Keywords: nano free volumes, positron annihilation life time spectroscopy, PALS, polycarbonate, plastic deformation, physical aging, uniaxial compression, plane strain deformation, amorphous-amorphous transition, nanomaterials, nanotechnology
Effects of deformation and physical aging on nano-scale free volumes in polycarbonate studied by positron annihilation lifetime spectroscopy
Positron annihilation lifetime spectroscopy (PALS) has been employed to measure the variation of free volume hole parameters in poly(carbonate) (PC) after plastic deformation below the glass transition temperature (Tg). Changes in nano-scale free volume holes (Vh) and in their fraction (%fv) due to plane-strain and uniaxial compression and aging time were investigated at temperatures below Tg. For both deformation modes, %Δfv showed weak variations up to 30% thickness reduction followed by significant decrease at higher thickness reduction. As would be expected, trends in the variation of Vh were discernibly different for plane-strain and uniaxial deformation owing to shape transformation in free volumes. Vh showed a decrease followed by an increase during physical aging for both modes of deformation indicating the possibility of an amorphous-amorphous transition. Δfv showed a decrease only under uniaxial compression. The corresponding Vh size distributions showed high dependency on the mode of plastic deformation.