Material properties filler/matrix interaction

Interfacial structure is known to be different from bulk structure, and in polymers filled with nanofillers possessing extremely high specific surface areas, most of the polymers is present near the interface, in spite of the small weight fraction of filler. This is one of the reasons why the nature of the reinforcement is different in nanocomposites and is manifested even at very low filler loadings (<10 wt%). Crucial parameters in determining the effect of fillers on the properties of composites are filler size, shape, aspect ratio, and filler-matrix interactions [2-5]. In the case of nanocomposites, the properties of the material are more tied to the interface. Thus, the control and manipulation of microstructural evolution is essential for the growth of a strong polymer-filler interface in such nanocomposites. 

The amount of carbon black, its particle size and structure, the filler-matrix interaction, and the processing technique determine the electrical properties of a product. At a certain concentration of filler, the conductivity of the material increases dramatically. This concentration is known as the percolation threshold and the conductivity of the material is expressed by equation ... 

Mittal, V. 2007. Pol5 ropylene-layered silicate nanocomposites Filler matrix interactions and mechanical properties. Journal of Thermoplastic Composite Materials 20 575-599. 

The addition of suitable compatibilizer compounds to the material as a possible way to enhance the filler-matrix interaction, and therefore improving the mechanical properties, has been studied by Spirkova et al. [75]. Polyethylene glycol (PEG) is the best compatibilizer studied. It is soluble in the water-alcohol mixture needed for the matrix synthesis, it is commonly available and relatively cheap, and the enhancement of the mechanical properties is the highest between the polyalcohols tested. PEG was able to form strong physical bonds with the filler and direct covalent bonds with the organic part of the hybrid matrix. This bonding helps bentonite nanoclay to disperse in the matrix. 

The properties of filled materials are eritieally dependent on the interphase between the filler and the matrix polymer. The type of interphase depends on the character of the interaction which may be either a physical force or a chemical reaction. Both types of interaction contribute to the reinforcement of polymeric materials. Formation of chemical bonds in filled materials generates much of their physical properties. An interfacial bond improves interlaminar adhesion, delamination resistance, fatigue resistance, and corrosion resistance. These properties must be considered in the design of filled materials, composites, and in tailoring the properties of the final product. Other consequences of filler reactivity can be explained based on the properties of monodisperse inorganic materials having small particle sizes. The controlled shape, size and functional group distribution of these materials develop a controlled, ordered structure in the material. The filler surface acts as a template for interface formation which allows the reactivity of the filler surface to come into play. Here are examples ... 

Properties of particle-filled composites, such as strength, toughness, and impact resistance, depend on the material properties of both matrix and filler. Of importance are the size and shape of the filler particles and interactions between them, the total volume occupied by the filler, the presence of voids in the structure, and the degree of adhesion between filler and matrix. When the elastic modulus of the filler is higher than that of the matrix, the modulus of the composite usually increases in proportion to the volume fraction of filler. Opposite behavior is expected if the matrix is more rigid than the filler. 

Formulating BMIs as matrices for composites and hybrid materials is another effective approach. The use of micro- and nanometer scale fillers allowed materials with new or improved properties. Studies of interactions at the interface among nanometric particles and a multicomponent polymer matrix have indicated that the interface itself can be equally important as the individual components regarding the overall effects because not all the principles from macro- and microscale can be used to explain the properties and behavior of nanocomposites. Combining these methods provides the ability to tailor and control the overall composition of these new materials, their structure (nanostructure, as well as supramolecular architecture), and also allows tunable properties by tunable structure-property relationship. 

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