An Atomic Force Microscopy Observation of Poly(Vinylidene Fluoride) Banded Spherulites

Abstract

Wehave examined the free surface of a banded spherulite of poly(vinylidene fluoride) (PVDF) by an atomic force microscopy. The directions of the slope of multilayer terraces of lamellar crystals are retained in each half of a banded spherulite; this evidence confirms the macroscopic selection of one handedness in the formation of spiral terraces in each growth direction of the sheaf at the center of a banded spherulite of PVDF. In a previous paper it was confirmed that the three-dimensional morphology of all single crystals of PVDF grown from the melt is chair-type, and hence it is most probable that the stress in the chair crystal is responsible for the formation of spiral dislocations and terraces keeping the same handedness in each growth direction. The chair-type morphology is created because of the chain tilting to the fold surface, which can introduce symmetry breaking and consequently the selection of handedness in non-chiral polymers such as PVDF.

Crystallization of Cyclic Polymers

“…This rotation is a result of lamellar twisting. Lamellar twisting is a complicated phenomenon that is believed to be caused by (a) cumulative reorientation of lamellae at successive screw dislocation [74,75] or (b) different surface stresses on opposite fold surfaces of individual lamellae [76,77]. Tezuka et al [40] speculated that, in C-PTHF, the banded spherulites are caused by the surface stresses developed by the folded chains, such as uneven fold volume, and that the morphological differences observed between linear and cyclic PTHFs might be caused by the distinctive chain folding structures.…”

A Defect‐Free Ring Polymer: Size‐Controlled Cyclic Poly(tetrahydrofuran) Consisting Exclusively of the Monomer Unit

“…The banded spherulites indicate rotation of the optical indicatrix along a radial direction. This rotation is caused by the lamellae twisting, which is associated with cumulative reorientation of lamellae at successive screw dislocation [23,24] or different surface stresses on opposite fold surfaces of individual lamellae. [25,26] The surface stress tends to be developed by the fold structures, such as uneven fold volume, and the morphological difference observed between the linear and the ring poly(THF)s might be caused by the distinctive chain folding structures.…”

Three-dimensional shape of polyethylene single crystals grown from dilute solutions and from the melt

“…Actually for polyethylene and PVDF, it is known that polymer molecules and their crystal structures are non-chiral, and hence the selection of the handedness of the twisting in their banded spherulites must be introduced by a higher order structure [12], such as the three-dimensional shape of single crystals. As we have pointed out in our recent papers [8,9,13], the consecutive formation of spiral terraces [14] in the chair-type can be one of the candidates to produce the twisting correlation in the banded spherulites of polyethylene and PVDF.…”