Synchrotron small angle X-ray scattering study on the conformation of polystyrene in compressed CO2-toluene mixture

Synchrotron small angle X-ray scattering (SAXS) was performed to investigate the effect of dissolved CO2 in toluene on the conformation of polystyrene (PS) in the solution. It has been found that the second virial coefficient A2 and the radius of gyration Rg decrease with the increasing antisolvent CO2 pressure. The scattering intensity of PS chain followed l(h)∞h-αunder different antisolvent pressures (0, 0.6, 1.5, 2.4, 3.3, and 4.2 MPa), suggesting that the PS chain has self-similar structure behavior or a fractal structure in the presence of antisolvent CO2.All this reveals a large effect of antisolvent pressure or the solubility of CO2 in the solution on PS structure. The fractal dimensions increase with the increasing antisolvent pressure, indicating that the polymer chain changes from a swollen coil into a rather dense globule in the course of adding antisolvent CO2.     

Atomic force microscopy as a suitable technique for surface characterization of activated composite membranes for metal ion facilitated transport

Activated composite membranes (ACM) have been made based on a polysulfone layer over a non-woven support with a dense layer of aromatic polyamide, and deposited on the polysulfone using interfacial polymerisation by a carrier agent – di(2-ethylhexyl) dithiophosphoric acid – added to the membranes at several concentrations. Two polysulfone supports have been used, one of them commercial (PSf-Com) an other made ad hoc by us (PSf-GTS).The membrane structure has been characterised by both atomic force microscopy (AFM) and scanning electron microscopy (SEM). Firstly, the two polysulfonic bases were studied. The results show that structurally both are quite similar. PSf-Com presents a more regular sponge like structure in the bulk with some macrovoids randomly distributed, with an average size of 25 μm.The results obtained demonstrate that after interfacial polymerisation, some structural defects appear with relatively big valleys and peaks. The roughness has been studied versus the AFM scan size, which allowed the evaluation of the corresponding fractal dimensions. This permitted a detailed comparison and detection of the differences and similarities of the surface structure of all the membranes studied.The membranes made on PSf-GTS, whose surface structure seems to yield a better coverage of polyamide, gave good performances in the extraction of certain heavy metals. After extraction the membranes were analysed by EDS to confirm the permanence of the extractant along with some deposits of salt and extracted ions. PACS 68.37.Ps; 68.35.Ct; 82.39.Wj     

Preparation and Characterization of Poly(Vinyl Alcohol) (PVA)/SiO2, PVA/Sulfosuccinic Acid (SSA) and PVA/SiO2/SSA Membranes: A Comparative Study

Abstract

New organic–inorganic nanocomposites based on PVA, SiO₂ and SSA were prepared in a single step using a solution casting method, with the aim to improve the thermomechanical properties and ionic conductivity of PVA membranes. The structure, morphology, and properties of these membranes were characterized by Raman spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), water uptake (Wu) measurements and ionic conductivity measurements. The SAXS/WAXS analysis showed that the silica deposited in the form of small nanoparticles (～ 10?nm) in the PVA composites and it also revealed an appreciable crystallinity of pristine PVA membrane and PVA/SiO₂ membranes (decreasing with increasing silica loading), and an amorphous structure of PVA/SSA and PVA/SSA/SiO₂ membranes with high SSA loadings. The thermal and mechanical stability of the nanocomposite membranes increased with the increasing silica loading, and silica also decreased the water uptake of membranes. As expected, the ionic conductivity increased with increasing content of the SSA crosslinker, which is a donor of the hydrophilic sulfonic groups. Some of the PVA/SSA/SiO₂ membranes had a good balance between stability in aqueous environment (water uptake), thermomechanical stability and ionic conductivity and could be potential candidates for proton exchange membranes (PEM) in fuel cells.     

Ultrasound-enhanced membrane-cleaning processes applied water treatments: influence of sonic frequency on filtration treatments

Ultrasound (US) cleaning technique was applied to remove fouling of ultrafiltration (UF) and microfiltration (MF) membranes which were used to treat peptone and milk aqueous solutions, respectively. Membrane operations were performed by cross-flow filtration with 60 kPa operating pressure in an US field. The US employed had 28, 45 and 100 kHz frequency with 23 W/cm(2) output power. For each polymeric membrane made of polysulfone UF and cellulose MF, cleaning experiments were carried out with and without US after fouling. The fouled UF and MF membranes showed volume flux decline, but the membrane property was recovered by US irradiation. It was found in 28 kHz frequency that water cleaning was effective for recovery of declined condition due to fouling. Also, US-enhanced permeability of membranes was discussed in both membrane systems. We observed that US decreased the fouling condition in both membrane systems when US was irradiated before fouling. It was found that 28 kHz frequency US could enhance formation of the fouled layer in both filtration systems of peptone and milk solution.     

Poly-benzyl domains grown on porous silicon and their I-V rectification

Microwave-irradiated polymerization of benzyl chloride and triphenyl chloromethane on hydride-terminated porous silicon (PS) was achieved through the use of Zn powder as a catalyst. Transmission infrared Fourier-transform spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses confirmed the poly-benzyl membranes grafted on PS. Topographical images by AFM revealed crystal-like domains rather than homogenous monolayers on the surface. The current-voltage measurements in nano-scale by current sensing atomic force microscopy (CS-AFM) showed the rectification behavior of this polymer membrane. Finally, mechanism of a radical initiation on the surface and a following Friedel-Crafts alkylation was proposed for the covalent assembly of poly-benzyl domains.     

Strong correlation between membrane effective fixed charge and proton conductivity in the sulfonated polysulfone cation-exchange membranes

The effectiveness of fixed charge in sulfonated polysulfone membranes and its correlation with proton conductivity and physicochemical properties have been investigated in this work. The membranes were prepared with various concentrations of sulfonating agent (6% to 10% v/v) and followed by the characterizations that include membrane potential measurements, proton conductivity, and physicochemical properties (contact angle, water uptake, and ion-exchange capacity). Here, the effective fixed-charge concentrations of the membranes were obtained based on the data of membrane potential measurements using the Teorell–Meyer–Siever equation. The analysis results exhibit that a strong correlation between effective charge concentration and proton conductivity, which is expressed by the linear increase of proton conductivity with QX. This correlation is also supported by the membranes physicochemical data, such as water uptake, ionic exchange capacity, surface contact angle against water and functional analysis using FTIR. Finally, it was also developed an ionic conductivity equation that describes the correlation between proton conductivity and QX values.     

Synchrotron small angle X-ray scattering study on the conformation of polystyrene in compressed CO<Subscript>2</Subscript>-toluene mixture

Synchrotron small angle X-ray scattering (SAXS) was performed to investigate the effect of dissolved CO₂ in toluene on the conformation of polystyrene (PS) in the solution. It has been found that the second virial coefficientA ₂ and the radius of gyrationR _g decrease with the increasing antisolvent CO₂ pressure. The scattering intensity of PS chain followedI(h) ∞h ^−α under different antisolvent pressures (0, 0.6, 1.5, 2.4, 3.3, and 4.2 MPa), suggesting that the PS chain has self-similar structure behavior or a fractal structure in the presence of antisolvent CO₂. All this reveals a large effect of antisolvent pressure or the solubility of CO₂ in the solution on PS structure. The fractal dimensions increase with the increasing antisolvent pressure, indicating that the polymer chain changes from a swollen coil into a rather dense globule in the course of adding antisolvent CO₂.     

小角x射线散射法研究甲基改性氧化硅凝胶的双分形结构

以正硅酸乙酯［Si(OC2H5)4,TEOS］和甲基三乙氧基硅烷［CH3Si(OC2H5)3,MTES］为前驱体，通过共水解法和两步法制备出两种不同的甲基改性氧化硅凝胶，在北京同步辐射光源(BSRF)小角x射线散射(SAXS)站测量了凝胶的散射强度，计算了凝胶的平均粒径、两相间比表面积等参数，在此基础上分析了凝胶的分形特征，发现存在两个尺度上的分形结构，分别对应于从SiO2原生颗粒到一次团聚体和从一次团聚体到簇团两种尺度.辅以透射电子显微镜(TEM)观测，证实由两种方法获得的凝胶具有非常不同的微观结构.实验证明，利用SAXS技术研究甲基改性凝胶的分形特征是获得凝胶微观结构的有力工具. 关键词： 甲基改性凝胶 氧化硅 小角x射线散射(SAXS) 分形结构     

Beamline setup for in situ measurements of particles in turbulent spray flames using small angle X-ray scattering

The particle formation in spray flame synthesis (SFS) is a fast and complex process involving many sub-steps that may happen simultaneously. To investigate the mechanisms that typically lead to small aggregated primary particles, a sophisticated technique for in situ measurements in the flame is necessary to provide information about primary particles and the aggregates as well. This work describes the development of an in situ measurement setup using small angle X-ray scattering (SAXS) to investigate the entire particle formation mechanism of zirconia nanoparticles in and above a turbulent spray flame. In preparation for the in situ measurements, a beamline for single crystal diffractometry at Karlsruhe Research Accelerator (KARA) was adapted for low scattering SAXS experiments including optimizations of the optics and measurement protocol. As a result, a significant dependence of scattering intensity was detected as a function of the height above the burner. A detailed analysis of the SAXS data and comparison with TEM images allow insights into the primary particle growth, the development of fractal properties and the aggregation process.     

Modification of polysulfone membranes via surface-initiated atom transfer radical polymerization

Hydrophilic poly((poly(ethylene glycol) methyl ether methacrylate) (P(PEGMA)) and poly(glycidylmethacrylate) (PGMA) brushes were grafted from chloromethylated polysulfone (CMPSF) membrane surfaces via surface-initiated atom transfer radical polymerization (ATRP). Prior to ATRP, chloromethylation of PSF was performed beforehand and the obtained CMPSF was prepared into porous membranes by phase inversion process. It was demonstrated that the benzyl chloride groups on the CMPSF membrane surface afforded effective macroinitiators to graft the well-defined polymer brushes. ¹H NMR was employed to confirm the structure of CMPSF. The grafting yield of P(PEGMA) and PGMA was determined by weight gain measurement. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the grafting of P(PEGMA) and PGMA chains. Water contact angle measurements indicated that the introduction of P(PEGMA) and PGMA graft chains promoted remarkably the surface hydrophilicity of PSF membranes. The effects of P(PEGMA) and PGMA immobilization on membrane morphology, permeability and fouling resistance were investigated. It was found that P(PEGMA) and PGMA grafts brought higher pure water flux, improved hydrophilic surface and better anti-protein absorption ability to PSF membranes after modification. And evidently, macromonomer P(PEGMA) brought much better properties to the PSF membranes than PGMA macromonomer.     

GISAXS and SAXS studies on the spatial structures of Co nanowire arrays

The spatial structures of magnetic Co nanowire array embedded in anodic aluminium membranes were investigated by grazing incidence small angle X-ray scattering (GISAXS) and conventional small angle X-ray scattering (SAXS) techniques. Compared with SEM observation, the GISAXS and SAXS measurements can get more overall structural information in a large-area scale. In this study, the two-dimensional GISAXS pattern was well reconstructed by using the IsGISAXS program. The results demonstrate that the hexagonal lattice formed by the Co nanowires is distorted (a ≈ 105 nm, b ≈ 95 nm). These Co nanowires are isolated into many structure domains with different orientations with a size of about 2 μm. The SAXS results have also confirmed that the nanopore structures in the AAM can be retained after depositing Co nanowires although the Co nanowires can not completely but only just fill up the nanopores. These results are helpful for understanding the global structure of the Co nanowire array.     

Design of novel SPEEK-based proton exchange membranes by self-assembly method for fuel cells

Fuel cell represents a new energy conversion device, which promises to provide clean source of power. Fuel cell [particularly proton exchange membrane fuel cell and direct methanol fuel cell (DMFC)] is a promising candidate for transportation and portable power source applications. In DMFC, there is a problem of methanol crossover. In order to reduce such a problem, there has been an intensive research activity in the modification of Nafion. In the present investigation, self-assembled membranes were fabricated with sulfonated polyether ether ketone as the core part of the membrane. Aminated polysulfone and sulfonated polysulfone were used as the layers in order to prevent the crossover of methanol. The assembled membranes were characterized by ion exchange capacity, water and methanol absorption, and durability. The methanol permeability and selectivity ratio proved a strong influence on DMFC application. Scanning electron microscopy proved smooth surface, which established strong cohesive force for the polymer chains. Among the synthesized self-assembled membranes, the membrane with two bilayers was the best in terms of power density in DMFC. The membrane electrode assembly with two bilayers showed higher performance (~61.05 mW/cm²) than sulfonated poly(ether ether ketone) and Nafion in DMFC.     

Nanoscale Structure of Urethane/Urea Elastomeric Films

The nanostructure of urethane/urea elastomeric membranes was investigated by small-angle X-ray scattering (SAXS) in order to establish relationships between their structure and mechanical properties. The networks were made up of polypropylene oxide (PPO) and polybutadiene (PB) segments. The structural differences were investigated in two types of membranes with the same composition but with different thermal treatment after casting. Type I was cured at 70–80 °C and type II at 20 °C. Both membranes showed similar phase separation by TEM, with nanodomains rich in PB or PPO and 25 nm dimensions. The main difference between type I and type II membranes was found by SAXS. The type I membrane spectra showed, besides a broad band at a 27-nm q value (modulus of the scattering vector), an extra band at 6 nm, which was not observed in the type II membrane. The SAXS spectra were interpreted in terms of PPO, PB soft segments, and urethane/urea links, as well as hard moiety segregation in the reaction medium. This additional segregation (q = 7 nm), although subtle, results in diverse mechanical behavior of in both membranes.     

Polydopamine Bilayer Nanofiltration Membranes with Excellent Resistance to Delamination

Abstract

Bilayer nanofiltration (NF) membranes tend to delaminate and have poor stability when applied in organic solvents due to their bi-layered structure. In this study we prepared two types of polydopamine (PDOPA) modified NF membranes including PDOPA-TMC (trimesoyl chloride)/PSF and PDOPA/PIP(Piperazine)-TMC/PSF NF membranes on polysulfone (PSF) ultrafiltration membranes via interfacial polymerization based on PDOPA’s specialized molecular structure and high adhesion property. The separation performance and stability of the NF membranes were investigated. Both the polyester bonds of the PDOPA bilayer membranes and the bioadhesion of the PDOPA were simultaneously beneficial to improving the structure and chemical stabilities of the bilayer membranes. After soaking both the PDOPA-TMC/PSF and PDOPA/PIP-TMC/PSF NF membranes in ethanol solvent for 12?days, the rejection of Congo red only decreased by 1.8% (original, 99.9%) and 1.2% (original, 99.9%), respectively. For the PDOPA/PIP-TMC/PSF NF membrane, the rejection of Na₂SO₄ was only reduced by 1.6% (original, 98.5%). Moreover, the separation performances of both the PDOPA-TMC/PSF and PDOPA/PIP-TMC/PSF NF membranes were still excellent after soaking in a sodium hypochlorite solution (50?ppm) for 240?h (12,000?ppm·hours). The NF membranes thus exhibited long-term structural stability in ethanol and excellent chemical stability in the sodium hypochlorite solution. In particular, no delamination was observed in the above experiments, which is significant for their use in the wastewater treatment field.     

Fractal properties of macrophage membrane studied by AFM

Complexity of cell membrane poses difficulties to quantify corresponding morphology changes during cell proliferation and damage. We suggest using fractal dimension of the cell membrane to quantify its complexity and track changes produced by various treatments. Glutaraldehyde fixed mouse RAW 264.7 macrophage membranes were chosen as model system and imaged in PeakForce QNM (quantitative nanomechanics) mode of AFM (atomic force microscope). The morphology of the membranes was characterized by fractal dimension. The parameter was calculated for set of AFM images by three different methods. The same calculations were done for the AFM images of macrophages treated with colchicine, an inhibitor of the microtubule polymerization, and microtubule stabilizing agent taxol. We conclude that fractal dimension can be additional and useful parameter to characterize the cell membrane complexity and track the morphology changes produced by different treatments.     

Small angle neutron scattering and small angle X-ray scattering studies of platinum-loaded carbon foams

The morphology of carbon nanofoam samples comprising platinum nanoparticles dispersed in the matrix was characterized by small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) techniques. Results show that the structure of pores of carbon matrix exhibits a mass (pore) fractal nature and the average radius of the platinum particles is about 2.5 nm. The fractal dimension as well as the size distribution parameters of platinum particles varies markedly with the platinum content and annealing temperature. Transmission electron micrographs of the samples corroborate the SANS and SAXS results.      

利用小角X射线散射技术研究煤干馏过程中的孔隙结构变化

煤干馏是煤炭高效利用的重要途径之一。同步辐射小角X射线散射(Small Angle X-Ray Scattering,SAXS)技术是研究煤干馏过程中内部孔隙结构变化的常用手段。本文利用SAXS对山西余吾烟煤干馏过程(100~1200℃,温度梯度100℃)进行了表征,并对分形维数和粒径分布的变化进行了分析。结果发现煤干馏过程中,散射图像类似,具有各向同性特征,始终保持表面分形结构,且分形维数总体上呈现增大的趋势;随着煤干馏温度的升高,粒度分布发生了显著变化,充分反映了煤在不同干馏阶段的结构特征,对后续的煤炭研究具有一定的指导意义。     

Phase-contrast scanning force microscopy and chemical heterogeneity of GR polysulfone ultrafiltration membranes

The surfaces of three commercial urea formaldehyde polysulfone membranes from Dow Denmark^TM (GR51, GR61 and GR81) are characterised both topographically and chemically. Their topography is studied by scanning force microscopy to obtain the corresponding pore-size distributions, which are in fair agreement with nominal molecular weight cut-offs. The composition of the surfaces of the membranes is analysed by X-ray photoelectron spectroscopy. The resulting percentage content of nitrogen, which could be attributed probably to an additive used in the manufacturing process, is shown to correlate with the portion of the total surface with different viscoelastic properties as investigated by using phase-contrast scanning force microscopy. Both parameters are increasing for membranes with decreasing molecular weight cut-off. Also, the additive seems to be more sparsely distributed for the membranes with bigger pores, according to fractal analysis. Finally, all the membranes are very similarly wettable. Received: 22 May 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001