Particle-matrix interface

The alternative rate-determining process to diffusion is die transfer of atoms across tire particle-matrix interface. In this case there is a rate constant for... 

If structural failure of the fabricated composite occurs by cracks in the matrix, fracture of the particle-matrix interface, or case debonding under any applied load, the extra and exposed surface will cause an enormous rise in the motor pressure during the combustion event with disasterous consequences. 

The latter interpretation of data is more in accord with the recent Al and Si NMR findings of Ellison Warrens (1987), who found that the structure of an appreciable fraction of the glass changed under acid attack with some loss of aluminium including all in fivefold coordination (see Section 5.9.2). Thus, acid attack was not entirely confined to the surface layer of a glass particle. If this is so then silicic acid as well as ions must migrate from the body of the particle and it is reasonable to suppose that silicic acid deposits as siliceous gel at the particle-matrix interface. 

If the adhesion is low, debonding at the rubber particle matrix interface can occur. In both cases voids are formed and this reduces the degree of stress triaxiality in the surrounding matrix and favors the further growth of shear bands. 

Griffin32 demonstrated that the decline in properties of starch-filled composites could be mitigated somewhat by treating the surface of the starch granules to make them more hydrophobic. This treatment improved the adhesion and stress transfer across the particle/matrix interface and resulted in improved properties relative to no treatment, although properties were still generally reduced compared to the unfilled polymer. 

Polymers can be confined one-dimensionally by an impenetrable surface besides the more familiar confinements of higher dimensions. Introduction of a planar surface to a bulk polymer breaks the translational symmetry and produces a pol-ymer/wall interface. Interfacial chain behavior of polymer solutions has been extensively studied both experimentally and theoretically [1-6]. In contrast, polymer melt/solid interfaces are one of the least understood subjects in polymer science. Many recent interfacial studies have begun to investigate effects of surface confinement on chain mobility and glass transition [7], Melt adsorption on and desorption off a solid surface pertain to dispersion and preparation of filled polymers containing a great deal of particle/matrix interfaces [8], The state of chain adsorption also determine the hydrodynamic boundary condition (HBC) at the interface between an extruded melt and wall of an extrusion die, where the HBC can directly influence the flow behavior in polymer processing. 

Above the threshold, deformation occurs as a consequence of direct particle interaction. Several mechanisms of interaction have been suggested solution-precipitation flow of fluid between particles and cavity formation at the particle matrix interface. These theories of creep suggest several rules to improve creep behavior (1) increase the viscosity of the matrix phase in multiphase materials (2) decrease the volume fraction of the intergranular phase (3) increase the grain size (4) use fiber or whisker reinforcement when possible. As the creep rupture life is inversely proportional to creep rate, lifetime can be improved by improving creep resistance. 

Decohesion and void growth are controlled by the debonding stress at the particle/matrix interface it only occurs when the local debonding stress is lower than the fracture stress (crazing stress) of the matrix itself G is correlated with the local toughness at the interface it is dependent on the particle/matrix adhesion energy. 

Overview of Mechanical Behavior. The current understanding of the mechanics and mechanisms of fracture in filled rubbers, including composite propellants, is highly advanced in some areas but surprisingly limited in others. The highly heterogeneous structure of this material leads to specific phenomena that occur mainly at the particle-matrix interface and produce a particular response to mechanical loading. 

In composite propellants, the cavitation (or debonding) process, which has been shown to take place near (or at) the particle-matrix interface, is dependent on pressure, deformation, and additional viscoelastic and dissipative considerations (10). 

Case a stress-induced formation of fibrillated crazes. The weak rubber particles act as stress concentrators. Crazes are formed starting from the particle-matrix interface around the equatorial region of particles. The voids inside the crazes initiate a stress concentration at the craze tip, which propagates together with the propagating craze therefore, the crazes reproduce the stress state necessary for their propagation. Cavitation inside the rubber particles is not necessary, but it enables a higher stress concentration and easier deformation of the particles. 

Case b stress-induced formation of homogeneous crazes. The stress concentration at the particles causes homogeneous crazes to start at the particle-matrix interfaces. Propagation of these crazes into the matrix is accomplished by an increase of volume, which arises from cavitation inside the particles (the possible mechanism of cavitation inside the originally homogeneous crazes is unlikely). Therefore, these crazes are closely connected to the cavitated rubber particles—they cannot propagate for distances as long as those of the fibrillated crazes—and appear mainly between particles. 

Utracki [1973] studied steady-state shear coagulation of PVC lattices for a wide range of variables. Assuming that the locus of coagulation is at the particle-matrix interface and that the rate of coagulation depends on the frequency of particle collisions, the critical time for coalescence was calculated as ... 

When analyzing the optical properties of nanoparticles embedded in a medium, one should take into account effects arising at the particle-matrix interface, such as the static and dynamic redistributions of charges between electronic states in the particles and the environment in view of their chemical constitution [59]. 

In this chapter, we studied the formation of silver nanoparticles in PMMA by ion implantation and optical density spectra associated with the SPR effect in the particles. Ion implantation into polymers carbonizes the surface layer irradiated. Based on the Mie classical electrodynamic theory, optical extinction spectra for silver nanoparticles in the polymeric or carbon environment, as well as for sheathed particles (silver core -l- carbon sheath) placed in PMMA, as a function of the implantation dose are simulated. The analytical and experimental spectra are in qualitative agreement. At low doses, simple monatomic silver particles are produced at higher doses, sheathed particles appear. The quantitative discrepancy between the experimental spectra and analytical spectra obtained in terms of the Mie theory is explained by the fact that the Mie theory disregards the charge static and dynamic redistributions at the particle-matrix interface. The influence of the charge redistribution on the experimental optical spectra taken from the silver-polymer composite at high doses, which cause the carbonization of the irradiated polymer, is discussed. Table 8.1, which summarizes available data for ion synthesis of MNPs in a polymeric matrix, and the references cited therein may be helpful in practice. 

Physical traps are generally associated with discontinuities in the lattice, such as voids, particle-matrix interfaces, and grain boundaries. A hydrogen atom near a purely physical trap is not specifically attracted but, once trapped, has difficulty escaping. Most traps can probably be considered to have both attractive and physical characteristics. An edge dislocation is a good example of a mixed trap with both sets of characteristics the tensile stress field provides some attractive character, while the core region provides some physical character. 

Fu, S.Y., Feng, X.Q., Lauke, B., Mai, Y.W., 2008. Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate-polymer composites. Compos. Eart B Eng. 39, 933-961. 

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