Zener–Stroh crack at the interface of multi-layered structures

A Zener–Stroh (Z–S) crack can be nucleated on the interface of a multi-layered structure when a dislocation pileup is stopped by the interface which works as an obstacle. During the entire fracture of a crack, Z–S crack mechanism controls the initial stage, or the first phase of crack initiation and propagation. In our current research, investigation on a Z–S crack at the interface of a multi-layered structure is carried out. The problem is formulated into a set of singular integral equations by applying the distributed dislocation based fracture mechanics. The obtained integral equations are then solved with numerical method after the singularities at crack tips are carefully checked. In the solution procedure, the contact zone model is adopted to cease the oscillation behavior. The contact zone length, the stress field near the crack tips and the stress intensity factors (SIFs) of the crack are discussed based on the numerical results of two typical structures. It was found that the contact zone length could be very large and was determined by the properties of all the three materials and loading conditions. Our analysis also shows that the thickness of the middle thin layer plays a critical role for the fracture behavior of the crack when it is comparable to the crack length.     

Infrared nanoscopy of dirac plasmons at the graphene-SiO₂ interface

We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding 2 orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO(2) substrate. Our data augmented by detailed modeling establish graphene as a new medium supporting plasmonic effects that can be controlled by gate voltage.     

Cooperative effects at the interface of nanocrystalline metal–organic frameworks

Controlling the chemistry at the interface of nanocrystalline solids has been a challenge and an important goal to realize desired properties. Integrating two different types of materials has the potential to yield new functions resulting from cooperative effects between the two constituents. Metal–organic frameworks (MOFs) are unique in that they are constructed by linking inorganic units with organic linkers where the building units can be varied nearly at will. This flexibility has made MOFs ideal materials for the design of functional entities at interfaces and hence allowing control of properties. This review highlights the strategies employed to access synergistic functionality at the interface of nanocrystalline MOFs (nMOFs) and inorganic nanocrystals (NCs).

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Study of a reaction at the solid Cu/α-SiC interface

A solid-state wetting technique has been used to investigate the interface between solid Cu and -SiC at high temperatures. An intermediate phase is found to form as an interfacial reaction product between Cu and SiC at high temperature, and to thicken upon further heating at 1123 K. The interfacial phase has an approximate composition of Cu–19 at%Si–5 at%C and displays an f.c.c. structure. Such a phase is not present in the published Cu–Si phase diagram, and forms under conditions which cannot be explained from that phase diagram. It is postulated that this phase represents a previously unreported silicide of Cu which may be stabilized by the presence of C in solution. © 1998 Chapman & Hall     

Mechanical properties of the interface of gelcoat resin–composite materials and improvements via surface treatment methods

A gelcoat resin was applied to improve the surface properties of composite materials. Combinations of a gelcoat with a glass/epoxy or carbon/epoxy result in a prime composite structure. Prior to application, however, the mechanical properties of these bonds should be studied. Three material pairs, glass/epoxy-gelcoat (GEG), carbon/epoxy-gelcoat (CEG), and glass/polyester-gelcoat (GPG), were studied to experimentally determine the interfacial properties. Then, four surface treatment methods were applied to the GEG and CEG composite, and the resulting materials were investigated to assess potential improvements to the interfacial properties. Three tests, single-leg bending, peel, and single lap joint, were carried out, and experimental results were combined with equations to obtain the strength or energy. It was observed that the strength or energy of the GPG material was higher than that of the GEG and CEG. After the surface treatment, the energy and strength of the interfaces had increased over that of the values of the untreated surfaces.     

Special features of the interface between glass–metal coatings of superhard materials powders and metal matrices

The main results of the investigation of special features of the formation of the interface between the glass coating on the diamond and cBN powders with metals, that are bonds of grinding tools are described and generalized. It has been shown that the mutual diffusion occurring in the contact zone results in the increase of the adhesion at the interphase boundary, which ensures a strong fastening of a metal coating on a glass aggregate and the glass aggregate itself in a metal bond.     

Characteristic times of oxygen mass transfer at the liquid metal–vapour interface

The interactions of liquid metals and alloys with the environment mostly depends on the thermodynamic properties of the liquid surface. In fact, the surface tension is strongly influenced by the presence in the surrounding atmosphere of reactive gases through solution, adsorption mechanisms and/or surface reactions. In particular, oxygen, which shows a high surface activity towards a large number of metallic systems, is the most important contaminant of liquid metals and alloys.Theoretical approaches for estimating the oxygen mass transfer at the liquid–vapour interface under inert atmosphere and vacuum have been developed already in order to relate the observed physical properties to the real surface composition data.In the present work a model of the interfacial transport of a liquid metal–oxygen system under Knudsen conditions that foresees the temporal evolution of the interfacial composition is presented. The diffusion characteristic times for reaching steady-state conditions are evaluated in order to define two system sizes depending on the different oxygen transport mechanisms in the liquid phase.An experimental study of the interface evolution is at present under way and preliminary results show a satisfactory agreement with theoretical studies.     

Monolayer studies of sugar- and nucleoside-terminated dendrimers at the air–water interface

Sugar- and adenosine-terminated dendrimers, [1,2-o-Isopropylideneribosyl-(G₁-12acid), -(G₂-36acid)] and [Adenosyl-(G₁-12acid), -(G₂-36acid)], were synthesized using Newkome's dendrimer synthetic method. Langmuir and Langmuir–Blodgett (LB) monolayers of these dendrimers have been constructed and characterized at the air–water interface and on solid substrates by measuring surface pressure–molecular area (Π–A) isotherms, atomic force microscopy (AFM), ellipsometry and contact angle measurement. Π–A isotherms and AFM images showed that these dendrimers formed stable and homogeneous monolayers without aggregation on pure water surface. The first and second generation of sugar-terminated dendrimers show molecular areas of 647 and 1359 Ų, respectively. Ellipsometry measurement indicates that the thickness of both the first and the second generation of sugar-terminated dendrimers were about 10 Å. This reflects a flat orientation of both molecules at the air–water interface. On the other hand, the first generation of adenosine-terminated dendrimer shows an area of 105.6 Ų per molecule with a thickness of 16 Å, and for the second generation, the area was 738.4 Ų with a thickness of 27 Å. These results suggested that adenosine-terminated dendrimers maintain a spherical form at the air–water interface. It was found that small difference in the structure of thymine and uracil in the subphase critically affects the interaction of the molecules and conformation of the dendrimers at the interface.     

Frictional stresses at the disc–jaw interface during the standardized execution of the Brazilian disc test

An attempt to more accurately describe the boundary conditions of the standardized Brazilian disc test is presented. Specifically addressed is the problem of quantitatively relating the radial pressure with the tangential (frictional) stresses generated at the disc–jaw interface according to a physically acceptable law. A novel approach is proposed based on the notion that friction is directly related to the mismatch between the tangential components of displacement of the disc and jaw along their common interface due to the different deformability of the two materials. The surface displacements in both jaw and disc are determined using the complex potentials method, and the difference between their tangential components along the common contact arc is calculated. This difference in combination with the radial contact pressure tends to generate relative lateral displacements between the disc and jaw that are counterbalanced by frictional forces. The distribution of friction stresses along the contact rim obtained from the present approach fulfils all physical and intuitive imposed conditions. In addition, it is strongly skewed, attaining its maximum value at two-thirds distance from the centre of the contact arc, in good agreement with the earlier results based on a completely different approach.     

Modelling the leaching kinetics of cement-based materials––influence of materials and environment

The leaching of cement-based materials in aggressive water is studied according to several protocols of accelerated or non-accelerated tests. The paper analyses international experimental published data on leaching concerned with several parameters, like material parameters as water-to-binder ratio and silica fume content, and environmental parameters, like pH and temperature. Then, a simplified model based on this analysis is developed to predict the kinetics of leaching. This model assumes that the rate of leaching follows a square root of time. Each parameter is introduced as a weight function. Particularly, the paper introduces the coupling between the built database and the model.     

Chiral interactions of the drug propranolol and α1-acid-glycoprotein at a micro liquid-liquid interface

The investigation of chiral interactions of drugs with plasma proteins is of fundamental importance for drug efficacy and toxicity studies. In this paper, we demonstrate a simple liquid-liquid interface procedure for investigating chiral interactions. Chiral discrimination of the enantiomers of a basic drug, propranolol, was achieved at a micro liquid-liquid interface, using α(1)-acid-glycoprotein (AGP) as a chiral acute phase plasma protein. When the protein is added to an aqueous phase containing the enantiomers of propranalol hydrochloride, the binding of (S)- and (R)-propranolol hydrochloride to the protein results in a decrease in the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) current responses corresponding to the decrease in transfer of propranolol at an aqueous-1,2-dichloroethane interface. This decrease is a consequence of the complexation of the drug and the protein. The complex drug-protein does not transfer across the interface nor changes the transfer potential of the uncomplexed form of propranolol enantiomers. The bound concentration of propranolol enantiomers in the presence of AGP was found to be greater for (S)-propranolol than (R)-propranolol for solutions containing constant concentrations of AGP (50 μM). Scatchard analysis yielded association constants of 2.7 and 1.3 × 10(5) M(-1) for (S)- and (R)-propranolol, respectively.