Interphase microstructure

Finally, how do the mechanical properties and typical failure modes of a particular interphase microstructure influence stiffness, strength and durability under various conditions (Mechanics)... 

N. Ricca, A. Guette, G. Camus and J. M. Jouin, SiC (ex-PCS)/MAS Composites with a BN Interphase Microstructure, Mechanical Properties and Oxidation Resistance, in High Temperature Ceramic Matrix Composites, Vol. 1, R. Naslain, J. Lamon and D. Doumeingts eds., Woodhead Publ. Ltd. (1993) 455- 62. 

Despite SEM evidence for significant microstructure development by highly chemically coupled composites, actual quantitative determination of interphase thickness still remains as a rather controversial topic of research. Pukanszky (18) cited values from the literature ranging from 1 nm to several millimeters depending on the type of interfacial interaction and method used to probe the interphase microstructure. 

Schaefer et al. (19) studied the interphase microstructure of ternary polymer composites consisting of polypropylene, ethylene-propylene-diene-terpolymer (EPDM), and different types of inorganic fillers (e.g., kaolin clay and barium sulfate). They used extraction and dynamic mechanical methods to relate the thickness of absorbed polymer coatings on filler particles to mechanical properties. The extraction of composite samples with xylene solvent for prolonged periods of time indicated that the bound polymer around filler particles increased from 3 to 12 nm thick between kaolin to barium sulfate filler types. Solid-state Nuclear Magnetic Resonance (NMR) analyses of the bound polymer layers indicated that EPDM was the main constituent adsorbed to the filler particles. Without doubt, the existence of an interphase microstructure was shown to exist and have a rather sizable thickness. They proceeded to use this interphase model to fit a modified van der Poel equation to compute the storage modulus G (T) and loss modulus G"(T) properties. 

Theocaris (21) developed a method for estimating interphase thickness in composites via dynamic mechanical measurements. This type of method provides a more fundamental relationship between interphase thickness and mechanical properties attributed to the interphase structure. Chapter 11 discusses this technique to probe the interphase microstructure. 

More recently, Karian (1) used DSC methodology to determine the magnitude of interfacial thickness and correlate calculated values with measured tensile strength for a spectrum of composite materials having varying degrees of chemical coupling. This thermodynamic probe of the interphase microstructure is based on the Lipatov model (22) of the interphase microstructure. 

The basis for a thermodynamic probe to describe interphase microstructure is founded on fundamental concepts of the abrupt change in molecular mobility at the glass transition temperature. If filler-polymer matrix interactions were limited to a thin interfacial boundary layer, it would not be possible to observe any difference in glass transition temperature behavior for the composite materials having different levels of filler loading or glass fiber reinforcement. 

This indicates that the PTFE particles are being pulled out of the matrix on application of stress. The microstructures of the corresponding CR composites measured by are shown in Fig. 45. The enhanced interfacial compatibility of modified PTFE particles in PTFE500kGy-CR is clearly visible in the corresponding micrographs. The modified agglomerate particles are embedded and partially enwrapped by the CR matrix. No clear and sharp interphase is... 

Figure 5.10 shows the microstructure of a pyrocarbon interphase in C/SiC composites. 

This work investigates the behaviour of elastomeric chains (polybutadienes of identical molecular weight but different microstructures) in the close vicinity of carbon black surfaces in order to attain a better understanding of the structure and properties of interphases. Elastomer-filler interactions are assessed through the study of the thermal properties and NMR relaxation characteristics of the corresponding materials. MAS solid-state NMR provides information on the effect exerted by polymer-filler interactions on the mobility of the various constitutive species of the macromolecular backbone. 

Therefore, the surface and bulk modifications of microstructure of the SE in any particular case can change the metrological characteristics of the YSZ-based gas sensor. This fact has been proven by various publications, where the same material of the SE has been sintered at the different conditions, and subsequently, such characteristics of the gas sensor as sensitivity and response/recovery time at the same temperature differ significantly from one publication to another. The efficiency of such modifications can be determined by changing the value for ctoPo in nonequilibrium conditions from its equilibrium condition Oo 3o. hi case of ctoPo = cto 3o, the surface modifications cannot change the permeability of the thick electrodes because the value of Oo 3o = (Xg 35 exp (-2c0g) can only be determined by the concentration of the measuring gas within the SE and does not connect to the state of the interphase boundaries. 

The performance and long-term stability of adhesive joints and coatings are strongly affected by the chemical and stractural properties of the interphase region situated between the uninfluenced adhesive polymer bulk and the adherend [1-16]. Unfortunately, this interphase is often hidden to the experimentalist, e.g., in closed joints. However, the interphase can be elucidated to a good approximation by studying thin polymer films [16-20] which are often referred to as open joints . Film thickness is varied in this approach to obtain information on microstructure gradients (e.g., in Refs. [1, 3, 4, 19, 20]). Bulk properties are expected to... 

The chemical structure and morphology of thin polyurethane films with various thicknesses have been characterized in order to gain insight into different formation and, different resulting microstructure of interphases on Au, Al, and Cu substrates as compared with the bulk. 

Note that in addition to the standard Dirichlet boundary data for the displacements, Dirichlet boundary data for the microstructural parameter also have to be prescribed. Experimentally [24, 37] the local mechanical properties in the interphase depend on both the polymer and the substrate. The possibility of prescribing additional boundary conditions for k is utilized to describe the variations of the mechanical properties in the interphase depending on the substrate. If on the one hand ic = ko is chosen as Dirichlet data for the structural parameter, no interphase is predicted by the model. If on the other hand, ic > Kq or K < Ko is chosen, an interphase is predicted which is either stiffer or weaker than the bulk material, respectively. The thickness of the interphase is mainly governed by the material parameters a and yS. 

Reinforced plastics, sometimes called polymer composites, consist of reinforcing fibres or particles embedded in a polymeric matrix. It is now recognized that a third component, called an interphase region, can exist at the interface between the fibre and resin. The properties of the interphase are probably not constant but vary to give a graded region. Thus the environmental durability of a composite material is a complex interplay between the various microstructural aspects of the material, which are ... 

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