Fabrication of microporous membranes from melt extruded polypropylene precursor films via stretching: Effect of annealing

In this work, the effects of annealing conditions on the microstructure of polypropylene(PP) precursor films and further on the porous structure and permeability of stretched membranes were investigated. Combinations of WAXD, FTIR, DSC and DMA results clearly showed the crystalline orientation and crystallinity of the precursor film increased with annealing temperature, while the molecular chain entanglements in the amorphous phase decreased. Changes in the deformation behavior suggested more lamellar separation occurred for the films annealed at higher temperatures. Surface morphologies of the membranes examined by SEM revealed more pore number and uniform porous structure as the annealing temperature increased. In accordance with the SEM results, the permeability of the membranes increased with annealing temperature. On the other hand, it was found that 10 min was almost enough for the annealing process to obtain the microporous membranes with an optimal permeability.     

Latex film formation studied with the atomic force microscope: Influence of aging and annealing

The surface structure of latex dispersion films was examined with an atomic force microscope. All measurements were done in air on latex films having a minimum film formation temperature of 12°C and a glass transition temperature of 18°C. One aim of this study was to follow structural changes during film formation. Three minutes after spreading the film, its surface layer dried. Afterwards, the structure of the film did not change anymore. Only after 4 months could structural changes be observed: Though individual latex particles could be identified, the particles partly melted into one another.After annealing films at 50° or 60°C for 4 h, the latex particles partly melted into one another, but individual particles could still be identified. When annealing at or above 80°C, no individual latex particles were visible anymore. With increasing temperature the film roughness decreased from 3 nm without annealing to 0.8 nm at 100°C annealing temperature. In addition, islands of 2–4 nm thickness appeared on the film surface. These islands could be scraped off the film by increasing the force between tip and sample, indicating that they are composed of surfactant which was squeezed out of the film.     

Noncontact atomic force microscopy studies of ultrathin films of amorphous solid water deposited on Au(111)

Noncontact atomic force microscopy was used to study the morphological changes of an ultrathin amorphous solid water (ASW) film as a function of deposition temperature, annealing temperature, and annealing time. ASW deposited at 80 or 108 K on Au(111) formed truncated hemispherical clusters of increasing size during annealing at 134 K; these clusters were inferred to be crystalline. The number of nuclei present at the outer surface of the film after deposition was greater for higher deposition temperature. For lower cluster densities, depletion of the ASW film around the clusters was observed when the clusters became larger and dendritic growth was observed when the apparent cluster footprint radius exceeded 100 nm.     

Radiolytic Grafting of Styrene on Polymethylpentene Film

Gamma ray initiated grafting of styrene on three polymers gave rates in the order polyethylene > polypropylene > polymethylpentene, with saturation absorption of styrene in the order polymethylpentene > polypropylene > polyethylene, indicating that the plasticizing action of absorbed styrene possibly causes increased termination rate and reduced over-all grafting rate. The rate of styrene grafting on polymethylpentene was unaffected by temperature change in the range from 23 to 85°C. Above a certain critical film thickness, styrene grafting rate is proportional to film surface area rather than film weight.     

Kinetics of latex formation of PBMA latex in the presence of alkali soluble resin using atomic force microscopy

 The effect of alkali-soluble resin (ASR), poly(ethylene-co-acrylic acid), EAA, postadded to emulsifier-free monodisperse poly(butyl methacrylate) (PBMA) latexes on the kinetics of film formation was investigated using atomic force microscopy (AFM). Corrugation height of latex particles in films was monitored at various annealing temperatures as a function of annealing time. Enhanced polymer diffusion was found in a latex film containing ASR regardless of anneal-ing temperature. With increasing annealing temperature, a much higher rate of polymer diffusion was found in latex films containing ASR. These results can be interpreted that the low molecular weight and low Tg EAA resin adsorbed at the particle surface is more susceptible to diffusion than that of the PBMA in the film formation stage, thus it enhances the mobility of PBMA polymer. Received: 30 October 1997 Accepted: 20 March 1998     

Specifics of change in the surface area of amorphous poly(vinyl chloride) during its inelastic deformation

A direct microscopic observation procedure was used to study the processes of deformation and shrinkage of poly(vinyl chloride) above its glass transition temperature. Prior to stretching or contraction of the polymer, its surface was decorated with a thin (10–15 nm) metal layer. As a result of subsequent deformation (shrinkage), the decoration underwent structural rearrangements, which were detected by means of direct microscopic examination. These rearrangements contain information on the mechanism of deformation of the polymer substrate. In particular, the procedure makes it possible to characterize the process of development of the interface in the polymer during deformation and the reverse process of interface contraction during the shrinkage of the material. It was found that, in the case of an increase in the interfacial area, its growth is accompanied by a growth in imperfection of the polymer surface layer. These defects can concentrate mechanical stress, thus strongly affecting the fragmentation of the metal decoration on the polymer surface. It was shown that the surface defects could be eliminated by annealing of the polymer above its glass transition temperature. The introduction of a plasticizer that decreases the glass transition temperature below the deformation temperature likewise prevents the development of these defects during an increase in the surface area of the polymer in the process of its inelastic deformation.     

Thin ORMOSIL Films with Different Organics

Structural, optical and electrical properties of silicate films modified by structure fragments containing different organic groups were studied. The ORMOSILs were produced by a cohydrolysis of tetraethoxysilane with different types of alkyl (aryl) substituted alkoxysilanes. Film structure and its evolution during heat treatment were studied by ellipsometry and IR spectroscopy. For methyl- and phenyl-modified silicate films the shrinkage is lower than for silicate ones in the range of annealing temperature from 200 to 500°C. The shrinkage of phenyl-modified silicate film is more than three times lower than of methyl- and trimethyl-modified ones. The presence of single or double C=C bonds in the organic chain leads to an increase in the film shrinkage due to the thermodestruction of the bond as it is confirmed by IR data. In the case of phenyl- and methyl-modified silicate films this process starts from 500°C and it is accompanied by abrupt film shrinkage. The dielectric constant and the loss tangent of methyl and phenyl groups decrease due to reduction of hydroxyl content and film density. Other groups are not effective due to their thermodestruction at lower temperatures.     

Surface morphology of poly(cyano-p-xylylene) thin films

The surface morphology of poly(cyano-p-xylylene) thin films of different thicknesses (25–1500 nm or more than 5 μm) that were synthesized by vapor-deposition polymerization on the substrate surface in the temperature range from −22 to +35°C has been studied by atomic force microscopy. The surface topography is quantified through analysis of the height-height correlation function. The surface of all films is characterized by a similar granular morphology with a transverse size of granules of 50–500 nm. The surface morphology changes with the polymerization temperature (the substrate temperature) and the film thickness. The effect of film annealing on its surface morphology is considered. It has been established that annealing at 200°C leads to a change in the surface morphology of the films. Original Russian Text ? A.I. Buzin, D.S. Bartolome, K.A. Mailyan, A.V. Pebalk, S.N. Chvalun, 2006, published in Vysokomolekulyamye Soedineniya, Ser. A, 2006, Vol. 48, No. 9, pp. 1640–1646. This work was supported by the Russian Foundation for Basic Research (project nos. 03-03-32665 and 03-03-32634) and the Russian Science Support Foundation.     

Structural and mechanical study of elastomers under plane deformation

The plane shrinkage of various elastomers [natural rubber, synthetic isoprene rubber, and plasticized poly(vinyl chloride)] at room temperature has been studied via direct microscopic observations. Prior to deformation, the surface of polymer samples is decorated with a thin (several nanometers) metallic layer. Further deformation leads to formation of the surface relief in the coating. An analysis of the formed microreliefs allows one to visualize and characterize the induced stress field in the sample. The shrinkage of poly(vinyl chloride) samples is accompanied by development of the uniform surface relief over the whole surface of the deformed polymer. This fact suggests a homogeneous character of the stress field and, hence, a homogeneous structure of the polymer sample. In the case of crosslinked rubbers (natural rubber and synthetic isoprene rubber), their plane shrinkage leads to the development of an irregular pattern on the polymer surface. In addition to the folded surface relief that is typical of the poly(vinyl chloride) structure, one can observe 20-to 50-μm “islands,” which are characterized by their own morphological features. Information on structural inhomogeneity of rubbers that is obtained by scanning electron microscopy correlates with the data of DSC measurements. The advantages of electron microscopic procedure for studying structural rearrangements in polymers during strain recovery of elastomers are demonstrated.     

Visualization of temperature-induced structural rearrangements in oriented amorphous polymers

Thermally stimulated shrinkage of amorphous poly(ethylene terephthalate) and poly(vinyl chloride) oriented above their glass transition temperatures over a broad range of strain rates was studied by direct microscopic examination. The principle of revealing structural rearrangements is as follows. Before annealing, an oriented sample is coated with a thin (a few nanometers) metal layer. Subsequent annealing, which entails a change in the geometric dimensions of a polymer, leads to the appearance of a surface relief in the coating. The direct microscopic examination of the microrelief provides information on structural rearrangements in the polymer substrate. It was shown that identical microreliefs were formed in PVC independently of its preliminary stretching. For PET, it was found that the self-extension process in the direction of the draw axis was effected along with contraction during annealing. The superimposition of these processes is imaged as relief with two perpendicular folded structures. The obtained results give direct information on stress fields responsible for processes that occur in oriented polymers during their annealing; such information is difficult or even impossible to gain by any other means.     

Y_2O_3∶Eu~(3+)薄膜的制备及发光性能的研究

以稀土氧化物为原料,用溶胶-凝胶法制备前驱液,加入适量的聚乙烯醇做成膜物质,用浸渍拉提法在石英玻璃表面上得到均匀的薄膜,然后经过适当的干燥和热处理得到Y2O3∶Eu3+发光薄膜.讨论了Eu3+的掺杂浓度和热处理温度对薄膜发光性能的影响.试验表明:Eu3+的最佳掺杂浓度为8%(摩尔分数),薄膜的发光性能随热处理温度提高而增强,当热处理温度达到700℃后,薄膜的发光性能基本上稳定.同时用原子力显微镜和X射线衍射分析了薄膜的表面形貌和结构.     

New aspects of migration and flame retardancy in polymer nanocomposites

Annealing of pristine polypropylene blended with the organomontmorillonite (OMMT) at temperatures of 180-340 °C under a stream of nitrogen and of nitrogen-air mixtures is investigated. The oxidative annealing brings about the dispersion of the OMMT in the polypropylene and the formation of a nanocomposite structure. This is evidenced by the increase in the interlayer distance ‘d’ as measured by small angle XRD, with time of annealing and with the weight percent of air. This indicates progressive intercalation of the polymeric matrix into the clay gallery and subsequently exfoliation. The degree of exfoliation is estimated by the extent of migration determined spectroscopically on the surface of the annealed sample. The accumulated clay on the surface due to migration hinders the penetration of the oxygen into the annealing melt as expressed by the decrease in the rate of migration with the increase in the air concentration. This indicates the increase in ageing and storage stability of nanocomposites with increase in the extent of migration. The extent of migration is proportional to the polar carbonyl groups formed on the matrix. The energy of activation of the migration was found to be 37.82 kJ/mol indicating that the rate-determining step of migration is diffusion controlled reaction. The penetration of oxygen into the melt is the first of five steps, followed by oxidation, intercalation, exfoliation and migration. Monitoring the migration with increase in the temperature enables the observation at 275 °C of the transition of the nanocomposite structure to noncolloidal microcomposite. Increasing the annealing temperature above 300 °C brings about a slow, low-temperature combustion and formation of a new kind of char on the surface of the sample.     

Characterization of Tin Oxide Based Sol-Gel Coatings on Borosilicate Glasses by X-Ray Reflectivity

The X-ray reflectivity technique was applied in the study of tin oxide films deposited by sol-gel dip-coating on borosilicate glasses. The influence of the withdrawal speed and temperature of thermal treatment on the film structure was analyzed. We have compared the thermal evolution of the density and the shrinkage of the films with these properties measured for the monolithic xerogel by helium picnometry and thermomechanical analysis. In agreement with the Landau-Levich model, the layer thickness increases by increasing the withdrawal speed. Nevertheless, it decreases with the increase of the thermal treatment temperature, due to the densification process. The values of apparent density are smaller than the skeletal density, which shows that the films are porous. The comparison between the film and the monolith indicates that shrinkage during firing is anisotropic, occurring essentially perpendicular to the coating surface.     

Aging of piezoelectricity in poly(vinylidene fluoride)

This report describes isothermal aging of piezoelectricity in poly(vinylidene fluoride) (PVDF) based on long-term heat treatments between 40 and 160°C. The results demonstrate that no piezoelectric decay occurs below about 60°C, that between 60 and 160°C the aging behavior follows logarithmic kinetics, and that aging is linearly dependent on temperature. Both uniaxial and biaxial PVDF show similar trends, but piezoelectric decay is more rapid for uniaxial film. Decay of permanent poling-induced polarization is identified as the likeliest cause of piezoelectric aging, and piezoelectric decay is found to be associated with long-range annealing effects which also produce macroscopic shrinkage of the PVDF film.     

Diffusion Structural Analysis Study of Titania Films Deposited by Sol-Gel Technique on Silica Glass

The diffusion structural analysis (DSA) was used to characterize microstructure changes of hydrous titania gel films under in situ conditions of heating. TG and DTA were used in order to elucidate the processes controlling the formation of anatase film during heating of hydrous titania gel film. The annealing of porosity and near surface structure defects of the dehydrated titania films was indicated by DSA in the temperature range 255–700°C as the decrease of radon release rate. It was demonstrated that the annealing was enhanced on heating in oxygen in comparison with heating in argon. The DSA experimental results were compared with model curves describing the radon diffusion mobility and the annealing of radon diffusion paths.     

Thermal and crystallization studies of short flax fibre reinforced polypropylene matrix composites: Effect of treatments

The effect of fibre treatments on thermal stability of flax fibre and crystallization of flax fibre/polypropylene composites was investigated. For thermal stability study, flax fibres have been treated using maleic anhydride, maleic anhydride polypropylene copolymer, vinyltrimethoxy silane and alkalization. In order to compare thermal stability of flax fibres thermogravimetry (TG) analysis has been used. Kinetic parameters have been determined by Kissinger method. Results showed that all treatments improved thermal stability of flax fibres. For crystallinity analysis, three different techniques have been used, differential scanning calorimetry analysis (DSC), pressure–volume–temperature (PVT) measurements for analysis of volume shrinkage and polarized optical microscopy (POM). All techniques results showed that addition of flax fibre increased crystallization rate. Besides, depending on fibre surface treatment and crystallization temperature, flax fibre/PP composites can show transcrystallinity.     

Immobilization of Ciliary Neurotrophic Factor on Model Biomaterials by Plasma Graft Polymerization

Acrylic acid was grafted on the surface of polypropylene (PP) film via plasma‐induced technology. It was shown by FT‐IR that there were carboxyl groups on the surface of the modified PP film. The grafting ratio was analyzed quantitatively through a dyeing process. The effects of the technology parameters of the plasma‐treatment and graft polymerization on the grafting ratio, such as power, discharge time, concentration of monomer and active species density, reaction temperature and time, were characterized. Moreover, the content of ciliary neurotrophic factor (CNTF) that was anchored on the surface of the modified PP film was measured through enzyme‐linked immunosorbent assay (ELISA). The results show that the amount of CNTF immobilized on the surface of the modified PP film increase with increasing content of carboxyl groups, showing that the existence of carboxyl groups on the surface of the PP film is beneficial to the immobilization of CNTF.     

Sintering of Sol-Gel Films

The sintering of films differs from that of bulk gels in several ways. The initial state of a film is generally denser and less crosslinked than a bulk gel made from the same sol, and these factors enhance the densification rate of the film. The substrate constrains the shrinkage of the film, leading to high stresses that retard densification and can influence phase changes. The substrate is a site for heterogeneous nucleation, and crystallization makes densification more difficult, so the competition between sintering and crystallization is particularly important for films. Fast heating favors densification over crystallization, so rapid thermal annealing usually produces denser films. The high surface to volume ratio of a thin film makes it susceptible to degradation by reaction with the substrate and the atmosphere, so choosing compatible materials and avoiding over-firing is essential.     

ESR study of radical sites in crystalline texture of irradiated polypropylene by means of nitric acid etching

Bulk-crystallized isotactic polypropylene samples with different crystalline textures were etched by fuming nitric acid to remove the disordered region. The radicals produced by irradiation of γ-rays or ultraviolet light on these etched samples in vacuum at liquid nitrogen temperature were investigated by the ESR method. A triplet spectrum in addition to the original spectrum of polypropylene radicals was separated for the etched samples. It was concluded that this triplet was caused by radical species associated with nitro groups introduced on the surface of the crystalline residues by etching. The difference in the intensity of this triplet among the samples was ascribed to differences in crystalline textures and interpreted in a quantitative way. The concentration of polypropylene radicals corrected for the triplet differed among the quenched, annealed, and cold-drawn samples and the sample annealed one after drawing. This fact was interpreted on the basis of the hypothesis that radical sites were almost concentrated in the defects of crystal domain. The well known nonet spectrum, which can be observed at liquid nitrogen temperature after annealing the irradiated samples at room temperature, was also confirmed to be attributable to the defects of crystals. The behavior of free methyl radicals induced by ultraviolet irradiation was also found to be strongly dependent on the state of aggregation of the polymer molecules.