Binder filler interface

An important consideration is the effect of filler and its degree of interaction with the polymer matrix. Under strain, a weak bond at the binder-filler interface often leads to dewetting of the binder from the solid particles to formation of voids and deterioration of mechanical properties. The primary objective is, therefore, to enhance the particle-matrix interaction or increase debond fracture energy. A most desirable property is a narrow gap between the maximum (e ) and ultimate elongation ch) on the stress-strain curve. The ratio, e , eh, may be considered as the interface efficiency, a ratio of unity implying perfect efficiency at the interfacial Junction. 

The properties of syntactic materials are influenced by several factors including the binder/filler ratio, the process and hardening conditions, and the physicochemical processes at the binder/filler interface 12,76,99). The best syntactic foams, at given apparent densities of 680-700 kg/m3, have a compression strength of 10 MPa, shear and tension elastic moduli of 2500—3000 MPa ultimate bending strengths of 40 to... 

The strength of adhesion also depends on the filler, being better with glass than with phenolic microspheres. This is due to better adhesion at the binder-filler interface (See Sect. 5.2.2) 6-124). 

The mechanical parameter of a highly filled syntactic foam must in general be analyzed taking into account the interactions at the binder—filler interface and the system s stresses since both of these factors are important for highly filled systems 8 W0). 

The first step of the failure process in filled rubber is the formation of vacuoles within the binder or at the binder-filler interface. Depending on the ratio of the strength of the adhesive bond between filler and binder to the cohesive strength of the binder, different phenomena may be observed at the yield point. 

There was proposed another view on the mechanism of reinforcement of plastics. The main factor in reinforcement is ascribed to the forces of friction at the polymer-filler interface, which determine the possibility of their joint functioning. These forces occur as a result of shrinkage of the poljnner on curing. In this case, the elasticity and stressed state of the ciued binder in the layers contacting the siuface of the fibers are the decisive factors, not the adhesion. ... 

The in-plane view onto the surface of the C3 sample in Fig. 9.4(c) shows a situation where the embedding of the filler (2) by the binder (1) can be recognized along the fiber axis. The wetting between the two phases is not perfect and varies from location to location highlighting the serious issue of preparing the molecular structure of the interface between binder and filler by functionalization [39,60,61] of the filler. 

It should be noted that a similar approach can be used for an optimum composition of a composite based on a polyfractional filler with a maximum possible packing fraction. One should remember, however, in that case that for a correct choice of the composite composition it is necessary to take into account the interactions existing at the mineral filler — liquid binder interface and leading to formation on the filler surface of the so-called boundary layers [105]. A comparatively simple method for a rough estimation of these interactions for highly-loaded composites is to be found in [106]. 

Tensile properties of composite propellants depend on the tensile properties of the matrix, concentration of the components, particle size, particle-size distribution, particle shape, quality of the interface between fillers and polymeric binder, and, obviously, experimental conditions (strain rate, temperature, and environmental pressure). Many authors (2, 3) have explained the effect of fillers on the mechanical properties of composites, the importance of the filler-matrix interface on physical properties, and the mechanism of reinforcement of the material. Other efforts have examined the effect of experimental conditions on the failure properties of filled elastomers. Landel and... 

Figure 6. The cavitation process near the filler-binder interface during a tensile test.

Electrochemical reactions are heterogeneous reactions which occur on the electrolyte-electrolyte interface. In fuel cell systems, the reactants are supplied from the electrolyte phase to the catalytic electrode surface. In battery systems, the electrodes are usually composites made of active reactants, binder and conductive filler. In order to minimize the energy loss due to both activation and concentration polarizations at the electrode surface and to increase the electrode efficiency or utilization, it is preferred to have a large electrode surface area. This is accomplished with the use of a porous electrode design. A porous electrode can provide an interfacial area per unit volume several decades higher than that of a planar electrode (such as 10" cm ). 

To improve adhesion of binders to fibres, including carbon fibers, methods of surface treatment by cold plasma were developed. In the course of such treatment, the removal of a weak border layer of the fiber proceeds and the contact between the surface and a binder is improved. At the same time, the number of active centers capable of chemical interaction with a binder increases and the wetting becomes better. It may be expected that pol5mierization under plasma action may also serve as a tool adhesion improvement at the phase border. In spite of the existence of many ways of surface treatment of the reinforcement surface, no model of interaction was proposed which is effective in predicting the t5T)e of reinforcement by surface treatment of a given filler-matrix combination. According to Drzal, the major reason for this lack of theoretical developments is in the over-simplification of the composition and nature of the filler-matrix interface. 

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