Geometry of the filler is important factor that can affect the dispersion and distribution states and then thermomechanical properties of the final composites will be effected.
By adding fillers large amount of fillers the mechanical properties pf polymers will reduce while the thermal properties may enhance depending on the properties of fillers. Dispersion is also very important here which depends on filler size and geometry.
There is a phenomenon called "mechanical percolation" somewhat similar to electrical percolation. It means that the dispersed phase forms a network, i.e. the size of the longest aggregates in the system become comparable with the sample size. In electrical terms it means the onset of conductivity (if the filler is conductive and the matrix is insulating). In mechanical terms it means that the low frequency modulus (G') becomes finite even is the matrix is viscous (elastic melt). This depends on the state of aggregation and on the filer shape. The critical volume fraction where mechanical (and electrical) precolation is sphere > oblate spheroid > prolate spheroid. Aggregation manifests itself in a broader distribution of particle shapes, i.e. the critical volume fraction (percolation threshold) decreases. It may also depend on the orientation. In the case of spheroidal particles the percolation threshold is smaller for random orientation than for parallel one. (http://scholarcommons.sc.edu/cgi/viewcontent.cgi?article=3231&context=etd). The dependence of the modulus on particle shape is described by the Halpin-Tsai and by the Lewis-Nielsen equations. The maximum filling factor also depends on the particle shape. If you are interested in thermomechanical properties, you have to take into account the changes of the matrix modulus with temperature. The orientation may also change with temperature if the matrix becomes soft and the stress is high.
Normally, the addition of small amount of well dispersed nanofillers can increase the thermomechanical properties of polymer composites. The filler size and filler geometry have great effect on the thermomechanical properties. The well oriented high aspect ratio filler can significantly increase the thermomechanical properties of the materials if you apply the force on the filler direction.
Thank you all for your answers. It will be very helpful if somebody can refer me few research papers regarding this.
@ Deerah Bds.
The question was in general. I am working on the choice of filler and matrix. Thanks.
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