Spiral-stacked crystal assembly leading to intensified iridescence in poly(trimethylene terephthalate)

Abstract

Poly(trimethylene terephthalate) (PTT) is used as a model material to study how the internal 3D crystal structure connects with the surface banded patterns, by using physical and chemical etching methods to better reveal the crystal arrangement. Narrow crystal shells are observed to be sandwiched within the crevices of successive bands in chemically etched PTT. Furthermore, the distinct gaps between adjacent crystal bands revealed by physical etching provide additional evidence for discontinuous radial growth between bands. Spiral-spin assembly with periodic conical banded aggregates is observed, in which periodicity originated from a core nucleus whose initial geometry guided the formation of different types of banded crystals. The intensified iridescence arises from the highly ordered lamellar arrangement.