Effect of carbon nanotube content on the free volume and mechanical properties of nylon6/carbon nanotubes (CNTs) nanocomposites have been investigated by positron annihilation lifetime spectroscopy (PALS). Experimental results found that the variation of free volume hole size is very small

while the concentration of free volume and apparent free volume fraction decrease with increasing the content of CNTs.These decreasing are due to the confining effect on polymer chains in the interfacial layer caused by CNTs

and to the enhancement of crystallinity caused by CNTs filler.The measurements of the mechanical properties revealed that the uniformly dispersion and good interfacial properties between CNTs and polymer matrix can improve the stiffness of material

but the decreasing in free volume fraction will decrease its toughness.