Three-dimensional shape of polyethylene single crystals grown from dilute solutions and from the melt

Three-dimensional morphology of polyethylene single crystals grown from dilute solutions and from the melt has been examined by atomic force microscopy. The observation of single crystals clarifies the morphology of chair-type as well as hollow pyramidal type for solution crystallization. From the melt, only chair-type was obtained. It has been confirmed that the screw dislocations in the chair-type follow a selection rule of the handedness in a manner to relieve the distortion in the chair-type. The meaning of the selection is discussed in connection with the twisting correlation in the banded spherulites grown from the melt of non-chiral polymers, such as polyethylene.     

Thermal properties of solution flow-induced PVA crystals

Poly(vinyl alcohol) was crystallized from its aqueous solution under a steady-state flow with different conditions. Using a differential scanning calorimeter (DSC), the thermal properties of PVA precipitates obtained by the flow-induced crystallization were measured, showing a single melting peak in the DSC curve. The melting temperature of PVA crystallized depended on the rate of stirring, crystallization temperature, concentration of PVA, yield of precipitates, and morphology of the crystals. Particularly, there was a closer relationship between the melting temperature and the yield of precipitates, i.e., it was through the effect on the yield of precipitates that crystallization conditions influenced the melting temperature. Generally, with certain conditions, the higher the yield of precipitates, the lower the melting temperature. Moreover, using electron microscopy, it was observed that there were some structural differences between the inner and outer sides of a PVA crystal mat round stirrer and between film-shaped and block-shaped crystals, leading to different melting temperatures. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1337–1344, 1997     

In situ synthesis and characterization of nano-size hydroxyapatite in poly(vinyl alcohol) matrix

Hydroxyapatite (HAp) crystals were prepared via an in situ biomimetic process in the presence of poly(vinyl alcohol) (PVA). The effect of polymer amount and its molecular weight on the physical properties of the HAp crystals were investigated. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) analysis, confirmed the formation of the crystalline HAp at room temperature. Microstructural features such as size and morphology of the resulting HAp samples were characterized using BET, scanning and transmission electron microscopy. The results indicate that the development (size and shape) of the HAp nanocrystals precipitated in an aqueous solution of PVA was influenced by the molecular weight of the polymer in such a way that smallest crystallite size was observed in the case of PVA with the highest molecular weight. It is believed that the HAp formation was initiated through the interaction of Ca²⁺ ions with the negative side groups on the polymer surface. The larger number of reaction sites in the PVA polymer with higher molecular weight led to a higher number of HAp nuclei and therefore smaller crystallite size.     

Growth control of ice crystals by poly(vinyl alcohol) and antifreeze protein in ice slurries

Effect of poly(vinyl alcohol) (PVA) in inhibiting an increase in ice crystal size in isothermal ice slurries was investigated, and then compared with the effect of an antifreeze protein (AFP), NaCl, and three other polymers, namely, poly(ethylene glycol), poly(vinyl pyrrolidone), and poly(acrylic acid). First, ice slurries, in which the initial size distribution of ice crystals was known, were isothermally preserved for given periods of time (typically 300 min) in the presence of PVA, AFP type I, NaCl, or the other three polymers. Then, the average size of the ice crystals was measured using image processing. Both the PVA and AFP type I completely inhibited the increase in ice crystal size at such low concentrations that the melting temperature of the solution was , whereas NaCl and the other three polymers clearly increased the ice crystal size due to Ostwald ripening. This inhibition effect of PVA and AFP type I was caused by thermal hysteresis, which is often taken as the primary manifestation of non-equilibrium antifreeze activity of these additives and defined as the difference between the melting temperature and non-equilibrium freezing temperature at which ice crystals start to grow in solution. The increase in ice crystal size was inhibited when the thermal hysteresis surpassed the driving potential for Ostwald ripening. Using PVA, which exhibits thermal hysteresis, is a novel technique to completely inhibit the increase in ice crystal size in isothermal ice slurries.     

Fast synthesis and morphology control of silicalite-1 in the presence of polyvinyl alcohol

Silicalite-1 crystals with various morphologies were prepared by addition of polyvinyl alcohol (PVA) in silicalite-1 synthesis solution at 180 °C for 6?C40 h. The samples were characterized by X-ray diffraction, scanning electron microscopy, FT-IR, thermogravimetric analysis and N₂ sorption. PVA in the synthesis solution promoted the fast crystallization of silicalite-1 within 6 h due to its adsorption on the surface of silicalite-1 precursors and the hydrogen bonding effect. The addition of PVA would produce silicalite-1 without aggregation because PVA served as temporary physical barriers. However, more PVA in the system (weight ratio of PVA/SiO₂ = 1.75) slowed down the nucleation rate of silicalite-1 as the high viscosity of PAV hindered the selectivity between PVA and crystal facet. PVA also changed the surface energy of silicalite-1 precursors, and resulted in silicalite-1 crystals with sizes from 6 × 2 × 0.6 to 15 × 10 × 3 ??m³. Silicalite-1 crystals exhibited coffin-, plate-, and rod-like structure when different weight ratios of PVA/SiO₂ were applied, and the silicalite-1 crystals had high BET surface areas of 485?C513 m²/g.     

Effects of organic additives on zinc electrodeposition from alkaline electrolytes

This work reports the effects of four organic compounds (referred to as levelers) on the electrodeposition of Zn on steel from alkaline free-cyanide electrolytes. The additives tested included polyvinylalcohol (PVA) and the condensation products of epichlorhydrin with amines, called polyamines (PAs), that were synthesized using an aliphatic amine (PA-I, from diethylamine and PA-II from diethylamine-triethylamine), and a heterocyclic quaternary imidazolium molecule (PA-Imid, from imidazole). These compounds were evaluated in the absence and in addition to a quaternary ammonium brightener, N-benzyl-3-carboxylpyridinium chloride (3NCP). The imidazole derivative-based polyamine (PA-Imid) causes greater inhibition of the zinc reduction process than the aliphatic polyamine, and more cathodic overpotential is necessary to promote massive metal deposition. The morphology of the deposits is modified when polyamines are added to the bath; more compact and smaller crystals are obtained with PVA as well as with polyamine PA-I. The addition of PA-II as well as PA-Imid yields crystals growing perpendicular to the substrate. The addition of 3NCP with PVA, PA, or PA-Imid increased the deposition overpotential and modified the morphology by diminishing the grain size. In the absence of additives, crystallographic orientation favored the basal Zn(002) with high atomic packing. The addition of the levelers favored the high-angle pyramidal Zn(101) with low atomic packing. The combination of the levelers with (3NCP) favored the prismatic Zn(100) crystallographic orientation. Additives decrease the size of zinc crystals and tend to increase the energy of lattice favoring the growth of pyramidal and prismatic planes.     

Preparation of porous TiO2 by a novel freeze casting

Highly porous and open interconnected pore structural TiO₂ were prepared by a novel freeze casting method. In the experiment, the well-dispersed aqueous slurries were first frozen, and then dried at a reduced vacuum. Since the sublimation of ice crystals developed in the freezing process, the green bodies with highly porous were obtained. The phase composition and the microstructure of the sintered samples were characterized by XRD, SEM, porosity and the pore size distribution was measured by mercury porosimetry. The results demonstrated that the PVA concentration in the slurries remarkably affect the microstructure of TiO₂ ceramics. The pore morphology of TiO₂ ceramics with 3 wt.% polyvinyl alcohol (PVA) addition was dendritic, and however, the pore morphology of TiO₂ ceramics with 6 wt.% PVA addition changed into columnar. The reason for the variation of the pore morphology was ascribed to the effect of the PVA gelation on the growth behavior of the ice crystals.     

Production of oil-containing crosslinked poly(vinyl alcohol) microcapsules by phase separation: Effect of process parameters on the capsule size distribution

Oil-containing poly(vinyl alcohol) (PVA) microcapsules in the size range of 5–20 μm were prepared by the simple coacervation of PVA followed by chemical crosslinking of the coacervated PVA membrane with glutaraldehyde. Coacervation of the aqueous polymer solution was achieved by the addition of a phase separation inducer (e.g., sodium sulfate). PVA of different grades (e.g., molecular weight and degree of hydrolysis) was utilized both as stabilizer and wall-forming material. Dispersion of the oil phase in the aqueous PVA solution was effected by a homogenizer. The effects of the various process parameters, such as the agitation speed, the type and concentration of PVA, the volume ratio of the internal oil phase to the external aqueous phase, the viscosity of the oil phase as well as the electrolyte concentration in the aqueous solution, on the stability and the size distribution of the emulsion droplets and microcapsules were experimentally investigated. It was shown that high agitation rates and low interfacial tension (e.g., high PVA concentrations) resulted in a significant reduction of the size of the emulsion droplets and microcapsules. On the other hand, as the viscosity and the amount of the dispersed oil phase increased, the capsule size increased. Finally, it was found that the concentration of the electrolyte significantly affected the stability of the (o/w) emulsion, the size and concentration of coacervated PVA colloidal aggregates, as well as the morphology of the polymer wall membrane formed by the adsorption of the polymer-rich phase to the oil/water interface. © 1996 John Wiley & Sons, Inc.     

Studies on fibers spun from poly(vinyl alcohol‐b‐acrylonitrile) emulsions prepared by ultrasonic technique. I. Characterization of fiber structure

The structural characteristics of poly(vinyl alcohol‐b‐acrylonitrile) fibers with different AN contents were studied by comparison with that of PVA and PAN fibers. X‐ray diffraction analysis showed that both PVA and PAN blocks in the copolymer fibers formed crystals. Two glass transition temperatures corresponding to PVA and PAN components appeared on the dynamic mechanical spectrum of the copolymer fiber, indicative of their incompatibility in the fiber. SEM intuitively exhibited a longitudinal cracked and grooved surface morphology similar to that of PAN fiber and revealed an internal microdomain separation morphology for the block copolymer fibers. TEM showed a morphological structure intermediate between those of PVA and PAN fibers for the block copolymer fibers. It was also found that the copolymer fiber with the lower AN content has a sheath–core structure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 979–988, 2001     

Crystal violet dye sorption and transport in/through biobased PVA cryogel membranes

Cryogels based on poly(vinyl alcohol) [PVA] and three types of bioinsertions such as scleroglucan, cellulose microfibers, and zein, respectively, have been prepared using capacity of PVA to crosslink by repeated freezing–thawing cycles. The effect of the incorporation of biopolymers on the properties of PVA cryogel has been studied by using several techniques such as: scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared studies. The obtained biobased cryogel membranes were subjected to sorption and to diffusion experiments using Crystal Violet (CV), a dye commonly used in the textile industry and in medicine. Image analysis with CIELAB system was used both to monitor the cryogels loading with CV and to gain insight in the dye state into the gel, in correlation with the bioinsertion type and gels morphology. Dye diffusion but also sorption capacity of the cryogels was found to be closely related to the type of biopolymer. In this article the equilibrium (sorption isotherms) and transport properties (diffusion and permeability coefficients) of CV, in/through physical cross‐linked PVA hydrogel membranes with bioinsertions has been reported. The highest efficiency for the CV removal from aqueous solutions was obtained for the PVA/Scl cryogels. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41838.     

纳米MnO2/PVA石墨纸多层电极电催化降解聚丙烯酰胺

采用涂覆法制备纳米MnO₂-PVA/GP多层复合电极,经FTIR、SEM、循环伏安特性曲线分别表征电极的分子结构、表面形貌和电化学性能。复合电极表面聚乙烯醇（PVA）涂层光滑,PVA薄层均匀内嵌γ晶型球形纳米MnO₂颗粒,粒径约15～20nm,具有较高催化活性。该电极为多层复合结构,以石墨纸为基底电极,集合PVA强吸附性和纳米MnO₂催化活性,应用于电催化降解石油三采过程中产生的高黏性的聚丙烯酰胺溶液。考察了电流密度、溶液pH、电解质浓度等因素对复合电极电催化降黏性能的影响。该电极电催化降黏性能优于石墨纸电极和纳米MnO₂催化,在pH=7、电解质Na₂SO₄溶液浓度为0.3mol/L、电流密度10mA/cm²、电催化2.0h后PAM溶液的黏度下降90.2%以上,达到石油三采中聚丙烯酰胺废水回用的黏度要求,同时节约了采油业用水资源。     

Annealing behavior of solution grown polyethylene single crystals

The morphology evolution of solution grown polyethylene single crystals has been studied upon annealing below their melting temperature by using atomic force microscopy (AFM). AFM investigations have been performed ex situ, which means AFM investigations at room temperature after the annealing treatment, and in situ at real temperature. Beside the well-known Swiss-cheese and picture frame appearance a novel morphological feature has been observed: the formation of saw-tooth-like patterns at the edges of the crystals, which become more and more pronounced with increasing annealing temperature. Controlled dissolution experiments have resulted in similar saw-tooth-like edge patterns of the single crystals, which indicate that the initial organization of the crystals influences the reorganization. This reorganization behavior upon annealing can be related to the presence of nano-sized fold defects, which have been monitored using the technique of n-alkane surface decoration.     

Preparation of asymmetric PVA membranes using ternary system composed of polymer and cosolvent

Integrally skinned PVA membranes have been prepared from PVA/NMP/water system by the phase inversion method in 2‐propanol bath, and the pervaporation characteristics of these membranes were investigated. With an increase in the NMP content in the polymer solution, the formation of skin layer depended on the NMP content in the cosolvent, and the overall morphology of membranes changed from porous to dense structure. Particularly, PVA membranes showed an asymmetric structure composed of a dense skin layer and a porous sublayer with finger‐like type and cellular structure in solvents of 50–60% NMP compositions. The experimental results from the pervaporation separation of MTBE and methanol mixtures were also in good agreement with the morphology for the formation of skin layer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2884–2890, 2003     

One-step fabrication of branched poly(vinyl alcohol) nanofibers by magnetic coaxial electrospinning

Branching has been emerging in 3-D interconnecting building blocks. Branched and hyperbranched poly(vinyl alcohol) (PVA) nanofibers were fabricated by coaxially electrospinning two-liquids under an alternating magnetic field in a facile manner. Both the PVA nanofiber trunks with diameter of 100–200 nm and the PVA nanofiber branches with diameter of 10–30 nm were formed in a single step. The length and the morphology of the branched PVA nanofibers could be controlled through a rational design of the magnetic field. The facile technique may readily be extended to prepare 3-D branched nanofibers from other materials such as various polymers and polymer–ceramic materials. Moreover, the multifunctional and multicomponent materials with branched nanostructure could be expected by using the magnetic coaxial electrospinning technique. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

聚乙烯醇静电纺丝纳米纤维的制备及形貌研究

利用静电纺丝技术制备聚乙烯醇（PVA）纳米纤维材料,通过正交试验调节制备过程中纺丝电压、纺丝距离和纺丝溶液浓度等工艺参数,探究其对PVA纳米纤维直径大小、直径分布以及纤维形貌的影响。结果表明,影响纳米纤维形貌的主要因素排序是纺丝溶液浓度＞纺丝距离＞纺丝电压,并确定最优水平组合为纺丝电压为20 kV,PVA纺丝溶液浓度为6 %(质量分数,下同),纺丝距离为12 cm。     

Functional modification of poly(vinyl alcohol) by copolymerizing with a hydrophobic cationic double alkyl‐substituted monomer

In this paper, a hydrophobic monomer (HM) that has a cationic double alkyl‐substituted group bonded to the nitrogen atom was first synthesized. Then a hydrophobic poly(vinyl alcohol) (PVA) was prepared by a radical solution copolymerization of vinyl acetate (VAc) with the HM followed by an alcoholysis reaction in alkaline conditions. The structures of HM and hydrophobically modified PVA (H‐PVA) were confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance. The effect of hydrophobic cationic segments on crystallization behaviors, mechanical properties, morphology, solution viscosity, and hydrophobic property were investigated. The results indicated that the crystallinity decreased from 37.2% of pure PVA to the minimum 23.2% of H‐PVA with the incorporation of 1.15 mol % HM. The thermal decomposition temperature of H‐PVA increased by about 50 °C compared with that of pure PVA. The viscosity of the H‐PVA solution was several times higher than that of the corresponding unmodified PVA solution over the whole shear rate range, which demonstrated that the H‐PVA had good shear‐resistance ability. Furthermore, the contact angle was significantly increased from 55.1° to 115° with the incorporation of only 0.83% HM, which illustrated that the H‐PVA had high hydrophobicity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43888.     

Growth of Monoclinic ZrO2 Thin, Flaky Crystals by Hydrothermal Decomposition of Zirconium Oxide Sulfate Crystals

Thin platelike hexagonal crystals of zirconium oxide sulfate (ZOS) with a chemical composition of Zr₃O₅SO₄. n H₂O were previously synthesized by the hydrolysis of an aqueous solution of 2 mol/L ZrOSO₄ at 240°C. The ZOS particles obtained were hydrothermally treated again in dilute sulfuric acid solution (<0.15 mol/L) at 240°C. The decomposition of ZOS and the nucleation and growth morphology of the monoclinic ZrO₂ crystals were automatically controlled with increasing sulfuric acid released by the decomposition of ZOS, and were influenced by the morphology of ZOS as precursors. Anisotropic monoclinic ZrO₂ single crystals, elongated thin and flaky particles (length: >2 (Am; width: about 0.1 μm; thickness:«0.01 μm), could be obtained under some conditions without the coexistence of another type of anisotropic ZrO₂ fibrous twin crystal.     

Green fabrication route of robust,biodegradable silk sericin and poly(vinyl alcohol) nanofibrous scaffolds

Silk sericin (SS) has been extensively used to fabricate scaffolds for tissue engineering. However, due to its inferior mechanical properties, it has been found to be a poor choice of material when being electrospun into nanofibrous scaffolds. Here, SS has been combined with poly(vinyl alcohol) (PVA) and electrospun to create scaffolds with enhanced physical properties. Crucially, these SS/PVA nanofibrous scaffolds were created using only distilled water as a solvent with no added crosslinker in an environmentally friendly process. Temperature has been shown to have a marked effect on the formation of the SS sol–gel transition and thus influence the final formation of fibers. Heating the spinning solutions to 70 °C delivered nanofibers with enhanced morphology, water stability and mechanical properties. This is due to the transition of SS from β‐sheets into random coils that enables enhanced molecular interactions between SS and PVA. The most applicable SS/PVA weight ratios for the formation of nanofibers with the desired properties were found to be 7.5/1.5 and 10.0/1.5. The fibers had diameters ranging from 60 to 500 nm, where higher PVA and SS concentrations promoted larger diameters. The crystallinity within the fibers could be controlled by manipulation of the balance between PVA and SS loadings. In vitro degradation (in phosphate buffer solution, pH 7.4 at 37 °C) was 30–50% within 42 days and fibers were shown to be nontoxic to skin fibroblast cells. This work demonstrates a new green route for incorporating SS into nanofibrous fabrics, with potential use in biomedical applications. © 2019 Society of Chemical Industry     

Fabrication and characterization of chitosan/poly(vinyl alcohol) electrospun nanofibrous membranes containing silver nanoparticles for antibacterial water filtration

Electrospun nanofibrous membranes (ENMs) were fabricated based on chitosan/poly(vinyl alcohol) (CS/PVA) with a 70/30 mass ratio containing silver nanoparticles (AgNPs) via the electrospinning method. AgNPs were produced on the surface of CS/PVA nanofibers by adding AgNO₃ to a CS/PVA blend solution as a silver rendering component. The presence of AgNPs in the polymer blend solution was detected by UV spectrophotometry. The morphology of nanofibers before and after cross-linking with glutaraldehyde was investigated by the field emission scanning electron microscopy. The formation and size distribution of AgNPs onto the surface of nanofibers were observed by transmission electron microscopy and confirmed by energy dispersing X-ray spectroscopy. As-spun and cross-linked CS/PVA nanofibers revealed a smooth surface with diameters ranging from 58 to 73 nm and 95 to 109 nm, respectively. The effect of AgNP formation on the chemical structure of nanofibers was explored by Fourier transform infrared spectroscopy. Static and dynamic antibacterial filtration efficiencies of CS/PVA ENMs, containing differing amounts of AgNO₃, have been tested against Escherichia coli, a gram negative bacterium. The antibacterial assessment results exhibited a significant increase in both static and dynamic antibacterial filtration efficiencies of the prepared CS/PVA ENMs by addition of AgNO₃ as a bactericidal agent.     

Preparation of biocompatible magnetite-PLGA composite nanoparticles using supercritical fluid extraction of emulsions

We report a new strategy for the production via supercritical fluid extraction of emulsion of biocompatible magnetic nanocomposite particles made of magnetite nanocrystals dispersed in a poly(lactic-co-glycolic) acid (PLGA) matrix. Ricinoleic acid-stabilized magnetic nanocrystals have been prepared via coprecipitation of two iron salts in alkaline environment, and subsequently dispersed in a solution of PLGA in dichloromethane. The obtained oil phase has then been dispersed in an aqueous solution of polyvinyl alcohol (PVA) in order to obtain a kinetically stable oil-in-water miniemulsion. The solvent was finally extracted via supercritical fluid extraction of emulsions. The continuous extraction of dichloromethane by means of supercritical CO₂ leads directly to a stable suspension of magnetite-PLGA composite nanoparticles in water. The influence of those parameters affecting the final particle size distribution and morphology, primarily emulsifier amount and magnetite content, has been investigated, so as to optimize the process. Analysis of the products, performed through light scattering and electron microscopy, indicates that narrower size distributions are obtained with larger amounts of emulsifier and lower amounts of magnetite. The morphology of the particles tends to be of Janus type, with the magnetite accumulated on one hemisphere of the particle. The proposed approach is suitable for the preparation of large quantities of high-quality magnetite-PLGA composite nanoparticles for biomedical applications.