Morphological Control of Polymer Spherulites via Manipulating Radial Lamellar Organization upon Evaporative Crystallization: A Mini Review

Abstract

Abstract:Various spherulites or spherulitic crystals are widely encountered in polymeric materials when crystallized from viscous melts or concentrated solutions. However, the microstructures and growth processes are quite complicated and remain unclear and, thus, the formation mechanisms are rather elusive. Here, diverse kinds of spherulitic growths and patterns of typical polyesters via evaporative crystallization of solution-cast thin films are delineated after detailed investigating the microstructures and in situ following the developing processes. The spherulitic crystals produced under different evaporation conditions reflect variously optical features, such as the usual Maltese Cross, non-birefringent or half-birefringent concentric-rings, extinction spiral banding, and even a nested ring-banded pattern. Polymer spherulites are composed of stacks of radial fibrillar lamellae, and the diversity of bewitchingly spherulitic morphologies is dominated by the arrangement and organization of radial lamellae, which is predicted to be tunable by modulating the evaporative crystallization processes. The emergence of various types of spherulitic morphologies of the same polymer is attributed to a precise manipulation of the radial lamellar organization by a coupling of structural features and specific crystal evolving courses under confined evaporation environments. The present findings improve dramatically the understanding of the structural development and crystallization mechanism for emergence of diverse polymer spherulitic morphologies.

Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review

“…The surface height fluctuation of the two types of birefringent polymer banded spherulite is in the order of tens of nanometers, less than 1% of the film thickness. In contrast, in the nonbirefringent banded spherulites formed from all flat-on lamellar crystals, the height fluctuation is up to the whole thickness of the sample [1][2][3].…”

“…In the former case, the bands are due to the periodical modulation of sample thickness and there is no variation of refractive index in the spherulite. These nonbirefringent banded spherulites have been observed in some polymer single crystals formed from thin melt films [1] or solutions [2] and are reviewed by Li et al [3] in this special issue. In the latter case, the birefringent bands can result from the wavy bending growth or twisting growth of crystals.…”

2D Spherulites of a Semi‐Fluorinated Alkane: Controlled Access to Either Radial Or Ring‐Banded Morphologies

“…The former do not necessarily have a „real“ relief, while the latter can exhibit extinction bands or not. Lately, substantial interest has focused on non‐birefringent ring‐banded spherulites . The latter have only been observed with a few polymers and never with small molecules.…”

Secondary nucleation in polymer crystallization: A kinetic view

“…The competition of lamellar growth, self‐induced nucleation (or in other cases macro screw dislocations) and chain diffusion leads to formation of non‐birefringent banded spherulites caused by the periodical variation of the number of layers of the single crystals 114,116–119 . The formation of such non‐birefringent banded spherulites has been summarized in a review 120 . With increase of film thickness, the band spacing increases while the depletion length decreases, which implies that the band spacing may be affected mainly by the density of self‐induced nucleation or screw dislocations.…”