A rationale for the preparation of asymmetric pervaporation membranes

Pervaporation is carried out primarily with homogeneous membranes. An improvement in permeation rate can be achieved by using asymmetric or composite membranes. In order to maintain a high selectivity, very dense top layers are needed. The formation of asymmetric pervaporation membranes will be discussed in terms of the model proposed by our group: formation of the top layer by gelation; formation of the porous sublayer by liquid–liquid phase separation followed by gelation of the concentrated polymer phase. To obtain very dense top layers the following factors are important: the ratio of nonsolvent inflow and solvent outflow, polymer concentration, location of the liquid–liquid demixing gap, and location of the gel region. Asymmetric membranes have been prepared by varying these factors, and the obtained membranes have been tested on ethanol/water mixtures.     

丙烯酰胺/丙烯酸/甲基丙烯酸甲酯双水相共聚过程的临界分相

采用偶氮二异丙基咪唑啉盐酸盐（VA-044）引发丙烯酰胺（AM）/丙烯酸（AA）/甲基丙烯酸甲酯（MMA）在含一定量聚丙烯酸钠（PAANa）的硫酸铵（AS）水溶液中进行双水相共聚合。用分光光度计对聚合体系分相进行在线确定,采用溴化法测定了聚合体系临界分相时的转化率,用凝胶渗透色谱（GPC）对聚合体系临界分相时聚合物链的分子量进行了研究。随着MMA用量的增加,临界分相转化率和临界分相分子量逐渐减少;AM与AA单体总量增加,临界分相转化率逐渐降低,临界分相分子量逐渐变大;相似文献   

Preparation of Macroporous Titania Films by a Sol-Gel Dip-Coating Method from the System Containing Poly(ethylene glycol)

Macroporous titania (TiO₂) films have been prepared via a sol-gel dip-coating method from a titanium tetraisopropoxide solution that contains poly(ethylene glycol) (PEG). The macroporous morphology-i.e., the size, distribution, and shape of the macropores-is controlled by varying the content and molecular weight of PEG, the withdrawal speed, and the temperature of the dipping solution. The morphology of the TiO₂ film is determined by competitive contributions of the following factors: (i) decrease in fluidity, because of the evaporation of solvent; (ii) network formation by polycondensation reactions; and (iii) domain formation during phase separation into gel phases and solvent phases.     

Phase separation phenomena in aqueous solutions of amphiphilic poly(ethylene oxide) star polymers

Three- and four-armed star polymers with poly(ethylene oxide) arms capped with hydrophobic end-groups were synthesized from nonylphenoxypoly(ethylene glycol)s and well defined tri- and tetraisocyanates. The latter were hydrosilylation products of m-isopropenyl-,-dimethylbenzyl isocyanate (m-TMI). In aqueous solution the arm ends associate, and above a critical star concentration the mixture phase separates into a dilute phase and a condensed gel phase. Their respective polymer concentrations remain constant as long as the two phases coexist, their volume fractions being proportional to the total polymer concentration. Brookfield viscosity measurements confirm the formation of the gel phase which resembles an amphiphilic hydrogel. It exhibits a high affinity for hydrophobic compounds.     

Über die strukturbildung in polymerfilmen durch phasentrennung bei der filmbildung aus lösungen in löser-nichtlöser-gemischen

Phase separation during film formation of a thermoplastic copolymer from solution in mixtures of high-volatile solvents and low-volatile non-solvents was studied. The parameters determining the void volume of the microcellular films formed by phase separation are the non-solvent fraction, polymer concentration of the initial solution and difference in volatility between solvent and non-solvent. The microcellular structure depends on the time at which phase separation occurs during film formation.     

Zur phasentrennung von polymergemischen in lösung

Usually, mixtures of solutions of two different polymers in the same solvent are incompatible. This incompatibility leads to an intensive turbidity of the mixture and finally, to the formation of two phases. The turbidity disappears on dilution with the same solvent, because the polymers are compatible below a certain polymer concentration c_kr. In principle, the same effects occur also with mixtures of polymers in the solid state (polymer blends), but here the aggregation of the microphases is impossible due to the high viscosity. Up to now, there is little known about the composition of the two phases above c_kr. Therefore, we studied the distribution of two different polymersin solution regarding molecular weight and concentration into both phases. It was varied the polymer ratio, the molecular weight, the overall concentration and the nature of the solvent. Polystyrene and polyvinyl acetate were used as polymers because they can easily be separated from each other which is necessary when analysing the different phases; this analytical separation was carried out for each individual phase. The following results were obtained: Each phase contains both polymers; in addition there occurs a fractionation according to molecular weight during the phase separation for both polymers. The polymer distribution in the two phases regarding molecular weight, amount of polymer, and concentration depends not only upon initial concentration, molecular weight and weight ratio of the two polymers but also upon the different degree of solvation of the macromolecules in different solvents. When mixtures of solvents are used, an additional partially separation of the solvent into both layers takes place.     

Complexation of chitosan and gelatin: From soluble complexes to colloidal gel

The formation of soluble and insoluble complexes between chitosan (CH) and gelatin type B (GB) was investigated as a function of pH (3.0–6.5), sodium chloride (NaCl) concentration (0–100 mM), and storage time (up to 40 days). The turbidity of the CH/GB complexes achieved a maximum value at pH 5.5 and increased with time. The increase of ionic strength first intensified the complex formation but then decreased it at higher salt content. After phase separation, the main component of the separated dense phase was water, from 95.5 to 97.8 wt%, depending on NaCl concentration. With increasing storage time, the insoluble phase changed from a liquid-like system to a thermoreversible colloidal gel, as supported by confocal laser scanning microscopy as well as rheological data. The formation of this colloidal gel is explained in terms of electrostatic complexation and hydrogen bonding.     

Thermal and NMR investigation of the change in the states of water caused by volume phase transition of gelatin gel

The occurrence of volume phase transition (VPT) of a polymer gel is often accompanied by the loss of water. In view of the fact that few studies have been made on the change in different states of water during VPT, in this paper, DSC and NMR are used to check the variation in states of water during VPT of glutaraldehyde crosslinked gelatin gel caused by the variation in composition of water–acetone mixture. The results indicate that the volume of gel collapses at 50 % acetone concentration. The contents of free, intermediate and bound water absorbed by gelatin gel decrease with an increase in the amount of acetone. At 50 % and 60 % acetone content, free water disappears; because acetone accounts for 70 % and 85 %, there remains only bound water. Near VPT the relative content of bound water to total water increases sharply. The spin–lattice relaxation times (T₁) determined by NMR show that the T₁ values of intermediate and bound water, respectively, decrease by approximately four and ten times compared with that of free water. Before VPT, most of the water is freezable and highly mobile. After VPT, bound water gradually plays a dominant role in the mobility of water in the gel. The findings are helpful in understanding the dehydration process of protein induced by poor solvent. © 2000 Society of Chemical Industry     

Formation of macroporous styrene–divinylbenzene copolymer networks: Theory vs. experiments

A kinetic–thermodynamic model is presented to predict the total porosities of macroporous copolymer networks formed by free‐radical crosslinking copolymerization of styrene (S) and commercial divinylbenzene (DVB, a mixture of meta and para DVB isomers and ethylstyrene). The kinetic part of the model predicts, based upon the method of moments, the concentration of the reacting species, the gel, and sol properties as a function of the monomer conversion. The thermodynamic part of the model describes the phase equilibria between the gel and separated phases during the S–DVB copolymerization and predicts the volume of the separated phase, which is the pore volume of the crosslinked material, as a function of the monomer conversion. Calculation results show that the porosity of S–DVB networks increases as the polymer–diluent interaction parameter increases, or as the initial monomer concentration decreases. Porosity also increases on increasing the DVB content of the monomer mixture. Both the polymerization temperature and the initiator concentration affect significantly the kinetics of S–DVB copolymerization. However, the final porosity of S–DVB copolymers is largely insensitive to the amount of the initiator and to the polymerization temperature. All calculation results are in accord with the experimental data published previously. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2181–2195, 1999     

Effect of the interface with solid on the interfacial region in the blends of linear polymers formed in situ

Blends of polyurethane and poly (methyl methacrylate) of various compositions were synthesized in situ in presence of various amounts of nanoparticles (fumed silica). From thermo‐ physical measurements it was found that the reaction is accompanied by the phase separation and evolution of two phases. The temperature transitions in the systems and their positions depend on the blend composition and on the filler amount. Using scanning differential calorimetry, the fraction of an intermediate region between two main phases has been estimated from the changing of heat capacity increments. It was observed that in filled polymer blends in the temperature region between two main relaxation transitions, there appears the third transition. This transition is supposed to be the result of the formation of adsorption layer at the interface with solid. The appearance of such an intermediate regions increases essentially the total fraction of an interfacial region in the system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4646–4651, 2006     

Preparation of polyacrylamide via dispersion polymerization with gelatin as a stabilizer and its synergistic effect on organic dye flocculation

In this study, we successfully prepared a polyacrylamide (PAM) water‐in‐water (W/W) emulsion through dispersion polymerization with only a small concentration of gelatin as the stabilizer. Types of identical methods were used to study the structure of this material, among which Fourier transform infrared and ¹H‐NMR spectroscopy indicated that the polymer was composed of PAM and a few gelatin, transmission electron microscopy (TEM) verified the W/W emulsion structure, and gel permeation chromatography confirmed the existence of the graft polymer of gelatin and PAM. In addition, TEM and dynamic light scattering confirmed the morphology and particle size distribution of the PAM W/W emulsion particles and demonstrated that the formation mechanism of the particles during the polymerization process was quite fitted with phase‐separation theory. The effects of the temperature, pH value, and gelatin concentration on the properties of the PAM W/W emulsion were also investigated systematically. Moreover, PAM W/W emulsions prepared with various gelatin concentrations were applied to the flocculation of Reactive Turquoise Blue K‐GL; it turned out that the PAM W/W emulsion had a higher removal efficiency with increasing gelatin concentration. Therefore, the PAM W/W emulsion could be regarded as an effective flocculant for wastewater treatment; it also showed an excellent redispersion ability in water and good storage stability. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46298.     

Liquid–liquid phase separation and crystallization of polydisperse isotactic polypropylene solutions

Phase diagrams were calculated based on Flory-Huggins solution thermodynamics to investigate the effects of polydispersity of polymer molecules and interaction parameter on the phase equilibria of crystallizable polymer solutions. The polydispersity was modeled with blends of two monodisperse polymers differing in chain lengths as a simplification. It was found that a longer chain length component could be separated easily to a polymer-rich phase by liquid demixing, but a shorter chain length component might exist at relatively constant concentration in each phase on fractionation. The influence of polydispersity on the liquid–solid phase equilibrium was small, and the phase boundary could be moved significantly in the region of low concentration of polymer by a small change of temperature. Liquid–liquid phase separation was more sensitive to the interaction between polymer and solvent than liquid–solid phase transition. Numerical calculations showed that the temperature at which liquid–liquid phase separation was coupled with liquid–solid phase equilibrium increased with a lower concentration of the polymer due to polydispersity of polymer chain lengths, and this phenomenon was observed at a lower temperature with more favorable interaction. The results were consistent with the experimental observations of isotactic polypropylene solutions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 849–857, 1998     

多糖的共价键合对7S球蛋白凝胶性能的影响

引入细胞学说中的大分子拥挤体系并在该体系通过Maillard反应制备了大豆7S球蛋白(b-conglycinin,7S)和葡聚糖(dextran,Dex)的共价复合物,利用转谷氨酰胺酶(transglutaminase,TGase)的交联作用制得蛋白-多糖共价复合物凝胶.对其流变学、质构特性及微结构进行分析.结果表明,在大分子拥挤环境下,7S-葡聚糖比例为2:1的共价复合物制得具有致密且孔洞分布均匀的凝胶网络结构.单纯的蛋白自聚集或者与多糖的共混状态时形成的凝胶弹性模量都较高,但蛋白过度的聚集并不能得到孔洞均匀的凝胶网络结构,共价复合物制备的凝胶中葡聚糖的共价键合作用抑制了TGase交联过程中蛋白质分子间发生过度的相互作用.形貌学观察表明,共价复合物制备的凝胶形成了网络孔径均匀且非常致密的凝胶网络结构.     

Preparation and characterization of poly(vinyl alcohol) and gelatin blend films

Poly(vinyl alcohol) (PVA) is a water-soluble polymer that has been studied intensively because of several interesting physical properties that are useful in technical applications, including biochemical and medical applications. In this article, we report the effects of the addition of gelatin on the optical, microstructural, thermal, and electrical properties of PVA. Pure and PVA/gelatin blend films were prepared with the solution-casting method. These films were further investigated with Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, and dielectric measurements. The FTIR spectrum shows a strong chemical interaction between PVA and gelatin molecules with the formation of new peaks. These peaks are due to the presence of gelatin in the blend films. The DSC results indicate that the addition of gelatin to PVA changes the thermal behavior, such as the melting temperature of PVA, and this shows that the blends are compatible with each other. This also shows that the interaction of gelatin and PVA molecules changes the crystallite parameters and the degree of crystallinity, and this supports the XRD results. The UV–vis optical study also reflects the formation of the complex and its effect on the microstructure of the blend film. Moreover, the addition of gelatin also gives rise to changes in the electrical properties of PVA/gelatin blend films. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hybrid ternary organic-inorganic films based on interpolymer complexes and silica

Homogeneous transparent hybrid films consisting of chitosan (CHI), poly(monomethyl itaconate) (PMMI) and silica were obtained indicating the absence of microphase separation. These ternary hybrid materials are very interesting since materials with high functionality can be obtained presenting different properties from those of the starting materials but with the advantage of preserving the inherent property of each component. The inorganic phase was prepared by sol-gel process of tetraethoxysilane (TEOS). Most of the amine groups from CHI (pK_b 7.7) are quaternized in the acidic medium used in the preparations (pH=2), where a physical crosslinking via hydrogen bonding could occur through carboxyl groups from PMMI. Silica gel obtained from TEOS has been intercalated as a very fine dispersion in the polymer complex formed between CHI and PMMI. Transmission electron microscopy and atomic force microscopy was used to examine the homogeneity of the ternary polymer hybrids (CHI/PMMI/SiO₂), obtained as self-supported films. The results support the nanometer scale dispersion of the phases. Porous silica films with high BET area were obtained by calcination of the hybrid films. The mean pore diameter of these silica films corresponds to the dimension of the polymer domains observed in the pristine hybrid films. Moreover, it was found that the swelling behavior of the samples was influenced by the organic and inorganic phases, where the inorganic phase tends to diminish the swelling.     

Two-Phase Electrophoresis of Proteins

Abstract

Proteins have been directed into either the top or bottom phase of a polyethylene glycol/dextran aqueous two-phase system by applying an electric field perpendicular to the phase interface. Protein migration across the interface was manipulated by varying polarity, pH, electrophoresis time, field strength, and phase volume ratio. Mixtures of hemoglobin and albumin were separated by operating between isoelectric points and directing oppositely charged proteins into separate phases. Applying 50 V/cm for 2 hours to 58 mL of an equal phase volume two-phase system containing 0.2 g/L of each protein at pH 6 resulted in a bottom phase containing 99% of the hemoglobin and a top phase containing 95% of the albumin. This represents a significant improvement over the separation obtained either by partitioning in the same two-phase system with no applied field or by electrophoresis under the same conditions in homogeneous buffer. The two-phase system divides the electrophoresis device into two distinct regions, providing stability against convective mixing and facilitating product isolation.     

Swelling and Diffusion Characteristics of Interpenetrating Network Films Composed of Sodium Alginate and Gelatin: Transport of Azure B

Interpenetrating polymer network (IPN) films have been made from two hydrophilic natural polymers, namely, sodium alginate (NaAlg) and gelatin (Gltn) in the presence of glycerol (Glrl) using Ca²⁺ as crosslinkers. Films have been prepared with varying amounts of crosslinking agent, plasticizer and the component polymers. The effect of these parameters, the preparation conditions and the pH of the medium on the swelling behavior of these gel films has been investigated. Dynamic swelling studies have been carried out and the kinetic parameters for the swelling process have been evaluated. The influence of film characteristics and pH of the medium on the permeability behavior of the films has been studied for a cationic dye, Azure B (AzrB). The results revealed pH sensitivity of the films towards swelling and solute transport. Based on the results, possible mechanisms of water and dye transport through the films have been proposed.     

Polymer mixing in aqueous solution

The phase separation behaviour of two polymers (1 and 2) in organic solvents is relatively well understood and is usually due to repulsive interactions between 1 and 2 chain segments. In aqueous solutions, however, where the interaction of the polymer with the solvent is expected to be large, the behaviour is less well understood. In this paper the phase separation of polymers in aqueous solution has been studied and some of the factors which could control the phase separation have been investigated. The volumes of the separated phases were found to be related to the sizes of the polymer/solvent interactions. The polymer with the most positive second virial coefficent was found to occupy the phase with the largest volume. For both miscible and immiscible pairs the mixed second virial coefficients (A₁₂) was assessed from osmotic pressure measurements and was found to be an average of the individual second virial coeffients (A₁₁ and A₂₂). A few polymer pairs were found to mix and this was thought to be caused by hydrogen bonding between 1 and 2 chain segments. Mixtures of rod-like and coiled polymers were expected to phase separate to give a concentrated, ordered phase containing nearly all of the rod-like polymer and a larger phase containing the coiled polymer. However this behaviour was not found when a cellulose derivative (rod-like) was mixed with dextran (flexible).     

On the nature of junction zones in gelatin gels

The structural modifications and the phase state of the gelatin matrix during the sol-gel transition and gelatin gel deswelling were studied by optical rotation and wide-angle X-ray scattering (WAXS) methods. It is shown that the quenching of a solution results in rapid renaturation of macromolecular fragments of gelatin and in collagen-like structures forming junction zones in the polymer network. Microcrystallites in the polymer matrix of gelatin gels were not revealed which shows that the aggregation of renaturated helices and the formation of collagen-like fibrillar crystals do not occur. However, the crystalline phase appears upon gel drying or its deswelling in a nonsolvent.     

H_2O_2对木质素—聚丙烯酰胺凝胶体系的破胶性能评价

有些已被封堵的地层需重新解封,为此,对有机聚合物凝胶进行了降解试验研究。通过实验来研究破胶剂合成,得到最安全、最迅捷、最有效的破胶剂。H2O2的浓度越大,破胶越明显,并且温度越高,破胶能力越强。H2O2对木质素—聚丙烯酰胺冻胶体系破胶的结果较为理想,破胶后,剩余物较少。