic and viscoelastic properties of solutions in various solvents of four polymers (polyisobutylene, polystyrene, polymethyl methacrylate and acetyl cellulose) differing in chain rigidity and the intensity of molecular interaction, over a wide range of compositions for the linear region of the mechanical behaviour of these systems. For solutions of polyisobutylene and polystyrene, the effect of the nature of the solvent on the viscosity is determined by the inherent viscosity of the solvent and by the fact that solutions under isothermal conditions are not in corresponding states with respect to their glass transition temperatures. The high-elasticity modulus of polyisobutylene and polystyrene solutions is independent of the nature of the solvent and of temperature. This indicates that the fluctuating network of entanglements is insensitive to the nature of the solvent and that the free volume plays the determining role in the behaviour of these solutions. Solutions of acetyl cellulose and polymethyl methacrylate are characterized by a very strong dependence of the viscosity on the nature of the solvent (which cannot be explained by notions valid for solutions of the first two polymers) and also by a change in the high-elasticity modulus with variation in the nature of the solvent and temperature. This proves that the properties of solutions of polar polymers are determined both by the free volume and the density of the fluctuating network, which changes with the solvent and temperature. The shape of the relaxation spectra of solutions of various polydisperse polymers in solvents of different natures is the same, while the specific properties of the solutions are associated with the position of the spectra on the time scale, which determines the fundamental constants of the solutions, viz. the zero shear viscosity and the initial high-elasticity modulus.     

Effect of Ultrasonication on Optical Properties and Electronic States of Conjugated Polymer MEH-PPV

Poly[2-methoxy-5-（2＇-ethyl-hexyloxy）-1,4-phenylene vinylene]（MEH-PPV）solutions with different concen-trations were prepared in chloroform for different ultrasonication times.The ultraviolet absorption and photoluminescence（PL）spectra of the MEH-PPV solutions were measured,and the electronic states of the polymer chains under different experimental conditions were studied.The results showed that the effects of ultrasonication on the dilute and concentrated solutions were different.After ultrasonication,the intensity of the absorption peak at 280 nm significantly decreased,relative to the absorption peak at 500 nm for both dilute and concentrated solutions,indicating that the proportion of the two excited states in the polymer chains had changed.For dilute MEH-PPV solutions,the blue-shifted absorption（at about 500 nm）and PL spectra show that ultrasonication also led to polymer chain degradation and thus shortened the effective conjugation length.For concentrated solutions,however,the peak positions of the absorption spectra remained unchanged.In addition,the effects of the solution temperatures on the optical spectra for the MEH-PPV solutions were also discussed.     

The dependence of the osmotic coefficient on the composition of multicomponent solutions

The thermodynamic theory of binary aqueous solutions of electrolytes taking into account the electrostatic interaction of ions and their hydration and association was extended to multicomponent solutions. Equations for calculating the osmotic coefficient of multicomponent solutions from parameter estimates (hydration and association numbers under standard conditions) determined for the corresponding binary subsystems were substantiated. Interval parameter estimates were used to calculate the osmotic coefficients for several three-five-component aqueous solutions containing both nonelectrolytes and electrolytes. A comparison of the results with the literature data showed that cross interactions between components could be ignored for the multicomponent solutions studied.     

Concentration dependence of the structure of aqueous solutions of samarium trichloride according to X-ray diffraction

Aqueous solutions of samarium chloride in a wide range of concentration under ambient conditions are studied by X-ray diffraction analysis. The small-angle peaks in experimental scattering intensity curves are interpreted. It is shown that highly concentrated solutions are characterized by a unique structure that differs heavily from the structure of dilute systems. It is found that small-angle peaks also appear in the intensity curves of dilute solutions, indicating that the so-called long-range order is preserved in these solutions. It is revealed that the contributions to the total scattering pattern that govern the appearance of prepeaks are interionic interactions of different types (e.g., cation-cation, anion-cation, and anion-anion interactions) in concentrated systems and the distances between the cations in dilute solutions.     

Extraction of antimony with tertiary amines

The extractability of antimony(III) and (V) with tridodecylamine from various aqueous solutions is reported. Extraction from nitric and hydrofluoric acid solutions is low, but extraction from sulphuric, hydrochloric and hydrobromic solutions is high. Antimony-(III) can be separated from antimony(V) in 7M nitric acid or 0.64M hydrobromic acid. The extraction of antimony from hydrochloric acid solutions in methanol, ethanol, and acetone-water mixtures is greater than from pure aqueous solutions of the same acidity. The elements from which antimony can be separated with tertiary amines are given.     

Coordination of ions in aqueous solutions of dysprosium chloride according to the X-ray diffraction data

Aqueous solutions of dysprosium chloride in a wide concentration range are studied by X-ray diffraction analysis under standard conditions. The scattered X-ray radiation intensity curves are characterized by prepeaks at low values of the wave vector. Their interpretation and an analysis of changes at different concentrations are performed. The structure of concentrated solutions is formed due to interionic interactions of different types. On the contrary, dilute solutions are characterized by the determining role of the quasi-tetrahedral structure of the solvent. The prepeaks are also observed on the intensity curves of dilute solutions, indicating that these solutions retain the “long-range” ordering.     

Exceptional electrochemical performance of Si-nanowires in 1,3-dioxolane solutions: a surface chemical investigation

The effect of 1,3-dioxolane (DOL) based electrolyte solutions (DOL/LiTFSI and DOL/LiTFSI-LiNO(3)) on the electrochemical performance and surface chemistry of silicon nanowire (SiNW) anodes was systematically investigated. SiNWs exhibited an exceptional electrochemical performance in DOL solutions in contrast to standard alkyl carbonate solutions (EC-DMC/LiPF(6)). Reduced irreversible capacity losses, enhanced and stable reversible capacities over prolonged cycling, and lower impedance were identified with DOL solutions. After 1000 charge-discharge cycles (at 60 °C and a 6 C rate), SiNWs in DOL/LiTFSI-LiNO(3) solution exhibited a reversible capacity of 1275 mAh/g, whereas only 575 and 20 mAh/g were identified in DOL/LiTFSI and EC-DMC solutions, respectively. Transmission electron microscopy (TEM) studies demonstrated the complete and uniform lithiation of SiNWs in DOL-based electrolyte solutions and incomplete, nonuniform lithiation in EC-DMC solutions. In addition, the formation of compact and uniform surface films on SiNWs cycled in DOL-based electrolyte solutions was identified by scanning electron microscopic (SEM) imaging, while the surface films formed in EC-DMC based solutions were thick and nonuniform. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy were employed to analyze the surface chemistry of SiNWs cycled in EC-DMC and DOL based electrolyte solutions. The distinctive surface chemistry of SiNWs cycled in DOL based electrolyte solutions was found to be responsible for their enhanced electrochemical performances.     

Concentration dependence of the structure of aqueous solutions of lutetium nitrate according to X-ray diffraction

Aqueous solutions of lutetium nitrate over a wide range of concentrations are studied by X-ray diffraction under standard temperature and pressure. The low-angle peaks in experimental scattering intensity curves are interpreted. It is shown that the structure of these solutions can be of two types. It is found that a saturated solution and solutions concentrated to a molar ratio of 1: 20 have a quasi-crystalline structure resulting from interionic interactions. It is determined that dilute solutions form a water-like structure characterized by a tetrahedral network of hydrogen bonds between the water molecules. It is found that low-angle peaks also appear in the intensity curves of dilute solutions; this proves that the so-called “long-range” order is preserved in these solutions. It is revealed that in all the studied systems, the contributions to the total scattering pattern that are responsible for the occurrence of pre-peaks are intercationic interactions.     

Reliability criteria of experimental results for the method of field evaporation of ions from solutions

The method of field evaporation of ions from solutions (FEIS) using electrospraying for ion emission from electrolyte solutions into a vacuum chamber of a mass spectrograph allows obtaining unique information on ion salvation in solutions when solutions with low electrolyte concentration are used and recording only ions with the maximum energy. This conclusion was made on the basis of considering experimental data and phenomena accompanying implementation of the FEIS method.