Morphological Features of Polyethylene and Polyimides by Atomic Force Microscopy

Abstract

Lamellar crystals of linear polyethylene grown from dilute solution in xylene were observed by atomic force microscopy (AFM). Effects of crystallization conditions, annealing and deformation were studied. Features such as lamellar thickness, fold domain boundaries, wrinkles, and pleats were observed. A temperature growth step, produced due to sudden change in temperature during crystallization, was measured accurately.

Patches, not previously studied, on the fold surfaces of the crystals exist in a range of diameters. Patches were 3–70 nm in diameter and only 0.2–1.5 nm high. Localized changes in thickness of lamella and other morphological changes due to annealing at temperatures from 115° to 135° C were observed in great detail. Shearing of lamellae at overlaps and “accidental” tensile deformations were found.

Surfaces of fibers spun from (BPDA-PMB) were imaged from atomic to micrometer scale. The free surfaces of semicrystalline BTDA** films were observed. A single polyimide fiber (BPDA-PMB) was imbedded in polyamic acid of BTDA, which was thermally imidized at 250° C and then was annealed at 280° C. Orientation of the BTDA by the BPDA-PMB persists through many molecular layers. Surfaces of BPDA-PMB fiber observed with the AFM, showed features at the molecular scale.

* regularly repeating sequences synthesized from 3,3′,4,4′tetracarboxylicbiphenyl dianhydride (BPDA) and 2,2′bis(methylmethyl)-4,4′-diaminobiphenyl (PMB)

**1,3-bis(4-aminophenoxy)-2,2′dimethylpropane and 3,3′,4,4′benzophenonetetracarboxylic dianhydride (BTDA).