Effect of the shape and concentration of filler particles on the thermal expansion of polymer composites

The thermal expansion coefficient (TEC) of poly-2,6-dimethyl-1,4-phenylene oxide (PDPO) decreases upon the introductions of copper and aluminum powders or pieces of glass and carbon fibers into the compound. This effect is associated with the formation of boundary layers of the matrix around filler particles. Molecules in the boundary layers are “straightened” and packed parallel to the filler surface, which decreases the TEC. The concentration dependences of the TEC have a minimum, which is explained by partial destruction of the boundary layers, when the mean distance between the surfaces of filler particles becomes smaller than their triple diameter.