Towards shape-translational symmetry incommensurate polymer crystals

Poly (3-hexylthiophene) (P3HT) Crystalsomes: Tiling 1D Polymer Crystals on a Spherical Surface

Polymer crystalsomes are a class of hollow crystalline polymer nanoparticles with shells formed by single crystals with broken translational symmetry. They have shown intriguing mechanical, thermal, and biomedical properties associated with spherical packing. Previously reported crystalsomes are formed by quasi-2D lamellae which can readily tile on a spherical surface. In this work, the formation of polymer crystalsomes formed by 1D polymer crystals is reported. Poly (3-hexylthiophene) (P3HT) is chosen as the model polymer because of its 1D growth habit. P3HT crystalsomes are successfully fabricated using a miniemulsion solution crystallization method, as confirmed by scanning electron microscopy and transmission electron microscopy. X-ray diffraction (XRD) and selected area electron diffraction experiments confirm that P3HT crystallized into a Form I crystal structure. XRD, differential scanning calorimetry and UV-Vis results reveal curvature-dependent structural, thermal and electro-optical properties.

Sectorization of Macromolecular Single Crystals Unveiled by Probing Shear Anisotropy

Polymer single crystals continue to infiltrate emerging technologies such as flexible organic field-effect transistors because of their excellent translational symmetry and chemical purity. However, owing to the methodological challenges, direct imaging of the polymer chains folding direction resulting in sectorization of single crystals has rarely been investigated. Herein, we directly image the sectorization of polymer single crystals through anisotropic elastic deformation on the surface of macromolecular single crystals. A variant of friction force microscopy, in which the scanning direction of the probe tip is parallel with the cantilever axis, allows for high contrast imaging of the sectorization in polymer single crystals. The lateral deflection of the cantilever resulting from shear forces transverse to the scan direction shows a close connection with the in-plane components of the elastic tensor of the polymer single crystals, which is of a fundamentally different origin than the friction forces. This allows for fast, facile, and nondestructive characterization of the microstructure and in-plane elastic anisotropy of compliant crystalline materials such as polymers.

Confined Crystal Melting in Edgeless Poly(l-lactic acid) Crystalsomes

Polymer single crystals tend to be quasi two-dimensional (2D) lamellae and their small lateral surfaces are the starting points of lamella melting and thickening. However, the recently discovered crystalsomes, which are defined for hollow single crystal-like spherical shells, are edgeless, self-confined, and incommensurate with translational symmetry. This work concerns the structure and melting behavior of these edgeless crystalsomes. Poly(l-lactic acid) crystalsomes were grown using a miniemulsion solution crystallization method. Differential scanning calorimetry and in situ wide-angle X-ray diffraction were used to follow the structural evolution of the crystalsomes upon heating. Our results demonstrated that the structure and melting behavior of crystalsomes are curvature-dependent and significantly different from their flat crystal counterpart.

Fabrication of 2D Block Copolymer Brushes via a Polymer-Single-Crystal-Assisted-Grafting-to Method

Block copolymer brushes are of great interest due to their rich phase behavior and value-added properties compared to homopolymer brushes. Traditional synthesis involves grafting-to and grafting-from methods. In this work, a recently developed "polymer-single-crystal-assisted-grafting-to" method is applied for the preparation of block copolymer brushes on flat glass surfaces. Triblock copolymer poly(ethylene oxide)-b-poly(l-lactide)-b-poly(3-(triethoxysilyl)propyl methacrylate) (PEO-b-PLLA-b-PTESPMA) is synthesized with PLLA as the brush morphology-directing component and PTESPMA as the anchoring block. PEO-b-PLLA block copolymer brushes are obtained by chemical grafting of the triblock copolymer single crystals onto a glass surface. The tethering point and overall brush pattern are determined by the single crystal morphology. The grafting density is calculated to be ≈0.36 nm^-2 from the atomic force microscopy results and is consistent with the theoretic calculation based on the PLLA crystalline lattice. This work provides a new strategy to synthesize well-defined block copolymer brushes.