The estimation of a mechanically affected zone (MAZ) during AFM force measurements on polymers or composites requires a precise knowledge of the probe tip geometry. A new calibration method is ...proposed to determine the tip geometry from force measurements on reference materials. The test is then modelled by finite element method in order to validate the probe geometry and to determine the (MAZ) on these materials. The numerical simulation is used to show the influence of test parameters and sample elastic modulus on the impacted volume. The evolution of MAZ diameter and depth with Young's modulus and sample displacement can be correctly described by two analytical models. It is then possible to predict the lateral resolution or depth penetration associated to an AFM force measurement on a given polymer. The aim is to optimize test parameters to characterize mechanical interphases at nanometre scale in multiphase materials and to measure polymer surfaces modulus in thin layer systems.
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•New method to determine AFM probe tip wear from force measurements on known polymers•Good correlation between the numerical simulation of the test and experimental data•Determination of the volume of material impacted during a force measurement•Prediction of spatial resolution during an AFM force measurement on polymers•Method applicable to interphases characterisation in composites or thin layer systems
In this study, different primer formulations were used for enhancing the adhesion between a high consistency methyl phenyl vinyl silicone rubber (HCR) and AA6061 aluminum alloy. These formulations ...were selected on the basis of their different chemical composition. One contains only silanes and a titanate catalyst, a second contains only reactive macromolecular polysiloxane chains and a third contains both silanes and reactive macromolecular polysiloxane chains as the main components. The effect of the metal surface topography on the efficiency of the primers was investigated. The condensation reactions in the primers were followed by Fourier Transform Infrared Reflexion Absorption (FTIR-RA) spectroscopy and rheological measurements. 90° peel test was used to measure the adhesive strength of the silicone on metal and the fracture surfaces after peeling were analysed using SEM-EDS to determine the loci of failure. Cure monitoring of the silane based formulations showed that hydrolysis/condensation of silanes occur rapidly after their application on AA6061 surfaces and lead to a high degree of crosslinking even in the formulations with PDMS additives. The heat cure of the formulation based on a one-component addition curing system (SiH oligomer, vinylated-PDMS with a platinum catalyst) resulted in a film with a high cohesive strength. The primer formulation containing silanes and reactive PDMSs as the main components resulted in the best adhesion of the silicone elastomer with a dominant cohesive failure. However, a weaker adhesion was obtained at a high roughness of the substrate due to a weak adhesive strength at the metal/primer interface. A pretreatment composed of a first layer of activated silanes and a second layer of reactive silicone chains gave a good adhesion both at low and high roughness of the aluminum substrate.
Roughening of the metal surface did not improve the adhesion of silicone elastomers on the primed metals in any of the studied treatments, indicating that mechanical interlocking and increase in contact area do not contribute to adhesion. The results were discussed based on the different chemical composition and rheological properties of the primer formulations.
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•Significant stresses are generated in the steel cylinder due to the welding.•The coating stress level can be neglected during the welding.•The coating cutback protects the coating of ...the thermal load.•Critical interface of the assembly is the Steel/FBE.•Residual stress can explained the disbanding especially in humid environment.
The safety of pipeline networks is a priority, especially when these networks get older. The protection against corrosion is realized by coupling a passive coating with an active cathodic protection. It is well known that the presence of internal stresses in organic coatings is a current phenomenon which can result in the loss of adhesion. This phenomenon is critical for the durability of pipelines. The welding process and its consequences on the stress generated in the pipeline are investigated in this paper. Using a finite element approach, the welding process is simulated, and the thermal and mechanical evolutions are analyzed. From these results, the stress is essentially concentrated in the steel cylinder. Indeed, the cutback realized on the coating allow its protection during the welding.
The effects of humid tropical conditions and artificial ageing tests on a UD glass-fibre/epoxy composite are compared at different scales. A modified network of 500nm width around each fibre is ...identified by AFM force measurements. The evolution of this interphase is correlated to the composite embrittlement observed in transverse bending tests during ageing. DSC and DMA show up the matrix plasticization under tropical conditions and hygrothermal ageing. Chain scissions are also involved under artificial and natural UV exposure on surface layers and photoproducts are identified by FTIR analysis. The effects of artificial and natural hygrothermal conditions are emphasised inside interphases. The interfacial areas situated close to the composite surface are highly degraded by UV radiation. Cracks can then be initiated in these areas during bending tests. Finally, AFM force measurements highlight synergistic effects during natural weathering due to the combined effects of UV radiation and hygrothermal conditions.
► An interphase of several micrometers width present around each monofilament. ► Numerical model with barrier effect (contact fibres) and closed matrix areas. ► Matrix strongly modified by the ...presence of fibres. ► Matrix diffusion coefficient higher to fit the experimental data.
This study is a first approach of water diffusion in unidirectional (UD) composite, associating experimental measurements, analytical and numerical modelling. In the initial state, an interphase of several micrometers width around each monofilament is revealed from micro-thermal analysis measurements. This interphase is characterized by a higher molecular mobility than the bulk resin, which is a determining parameter for water diffusion. Water absorption measurements on both the resin and the UD composite show a Fickian kinetic in first approximation. A finite element analysis of water diffusion in the composite clearly shows the influence of the interphase properties on water diffusion kinetic.
► Viscoelastic model allows obtaining realistic behaviours and stress values. ► Stresses are concentrated near the interfaces. ► Stresses are in agreement with experimental observations. ► ...Epoxy/steel interface presents several MPa on the whole length of the pipe. ► Stresses are similar whatever the coating thicknesses are.
Internal stresses in organic coatings can generate loss of adhesion. This phenomenon must then take into account in order to achieve long-term protection. For corrosion protection of steel pipelines, the external coatings are usually three layered. They are composed of an epoxy primer, an adhesive and a thick layer of polyethylene. The presence of internal stresses has been suggested to explain the appearance of some spontaneous disbondments of these coatings after only few years in-service.
This finite element study aims to calculate the internal stress generated during the application process for different thicknesses of coating and to compare these with measured values of adhesion. This comparison should allow concluding if this phenomenon is responsible for the loss of adhesion observed. Whatever the thickness of the coating, internal stresses at the interfaces have similar values. However, there in an edge effect at the end of the pipeline that affects values of these stresses.
•Significant stresses are generated in the coating due to the process.•The stress level is more significant after the air cooling stage.•Relaxation behavior of the coating allows to reduce around 75% ...of stress.•Critical interface of the assembly is the Steel/FBE.•Residual stress can explained the disbanding especially in humid environment.
Three-layer coatings are highly used to achieve long-term protection against corrosion. The coating is composed by a thick polyolefin topcoat, a modified polyolefin adhesive and a fusion bonded epoxy. Many observations suggest that significant internal stresses are present in the coating. Moreover, internal stresses in organic coatings can generate loss of adhesion and decrease the lifetime of the assembly. The aim of the study is to simulate relaxation phenomena during storage phase and to quantify residual stresses, in order to appreciate if they are critical for adhesion and sustainability of the assembly. During this stage, polyethylene or epoxy are able to relax all or a part of internal stresses as it necessarily occurs with any polymer.
Macrophagic myofasciitis (MMF) is an emerging condition of unknown cause, detected in patients with diffuse arthromyalgias and fatigue, and characterized by muscle infiltration by granular periodic ...acid–Schiff's reagent-positive macrophages and lymphocytes. Intracytoplasmic inclusions have been observed in macrophages of some patients. To assess their significance, electron microscopy was performed in 40 consecutive cases and chemical analysis was done by microanalysis and atomic absorption spectrometry. Inclusions were constantly detected and corresponded to aluminium hydroxide, an immunostimulatory compound frequently used as a vaccine adjuvant. A lymphocytic component was constantly observed in MMF lesions. Serological tests were compatible with exposure to aluminium hydroxide-containing vaccines. History analysis revealed that 50 out of 50 patients had received vaccines against hepatitis B virus (86%), hepatitis A virus (19%) or tetanus toxoid (58%), 3–96 months (median 36 months) before biopsy. Diffuse myalgias were more frequent in patients with than without an MMF lesion at deltoid muscle biopsy (P < 0.0001). Myalgia onset was subsequent to the vaccination (median 11 months) in 94% of patients. MMF lesion was experimentally reproduced in rats. We conclude that the MMF lesion is secondary to intramuscular injection of aluminium hydroxide-containing vaccines, shows both long-term persistence of aluminium hydroxide and an ongoing local immune reaction, and is detected in patients with systemic symptoms which appeared subsequently to vaccination.
To assess dynamics of HIV-1 DNA in highly antiretroviral (ARV)-experienced HIV-infected patients successfully treated with raltegravir (RAL)-containing therapy. Nineteen patients with virological ...failure whose ARV treatment was switched to a RAL-based salvage regimen with virological success were included (Group I). Ten patients in virological failure and responding to ARV salvage therapy not containing RAL were also included (Group II). The HIV-1 DNA level in peripheral blood mononuclear cells (PBMC) was assessed by real-time PCR at baseline, W12, W24, W36 or W48. In group I, a marked decrease in the HIV-1 DNA level was observed at W12 both in PBMC (median decrease = 0.38 log
10
copies/10
6
PBMC;
P
< 0.001) and in CD4 T cells (0.85 log
10
copies/10
6
CD4 T cells;
P
< 0.001). Plasma HIV-1 RNA decrease was correlated with HIV-1 DNA decrease expressed as copies/10
6
CD4 T cells (
r
= 0.55,
P
= 0.03). HIV-1 DNA level reached a steady state by W24. Thus, RAL-containing treatment in highly ARV-experienced patients was associated with a rapid HIV-1 DNA decrease, mainly in the circulating CD4 T cells compartment. Group II patients showed an early decrease in the HIV-1 DNA load until W12, which was 2.5-fold less pronounced in the CD4 T cells compartment than in the RAL-treated patients. The potent action of RAL-containing treatment observed in the CD4 T cells compartment may suggest a pronounced reduced inhibition in the pool of regenerating CD4 T cells on a RAL-based therapy.
Kaolin–polymer hydrogel composites were synthesized via redox-initiated polymerization of acrylic acid (AA) in a concentrated aqueous dispersion of kaolin, using N,N′-methylene bisacrylamide as a ...crosslinker. The mechanical and thermal properties of the composites were investigated by systematic variation of the monomer feed composition. From rheological measurements, it was found that kaolin had a negative effect on the polymerization rate, which decreased the stiffness of the green bodies prepared at room temperature with increasing kaolin content. The gelation time was varied by changing the concentration of the redox initiator. On drying at 105°C, the crosslinking continued to a higher degree. Larger kaolin contents yielded to stiffer composites, as determined from uniaxial compression measurements. The compressive strength increases with the AA concentration, up to AA concentrations>25 mass% (relative to kaolin). The equilibrium swelling ratio of the fully-cured kaolin/poly(acrylic acid) composites in water increased as expected with increasing AA content. These particular composite systems formed porous kaolin ceramics with porosity >60% after burning off the organic materials.
► High strength machinable kaolin/polymer composites were prepared by a waterborne process ► kaolin particles inhibited the polymer gel formation ► gelation times could be easily modulated ► The acrylic acid served as a network component and as a sacrificial porogen ► Kaolin ceramics with porosity >60% were obtained after burning out the organic materials
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