Morphological instabilities of polymer crystals

Abstract

We present experimental observations at comparatively low supercooling of morphology transitions from dendritic to faceted structures in polymer crystals growing in thin films of a poly-2-vinylpyridine-block-polyethyleneoxid copolymer. Our results are compared with theoretical concepts describing morphological instabilities of single crystals. Although these concepts originally were not developed for polymers, they allow to describe and interpret our experimental results quite well. In particular, the measured temperature dependence of the width W and frequency of dendritic side branches and the radius of curvature p of the growth tips of the crystals follow these concepts. We present preliminary evidence for the influence of polymer attachment kinetics and reorganisation processes behind the growth front. Polymer thin films provide valuable model systems for studying general concepts of crystallisation and allow to distinguish at which point the connectivity of the crystallising units within chain-like molecules starts to play a measurable role.

Can the Structures of Semicrystalline Polymers be Controlled Using Interfacial Crystallographic Interactions?

“…Dynamic Monte Carlo simulations indicate that, at high temperatures, thin polymer films on a slippery surface grow dominantly in edge‐on lamellar crystals, while flat‐on lamellar crystals are mainly observed on a sticky substrate 45. Reiter and Hu et al46–52 have performed experimental investigations on thin and ultrathin film crystallization of polymers. Abundant experimental results indicate that thin polymer films of tens to hundreds of nanometers crystallized at relatively lower supercoolings are in favor of a specific orientation, namely typical thin lamellar crystals with the molecular chains normal to the substrate (i.e., the lamellae lie “flat‐on” against the substrate 53–69.…”

Exploiting physical vapor deposition for morphological control in semi‐crystalline polymer films

“…Both lamellar thickness and width of the side branches increased with increasing crystallization temperature. [52] Similarly, Jeon and co-author observed a morphological transition for low-density polyethylene thin films atop silicon wafers when the crystallization temperature changed from 90 C to 115 C. [55] As a summary, confinement, polymer/substrate interactions, and crystallization temperature are critical factors in determining the final film morphology of semi-crystalline polymers.…”

Synthetic Covalent and Non‐Covalent 2D Materials

“…Another class of materials that can form uniform 2D nanocrystals are polymers 119. 120 The growth of polymer crystals is a complex process as it requires the organization of polymer chains which involves chain diffusion and chain folding 121. Over the past 50 years, self‐seeding has emerged as one of the best methods to produce uniform 2D polymer crystals 122.…”