The d forms (IIIau, IIIpu, IIIpd, and IIIad) possess smaller
Young’s modulus along the chain direction, suggesting their
poor chain rigidity. To date, the experimental data on the
mechanic properties of PVDF crystals are scarce. For the
phase Ip, the measured Young’s module is 177 GPa,19 signifi-
cantly less than the calculated value (287 GPa). The discrepancy
between the theory and experiment may be due to the
mix of different PVDF crystalline phases in the experimental
sample. In fact, an earlier experiment has shown some kink
bands existing within the crystallites of planar-zigzag form Ip,
which may lower the Young’s modulus along the chain
direction