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The four Mg-based bulk metallic glass forming alloys Mg59.5Cu22.9Ag6.6Gd11, Mg61Cu28Gd11, Mg54Cu28Ag7Y11, and Mg65Cu25Y10 are investigated to gain insight into their thermodynamic and kinetic properties. Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) in three point beam bending mode are used. The gathered data sets are used to evaluate the origin of the high glass forming ability of these systems, which is found in low thermodynamic driving forces for crystallization and sluggish kinetics. Furthermore, sub-Tg effects are observed via dynamic mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC) of as-cast samples. These are interpreted as related to the α-relaxation time spectrum instead of being caused by a Johari-Goldstein-type relaxation mechanism.

Post-cured epoxy layers (EP, approx. 100 nm and 1 µm) of three amine hydrogen – oxirane ratios are prepared in dried air on natively oxidised aluminium substrate. A less crosslinked interphase forms as the consequence of adhesive interactions. Even though the layers exhibit very good durability in moist-warm air for up to 100 d, two stages of chemical ageing are revealed. During a short initial stage, some water absorbs firmly in the EP networks. Residual oxirane rings and secondary amine groups are shown to hydrolyse, while network chains remain intact. Marking the 2nd stage, dedicated autoxidation reactions are proven to simultaneously attack tertiary amine crosslinks and α-CH2 groups at phenylene ether units. These reactions destroy network chains, and the release of network fragments was established. Moreover, network destruction proceeds more effectively in 100 nm layers as the surface erodes slightly, even under the given environmentally mild conditions. That observation proves a specifically reduced durability for the interphase at the contact with native aluminium oxide.

The paper introduces the technique of thread-by-thread tear mending in the conservation of canvas paintings and is dedicated to the investigation of difficulties in the reproducibility of bonding q...

The chemical structure, polymer mobility and mechanical properties are studied for a cross-linked amorphous poly(ether urethane) (PU) from glass transition to rubber elasticity for juvenile dry samples and for water-saturated states after exposure to humid air (r.h. = 29, 67, 95, 100%) at $$60~^\circ \hbox {C}$$ 60 ∘ C during 1 y of ageing. For saturated samples, network chain cleavage is the chemical ageing mechanism, but it is too weak and slow to affect on the physical properties significantly within 1 y. Water acts primarily in a physical manner. Within 1 d, $$\hbox {H}_{{2}}\hbox {O}$$ H 2 O molecules replace part of the weak urethane H-bonds by $$\hbox {H}_{{2}}\hbox {O}$$ H 2 O –urethane H-bonds and reduce all other physical interactions between network chains by solvating hydrophilic segments. Thus, the cooperative polymer mobility strongly amplifies: The gain of specific conformational entropy doubles across the caloric glass transition, which shifts by −17 K. A $$\hbox {H}_{{2}}\hbox {O}$$ H 2 O concentration of only $$\hbox {c}_{{\mathrm{H}_2\mathrm{O}}}~\approx ~(0.4~\ldots ~0.5)~\hbox {c}_{\mathrm{\mathrm{H}_2\mathrm{O},max}}$$ c H 2 O ≈ ( 0.4 … 0.5 ) c H 2 O , max suffices for the major part of these fast rearrangements. Some part of the water slowly forms (during 3–4 months) a finely dispersed water-rich mixed phase with the PU chains. Except the new phase, these molecular processes of physical ageing strongly affect the mechanical properties at damage-free deformation. For dry PU in the glass transition, the shear modulus, $$\mu _{\mathrm{relaxed}}$$ μ relaxed (T), after viscoelastic stress relaxation only depends on the deformation-induced entropy change—like in the rubber elastic state. Within one month, water drastically decreases the viscoelastic response, as expected for plasticisation. However, $$\mu _{\mathrm{relaxed}}$$ μ relaxed (T) slightly grows in wet PU. $$\hbox {H}_{{2}}\hbox {O}$$ H 2 O molecules cause these opposite trends by boosting the cooperative mobility (i.e. extension of the accessible conformational space and entropy by reduction in energy barriers) and by occupation of free volume compartments. Water quickly reduces the fracture parameters by about 50%. We explain that embrittlement by the $$\hbox {H}_{{2}}\hbox {O}$$ H 2 O -induced facilitation of cooperative network chain motions, which let fracture proceed with less energy. In summary, our findings provide a detailed conception of the molecular effects the $$\hbox {H}_{2}\hbox {O}$$ H 2 O molecules have on the PU network, and they explain the consequences for the mechanical properties.

A long-debated problem related to glass formation in amorphous materials is the interplay of thermodynamic, kinetic and α-relaxation processes. For the first time, low-frequency dynamics, as well as kinetic or quasi-static thermal expansion coefficients of a non-crystallizable glass-former are simultaneously measured. Based on the feedback between low-frequency dynamics and morphology, the study supports the viewpoint that glass formation can be observed in internal equilibrium, i.e. beyond kinetics, and might stem from spontaneous local-scale morphological changes.

In der Klebetechnik versteht man unter dynamischem Verhalten (Grenzschichtreifung) vorübergehende oder permanente Änderungen der mechanischen Eigenschaften und der Klebfestigkeit. Diese Änderungen treten innerhalb weniger Stunden oder Tage nach Fertigung der Klebverbindung auf und beeinträchtigen die Zuverlässigkeit von bestimmten Anwendungen. Das dynamische Verhalten von Polyurethan-Klebstoffen auf Basis von Polyetherdiolen, Polyethertriolen, Polyesterdiolen und MDI-Prepolymeren wurde untersucht. Die Zugscherfestigkeiten und Schälwiderstände auf Aluminiumlegierungen und Polycarbonat/ABS-Blends wurden bestimmt. Der Einfluss der Härtungskinetik, Luftfeuchte und Teilkristallinität wird beschrieben. Ein schnelles chemisches Abbinden durch Heißhärtung reduziert mögliche dynamische Effekte im Vergleich zur Härtung bei Raumtemperatur. Die Feuchteauslagerung der Klebeverbindungen führt zum Verlust der Festigkeit. Der Verlust des Kristallisationsgrades von Polyurethanproben auf Basis von Polyesterdiolen bewirkt einen Abbau der Festigkeiten bei Kunststoffproben. Bei Zweikomponenten-Klebstoffen, die bei Raumtemperatur härten, kann eine Beschleunigung der Härtung z.B. durch Katalysatoren mit Tensidcharakter, die sich in der Grenzschicht anreichern, erreicht werden. Die Beständigkeit von Klebstoffen gegenüber Feuchtigkeit kann durch Hydrophobierung oder Barrierefüllstoffe verbessert werden.

Due to their chemical and morphological versatility, polyurethanes may be susceptible to fabrication conditions (curing procedure, moisture). Industry reports ‘maturation’ phenomena, i.e. unstable mechanical properties of PU elastomers and PU based adhesive joints right after fabrication. This paper elucidates the impact of fabrication conditions and possible causes of maturation. Chemical and physical bulk properties of a crosslinking two-part PU are monitored during and after cure in dry atmosphere (at room temperature followed by a post-cure). The influence of curing procedure is revealed by processes characteristic of the post-cure, i.e. chemical side reactions (allophanate, carbodiimide) and a new dielectric relaxation. Tensile tests demonstrate the practical relevance of the findings (mechanical modulus). Properties of the fully crosslinked, dryly stored PU are stable during a three-week observation, indicating that maturation is preventable by complete cure and dry conditions. In contrast, chemical crosslinking after an insufficient cure likely causes maturation phenomena.

For the achievement of a complete understanding of the ageing and corrosion of adhesively bonded steel substrates, both the ageing of a polyurethane reference adhesive and the simultaneous corrosion of a mild steel substrate were studied by combined spectroscopic, electrochemical and microscopic techniques. A corundum-blasted mild steel was used as metal substrate in combination with a cross-linked reference polyurethane adhesive free from additional additives or fillers. The ageing was performed under full immersion in a chloride-free aerated electrolyte at elevated temperature. A strong influence of the water saturated polymer phase on the change in the interfacial oxide film structure of the metal substrate was observed. The thickening and hydroxylation of the metal oxide film during the corrosive delamination of the polyurethane film indicated that the de-bonding mechanism of the polyurethane adhesive is mainly based on interfacial water enrichment and a thereby induced growth of the interfacial oxide. The measured electrochemical properties of this oxide indicate that it is highly conductive and allows for oxygen reduction as the counter reaction to metal oxidation.

Crosslinked polyurethanes (PU) are employed as structural adhesives. Research has been done extensively on the interaction of water with thermoplastic PU but is still largely unexplored in the case of PU networks. A chemically simple but well-defined PU is utilized here as a starting point to understand the influence of water in this kind of polymer. For up to 15 days of immersion in water, no changes in the chemical composition of the PU were observed in the IR spectra. Depending on temperature, water saturates the PU samples much earlier. Plasticization is the result as a significant decrease of the mechanical modulus and a glass transition shift to lower temperature is observed in the polymer. Interestingly, only some 70% of the water saturation is sufficient for maximum plasticization. It is concluded from the IR spectra that water debilitates the interactions between polymer chains within the network. The bridging of at least a part of the originally hydrogen-bonded urethane groups is substituted by hydrogen bonds between water and the urethane moieties.

Temperature modulated DSC is used to study the fragility of three different bulk metallic glass forming liquids. Through applying various modulation frequencies, the dynamic glass transition shifts in temperature, allowing to determine the temperature dependence of the average relaxation time for each system. The resulting fragilities are compared with fragility investigations in literature obtained using thermo-mechanical analysis and the heating rate dependence of the calorimetric glass transition. Different methods to compare the data are evaluated and discussed.

Contact angles and wetting of solid surfaces are strongly influenced by the physical and chemical properties of the surfaces. These influence quantities are difficult to distinguish from each other if contact angle measurements are performed by measuring only the advancing θ a and the receding θ r contact angle. In this regard, time-dependent water contact angles are measured on two hydrophobic modified silicon wafers with different physical surface topographies. The first surface is nearly atomically flat while the second surface is patterned (alternating flat and nanoscale rough patterns) which is synthesized by a photolithography and etching procedure. The different surface topographies are characterized with atomic force microscopy (AFM), Fourier transform infrared reflection absorption spectroscopy (FTIRRAS) and Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR). The resulting set of contact angle data obtained by the high-precision drop shape analysis approach is further analyzed by a Gompertzian fitting procedure and a statistical counting procedure in dependence on the triple line velocity. The Gompertzian fit is used to analyze overall properties of the surface and dependencies between the motion on the front and the back edge of the droplets. The statistical counting procedure results in the calculation of expectation values E ( p ) and standard deviations σ ( p ) for the inclination angle φ , contact angle θ , triple line velocity vel and the covered distance of the triple line dis relative to the first boundary points X B ,10 . Therefore, sessile drops during the inclination of the sample surface are video recorded and different specific contact angle events in dependence on the acceleration/deceleration of the triple line motion are analyzed. This procedure results in characteristically density distributions in dependence on the surface properties. The used procedures lead to the possibility to investigate influences on contact angles more in detail.

Retarded deformation at the bond line edge of a thick, viscoelastic adhesive layer is observed using digital image correlation. Such information is required for proposing physical crack onset/propagation parameters which take into account viscoelastic and viscous mechanisms in the evaluation of dissipated energy. A complex stress/strain redistribution is observed in the early stage after specimen loading. The results illustrate that viscoelasticity dissipates a considerable amount of energy prior to crack nucleation and the lack of predictive models to account for that phenomenon.

Water is present in most technical applications of polyurethane (PU) adhesives, both from atmosphere and as adsorbate on the substrate. Hence, studies on the fundamental adhesion mechanisms have not only to cover the PU monomers but possible secondary reaction products like amines and ureas on the given substrate as well. In this work, diluted solutions of the monomer 4,4′-methylene diphenyl diisocyanate (4,4′–MDI) in tetrahydrofuran (THF) are exposed to the native surfaces of Au, Al and Cu in dried air. The resulting monomer adsorbate layers on the metals are stored in dried air for several hours. Therefore, any water essentially originates from the native metal surfaces. The chemical structure and the orientation of the adsorbed monomer molecules are evaluated in situ as a function of storage time by infrared external reflection absorption spectroscopy (IR-ERAS). A sequence of rinsing cycles with pure THF helps to discriminate between physisorbed and chemisorbed molecules. The changes of the spectra with storage time are significant and specific for each of the metal substrates. They reveal the formation of urea-like species which are easily removed by THF. Hence, they do not contribute to adhesion. The remaining isocyanate molecules adhere strongly and specifically to the substrates. The corresponding strong spectral modifications point to a chemical adhesion mechanism.

High-performance refractometry and infrared spectroscopy are combined in order to elucidate the gelation process and the glass transition during the network formation of epoxies and epoxy-based nanocomposites. Whereas infrared spectroscopy yields the chemical conversion due to the opening of oxirane rings during the covalent network formation, high-performance refractometry is extremely sensitive to the accompanying changes of the arrangement of the molecular network. In accordance with the Lorentz-Lorenz relationship, the evolution of the refractive index seems to reflect that of the mass density during polymerization of the epoxy-based systems within the limits of a few percent. The slight deviations from the Lorentz-Lorenz relationship, which occur during the gelation of the epoxy-based systems, are attributed to long-ranged dipole-dipole interactions, which respond at optical frequencies. This point of view is supported by the fact that chemically inert silica nanoparticles embedded in the pure epoxy ...

Understanding of fundamental adhesion is a key issue for bonding, polymer composites, and coatings. In this study, diluted solutions of polyurethane monomers (methylene diphenyl diisocyanate isomer mixture—MDI, polypropylene ether triol—PPET) are exposed to the native surfaces of Au, Al, and Cu. The adsorption state of the molecules (from multi- to sub-monolayers) is investigated in situ by infrared external reflection absorption spectroscopy (IR-ERAS). A sequence of solvent rinsing steps helps to distinguish physisorbed from chemisorbed molecules. PPET sticks very weakly to the metals. The spectra reveal a bulk-like state. MDI adsorbs weakly on Au but the spectra differ significantly from the bulk state. On Al and Cu, MDI establishes strong adhesion. Rich new spectral features indicate a probably chemical nature of adhesion, and a specific structure in the neighboring adsorbate layer. However, detailed final conclusions on the adhesion mechanisms must not be derived without appropriate quantum mechanical...

In the present contribution, a phenomenological material model is presented describing the viscoelastic behaviour of polyurethane bonds under finite deformations. The model includes the temperature dependency of the material behaviour close to the glass transition temperature. Experimentally observed size effects can also be described. It is known from previous investigations that the bonds show an effective behaviour that is influenced by the layer thickness. The physical reason for this behaviour can be found in the formation of boundary layers in the polymer which are located close to the substrate. In these boundary layers, the material behaviour differs from the bulk behaviour. The effective properties of bonds of different thickness are experimentally investigated in isothermal shear tests performed at different temperatures. In order to model the observed effects, a previously developed approach of viscoelasticity is extended including the temperature dependency. Furthermore, a supplementary parameter field is introduced, taking the formation of the boundary layers into account. This field is determined by a partial differential equation in form of a reaction–diffusion equation containing the boundary conditions. The local properties of the polymer are linked to the distribution of this additional field. It is shown that the model parameters can be identified and that the model is able to describe the complex experimentally observed behaviour.

The curing of an epoxy consisting of the solid hardener dicyandiamide (DICY) and the resin diglycidyl ether of bisphenol A (DGEBA) is studied in a system consisting of a tablet of DICY embedded in liquid DGEBA. Dissolution of DICY within the liquid DGEBA in combination with the transport of dissolved DICY from the tablet border into DGEBA and the chemical reaction of both reactants is studied by scanning Brillouin microscopy and infrared spectroscopy. Scanning Brillouin microscopy demonstrates the spatial and temporal evolution of the static and dynamic hypersonic properties in the course of curing in the vicinity of the DICY tablet. Infrared spectroscopy performed on epoxy pieces extracted from the final sample at different distances from the tablet surface give information about the spatial evolution of the curing process. The results achieved by both techniques are finally combined to yield a better understanding of the curing of DICY-based epoxies, which transform upon curing from strongly heterogeneo...

Static and dynamic hypersonic properties are probed to reveal the subtle interplay between demixing, matter transport, chemical network formation, polymer network swelling, and network damage in the vicinity of the interface between the reactants of amine-curing epoxies. An innovative time- and space-resolved acoustic microscopy, called scanning Brillouin microscopy, gives access to these competing transport and structure formation processes in epoxy systems consisting of either pure resin, alumina nanoparticles-filled resin, or various epoxy resin-hardener mixtures topped by a layer of pure hardener.

Epoxy–dicyandiamide (Dicy) formulations frequently contain a free accelerator for reducing the curing temperature and the time for network formation, which reduces the shelf life of these adhesives. This study compared the reaction kinetics during the storage at 60 °C for a precured epoxy adhesive (EP = diglycidyl ether of bisphenol A and Dicy, mass ratio 100:6.7, precured at 150 °C for 1 h) mixed either with free accelerator (=EPacc) or with the same concentration of accelerator immobilized in micro- or nanozeolite fillers (EPμ-filled and EPn-filled, respectively). During storage, the infrared (IR) study probed the chemical modifications. They lead to increasing cross-linking density and a loss of free volume as detected by positron annihilation lifetime spectroscopy (PALS). Cross-linking precedes to the chemical vitrification. Additionally, the glass transition and the free-volume parameters were investigated for the three EP’s as a function of temperature by PALS after thermal curing.

Aging of epoxy (EP)-metal-joints is studied by FTIR microspectroscopy, tapping mode scanning force microscopy and nanoindentation on sample cuts prepared with low angle microtomy. The influences of temperature and water are separated by exposure to dried or moist air (90% rel. humidity) at 60°C and dried air at 120°C for up to a few hundred days. In the course of aging, diffusion-controlled chemical reactions start at the interface to the metal and extend as a gradient up to 50 μm into the EP. Water is more detrimental to the epoxy than elevated temperature. The chemical aging proceeds slower than at the contact to ambient air, and, contrary to that surface zone, oxidation of amines dominates autoxidation of CH2 at other sites in the network chains. Thus, intensity and rate of chemical aging at epoxy-metal contacts cannot be deduced simply from the aging at the air-bulk contact. Chemical aging is accompanied by the formation of gradients of mechanical properties, at least in moist conditions.

Structural developments are investigated in network-forming reactive polymers by time- and space-resolved scanning Brillouin microscopy. Hypersonic properties are probed to reveal the subtle interplay between molecular transport, dissolution, polymerization and network defects in the vicinity of the interface between reactants, which are either pure epoxy resin or various epoxy resin–hardener mixtures, topped by a layer of pure hardener. The trans-interfacial polymerization produces heterogeneous epoxy structures of either gelatinous or glassy nature. Interestingly, the hardener can easily penetrate and swell these networks and epoxy network fragments can be transported over several millimetres by convective flow. The observed features may be used to form interpenetrating networks during self-healing procedures.

Cross sections of epoxy adhesive joints (DGEBA and DETA) of Al or Cu PVD substrates were prepared by ultra-microtomy and studied with STEM, EELS and EDX to reveal the metal concentration profile after curing and after ageing in moist–warm air for 300 days. After curing, ca. 0.3 at% of aluminium is detected in a thin interphase of less than 50 nm thickness. Up to 0.5 at% of copper is found within 20–75 nm from the interface and it is still detected at 1000 nm distance to the substrate. In aged samples, no further diffusion of Al species into the polymer took place whereas the Cu substrate shows a higher roughness and varying thickness after ageing. Accordingly, up to 0.9 at% of Cu is detected within the first 20–120 nm from the substrate. Thus, corrosive dissolution of the surface oxide layer and the metallic copper substrate and diffusion of Cu species into the polymer proceed under moist–warm conditions.

The developing chemical depth profile in an epoxy adhesive bulk (with varying amine content) is monitored during aging by FTIR microspectroscopy on sample cuts prepared with low angle microtomy. Three aging regimes are applied in order to separate the role of temperature and water: dried or moist air (90% rel. humidity) at 60°C and dried air at 120°C for up to 300 days. Quantitative evaluation of the IR spectra shows: thermo-oxidative aging (= dried air) is controlled by the diffusion of atmospheric oxygen. It affects a gradient region of more than 200 μm in depth. At given aging time, the depth profiles depend on temperature, humidity, and on the epoxy-amine ratio. Humidity mainly affects the IR band intensities. The plasticizing effect of water promotes the loss of small network fragments. At 120°C, autoxidation of α-CH2 at ether and amine groups and the oxidative attack on tertiary amines dominate aging. At 60°C in dried air, these processes proceed only very slowly. In the case of amine excess, aging ...

Epoxy formulations based on the multi-functional amine hardener, dicyandiamide (Dicy), regularly contain a free accelerator for reducing the curing temperature and the time needed to complete the network formation. Unfortunately, all accelerators reduce the shelf life of these adhesives at 25°C. In order to solve this problem, accelerator-loaded zeolites fillers were developed, optimised with respect to host–guest interactions and characterised by Fraunhofer IFAM (Bremen, Germany) with regard to the release and curing behaviour in epoxy adhesive formulations. They are added to an epoxy adhesive (diglycidylether of bisphenol A (EP) and dicyandiamide (Dicy), mass ratio 100:6.7), stored at 25°C in regular air or cured (heated with β = 10 K/min to 170°C subsequent isothermal curing for 45 min). That shelf life and curing behaviour are investigated by FT-IR spectroscopy and modulated DSC. Compared to the EP containing free accelerator, the zeolite-filled EP possesses a threefold increase in shelf life at 25°C ...

This work contributes to the understanding of focused ion beam (FIB) technology for polymers. The conditions of treatment are varied, in particular by etching under ‘dry’ ultra-high vacuum conditions or in the presence of water vapour. For a glassy epoxy network, the changes in chemistry and morphology are characterised. Energy-dispersive X-ray analysis reveals that gallium is always implanted in the epoxy but the content is higher in the case of ‘dry’ FIB milling. According to attenuated total reflection infrared micro-spectroscopy, new chemical structures form in the surface region of the epoxy during FIB milling with or without water vapour. Scanning electron microscopy and scanning force microscopy were used to image the topography of the etched epoxy surfaces. Quite smooth surfaces result under ‘dry’ etching conditions. In the presence of water vapour, rough surfaces with a sub-micrometre globular morphology are obtained. This is an indication of the heterogeneous morphology of the epoxy polymer. As compared to ‘dry’ conditions, the introduction of water vapour during FIB milling increases the milling yield significantly. As a result, the FIB treatment changes the chemistry and the structure of the epoxy network not only at the very surface but also in some significant surface layer of the sample. It can be expected that such a modified zone will also form on other cross-linked polymers. Copyright © 2009 John Wiley & Sons, Ltd.

Scanning Brillouin microscopy visualizes the temporal evolution of a heterogeneous hypersonic profile during chemical reactions and transport processes around a planar phase boundary between an epoxy resin and hardener. The hypersonic investigations are interpreted in terms of structural formation and annihilation in the layered sample and are compared to results obtained for a well mixed bulk sample of the same composition of reactants. Chaotic transport channels are made responsible for the creation of local glassy heterogeneities not observable in the bulk material on a macroscopic level.

For poly(methyl methacrylate) (PMMA) as a representative of amorphous thermoplastic polymers, the milling effects, and the chemical changes due to ion bombardment with a focused ion beam (FIB) at normal incidence are studied with scanning force microscopy (SFM), scanning electron microscopy (SEM)/energy dispersive X-ray (EDX), and infrared (IR) spectroscopy for varying conditions of Ga+ treatment, including the effect of partial water pressure. Stopping and Range of Ions in Matter (SRIM) simulation results for 30 keV Ga+ at normal incidence show that the zone of primary ion–polymer interaction extends ca 100 nm into the PMMA. Accordingly, this interaction region is much wider than the original beam diameter. The width of the region where the recoiled ions interact strongly with the polymer chains is larger. Secondary processes, such as fragment diffusion and phonon transport, are expected to extend even farther into the polymer. SEM and SFM reveal distinct topologies of areas milled without or in presence of water vapour. Water vapour–assisted FIB milling produces more roughness and defects. The infrared attenuated total reflection spectroscopy (IR-ATR) spectra indicate that ion milling in PMMA damages methacrylate side groups in particular. In contrary to metals, an increase in the degree of milling is found when the beam spot overlap parameter increases. Copyright © 2009 John Wiley & Sons, Ltd.

In this study we examine polyurethane bonds of varying thickness between anodised aluminium substrates. The performed shear tests showed an intriguing size effect of the kind “thinner equals softer”. This size effect occurs not only in the basic elasticity (relaxed state), but also in the viscoelastic behaviour of the tested material. The cause of such size effects is supposed to be found in the existence of so-called interphases or boundary layers, which may differ considerably from the bulk in terms of mechanical behaviour, thus having an enormous impact on thin bonds. In thick bonds, however, these interphases or boundary layers have a minor effect on the overall mechanical behaviour. To account for these experimental results in bond modelling, an extended phenomenological continuum mechanics-based model, which explicitly includes such size effects in its calculation, is developed and presented. For this purpose, an abstract structure parameter with its corresponding balance equation is established describing the formation of the interphases by means of a phase transition. This makes it possible to define the bond stiffness at a macroscopic level, without entering into the microstructure. The extended model brings up a set of model parameters, which are determined efficiently by an ES (evolution strategy). The study concludes with a summary and an outlook on our further research work.

The aging behavior of an epoxy adhesive (DGEBA and DETA) in the bulk surface region and in the contact region to metal substrates (Au, Cu) is studied locally. Therefore, the chemical depth profile during aging is recorded with FTIR microscopy on sample surfaces prepared with low angle microtomy. Two environmental conditions are applied at 60°C for up to 500 days to separate the role of temperature and humidity in aging. Quantitative evaluation of the IR spectra provides the following results: in the bulk surface region, three aging mechanisms form a gradient region of more than 200 μm. Their intensity and depth profile depend on the environmental conditions. Epoxy-metal contacts are unaffected under dry conditions. Humidity is needed to form a 50 μm thick region where the copper substrate accelerates aging. Based on the experimental results, chemical aging mechanisms are discussed.

Dynamic mechanical measurements on polymer layers between metallic substrate show a dependence of the mechanical properties on the thickness of the polymer layer. This is discussed on the example of a polyurethane adhesive between gold substrates. Measurements of the shear modulus show a decrease of the glass transition temperature with increasing the thickness of the polymer layer. This behavior can be described by an empirical equation.

Thin adhesive films on metals are used as an appropriate model for the characterization of the interphase in polymer‐metal compounds. This interphase is a result of the specific interactions between the adhesive partners. It is particularly relevant for the performance, and the long‐term stability of adhesively bonded structures and coatings. The influence of the metal substrate affects the formation of the polymer network during the polymerization, as well as its resulting structure and properties significantly as compared to the bulk. As examples, a thermosetting epoxy (EP) and a polyurethane (PU) elastomer are chosen for the investigation of the morphology and the chemical structure of the thin films (thickness between 20 nm and 3 μm) on native surfaces of gold, aluminium, and copper. The results for the two types of polymers reveal characteristic differences with respect to reaction rate and final degree of cure as a function of the film thickness on the different metals. The final structure turns out...

The non-linear viscoelastic behaviour of a polyurethane (PUR) network is determined by continuous uniaxial tension tests and stepwise relaxation tests. Following the concept of internal variables on the modelling side, the finite Neo-Hookean material model combined with linear evolution equations for the internal variables is applied to include the time-dependence caused by viscoelasticity. The parameters are identified by an evolution strategy combined with a non-linear finite element analysis which solves the boundary value problem given by the specimen geometry and testing conditions. In conclusion, the combination of the described experiments and modelling provides a full description of the mechanical behaviour of the given PUR.

It is known from applications that the mechanical behaviour of polymer bonds does not only depend on the properties of the polymer itself but also on the substrate. Therefore, the mechanical behaviour, i.e. the stiffness, of a polymer joint becomes thickness dependent. In the present work we describe experiments performed on polymer joints and we develop a continuum-based model which is able to describe the experimentally observed size effects without suggesting the microstructure in detail. The continuum mechanical model is enhanced by a scalar-valued structure parameter which describes all the effects taking place in the boundary layer which arises near the substrate. It is shown that the model parameters can be determined on the basis of simple shear experiments performed on polymer layers of different thickness.

Thermal investigations on two selected model-nanocomposites have been made. They differ with regard to the type of the anorganic nanoparticles that have been filled into an organic oligomer matrix. The properties of nanocomposites may vary between those of a simple mixture of independent components and those of a system, where specific interfacial interactions between the constituting parts lead to ‘new’ properties. Depending on the type of the nanoparticles filled into the matrix, the resulting properties might be closer to one or to the other extreme. We used temperature modulated differential scanning calorimetry (TMDSC) to investigate a matrix of the oligomer diglycidyl ether of bisphenol A (DGEBA) filled either with SiO2- or Al2O3-nanoparticles. The dependence of the complex specific heat capacity ( c p ′ ) on the concentration of nanoparticles shows a clear difference between the two systems as far as the glass transition of the oligomer is concerned. The SiO2 composite seems to behave more like a simple mixture, whereas the Al2O3 composite shows ‘new’ properties.

Films (20 nm d EP For the films , IR spectroscopy reveals the chemistry as a function of d EP . Curing is based on amine-epoxy reactions only. Compared to the bulk, the gross reaction rate slows down for the RT-curing. A metal-specific ‘chemical interphase’ with reduced epoxy group consumption extends over some 100 nm. Post-curing (393 K, 1 h) is not sufficient to consume all epoxy groups. Brillouin spectroscopy and microscopy provide local mechanical stiffness data ( c 11 ) with better than 10-μm resolution. The RT-cured films possess mechanical heterogeneities on the sub-mm scale. Their glass temperature is well below RT for most films while T G bulk = 326 K. In the adhesive joints , ‘mechanical interphases’ are detected on the metal side with an unexpected width of up to some 100 μm and with a c 11 -maximum inside the epoxy. Its shape, height and position depend on the metal and the epoxy curing state. It is interpreted as the result of competing influences from epoxy structure and internal stresses. During polymerisation, a ‘morphological interphase’ should form with a 3-dimensional heterogeneous structure that is specific for the metal and the route of compound formation. Hence, the properties of thin films are not generally equivalent to the situation in thick adhesive bonds. To cite this article: W. Possart et al., C. R. Chimie 9 (2006) .

From the structural point of view a simple Cauchy relation is not expected to hold for isotropic materials. Such a Cauchy relation would imply the reduction of independent elastic stiffness constants for the isotropic state from two to one. However, high frequency elastic data of glasses and viscous liquids show a linear transformation between the shear and the longitudinal elastic stiffness which is called a generalized Cauchy relation. It seems, that the parameters of the linear transformation are related to the global and local symmetry and/or order. Brillouin investigations on the elastic stiffness coefficients of a consolidated nano-crystalline material (CeO 2 ) and of DGEBA/SiO 2 nano-composites are used in order to elucidated the role of the discrepancy between local and global symmetry and/or order.

The thermal and hydro-thermal aging of a hot-cured epoxy system (diglycidylether of bisphenol A (DGEBA) + dicyandiamide (DDA)) in the glassy state is revisited using DSC and IR attenuated total reflection spectroscopy. Because of the diffusion of DDA from the solid particles into the liquid DGEBA matrix, curing produces a highly crosslinked amorphous matrix that contains low crosslinked amorphous regions. After full curing, the network possesses a relatively low molecular mobility and no residual reactive groups. Thermal and hydro-thermal loading is performed at 60°C, well below the principal glass transition temperature (Tg1 = 171°C). Both aging regimes cause significant chemical and structural changes to the glassy epoxy. It undergoes a phase separation of relatively mobile segments inside the low mobile matrix, providing a second glass transition that shifts from Tg2 = 86–114°C within 108 days of aging. This phase separation is reversible on heating into the viscoelastic state. Hydro-thermal aging leads to a reversible and a nonreversible plasticizing effect as well. On thermal aging, no chemical changes are observed but hydro-thermal aging causes significant chemical modifications in the epoxy system. These modifications are identified as a partial degradation of crosslinks produced by the cyano groups of the DDA and correspond to the nonreversible plasticitation. These changes in the cured epoxy should exert an influence on the mechanical properties of an adhesive bond. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Interfaces between cross-linked polymers and metals play a significant role in fields like splicing and coating, metallization of plastics, microelectronics, micro system technology and nanotechnology. In this paper, we present investigations on the interface formation due to metallization (Au, Ag, Cu and Al) by evapouration of the highly cured epoxy resin system diglycidilether of bisphenol a (DGEBA)–diethylene triamine (DETA) with the focus on the structure formation at the interface. A combination of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), atomic force microscopy (AFM) and a radiotracer technique was used to analyze the metal/epoxy interface. While a strong metal/epoxy interaction was found for Al, the noble metals Au, Ag and Cu grow in a Volmer–Weber mode due to an interplay of surface diffusion and metal cluster growth. Nevertheless, polymer bulk diffusion of these metals is negligible.