Atomic force microscopy and scanning electron microscopy characterization of the controlling of surface morphology of epoxy-amine-cured spin-coated films

Atomic force microscopy (AFM) was successfully used to study spin-coated, amine-cured epoxy film microstructure and morphology. The air-epoxy and epoxy-substrate interfaces were examined using tapping-mode height and phase imaging AFM. The impact of relative humidity on the morphology and microstructure of the surfaces was determined. AFM was able to elucidate the changes on the surface as relative humidity during processing increased. It was observed that large nodular formations formed on the epoxy surface expose to the air but not epoxy surface formed on the substrate in addition to varying regions of more or less compliant structures, which was attributed to carbamate formation caused by the amine curing agent reaction with atmospheric CO₂. Scanning electron microscopy (SEM) was used to further elucidate interface and interphase morphology of spin-coated epoxies. Experimentation also demonstrated that post-curing above the glass transition did not change the morphology structure, suggesting surface structures are “locked-in.” SEM was used to further elucidate how the interface and interphase change with changing environmental conditions at both the air-epoxy and epoxy-substrate interface/interphases, including the impact of atmospheric CO₂ on Marangoni cell formation.     

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.     

Surface morphology of styrene-butadiene rubber vulcanizate filled with novel electron beam modified dual phase filler by atomic force microscopy

Topographic and phase imaging in tapping mode atomic force microscopy (TMAFM) has been performed to investigate the effect of unmodified and modified dual phase fillers on the morphology of and the microdispersion of the filler particles in the rubber matrix. The above fillers were modified using acrylate monomer (trimethylol propane triacrylate, TMPTA) or a silane coupling agent (triethoxysilylpropyltetrasulphide, Si-69) followed by electron beam modification at room temperature. Both unmodified and surface treated fillers were incorporated in a styrene-butadiene rubber. The phase images of the above composites show three levels of contrasts that correspond to matrix, filler aggregates, and bound rubber around the filler aggregates. Also, the images further elucidate the aggregated nature of the filler due to modification, which is more pronounced in the case of electron beam modified acrylated filler loaded rubber. The corresponding topographic images have been characterized by various statistical quantities like roughness parameters and one- and two-dimensional power spectral densities (1D-PSD and 2D-PSD). As compared to the control, significant increase in surface roughness is observed in the case of the modified dual phase filler loaded composites. The higher fractal value of these vulcanizates confirms the above fact. AFM study also suggests that the electron beam modification of the above fillers significantly increases the filler-filler and filler-polymer interactions.     

Morphology,nanomechanical and thermodynamic surface characteristics of nylon 6/feather keratin blend films: an atomic force microscopy investigation

The surface structure and nanomechanical properties of solution‐cast nylon 6 (NY6)/feather keratin (FK) blend films were investigated using a combination of tapping‐mode atomic force microscopy (AFM) phase imaging and nanoscale indentation. A tendency for a nanoscale phase separation between NY6 and FK in their various blends was judged based on the blend phase images. The surface topography and roughness analysis of the AFM height images revealed that FK‐rich blends had coarser surfaces than NY6‐rich ones, possibly due to the heterogeneous nature of the FK chemical structure. Amplitude–phase–distance measurements involving the assignment of the darker and brighter regions of the phase images to NY6‐rich and FK‐rich, respectively, or vice versa led to the recognition of a phase inversion in the blend containing 40 wt% FK. The occurrence of the phase inversion phenomenon was related to the significant difference between the molecular weights of the blend constituents. Analysis of nanoindentation data showed that blending FK and NY6 at various ratios resulted in mixtures with modified mechanical and adhesion features. On the one hand, the NY6 component was responsible for an enhanced elastic modulus and stiffness of the blends, and on the other hand, the FK component provided higher pull‐off force and work of adhesion for the samples. A new approach is also proposed to directly determine the surface energy (γ) values of samples from the nanoindentation data. The excellent consistency between the calculated γ values and the results obtained from contact angle measurements lends credence to the proposed approach. Copyright © 2012 Society of Chemical Industry     

Matching the nano- to the meso-scale: Measuring deposit–surface interactions with atomic force microscopy and micromanipulation

Many researchers have studied the effects of changing the surface on fouling and cleaning. In biofouling the ‘Baier curve’ is a well-known result which relates adhesion to surface energy, and papers on the effect of changing surface energy to food fouling can be found more than 40 years ago. Recently the use of modified surfaces, at least at a research level, has been widespread. Here two different ways of studying surface–deposit interactions have been compared. Atomic force microscopy (AFM) is a method for probing interactions at a molecular level, and can measure (for example) the interaction between substrate and surfaces at a nm-scale. At a μm–mm level, we have developed a micromanipulation tool that can measure the force required to remove the deposit; the measure incorporates both surface and bulk deformation effects. The two methods have been compared by studying a range of model soils: toothpaste, as an example of a soil that can be removed by fluid flow alone, and confectionery soils. Removal has been studied from glass, stainless steel and fluorinated surfaces as examples of the sort of surfaces that can be found in practice. AFM measurements were made by using functionalized tips in force mode. The two types of probe give similar results, although the rheology of the soil affects the measurement from the micromanipulation probe under some circumstances. The data suggests that either method could be used to test candidate surfaces.     

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.     

Measuring interdiffusion at an interface between two elastomers with tapping-mode and contact-resonance atomic force microscopy imaging

Despite the common use of tapping-mode atomic force microscopy to image composites or polymer blends, very few studies have focused on the measurement of the interdiffusion at an interface between two polymers in contact. In this study, we show how to assess the interphase between two polymers with two methods. First, stable and robust tapping conditions are established, and the problem of the phase contrast is discussed. Second, a contact-resonance method is presented: the tip in contact with the sample is electrostatically excited at its resonance frequency by a self-controlled oscillator. The gain and frequency images allow us to measure the interdiffusion width. Both methods (using high and weak mechanical solicitation) give the same assessment of the interdiffusion width. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Intensive electric arc interaction with polymer surfaces: reorganization of surface morphology and microstructure

Intense electrical arcs were applied to thermoplastic (polyamide 66) and thermoset (fiber reinforced laminated polyester) materials and the resulting carbonization/metallization process was studied on a sub-micron scale with atomic force microscopy to understand very initial stage of reorganization of surface morphology. These changes can be critical in dramatic changes in surface resistivity preceding electric breakthrough. The surface microroughness and the localization of micro- and nanoparticles at the center (arc initiation area) and along the edges of the samples were significantly different for different arc regimes. We suggested that for thermoset, the material is pulled out of the surface in the arc formation area (the center of sample). Afterwards, the intensive re-deposition occurred along the edges enhancing non-uniform ablation around the arc initiation area. In contrary, for thermoplastic samples, the entire polymer surface was re-melted that resulted in dramatic smoothing of the initially non-uniform surface morphology.     

Reactivity at the film/solution interface of ex situ prepared bismuth film electrodes: A scanning electrochemical microscopy (SECM) and atomic force microscopy (AFM) investigation

Bismuth film electrodes (BiFEs) prepared ex situ with and without complexing bromide ions in the modification solution were investigated using scanning electrochemical microscopy (SECM) and atomic force microscopy (AFM). A feedback mode of the SECM was employed to examine the conductivity and reactivity of a series of thin bismuth films deposited onto disk glassy carbon substrate electrodes (GCEs) of 3 mm in diameter. A platinum micro-electrode (? = 25 μm) was used as the SECM tip, and current against tip/substrate distance was recorded in solutions containing either Ru(NH₃)₆³⁺ or Fe(CN)₆⁴⁻ species as redox mediators. With both redox mediators positive feedback approach curves were recorded, which indicated that the bismuth film deposition protocol associated with the addition of bromide ions in the modification solution did not compromise the conductivity of the bismuth film in comparison with that prepared without bromide. However, at the former Bi film a slight kinetic hindering was observed in recycling Ru(NH₃)₆³⁺, suggesting a different surface potential. On the other hand, the approach curves recorded by using Fe(CN)₆⁴⁻ showed that both types of the aforementioned bismuth films exhibited local reactivity with the oxidised form of the redox mediator, and that bismuth film obtained with bromide ions exhibited slightly lower reactivity. The use of SECM in the scanning operation mode allowed us to ascertain that the bismuth deposits were uniformly distributed across the whole surface of the glassy carbon substrate electrode. Comparative AFM measurements corroborated the above findings and additionally revealed a denser growth of smaller bismuth crystals over the surface of the substrate electrode in the presence of bromide ions, while the crystals were bigger but sparser in the absence of bromide ions in the modification solution.     

Mesoscale pore structure of a high-performance concrete by coupling focused ion beam/scanning electron microscopy and small angle X-ray scattering

This contribution couples (a) Small angle X-ray scattering (SAXS) experiments of a high-performance concrete (HPC) at the millimetric scale, and (b) Focused ion beam/scanning electron microscopy (FIB/SEM) of the cement paste of the HPC, with 10-20 nm voxel size. The aim is to improve the understanding of the 3D pore network of the HPC at the mesoscale (tens of nm), which is relevant for fluid transport. The mature HPC is an industrial concrete, based on pure Portland CEMI cement, and planned for use as structural elements for deep underground nuclear waste storage. Small angle X-ray scattering patterns are computed from the 3D pore images given by FIB/SEM (volumes of 61-118 μm³). They are positively correlated with SAXS measurements (volumes of 5 mm³). Aside from correlations with FIB/SEM data, experimental SAXS allows to investigate a wider range of effects on the pore structure. These are mainly the HPC drying state, the presence of aggregates (by analyzing data on cement paste alone), and the use of Poly Methyl MethAcrylate resin impregnation.     

Model catalysts fabricated by electron beam lithography: AFM and TPD surface studies and hydrogenation/dehydrogenation of cyclohexene + H2 on a Pt nanoparticle array supported by silica

Pt nanoparticle model catalysts with 28 ± 2 nm diameters and 100 ± 2 nm square periodicity have been fabricated with electron beam lithography on silica substrates. The reactivity of the Pt/SiO₂ arrays was compared to a Pt foil for cyclohexene + H₂ at 100°C. The overall reactivity of the Pt particle arrays was higher by a factor of two, the selectivity towards dehydrogenation was three times higher, and the rate of deactivation was about the same as for the Pt foil. Since the primary difference between the nanoparticle array and the Pt foil was the interface between the Pt and the SiO₂, the interfacial region was most likely responsible for the changes in reactivity on the arrays. Using AFM, SEM, and TPD, the arrays were characterized before and after being exposed to reaction conditions. AFM images of a sample cleaned by ion sputtering showed that the pattern of the Pt nanoparticle array was replicated in the silica during the sputtering process. This revised version was published online in June 2006 with corrections to the Cover Date.     

Stabilisation of lithiated graphite in an electrolyte based on ionic liquids: an electrochemical and scanning electron microscopy study

1-Ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide (EMI-TFSI) is shown to reversibly permit lithium intercalation into standard TIMREX^® SFG44 graphite when vinylene carbonate (VC) is used in small amounts as additive. The best performance was obtained when 5% of VC was added to a 1 M solution of LiPF₆ in EMI-TFSI. Intercalation of lithium in the SFG44 graphite host was demonstrated over 100 cycles without noticeable capacity fading. The reversible charge capacity was around 350 mA h g⁻¹ and an only small irreversible capacity loss per cycle could be observed. Li₄Ti₅O₁₂ was used as counter electrode material. Scanning electron microscopy indicates the reduction of the electrolyte without graphite exfoliation in the neat electrolyte and the formation of a passivation film in the case of a VC-containing electrolyte. Other additives that were tested comprise ethylene sulphite and acrylonitrile which show also a positive effect, but a smaller one than vinylene carbonate. LiCoO₂ positive electrodes were cycled in a 1 M solution of LiPF₆ in EMI-TFSI with good charge capacity retention over more than 300 cycles, when Li₄Ti₅O₁₂ was used as counter electrode. The formation of a passivation film is proven on the LiCoO₂-electrodes, when the electrolyte contained VC, but not in the neat ionic liquid. Finally, the stable cycling of a full cell configuration is proven in this electrolyte system. An ammonium-containing ionic liquid (methyltrioctylammonium-bis(trifluoromethylsulfonyl)-imide, MTO-TFSI) is shown to permit the cycling of both, graphite and lithium cobalt oxide when VC is used as additive in small amounts, but at slightly elevated temperatures.     

Structured polymer blends: 2. Processing of polypropylene/EDPM blends: controlled rheology and morphology fixation via electron beam irradiation

Electron beam irradiation has been used to improve the processability of polypropylene/ethylene-propylenediene monomer (PP/EPDM) blends (controlled rheology) in combination with fixation of morphology by inducing crosslinks in the dispersed EPDM phase. An optimum morphology for impact toughening has been obtained via extrusion-blending high molecular weight PP with EPDM. Upon irradiation before subsequent processing (injection moulding) this morphology is fixated, whereas the viscosity of the blend decreases as a result of chain scission of the PP matrix. Impact strength and elongation at break of these irradiated blends are better than those of blends of low molecular weight PP with EPDM, which possess comparable overall viscosity.     

Modeling the thermal decomposition and residual mass of a carbon fiber epoxy matrix composite with a phenomenological approach: Effect of the reaction scheme

The thermal decomposition of polymer matrix composites is a complex process involving hundreds of reactions and species, which are often modeled with simplified one-step schemes. These schemes can be improved by adding intermediate reactions of different nature (competitive, parallel, and consecutive). However, the optimal number and nature of intermediate reactions are rarely discussed. In this paper, several reaction schemes of increasing complexity have been developed to model the decomposition of a carbon/epoxy composite. The kinetic parameters describing each reaction have been extracted from thermogravimetric analysis (TGA) by means of isoconversional methods. The composite mass loss rate and residual mass have been modeled and compared to TGA and tube furnace data. This research shows that adding parallel or consecutive intermediate reactions improves the agreement against TGA data compared to a single-step model, but only competitive reactions can account for the variation of the residual mass observed in the tube furnace when the heating rate is varied.     

The C-S-H gel of Portland cement mortars: Part I. The interpretation of energy-dispersive X-ray microanalyses from scanning electron microscopy, with some observations on C-S-H, AFm and AFt phase compositions

Scanning electron microscopy (SEM) microanalyses of the calcium-silicate-hydrate (C-S-H) gel in Portland cement pastes rarely represent single phases. Essential experimental requirements are summarised and new procedures for interpreting the data are described. These include, notably, plots of Si/Ca against other atom ratios, 3D plots to allow three such ratios to be correlated and solution of linear simultaneous equations to test and quantify hypotheses regarding the phases contributing to individual microanalyses. Application of these methods to the C-S-H gel of a 1-day-old mortar identified a phase with Al/Ca=0.67 and S/Ca=0.33, which we consider to be a highly substituted ettringite of probable composition C₆A₂S?₂H₃₄ or {Ca₆[Al(OH)₆]₂·24H₂O}(SO₄)₂[Al(OH)₄]₂. If this is true for Portland cements in general, it might explain observed discrepancies between observed and calculated aluminate concentrations in the pore solution. The C-S-H gel of a similar mortar aged 600 days contained unsubstituted ettringite and an AFm phase with S/Ca=0.125.     

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.