Effect of surface‐modifying macromolecules and membrane morphology on fouling of polyethersulfone ultrafiltration membranes

Polyethersulfone (PES) ultrafiltration (UF) membranes with and without surface‐modifying macromolecules (SMMs) were prepared and characterized in terms of the mean pore size and pore‐size distribution, surface porosity, and pore density. The results demonstrated that both the mean pore size and the molecular weight cutoff (MWCO) of the SMM‐modified membranes are lower than those of the corresponding unmodified ones. Membrane fouling tests with humic acid as the foulant indicated that the permeate flux reduction of the SMM‐modified membranes was much less than that of the unmodified ones. Therefore, fouling was more severe for the unmodified membranes. Moreover, the dry weight of the humic acid deposited on the membrane surface was considerably higher for the unmodified membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3132–3138, 2003     

Optical and scanning electron microscope study of brown coals

Mid-European brown coals, especially topographical features, structure as revealed in polished surfaces, and the elemental composition of inorganic constituents, have been examined. It is suggested that the SEM and EDAX methods should be useful in future studies of their petrographic classification and in cataloguing petrological components.     

Surface morphology of Nafion 117 membrane by tapping mode atomic force microscope

Surface morphology of Nafion 117 membrane was studied by tapping mode atomic force microscopy. Three different samples were analyzed and correspond respectively to dry membrane and wet membrane equilibrated either with water or with tributylphosphate. These studies show the supermolecular structure of the membrane, which is made of nodules or spherical grains of a mean diameter of 11 nm, and are surrounded by interstitial regions of a mean thickness of 50 Å. Roughness analysis of the samples shows the influence of the swelling properties of the membrane on its surface morphology. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 503–508, 1998     

A scanning electron microscope study of fractured and etched metallurgical coke surfaces

The object of this work was to attempt to link more closely coke strength and structure by establishing whether features visible on fracture surfaces could be identified with coke carbon textural constituents revealed either by polarized light microscopy of polished surfaces or by scanning electron microscopy of atomic oxygen-etched surfaces. The cokes used were produced in a laboratory furnace from coals covering the whole range or rank normally encountered in metallurgical coke production in the UK. Fracture surfaces were created by tensile fracture during diametral compression. In all three surfaces examined, the appearance of components derived from reactive coal constituents varied with the rank of the coal carbonized. A clear similarity was evident between features visible in the etched and fracture surfaces. The marked variation of fracture features imply that the textural composition of the coke carbon may make some contribution, as yet unquantified, to the variation in strength among cokes.     

Surface morphology of homogeneous and asymmetric membranes made from poly(phenylene oxide) by tapping mode atomic force microscope

Surface morphology of asymmetric and homogeneous membranes prepared from poly(phenylene oxide) (PPO) was studied by tapping mode atomic force microscopy (TMAFM). As expected, a significant difference in the morphology between the top and the bottom surfaces of the asymmetric membrane was observed. The images of the top surface revealed a small variation in the vertical direction (6.7 nm), compared to the mean diameter of nodules (62 nm), while the images of the bottom surface were very porous (microfiltration structure). On the other hand, the observed difference in morphology between the top and the bottom surfaces of the membrane prepared by the complete evaporation of the solvent (homogeneous membrane) was rather unexpected. The nodules on the bottom surface were twice as large as those on the top surface. These studies also revealed some differences in the morphology of the top surface of asymmetric and homogeneous membranes. Both surface were made up of nodules having a similar size (62–64 nm); however, roughness parameters calculated for the top surface of the asymmetric membrane were approximately two times greater than those for the top surface of the homogeneous membrane. © 1996 John Wiley & Sons, Inc.     

The effect of heat-treatment on the ultrafiltration performance of polyethersulfone (PES) hollow-fiber membranes

Polyethersulfone (PES) hollow-fiber membranes were prepared by the dry-wet spinning method and then heated in an oven at different temperatures to investigate the effect of heat-treatment on their ultrafiltration performance. It was found that the hollow-fiber membranes shrank by heat treatment, as evidenced by a decrease in flux and an increase in solute separation, although there was no visible change in the hollow-fiber dimension. The best results were obtained when the hollow fibers were heated at 150°C. A further investigation was made on the effect of the heating period, while the temperature was fixed to 150°C. It was found that the best combination of the temperature and the heating period was 150°C and 5 min.     

Mechanical measurements of ultra-thin amorphous carbon membranes using scanning atomic force microscopy

The elastic modulus of ultra-thin amorphous carbon films was investigated by integrating atomic force microscopy (AFM) imaging in contact mode with finite element analysis (FEA). Carbon films with thicknesses of ～10 nm and less were deposited on mica by electron beam evaporation and transferred onto perforated substrates for mechanical characterization. The deformation of these ultra-thin membranes was measured by recording topography images at different normal loads using contact mode AFM. The obtained force-distance relationship at the center of membranes was analyzed to evaluate both the Young’s modulus and pre-stress by FEA. From these measurements, Young’s moduli of 178.9 ± 32.3, 193.4 ± 20.0, and 211.1 ± 44.9 GPa were obtained for 3.7 ± 0.08, 6.8 ± 0.12, and 10.4 ± 0.17 nm thick membranes, respectively. Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy were used for characterizing the chemical and structural properties of the films, including the content of sp² and sp³ hybridized carbon atoms.     

The influence of cure conditions on the morphology and phase distribution in a rubber-modified epoxy resin using scanning electron microscopy and atomic force microscopy

In this paper, we consider the effect of cure conditions on the morphology and distribution of the rubber in a phase separated rubber-modified epoxy resin, which in effect is a two phase composite. Novel aspects of this study were measuring the elastic modulus of the dispersed rubber phase particles by atomic force microscopy (AFM) and verifying the presence of nano-dispersed rubber.The purpose of introducing dispersed rubber particles into the primary phase in these systems is to enhance their toughness. It is known that both the rubber particle size and volume fraction affect the degree to which the epoxy is toughened. It is not known, however, how the specific mechanical properties of the rubber phase itself affect the toughness.The objectives of this study were to: (1) use scanning electron microscopy (SEM) and atomic force microscopy (AFM) to determine the morphology and phase distribution of the rubber particles and (2) to measure the mechanical properties of the rubber particles using AFM. Ultimately, we would like to develop a clear understanding of how the changes in morphology and mechanical properties measured at the micro and nano-scales affect both the elastic modulus and fracture toughness of rubber-modified epoxy polymers.The epoxy system consisted of a diglycidyl ether of bisphenol-A, Epon 828, cured with piperidine and incorporating a liquid carboxyl-terminated acrlonitrile-butadiene rubber (CTBN). The carboxyl groups of the rubber are capable of reacting with the epoxy. The cure conditions considered were based on a statistically designed full factorial curing matrix, with the variables selected being cure temperature, initiator (piperidine) concentration, and rubber acrylonitrile concentration.Each of these primary variables was found to affect the phase distribution that resulted during cure. A statistical analysis of the effect of these variables on the phase morphology showed that the acrylonitrile content (%) of the rubber affected both the rubber particle size and volume fraction. The cure temperature strongly influenced the rubber particle volume fraction and modulus. Volume fractions of the rubber phase of up to 24% were obtained even though the amount of rubber added was only 12.5%. The rubber particle modulus varied from 6.20 to 7.16 MPa. Both the volume fraction and modulus of the rubber particles were found to influence the macroscopic mechanical properties of the composite. While larger volume fractions favor improved toughness, we note that that the toughness is greatest when the particle modulus values do not exceed ∼6.2 MPa. Thus, increased volume fraction by itself may not always result in increased toughness. The particles also must be sufficiently ‘soft’ in order to improve toughness. In the system of interest here, the processing conditions are a key factor in achieving the most appropriate material properties. By inference, this is likely to be the case as well in other rubber-modified thermosets.     

Comparative performance study of polyethersulfone and polysulfone membranes for trypsin isolation from goat pancreas using affinity ultrafiltration

The comparative performance of polysulfone and polyethersulfone membranes (of 30 kDa MWCO) in isolation of trypsin from goat pancreas by affinity ultrafiltration is examined using cross-linked soybean trypsin inhibitor (STI) as affinity ligand, 0.1 M Tris–HCl as wash buffer and 0.5 M KCl–HCl as elution buffer in an unstirred, dead-ended module at 392.28 kPa (4 kg/cm²) transmembrane pressure and room temperature (ca. 30 °C) with 1:1 (v/v) ratio of pancreatic extract and wash buffer. No active trypsin was found to be detectably present in the washing phase permeate in any of the experiments, indicating good binding efficiency of the target enzyme with the ligand employed. The total protein recovery obtained with the polyethersulfone membrane (70%) is 1.5 times higher than that with the polysulfone (46%). Yields of active trypsin for the two membranes are, however, similar (74% for polyethersulfone and 70% for polysulfone) although comparable with earlier reported trypsin yield (from porcine pancreas). In both the washing and elution phases of affinity ultrafiltration, the polyethersulfone membrane facilitates consistently and substantially higher volumetric flux as well as permeated protein throughput than the polysulfone.     

Effect of solvents on performance of polyethersulfone ultrafiltration membranes: Investigation of metal ion separations

The new polyethersulfone (PES) based ultrafiltration membranes were formed using a two stage process of dry and wet phase inversion in non solvent coagulation bath. The effects of three different solvents such as, N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP) and Dimethyl sulphoxide (DMSO) of 82.5% and 85% concentrations on the performance of final membranes were extensively investigated. Scanning electron microscopy (SEM) image results proved that PES membranes with an asymmetric structure were successfully formed. The number of pores formed on the top layer of PES membranes using above-mentioned three solvents was the result of the combined effect of the thermodynamic properties of the system (composition, concentrations, and phase behaviour) and membrane formation kinetics, whereas, the formation of the macroporous sub layer of those membranes was controlled by the diffusion rate of solvent–nonsolvent. The flux of pure water, membrane resistance, mechanical stability, molecular weight cut-off (MWCO) and separation performance of the PES membranes were studied. Separation of metal ions from aqueous solutions was studied for Ni(II), Cu(II) and Cr(III) using two complexing polymer ligands: polyvinyl alcohol (PVA) and poly(diallyldimethylammonium chloride) (PDDA).The separation and permeate rate (flux) efficiencies of the new membranes are compared using different solvents and different PES/solvent compositions.     

A local field emission study of partially aligned carbon-nanotubes by atomic force microscope probe

Atomic force microscopy (AFM) was used to study the field emission (FE) properties of a dense array of long and vertically quasi-aligned multi-walled carbon nanotubes grown by catalytic chemical vapor deposition on a silicon substrate. The use of nanometric probes enables local field emission measurements to be made allowing the investigation of effects that are not detectable with a conventional parallel plate setup, where the emission current is averaged over a large sample area. The micrometric inter-electrode distance allows one to achieve high electric fields with a modest voltage. These features made us able to characterize field emission for macroscopic electric fields up to 250 V/μm and attain current densities larger than 10⁵ A/cm². FE behaviour is analyzed in the framework of the Fowler–Nordheim theory. A field enhancement factor γ ≈ 40–50 and a turn-on field E_turn-on 15 V/μm at an inter-electrode distance of 1 μm are estimated. Current saturation observed at high voltages in the I-V characteristics is explained in terms of a series resistance of the order of MΩ. Additional effects, such as electrical conditioning, CNT degradation, response to laser irradiation and time stability are investigated and discussed.     

A study of the adhesion of polyethylene to porous alumina films using the scanning electron microscope

An adhesive bond was formed by sintering low-density polyethylene onto aluminum with a porous anodic film. The topography of the polymer surface in contact with the anodized aluminum was studied in a scanning electron microscope, having removed the aluminum and alumina by dissolution in aqueous sodium hydroxide. The surface of the polymer appeared very rough with large projections of various forms, all of which were many times larger than the pores revealed in the anodic films by transmission electron microscopy. These projections are shown to consist, most probably, of “stacks” or “tufts” of much smaller polyethylene fibers, each of which had entered a pore in the anodic film. Thus, the scanning electron-microscopic investigation confirms the keying mechanism for the adhesionof polyethylene to porous anodic films on aluminum proposed in an earlier paper.     

Effects of polyaniline nanoparticles in polyethersulfone ultrafiltration membranes: Fouling behaviours by different types of foulant

Polyethersulfone (PES) was modified by blending it with polyaniline (PANI) nanoparticles to improve the membrane performance. Three types of membranes: PES (controlled sample), PES-PANI self-synthesised, and PES-PANI (commercial), were evaluated by direct interaction with BSA, humic acid, silica nanoparticles, Escherichia coli and Bacillus bacteria. The surface hydrophilicity of the modified PES membranes was enhanced by the addition of PANI nanoparticles and showed improved fouling resistance and a high flux recovery ratio as well as improvement in BSA and humic acid rejection even with higher pore sizes. The modified membrane also showed less attack from the bacteria, demonstrating improved biofouling activity.     

Characterization of protein immobilization on nanoporous gold using atomic force microscopy and scanning electron microscopy

Nanoporous gold (NPG), made by dealloying low carat gold alloys, is a relatively new nanomaterial finding application in catalysis, sensing, and as a support for biomolecules. NPG has attracted considerable interest due to its open bicontinuous structure, high surface-to-volume ratio, tunable porosity, chemical stability and biocompatibility. NPG also has the attractive feature of being able to be modified by self-assembled monolayers. Here we use scanning electron microscopy (SEM) and atomic force microscopy (AFM) to characterize a highly efficient approach for protein immobilization on NPG using N-hydroxysuccinimide (NHS) ester functionalized self-assembled monolayers on NPG with pore sizes in the range of tens of nanometres. Comparison of coupling under static versus flow conditions suggests that BSA (Bovine Serum Albumin) and IgG (Immunoglobulin G) can only be immobilized onto the interior surfaces of free standing NPG monoliths with good coverage under flow conditions. AFM is used to examine protein coverage on both the exterior and interior of protein modified NPG. Access to the interior surface of NPG for AFM imaging is achieved using a special procedure for cleaving NPG. AFM is also used to examine BSA immobilized on rough gold surfaces as a comparative study. In principle, the general approach described should be applicable to many enzymes, proteins and protein complexes since both pore sizes and functional groups present on the NPG surfaces are controllable.     

The study of domain rearrangement under external electric fields by scanning electron acoustic microscope

Compared with other methods, scanning electron acoustic microscope (SEAM) is a convenient, fast and nondestructive technique revealing ferroelectric domain without any special pre-treatment to the sample. It is also a promising technique for the dynamic study of domain structure of ferroelectric materials. In the initial research, detailed images of rearrangement of domains in BaTiO₃ ceramics induced by an external electric field were obtained. The results are discussed.     

Microcharacterization of CVD diamond films by scanning electron microscopy: morphology, structure and microdefects

This paper contains a survey of recent papers on the scanning electron microscopy (SEM) of CVD diamond films. Two analytical possibilities of the SEM instrument are discussed: the morphological investigations (secondary electron emission mode) and the recognition of impurities and defects (cathodoluminescence mode). Examination of the diamond films by SEM demonstrates that the morphologies of these films are affected by synthesis conditions, especially the substrate temperature, the methane concentration and the total pressure in the reactor. Cathodoluminescence spectra and images are a useful tool for clarifying the relationship between emission centres and different types of defects generated during the process of growing diamond crystals. The aim of this paper is to show that investigations of the morphology, crystallinity and local cathodoluminescence emission of CVD diamond films by SEM led to correlative information about the quality of these films in comparison with natural diamond.