title: Structural Hierarchy and Polymorphic Transformation in Shear-Induced Shish-Kebab of Stereocomplex Poly(Lactic Acid).
abstract: The realization of hierarchical shish-kebab structures for stereocomplex poly(lactic acid) (PLA) is achieved by the application of a shear flow (100 s(-1) for 1 s) mimicking what can be expected during polymer processing. Compared to the normal shearing scenarios, this transient and strong shear flow enables the creation of dense shish precursors in time- and energy-saving manner. The distribution of crystal form associated with the hierarchical structure is revealed by 2D Fourier transform infrared spectroscopy imaging, creating a unique visualization for both spatial resolution and polymorphism identification. Interestingly, in the shear stereocomplex chains are preferentially extended and crystallized as stable central cores with weak temperature dependence, whereas the development of lateral kebabs is defined by the distinct relation to the crystallization temperature. Below the melting point of homocrystals, both homo and stereocomplex crystallization are engaged in lamellar packing. Above that, exclusive stereocomplex crystals are organized into ordered lamellae. Combining the direct observations at multiscale, the ordered alignment of stereocomplex chains is recognized as the molecular origin of fibrillar extended chain bundles that constitute the central row-nuclei. The proposed hypothesis affords elucidation of shish-kebab formation and unique polymorphism in sheared stereocomplex PLA, which generates opportunities for engendering hierarchically structured PLA with improved performance.
authors.affiliation: College of Materials and Metallurgy, Guizhou University, Guiyang, 550025, China.|College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, 610065, China.
authors.forename: Lan
authors.initials: L
authors.lastname: Xie
authors.affiliation: College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, 610065, China.|Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, Stockholm, 100 44, Sweden.
authors.forename: Huan
authors.initials: H
authors.lastname: Xu
authors.affiliation: College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, 610065, China.
authors.forename: Zhong-Ming
authors.initials: ZM
authors.lastname: Li
authors.affiliation: Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, Stockholm, 100 44, Sweden.
authors.forename: Minna
authors.initials: M
authors.lastname: Hakkarainen
mesh_terms: D011091:Polyesters / Q000737:chemistry*; D033081:Shear Strength; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D011091:Polyesters; C033616:poly(lactide)
keywords: crystal structures; polymorphism; stereocomplex poly(lactic acid); transient shear flow