Atomic force microscope study of the rejection of colloids by membrane pores

An atomic force microscope (AFM) in conjunction with the colloid probe technique has been used to study the electrical double layer interactions between a 0.75 μm silica sphere and a polymeric microfiltration track etch Cyclopore membrane (nominally 1 μm) in aqueous solutions. The silica colloid probe was used to image the membrane surface (using the double layer mode) at different imaging forces in high purity water and at constant imaging force in sodium chloride solutions of different ionic strengths at pH 8. Force-distance measurements show clearly how the sphere detects the membrane surface. Quality of images produced from scanning the 0.75 μm silica particle across the surface deteriorates with increasing distance between the silica sphere and membrane surface. Such images were compared with those obtained from scanning a sharp silicon nitride tip over the membrane surface.     

A comprehensive review of nanofiltration membranes:Treatment, pretreatment, modelling, and atomic force microscopy

Nanofiltration membranes (NF) have applications in several areas. One of the main applications has been in watertreatment for drinking water production as well as wastewater treatment. NF can either be used to treat all kinds of water including ground, surface, and wastewater or used as a pretreatment for desalination. The introduction of NF as a pretreatment is considered a breakthrough for the desalination process. NF membranes have been shown to be able to remove turbidity, microorganisms and hardness, as well as a fraction of the dissolved salts. This results in a significantly lower operating pressure and thus provides a much more energy-efficient process. Similar to other membrane processes, a major problem in NF membrane applications is fouling. Several studies have investigated the mechanisms of fouling in NF membranes and suggested methods to minimize and control the fouling of NF membranes. For NF membrane characterizations and process prediction, modeling of NF processes and the use of atomic force microscopy (AFM) are very important. The ability to predict the performance of NF processes will lead to a lower number of experiments, saving of time and money, and help to understand the separation mechanisms during NF. A comprehensive review of NF in water treatments is presented including a review of the applications of NF in treating water as well as in the pretreatment process for desalination; the mechanism as well as minimization of NF membrane fouling problems; and theories for modelling and transport of salt, charged and noncharged organic compounds in NF membranes. The review will also address the application of AFM in studying the morphology of membrane surfaces as part of the NF membrane characterization.     

An atomic force microscopy study of ozone etching of a polystyrene/polyisoprene block copolymer

The ozone etching of a commercial poly(styrene)/poly(isoprene) (PS/PI) block copolymer (Kraton D1117) was studied by atomic force microscopy. The copolymer contains 17% PS and forms a cylindrical phase in the melt. The copolymer dewetted when spin coated onto a silicon wafer but the film was stable on a grown silicon oxide layer. The structure of the stripe pattern formed was examined on substrates with different oxide layer thicknesses (surface energies). Finally etching by ozone was investigated. For low ozone doses, no degradation of polymer was observable. Extended ozone treatment resulted in more obvious degradation, but the etching was non-selective.     

Investigation of oxidation profile in PMR-15 polyimide using atomic force microscope (AFM)

Nanoindentation measurements are made on thermosetting materials using cantilever deflection vs. piezoelectric scanner position behavior determined by atomic force microscope (AFM). The spring model is used to determine mechanical properties of materials. The generalized Sneddon's equation is utilized to calculate Young's moduli for thermosetting materials at ambient conditions. Our investigations show that the force-penetration depth curves during unloading in these materials can be described accurately by a power law relationship. The results show that the accuracy of the measurements can be controlled within 7%. The above method is used to study oxidation profiles in PMR-15 polyimide. The thermo-mechanical profiles of PMR-15 indicate that the elastic modulus at the surface portion of the specimen is different from that at the interior of the material. It is also shown that there are two zones within the oxidized portion of the samples. Results confirm that the surface layer and the core material have substantially different properties.     

Growth process of homogeneously and heterogeneously nucleated spherulites as observed by atomic force microscopy

A poly(bisphenol A octane ether) (BA-C8) was synthesized. The isothermal spherulitic growth process was studied in situ using atomic force microscopy (AFM) at room temperature. For spherulites formed by homogeneous nucleation, the growth process includes the birth of a primary nucleus, the development of a founding lamella and the growth of the founding lamella into a spherulite. An embryo below a critical size is unstable. A stable embryo grows into a founding lamella. There is only one founding lamella in each spherulite. All other lamellae originate from this founding lamella. Two eyes can be seen at the center of a spherulite. For spherulites formed through heterogeneous nucleation, many lamellae grow at the nucleus surface and propagate outward radially. The spherulites acquire spherical symmetry at the early stage of crystallization. No eyes are found for this kind of spherulites.     

An experimental study on adhesion between steel and cement pastes using particle probe scanning force microscopy

This paper presents a method of using particle probe scanning force microscopy to measure the adhesion between steel microspheres and cement pastes. Particle probes were fabricated by attaching steel microspheres to the free ends of microcantilevers. Adhesive forces were collected between steel microspheres and new (4-week old) and old (6-month old) cement substrates in air and saturated lime water. For new cement in saturated lime water, adhesive forces between steel and low density C-S-H, high density C-S-H and other hydrated products were intermediate among all groups selected. The adhesive forces between steel and calcium hydroxide were the smallest, whereas the adhesive forces between steel and the unreacted phases were the largest. For the 6-month old cement, the interweaving of calcium carbonate crystals and C-S-H during carbonation generated greater adhesive forces to steel.     

Determination of the influence of the polymer structure and particle size on the film formation process of polymers by atomic force microscopy

The particle size and morphology of a synthetic polymer latex were shown to influence the film formation behavior. Theoretical models predict that small particles coalesce more easily than large colloids do.The influence of particle size and morphology of differently structured lattices on the film-formation process was investigated by atomic force microscopy (AFM). Sequences of AFM images were acquired over a certain temperature range or at room temperature as a function of time. From the resulting images the average particle diameter of the latex particles in the surface layer was determined as a function of the time or temperature. The resulting curves could be compared to observe differences in the film formation kinetics of the different lattices. These AFM studies confirmed that the film formation behavior is influenced by the particle size and particle morphology, but that the core/shell ratio of core-shell particles has no significant influence on the film formation kinetics.     

Microstructural analysis of carbon black filled rubbers by atomic force microscopy and computer simulation techniques

Abstract

The present work concerns three-dimensional modelling of a filler network microstructure in rubber compounds. The model represents the carbon black filler in three states: primary fractal aggregates consisting of spherical over-lapped particles; secondary structures or agglomerates; and partially broken fragments of micropellets. The information about the structure hierarchy of the filler and its distribution in the matrix was obtained from the analysis of atomic force microscopy images of the material surface.     

The interactions of amphiphilic latexes with surfaces: the effect of surface modifications and ionic strength

The effect of surface modifications brought about by a polymeric stabilizer on the interactions between polymer colloid particles and various substrates in aqueous media are directly measured using atomic force microscopy. The interactions of polystyrene particles with grafted hydrophilic ‘hairs’ of hydroxypropyl cellulose (denoted HPC/PS), of molecular weight ∼10⁵, with mica, silica and graphite substrates are measured. HPC/PS is found to be compatibilized so that it will interact with both hydrophobic and hydrophilic substrates. The observed jump-to contact between HPC/PS and silica is characteristic of polymer solutions and is the result of the grafted hairy layer. Further direct evidence of HPC-substrate interaction is seen in a secondary adhesion with mica. The adhesion of the particles was found to follow the order silica>graphite>mica. The magnitudes of these interactions are rationalized in terms of the interactions of each of the substrate, core polymer and surface modification. It is concluded that the combined effects of surface roughness and hairy layer collapse due to compression give rise to the observed trend.     

Structure of polymer within the coating: an atomic force microscopy and small angle neutrons scattering study

Synthetic latex is widely used as a binder in waterbased paints. Upon dehydration of the dispersion, latex particles are brought into contact with mineral pigments: this process results in coating structuration and consolidation. This composite layer is described as a porous mineral structure, whose pores are covered by latex particles. Therefore, it is of fundamental interest to study the ordering of binder particles in the coating, and the wetting of pigments by polymer particles, toward understanding properties of coating such as: optical properties, adhesion, cohesion, sensitivity to water, etc. In this regard, we have used small angle neutron scattering and atomic force microscopy to study the ordering, the spreading, and the adhesion of latex particles on calcium carbonate within the coating. We discuss the structure of the coating.     

The use of atomic force microscopy to measure the formation and development of chocolate bloom in pralines

Atomic force microscopy (AFM) has been used to study the surface of chocolate as well as the progress of chocolate bloom over time. Fresh chocolate was found to be relatively smooth but with deep holes. These could be pipes leading deep down into the body of the chocolate, perhaps reaching the filling. After storage for a few weeks, we observed the growth of small drops around these holes. With increasing time, these drops became larger and more structured. After further storage, a crystalline structure and bloom were revealed. These results suggest that bloom growth in pralines is a two-phase process, with drops initially forming on the surface and then bloom crystals nucleating and growing from them. Further, we deduced pipes leading down into the center of the chocolate through which the migration of filling fats can preferentially occur.     

Metallo-functionalized first-generation salicylaldimine poly(propylenimine) tetraamine dendrimers: Electrochemical study and atomic force microscopy imaging

The adsorption and the redox processes of two first-generation salicylaldiamine dendritic ligands and their copper, cobalt and nickel metallo-functionalized complexes have been studied at two types of carbon electrode surface. Glassy carbon (GC) was used in an electrochemistry study and highly oriented pyrolitic graphite (HOPG) in ex situ atomic force microscopy (AFM) imaging. All salicylaldimine ligands and their metallo-functionalized complexes adsorb on the surface of the HOPG electrode, resulting in the formation of nanoclusters and films, which vary between 0.9 and 6 nm in size, depending on the metallo-functionalized salicylaldimine dendrimer chemical composition and solution concentration. Differential pulse voltammetry of the surface-confined films has shown that the anodic reactions observed correspond to the oxidation of the hydroxyl groups present in the ligand structure of all compounds. However, by following the changes in peak currents, potentials and width at half height it has been shown that destabilization of the ligand internal structure occurred in the metallo-functionalized complexes depending on the metal involved. The electrochemical behaviour of the surface-confined films observed in buffer solution was related to the morphology, obtained by AFM, of the immobilised first-generation salicylaldiamine dendritic ligands and corresponding salicylaldimine metallo-functionalized complexes.     

Nanoscale patterning in crosslinked methacrylate copolymer networks: An atomic force microscopy study

To understand the properties of materials, their phase structure must be established. It has been difficult in previous work to visualize the heterogeneous crosslinked structure of methacrylate‐based networks. In this work, nano‐sized phases with worm‐like features were detected in the surfaces of model crosslinked methacrylate copolymer containing hydrophobic/hydrophilic co‐monomers using tapping mode atomic force microscopy/phase imaging technique. The effects of different surface‐contact covers on the height and phase‐contrast images of model resin surfaces were also studied. Based on the experimental data, the identification of phase domains was proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

An atomic force microscopy study of the effect of surface roughness on the fracture energy of adhesively bonded aluminium

The effect of roughening an initially polished aluminium surface using the Forest Products Laboratory chemical etch on the adhesive joint strength has been determined. It was found that while the lap shear strength increased rapidly with etching for short times, the fracture energy did not increase significantly until etching had occurred for at least 15 min. An atomic force microscope (AFM) was used to study the surface/interface morphology and to quantify the surface roughness. The AFM images showed that etching occurs heterogeneously across the aluminium surface and a correlation was found between the fracture energy and the fraction of etched surface. A model based on Griffith's fracture energy approach has been proposed to explain this observation. The lap shear strength was found to be more sensitive to a finer scale roughness which is generated at shorter etching times. Other observations regarding the mode of fracture and the variability in joint strength as a function of the surface roughness are explained on the basis of varying stress concentrations at the crack tip.     

Plastic deformation of spherulitic semi-crystalline polymers: An in situ AFM study of polybutene under tensile drawing

The plastic deformation of semi-crystalline polybutene (PB) has been studied at the micrometric and nanometric scales by Atomic Force Microscopy (AFM). Owing to a movable tensile drawing stage, capturing images from the same locus of the sample allowed for quasi in situ observations of the plastic processes. In the case of PB films having an average spherulite diameter of about 20 μm, the macroscopic deformation was homogeneous over the whole gauge length of the sample, up to rupture. In parallel, the local deformation at the scale of the spherulites was very close to homogeneous and obeyed an affine deformation law over the whole strain range: the shape of the deformed spherulites was kept roughly elliptical up to rupture without clues of fibrillar transformation. The inter-spherulitic boundaries displayed very high cohesion. Fragmentation of the crystalline lamellae proved to be a predominant process, while crystal slip could not be detected at the scale of the AFM resolution, i.e. a few nanometers. Wide-angle and small-angle X-ray scattering yet revealed the occurrence of crystal plastic shear. Similar observations have been made in the case of PB films having an average spherulite diameter of about 5 μm. In the conclusion, a comparison is made with a previous study regarding the deformation mechanisms of a PB sample having 200 μm wide spherulites which displayed brittle behavior.     

EUROCAT oxide: an European V2O5–WO3/TiO2 SCR standard catalyst study: Characterisation by electron microscopies (SEM, HRTEM, EDX) and by atomic force microscopy

The morphology and the homogeneity in chemical compositions of fresh and used V₂O₅–WO₃/TiO₂ EUROCAT SCR samples, in their original monolith form and after gentle grinding, have been investigated by means of electron microscopies and EDX analyses. It appears clearly that the monoliths were constituted of fibres rich in Si, Al and Ca embedded without preferential orientation in a nearly homogeneous oxide phase containing Ti, V, and W. This phase was in the form of small particles of homogeneous size of around 20–40 nm. The used catalyst was very similar to the fresh one, only the presence of S element and of more defects and more fibres were observed on the surface of the monolith. This observation was confirmed by a higher roughness detected using AFM technique.

EDX–TEM studies on the powders obtained by gently grinding the monoliths have shown that W and V species were well distributed in TiO₂ support and that the repartition of the W species, very homogeneous in the fresh sample, became somewhat slightly more heterogeneous in the used sample. V species were not so well dispersed that W species and even, some particles rich in V were observed on the used sample. This may be due to the migration and agglomeration of some of the V species. More particles, very rich in Si, were also observed for the used sample suggesting that the coating of the fibres by the active phase was partly deteriorated during SCR reaction. This observation was supported by an AFM analysis which showed a higher surface roughness for the used sample.

It was also observed by high resolution TEM that the first one or two atomic layers at the surface of all crystallites appear amorphous, while the further layers are well crystallised with the anatase structure. For the used sample this amorphous layer is slighly larger. This is an important feature for electrical conductivity (mainly at the surface) and catalytic properties.     

A study on the adhesion of calcium carbonate to glass. Energy balance in the deposition process

This work describes an experimental investigation on the adhesion of in situ synthesized calcite colloidal particles to rotating glass slides. The relative importance of the hydrodynamic processes involved was analyzed by measuring the amount adhered as a function of both the temperature and the rotation velocity. The adhesion was found to be temperature-dependent. At a given rotation speed of the slide, there exists a value of the temperature for which the adhesion is maximum. This value is lower, the higher the rotation speed. Comparison between experimentally determined particle fluxes (number of particles adhered per unit time and unit surface area of collector) and those calculated from Levich's theory (where laminar flow and absence of particle-collector repulsion are assumed) suggests that the hydrodynamic regime in the vicinity of the slide changes from laminar to turbulent when either the velocity or the temperature is increased above a certain critical value, corresponding to maximum adhesion. The effect of the electrolytes CaCl₂ and MgCl₂ on the adhesion was also studied in the range of concentrations between 0.7 and 70 mM. For fixed hydrodynamic conditions and temperature, the adhesion between the particle and the collector was found to be controlled by the interfacial interactions, including Lifshitz-van der Waals (LW), electrostatic double layer (EL), and acid-base (AB). The calcite-solution and glass-solution interfaces were completely characterized by using electrophoresis, contact angle, and thin-layer wicking techniques, together with van Oss et al.'s model of interfacial thermodynamics. From these data, the total energy of interaction between the particle and the substrate was computed using either the classical DLVO model (EL + LW) or the extended theory (EL + LW + AB) for different electrolyte concentrations, and reasonably good agreement was found between the experimentally observed particle attachment and the predictions of the extended DLVO theory.     

Application of atomic force microscopy and scaling analysis of images to predict the effect of current density, temperature and leveling agent on the morphology of electrolytically produced copper

Atomic force microscopy (AFM) was used to study the morphology of electrodeposited Cu at current densities from 183 to 253 A m⁻². Digital image analysis was employed to parameterize the morphological information encoded in AFM images and to extract information concerning the mechanism of the electrodeposition reaction. It has been shown how the limiting roughness, δ, the critical scaling length, L_c and the aspect ratio, 4δ/L_c, vary as a function of the deposition time and electrodeposition conditions, such as temperature, current density and the amount of organic additives. It has been demonstrated how laboratory experiments of short duration and the scaling analysis of AFM images can be used to predict roughness of the metal sample after 2 weeks of industrial electrorefining.     

An investigation of atomic force microscopy,surface topography and adhesion of luting cements to zirconia: effect of silica coating,zirconia primer and laser

This study evaluated the effect various surface conditioning methods on the surface topography and adhesion of luting cements to zirconia. Zirconia blocks (N?=?25) were randomly assigned to five groups according to the surface conditioning methods: (a) No conditioning, control (CON), (b) tribochemical silica coating (TSC), (c) MDP-based zirconia primer (ZRP), (d) coating with nano aluminum nitride (ALN) (e) etching with Er: YAG laser (LAS). The conditioned zirconia blocks were further divided into five subgroups to receive the luting cements: (a) MDP-based resin cement (Panavia F2.0) (PAN), (b) 4-META-based cement (Super Bond) (SUB), (c) UDMA-based (GCem) (GCE), (d) bis-GMA based (Bifix QM) (BIF) and (e) polycarboxylate cement (Poly-F) (POL). Cements were applied in polyethylene moulds (diameter: 3?mm; height: 2?mm). The bonded specimens were first thermocycled for 5500 cycles (5–55?°C) and then adhesive interface was loaded under shear (0.5?mm/min). The data (MPa) were analyzed using 2-way ANOVA, Tukey’s and Bonneferroni tests (alpha?=?0.05). Regardless of the cement type, TSC resulted in significantly higher bond strength (p???0.05) (13.3?±?4.35–25.3?±?6.3) compared to other conditioning methods (2.96?±?1.5–5.4?±?5.47). Regardless of the surface conditioning method, no significant difference was found between MDP, 4-META and UDMA based cements (p?>?0.05) being significantly higher than those of bis-GMA and polycarboxylate cements (p???0.05). Failure types were frequently adhesive in all groups. Tribochemical silica coating provided superior bond results compared to other conditioning methods tested on zirconia especially in conjunction with UDMA- and 4-META-based resin cements.