Formation of epoxy-diamine/metal interphases

Epoxy-diamine networks are extensively used as adhesives or paints in many industrial applications. When the precursors are applied onto metallic substrates and cured, an interphase, having chemical, physical and mechanical properties quite different from that of bulk polymer, is created between the substrate and the polymer. Moreover, chemical reactions between diamine and metallic surfaces induce an increase in the practical adhesion (adherence). When the same epoxy-diamine mixtures are applied onto gold coated or polyethylene substrates, the interphase properties are the same as bulk ones. When epoxy-diamine mixtures are applied onto aluminum or titanium alloy surfaces, the glass transition temperature, amine and epoxy reaction extent, the interphase thickness, residual stresses within the interphase, Young's modulus of the interphase all depend on the amine nature (aromatic, aliphatic or cycloaliphatic), the stoichiometric ratio, the processing conditions (time and temperature), the organic layer thickness and the metallic surface treatment. Coating analyses (FTIR, FTNIR, DSC, DMTA, H⁺ and C¹³ NMR, SEC, ICP and POM) suggest that diamine monomers chemically react with and dissolve the metallic hydrated oxide layer. Then, metallic ions diffuse through the organic layer to form a complex by coordination with diamine monomers (chelate or ligand). Metal–diamine complexes are insoluble, at room temperature, both in diamine as well as in DGEBA monomers and they induce a phase separation during the curing cycle of the epoxy-diamine precursors. Furthermore, the chemical bonding of diamine monomers to the metallic surfaces and the diamine–metal crystal orientation parallel to the metallic surface within the interphase lead to chemical, physical and mechanical properties to the epoxy-diamine network which are different from those of the bulk.     

陶瓷基复合材料疲劳损伤模拟与界面优化设计

本文从界面损伤模拟出发研究了陶瓷基复合材料(CMCs)的抗疲劳设计方法.以CMCs微观结构演变为切入点,在微观尺度建立复合材料各组分损伤机制的物理模型,然后集成到细观尺度的有限元分析之中,从而建立CMCs疲劳损伤的数值模拟方法,并对界面相组成、结构等因素影响疲劳性能的作用机制进行探究,以实现界面的抗疲劳设计.通过多尺度...     

TREATMENT OF THE NONEQUILIBRIUM VAPOR MOTION NEAR AN EVAPORATING INTERPHASE BOUNDARY

Strong evaporation problems are characterized by the nonequilibrium vapor motion near the interphase boundary. The solution of this nonequilibrium region, known as Knudsen layer, requires the use of kinetic theory. Kinetic equations have been solved numerically for a plane evaporation problem. Numerical solutions have led to the establishment or the validity of a simple kinetic theory approach to calculate the jump conditions across the Knudsen layer and the net mass, momentum, and heat fluxes. This approach can be used together with the conventional continuum method to calculate How parameters at the outer edge of the Knudsen layer for heat transfer problems in which evaporation occurs at the interphase boundary.     

In situ electrochemical Scanning Kelvin Probe Blister-Test studies of the de-adhesion kinetics at polymer/zinc oxide/zinc interfaces

Fundamental investigations of the polymer/zinc oxide/zinc interface corrosion stability were performed in situ by means of the electrochemical Height Regulated Scanning Kelvin Probe Blister-Test (HR-SKP-BT) under controlled atmospheric conditions. A hole under an adhesive layer film served as electrolyte reservoir to initiate cathodic de-adhesion processes. Then a combinatorial approach was undertaken to simultaneously study the influence of electrolyte pressure at constant defect polarisation and of relative atmospheric humidity on the de-adhesion rate. The time resolved blister growth and the propagation of the three phase boundary polymer/oxide covered zinc/interfacial electrolyte layer could be detected. It could be proven that the oxygen reduction induced electrochemical damage of the interface precedes the subsequent mechanical de-adhesion process. By variation of the relative atmospheric humidity the water concentration within the bulk adhesive and its interphase adjacent to the metal substrate could be adjusted. These processes were further analysed by peel-tests and in situ Attenuated-Total-Reflection Infrared Spectroscopy (ATR-IR) studies of water diffusion. A decrease of the interphasial water concentration led to a deceleration of the de-adhesion kinetics for constant defect conditions and to smaller interfacial ion transport rates. This could be assigned to an inhibition of the electron transfer reactions at the front of de-adhesion and an increased adhesion force between polymer film and oxide covered metal preventing the formation of an extended interfacial electrolyte layer.     

Relationship between interfacial phenomena and viscoelastic behavior of laminated materials

A literature review shows that the main arguments used to describe viscoelastic behavior of polymer composites are the existence of an interphase and/or physico-chemical matrix-reinforcement interactions. The purpose of this investigation was to study the influence of both of these parameters on the viscoelastic behavior of a sandwich structure. Using a theoretical approach of the mechanical coupling between phases in laminate composites, the interphase influence is shown to be negligible. In order to understand the influence of an interphase on viscoelastic features of laminates, some metal/polymer/metal laminates were processed under various conditions to obtain different degrees of metal/polymer adhesion. Dynamic mechanical spectroscopy tests reveal that both the amplitude of the main loss factor peak and the low temperature apparent modulus increase with the adhesion. Finite elements calculations show that discontinuities of displacements at the metal/polymer interface explain the loss peak changes. The continuity of displacements is ensured only from a threshold value of the peel energy.     

Oxidation of SiC/Porous Al2O3 Laminated Ceramic Composites

The oxidation behavior of SiC/porous Al₂O₃ interphase laminated composites was studied using oxidation experiments and mathematical modeling of the reaction/porous diffusion kinetics in this system. Oxidation at 800°C produced both closure of the interlayer porosity at the lateral ends of the laminate and a limited penetration of the oxidation product layer front from the laminate edges to its interior. Oxidation at 800°C resulted in a persistent product layer of nearly uniform thickness that is more suited to test the effects of oxidation on laminate properties. The modeling approach, which explicitly considers the porous microstructure of the interphase and its evolution upon oxidation, reproduces these experimental observations successfully. The model was extended to study the effect that the mixing of SiC grains with Al₂O₃ grains to form a two-phase porous interphase has on pore closure at the interface and oxide product front penetration into the interior of the laminate. Pore closure was found to be accelerated considerably with increasing SiC content, and was not accompanied by any significant decrease in the distance from the laminate edges upto which an oxidation product layer was formed.     

Roles of the Interphase Stiffness and Percolation on the Behavior of Solid Propellants

Atomic force microscopy has provided access to local moduli for propellants prepared with bonding agents, which create a stiffness gradient in the matrix producing a stiffer interphase surrounding the fillers. The reinforcing impact of the bonding agent appears up to some distance and interphase percolation is observed. In order to better understand the impact of bonding agents on the stress and strain at break of propellants, finite element simulations are performed. Two‐dimensional periodic cells containing randomly dispersed particles are considered, including both a cohesive zone model at the filler/matrix interface to account for possible debonding and an interphase that percolates or not. The influence of the interphase stiffness and of its percolation, on the stress and strain at break of the model propellants are evaluated through the use of a microstructure‐based failure criterion.     

Nonlinear Heat and Mass Transfer with Consideration of Deformation in a Chemical Reaction Wave

A new approach is developed to perform mathematical modeling of heat transfer with consideration of deformation of a physical system in a chemical reaction zone. This approach describes boundary conditions using fractional differential-integral calculus. A numerical analysis using the model proposed is undertaken to examine processes during nonlinear heat transfer accompanied by deformation of a physical system due to intense gas release in chemical reactions, particularly in processes of the production of materials by self-propagating high-temperature synthesis.     

Characterizing elastic properties of carbon nanotube‐based composites by using an equivalent fiber

Effective elastic properties for carbon nanotube (CNT)‐reinforced composites are obtained through a variety of micromechanics techniques. An embedded CNT in a polymer matrix and its surrounding interphase is replaced with an equivalent fiber for predicting the mechanical properties of the CNT/polymer composite. Formulas to extract the effective material constants from solutions for the representative volume element under three loading cases are derived based on the elasticity theory. The effects of an interphase layer between the nanotubes and the polymer matrix as result of effective interphase layer are also investigated. Furthermore, this research is aimed at characterizing the elastic properties of CNTs‐reinforced composites using Eshelby–Mori–Tanaka approach based on an equivalent fiber. The variations of mechanical properties with tube radius, interphase thickness, and degree of aggregation are investigated. It is shown that the presence of aggregates has stronger impact than the interphase thickness on the effective modulus of the composite. This is because aggregates have significantly lower modulus than individual CNTs. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers     

Influence of Cure Conditions on the Adhesion of Rubber Compound to Brass-plated Steel Cord. Part II. Cure Time

The effect of the cure time of a rubber compound on the adhesion with brass-plated steel cord was investigated. The formation, growth and degradation of the adhesion interphase formed between the rubber compound and brass-plated steel cord was also observed as well as the formation of a weak boundary layer in the rubber near the adhesion interphase. With increase in the cure time from a fourth to four times of t₉₀, the pull-out force after vulcanization increased significantly up to one-half of t₉₀ followed by a slight increase to t₉₀, and then decreased slowly with further increase in cure time. This decrease in pull-out force upon prolonged vulcanization may be explained by the severe degradation of rubber compound attached to the adhesion interphase. Also, upon prolonged vulcanization, the adhesion interphase with a rich ZnS layer may act as a barrier to copper diffusion which is required to form the adhesion interphase of copper sulfide. After thermal aging of the adhesion samples, the pull-out force decreased in comparison with that of the unaged. The decrease of pull-out force after thermal aging stemmed mainly from the decline of tensile properties after thermal aging. The adhesion after humidity aging was different from that after thermal aging. Upon increasing the cure time to one-half of t₉₀, the pull-out force increased. But a further increase in the cure time caused a decline in pull-out force. This phenomenon can be explained by the degradation of the adhesion interphase. At longer cure time, a severe growth of copper sulfide and a large amount of dezincification were observed in the adhesion interphase. At shorter cure time, a significant growth of copper sulfide in the adhesion interphase does not occur, whereas the formation a of a ZnS layer appeared after humidity aging. With increasing cure time, the formation of a weak boundary layer in the rubber near the adhesion interphase increased, resulting in the cohesive failure of the rubber layer. The proper formation of the adhesion interphase and the good physical properties of the rubber compound at optimum cure time can lead to the high retention of adhesion.     

Electrodeposition of a polymer interphase in carbon-fiber composites

The performance of an electrodeposited interphase of poly(butadiene-co-maleic anhydride) (BMA) in carbon-fiber composites is investigated. Carbon fibers are electrocoated with BMA from an aqueous solution and the coated fibers are fabricated into composite bars for evaluation of mechanical properties. These composites show superior impact strength, but lower interlaminar shear strength, compared to composites made from commercially treated fibers. It is suggested that unsaturation in the butadiene segments of the interphase polymer leads to the formation of a crosslinked layer during electrodeposition and subsequent drying. Inadequate penetration of this interphase by bulky epoxy molecules leads to a weak interphase/matrix interface which is the locus of failure, generating the observed mechanical properties. These conclusions are supported by examination of the fracture surfaces by Scanning Electron Microscopy. Further evidence of lack of matrix penetration into the interphase comes from electron microprobe line scans for bromine performed on cross-sections of single-filament composites, the bromine being introduced into the matrix via a brominated epoxy resin. Appropriate control of the chemical structure and physical characteristics of the interphase polymer is thus indicated, for acieving simultaneous improvements in impact and interlaminar shear strengths.     

Modeling of structured polyblend flow in a laminar shear field

A new model is proposed for describing the negative deviating behavior, NBD, of polymer blends. The model was derived for a telescopic flow of two Newtonian liquids, flowing through a capillary at vanishing Reynolds numbers. The stress field was considered continuous along the radial position, while the velocity field, due to the slippage, was assumed to be discontinuous at each interface between the two adjacent polymeric layers. A special case of an interphase with its own characteristics, thickness and viscosity, was also considered. The model derived here is applicable for Newtonian fluids or for generalized Newtonian fluids (non-Newtonian) but at constant stress and for morphologies where the phases are structured in oriented layer in the direction of flow or for sheared sandwiches. The capability of the model for describing the NDB behavior was shown on some experimental data of the literature. The main future of the results is that the interlayer slip is caused by the interfacial lubrication due to low viscosity of the narrow interphase. The proposed model was compared with Heitmiller's and Lin's models. Some inconsistencies of Lin's approach have been indicated.     

XPS analysis of the coverage and composition of coatings on glass fibres

For a fundamental approach to glass fibres for composite applications, it is essential to develop efficient methods to analyse the composition and distribution of the sizing layer on the glass filaments. We have been investigating the use of X-ray photoelectron spectroscopy (XPS) as a tool for the rapid characterization of the sizing and interphase in glass fibre reinforcements. In this report we present and discuss a model, based on a patchy sizing overlayer hypothesis, to assist the data reduction of XPS spectra from glass fibres coated with organic sizings. We show how plots of atomic ratios can be used to estimate the surface coverage of the sizing on glass fibres and to obtain information on the stoichiometry of the sizing. The results generated using this model are in good agreement with previously published data. Using this model, we show that XPS results combined with the weight fraction of the sizing give a quantitative value for the coverage of the fibre surface by the sizing.     

Effect of the interphase properties on the fracture energy and fatigue behavior of thermoset resins containing spherical fillers

Interphase region in polymer based nanocomposites is a very thin layer that is created between the reinforcing phase and the matrix surface due to reaction forces between the nanoparticles and the matrix. The ability to determine the behavior of the interphase region can facilitate the understanding and prediction of the fracture toughness and fatigue behavior through multiscale modeling. In the present study, by using the fully analytical multiscale hierarchical modeling method, fracture toughness and also fatigue behavior of thermoset resins containing spherical fillers with consideration the influences of the main damage mechanisms and interphase properties (thickness and elastic modulus of the interphase region) were investigated. The novelty of this investigation is that it enables the application of a range of properties to the interphase zone and describes a technique for multiscale modeling based on this interphase zone. The present multiscale approach quantifies the dissipation energy due to main damage mechanisms at the nanoscale and accounts for the emergence of an interphase region as functionally graded (FG) properties surrounding nanofillers. Modeling of FG interphase power-varying properties, the derivation of governing equations, and the evaluation of the findings, all are parts of the achievements of this research. In addition, multiscale analyses have been carried out on fracture energy and fatigue behavior in various fiber volume fractions with and without interphase properties. It was found that the fracture toughness and fatigue behavior are significantly dependent on the interphase elastic properties and thickness. Furthermore, the critical debonding stress and the fracture energy were assessed with various interfacial fracture energy, elastic modulus, and thickness of interphase. Finally, the accuracy of the utilized multiscale approach with consideration of interphase properties was verified by comparing the modeling results with experimental tests on thermoset resins containing spherical fillers.     

A diffusional interphase in layered polyesters

The properties of the birefringent interphase in the laminates of unsaturated polyester resin were characterized using polarized microscopy and a birefringence compensation technique. The thickness of the interphase was found to depend on the casting conditions, and values ranging from 0.004 to 0.25 mm were observed. The location and dependence of the thickness on the curing conditions suggested that the interphase formed due to the diffusion of constituents from the liquid resin of the second layer into the previously cured layer. The index of refraction of the interphase was higher than that of the polyester above and below it. There was a sharp front marking a boundary of the interphase from the rest of the resin. These observations indicated characteristics of non-Fickian interfacial diffusion. Qualitative estimation of the birefringence in the interphase by interference colors indicated the first-order optical retardation. The birefringence was hypothesized to be due to residual stresses resulting from the fabrication procedure. The birefringence was quantified using a Berek compensator to measure the stresses. The approximate stress values were found to be in the range of 10–40 MPa. © 1996 John Wiley & Sons, Inc.     

Thermal Conductivity Coefficients of Unidirectional Fiber Composites Defined by the Concept of Interphase

In this paper, the thermal conductivity coefficients of unidirectional composites have been estimated. In the present analysis, a model which takes into account the influence of the boundary interphase has been proposed. The thermal conductivity coefficients of the composite were calculated by using this concept to determine the role of the interphase which mainly depends on the quality of adhesion between fibers and matrix. The interphase matter is the part of the polymer matrix lying on the close vicinity of the fiber bounding surface. It has been primarily assumed that the interphase is inhomogeneous with thermophysical properties varying from the fiber surface to the matrix. Five laws of variation have been taken into consideration in order to derive closed form expressions for the thermal conductivity coefficients in which the role of the interphase layer occurs, possessing properties different from those of the constituent phases. A thermal analysis method known in the literature has been adopted in order to find the extent of the interphase layer. According to this viewpoint, theoretical expressions in order to calculate the thermal conductivity coefficients of the glass fiber reinforced composite materials were derived taking into consideration the interphase layer.     

Influence of Cure Conditions on the Adhesion of Rubber Compound to Brass-plated Steel Cord. Part II. Cure Time

The effect of the cure time of a rubber compound on the adhesion with brass-plated steel cord was investigated. The formation, growth and degradation of the adhesion interphase formed between the rubber compound and brass-plated steel cord was also observed as well as the formation of a weak boundary layer in the rubber near the adhesion interphase. With increase in the cure time from a fourth to four times of t ₉₀, the pull-out force after vulcanization increased significantly up to one-half of t ₉₀ followed by a slight increase to t ₉₀, and then decreased slowly with further increase in cure time. This decrease in pull-out force upon prolonged vulcanization may be explained by the severe degradation of rubber compound attached to the adhesion interphase. Also, upon prolonged vulcanization, the adhesion interphase with a rich ZnS layer may act as a barrier to copper diffusion which is required to form the adhesion interphase of copper sulfide. After thermal aging of the adhesion samples, the pull-out force decreased in comparison with that of the unaged. The decrease of pull-out force after thermal aging stemmed mainly from the decline of tensile properties after thermal aging. The adhesion after humidity aging was different from that after thermal aging. Upon increasing the cure time to one-half of t ₉₀, the pull-out force increased. But a further increase in the cure time caused a decline in pull-out force. This phenomenon can be explained by the degradation of the adhesion interphase. At longer cure time, a severe growth of copper sulfide and a large amount of dezincification were observed in the adhesion interphase. At shorter cure time, a significant growth of copper sulfide in the adhesion interphase does not occur, whereas the formation a of a ZnS layer appeared after humidity aging. With increasing cure time, the formation of a weak boundary layer in the rubber near the adhesion interphase increased, resulting in the cohesive failure of the rubber layer. The proper formation of the adhesion interphase and the good physical properties of the rubber compound at optimum cure time can lead to the high retention of adhesion.     

Conductivity model and photoacoustic FT-IR surface depth profiling of heterogeneous polymers

A novel thermal model is developed for surface depth profiling of heterogeneous polymeric surfaces using step-scan photoacoustic Fourier transform (SS PA FT-IR) spectroscopy. This approach is based on the propagation of thermal waves generated during the photoacoustic effect which travel to the film-air (F-A) interface, thus generating acoustic signals above the surface, which upon Fourier transform, result in infrared spectra. The developed model volumetrically slices the surface into finite homogeneous layers parallel to the film-air (F-A) interface and a composition of each ith layer is assumed to be the same, but the layers among themselves (ith+1 and ith−1) may or may not exhibit compositional changes. Overall thermal properties of the multi-layered surface consist of the sum of in-series connected thermal conductor layers. The proposed model can be utilized to polymeric films containing the following parametrically analyzed inclusions: (1) inclusions with no interphase between the matrix polymeric and (2) inclusions with a finite interphase. This model is flexible, allowing variations of the particle size, shape, and surface/interfacial microstructural changes. It was tested for depths of penetrations in the range of 5-50 μm for carbon black inclusions imbedded into a two-component (2K) polyurethane (PUR) film deposited on acrylonitrile-butadiene-styrene (ABS) substrate. These studies show that the experimental results are consistent with the proposed model, allowing predictions of interphase layers on particles; for example, a 10 nm water layer adsorbed on carbon black particle surfaces can be detected.     

Mechanical Characterization of Si–C(O) Fiber/SiC (CVI) Matrix Composites witrTa BN–Interphase

The mechanical behavior of three CVT-processed 2D woven SiC/BN/SiC composite materials with different initial BN interphase thicknesses has been investigated by means of tensile and impact tests. The results have established the efficiency of a BN interphase in promoting a nonlinear/non–catastrophic tensile behavior and high impact resistance. The effect of the initial BN interphase thickness on the resulting mechanical behavior has also been demonstrated. Characterization of the fiber/matrix interfacial zones by AES and TEM has revealed the presence of a SiO₂/C double layer at the BN/fiber interface, which might result from a decomposition undergone by the Si–C(O) Nicalon fiber during processing. It has been suggested that the influence of the initial BN interphase thickness on the mechanical properties of the composites results from both changes occurring in the composition and morphology of the interfacial zones and modifications of the interfacial forces due to accommodation of the radial residual clamping stress.