Investigation of polymer deformation by positron annihilation

Abstract

Positron lifetimes in polytetrafluroethylene (PTFE) and polyethylene (PE) have been measured as a function of residual deformation [MATH]. For PTFE, the variation of o-Ps intensity shows a three-stage processes : the elastic region ([MATH]), plastic-f low region ([MATH]) and strain-strengthening region ([MATH]). The changes of free-volume hole size and concentration suggest the separation, scission and orientation of segments. For PE, the o-Ps parameters are sensitive to the elastic and plastic regions. Particularly, the hole concentration decreases linearly with [MATH], which indicates the crystallization during deformation

On the free volume evolution in a deformed epoxy composite. A positron annihilation study

“…From this figure, it can be concluded that there exists an increase in the size of the free-volumes when the deformation increases. This result agrees with those previously reported on similar studies [33,34]. For the composite epoxy resin the same behavior was found.…”

Molecular and nanoscale factors governing pressure‐sensitive adhesion strength of viscoelastic polymers

“…In the plastic flow stage (e ¼ 20-80%), chain reorientation and polymer crystallization led to a decrease in free volume. 106 These results indicate that the linear correlation between the growth of free volume and the value of maximum elongation, shown in Figure 16, applies only to viscoelastic amorphous polymers, which include all PSAs. In glassy polymers tensile stress can lead to a decrease in free volume.…”

“…46 It is noteworthy that both the size and the amount of free volume voids have been reported to depend on polymer strain. 106,107 For polytetrafluoroethylene 106 in the region of elastic tensile deformation (e ¼ 0-20%), hole concentration was shown to be nearly constant, with size slightly increasing with e. At the end of the elastic stage, the larger stresses induced separation of polymer segments and formation of new free volume holes, and free volume fraction increased. In the plastic flow stage (e ¼ 20-80%), chain reorientation and polymer crystallization led to a decrease in free volume.…”

Orientational order of Australian spider silks as determined by solid‐state NMR

“…X-ray diffraction results also suggest that Argiope argentata dragline silk contains a large amount of material with shortrange order or noncrystalline components. 9 Supporting data from positron annihilation spectroscopy, which gives quantitative information about the number and dimensions of free-volume sites, or amorphous regions, 43,44 indicated that the Nephila silk was more crystalline than Argiope silk (A. Hill, personal communication). We have previously shown that diet can vary the amino acid content of Argiope dragline silk 45 and this can show great inter-and intraspecies variation.…”