Reassessing chain tilt in the lamellar crystals of polyethylene.

Semicrystalline polymers are extensively used in various forms, including fibres, films, and bottles. They exhibit remarkable properties, e.g., mechanical and thermal, that are governed by hierarchical structures comprising 10-20-nm-thick lamellar crystals. In 1957, Keller deduced that long polyethylene (PE) chains fold to form thin single lamellar crystals, with the molecular chains perpendicular to the flat faces of the crystals (the chain-folding model). Chains inclining to the perpendicular orientation in single crystals have since been reported, along with their effects on the physical properties of PE. For bulk specimens, the chain tilt angle (φ) has been investigated only for model samples with well-annealed internal structures. However, for briefly annealed specimens, the φ values of lamellae and their origins are controversial owing to the disordered lamellar morphology and orientation. Herein, we report the direct determination of molecular-chain orientations in the lamellar crystals of high-density PE using a state-of-the-art electron-diffraction-based imaging technique with nanometre-scale positional resolution and provide compelling evidence for the existence of lamellar crystals with different inner-chain orientations. Clarifying the nanoscale variation in lamellar crystals in PE can allow precise tuning of properties and expedite resource-saving material design.

Rotaxane Formation of Multicyclic Polydimethylsiloxane in a Silicone Network: A Step toward Constructing "Macro-Rotaxanes" from High-Molecular-Weight Axle and Wheel Components.

Rotaxanes consisting of a high-molecular-weight axle and wheel components (macro-rotaxanes) have high structural freedom, and are attractive for soft-material applications. However, their synthesis remains underexplored. Here, we investigated macro-rotaxane formation by the topological trapping of multicyclic polydimethylsiloxanes (mc-PDMSs) in silicone networks. mc-PDMS with different numbers of cyclic units and ring sizes was synthesized by cyclopolymerization of a α,ω-norbornenyl-functionalized PDMS. Silicone networks were prepared in the presence of 10-60 wt % mc-PDMS, and the trapping efficiency of mc-PDMS was determined. In contrast to monocyclic PDMS, mc-PDMSs with more cyclic units and larger ring sizes can be quantitatively trapped in the network as macro-rotaxanes. The damping performance of a 60 wt % mc-PDMS-blended silicone network was evaluated, revealing a higher tan δ value than the bare PDMS network. Thus, macro-rotaxanes are promising as non-leaching additives for network polymers.

Correlative light and electron microscopy of poly(ʟ-lactic acid) spherulites for fast morphological measurements using a convolutional neural network.

Polarized optical microscopy (POM) and transmission electron microscopy (TEM) are widely used for imaging polymer spherulite structures. TEM provides nanometer resolution to image small spherulites of sub-micrometer in diameter, while POM is more suitable for observing large spherulites. However, high-resolution images with a large field of view are challenging to achieve due to the deformations of ultrathin sectioned samples used for TEM observations. In this study, we demonstrated that correlative light and electron microscopy (CLEM) combining POM and TEM could effectively characterize the spherulite structures in a wide range from nanometer to several hundred micrometers that neither TEM nor POM alone could cover. Furthermore, the deformations of the TEM ultrathin sections were corrected by referencing to the POM images at the same position of the sample, and large-area TEM images without deformations were successfully produced. The spherulite structures of poly(ʟ-lactic acid) were successfully analyzed using CLEM and TEM in a wide range of spatial scales at the same field of view. The large-area TEM image (250 µm × 250 µm), consisting of 702 TEM images stitched together, was subjected to machine learning to extract the essential structural information of spherulites. Analysis using the convolutional neural network, a well-known algorithm You Only Look Once (YOLO), demonstrated that it was practical to accurately obtain the diameter distribution and the space-filling factor (relative crystallinity) of the spherulites. This study presents a new approach for acquiring high-resolution images with a large field of view and processing the images at a fast speed.

Topology-transformable block copolymers based on a rotaxane structure: change in bulk properties with same composition.

The topology of polymers affects their characteristic features, i.e., their microscopic structure and macroscopic properties. However, the topology of a polymer is usually fixed during the construction of the polymer chain and cannot be transformed after its determination during the synthesis. In this study, topology-transformable block copolymers that are connected via rotaxane linkages are introduced. We will present systems in which the topology transformation of block copolymers changes their 1) microphase-separated structures and 2) macroscopic mechanical properties. The combination of a rotaxane structure at the junction point and block copolymers that spontaneously form microphase-separated structures in the bulk provides access to systems that cannot be attained using conventional covalent bonds.

Temperature-Directed Assembly of Crystalline Cellulose Oligomers into Kinetically Trapped Structures during Biocatalytic Synthesis.

Crystalline polysaccharides, such as cellulose and chitin, can form superior assemblies in terms of physicochemical stability and mechanical properties. However, their use as molecular building blocks for self-assembled materials is rare, possibly because each crystalline polysaccharide has its own unique monomer unit, preventing molecular design for controlling the self-assembly. Herein, we demonstrate the temperature-directed assembly of crystalline cellulose oligomers into kinetically trapped structures, namely, precipitated nanosheets, nanoribbon network hydrogels, and dispersed nanosheets (in descending order of temperature). It was found that enzymatically synthesized cellulose oligomers self-assembled in situ into those structures depending on the synthetic temperatures. Mechanistic studies suggested that the formation of the nanoribbon networks and the dispersed nanosheets at lower temperatures were driven by synergy between the decreased hydrophobic effect and the simultaneously induced self-crowding effect. Furthermore, nanoribbon network formation was exploited for the construction of cellulose oligomer-based hybrid gels with colloidal particles. Our findings promote the development of robust self-assembled materials composed of crystalline polysaccharides with highly ordered nano-to-macroscale structures.

High Thermal Diffusivity in Thermally Treated Filamentous Virus-Based Assemblies with a Smectic Liquid Crystalline Orientation.

Polymers are generally considered thermal insulators because the amorphous arrangement of the polymeric chains reduces the mean free path of heat-conducting phonons. Recent studies reveal that individual chains of polymers with oriented structures could have high thermal conductivity, because such stretched polymeric chains effectively conduct phonons through polymeric covalent bonds. Previously, we have found that the liquid crystalline assembly composed of one of the filamentous viruses, M13 bacteriophages (M13 phages), shows high thermal diffusivity even though the assembly is based on non-covalent bonds. Despite such potential applicability of biopolymeric assemblies as thermal conductive materials, stability against heating has rarely been investigated. Herein, we demonstrate the maintenance of high thermal diffusivity in smectic liquid crystalline-oriented M13 phage-based assemblies after high temperature (150 °C) treatment. The liquid crystalline orientation of the M13 phage assemblies plays an important role in the stability against heating processes. Our results provide insight into the future use of biomolecular assemblies for reliable thermal conductive materials.

Filamentous Virus-based Assembly: Their Oriented Structures and Thermal Diffusivity.

Organic polymers are generally regarded as thermal insulators because amorphous arrangement of molecular chains reduces the mean free path of heat-conducting phonons. However, recent studies indicated that single chains of polymers with highly oriented structures could have high thermal conductivity than bulk polymers because stretched polymer chains effectively conduct phonons through polymeric covalent bonds. Here, we demonstrated the possibility of non-covalent virus assembly prepared by simple flow-induced methods toward high thermal conductive polymeric materials. Films with high thermal diffusivity composed of non-covalent bond-based assemblies of liquid crystalline filamentous viruses were prepared using a simple flow-induced orientation method. Structural and thermal characterization demonstrated that highly oriented structures of the viruses in the film were attributed to the high thermal diffusivity. Our results will open attractive opportunities for biomolecular-based thermally conductive soft materials even though the assemblies are based on non-covalent bonds.

Effect of Component Mobility on the Properties of Macromolecular [2]Rotaxanes.

Macromolecular [2]rotaxanes comprising a polymer axle and crown ether wheel were synthesized to evaluate the effect of component mobility on the properties of the axle polymer, especially its crystallinity. Living ring-opening polymerization of δ-valerolactone with a pseudorotaxane initiator with a hydroxy group at the axle terminus was followed by end-capping with a bulky isocyanate. This yielded macromolecular [2]rotaxanes (M2Rs) possessing polyester axles of varying molecular weights. The crystallinity of the axle polymers of two series of M2Rs, with either fixed and movable components, was evaluated by differential scanning calorimetry. The results revealed that the effect of component mobility was significant in the fixed and movable M2Rs with a certain axle length, thus suggesting that the properties of the axle polymer depend on the mobility of the polyrotaxane components.

Crystal Polymorphism of Curdlan Propionate: 6-Fold versus 5-Fold Helices.

The molecular and crystal structures of curdlan propionate (CDPr) were examined by the X-ray fiber diffraction methods combined with energy calculations. CDPr forms two different crystal structures (CDPr forms I and II) depending on annealing conditions: solvent-annealing yields CDPr form I, whereas thermal-annealing gives CDPr form II. In CDPr form I, the 6/1 helix is packed in the hexagonal unit cell with a = b = 1.154 nm, and c (fiber axis) = 2.287 nm. In the case of CDPr form II, the 5/1 helix is packed in the pseudohexagonal cell with a = b = 1.175 nm, and c (fiber axis) = 1.859 nm. The crystal transition from CDPr forms I to II occurs by thermal-annealing at temperatures ≥ 160 °C.

Curdlan ester derivatives: synthesis, structure, and properties.

A series of ester derivatives of curdlan, which is a ß-(1 → 3)-D-glucan extracellularly produced by microorganism, with varying alkyl chain lengths (C2-C12) were synthesized by the heterogeneous reaction using trifluoroacetic anhydride. As a result, high-molecular-weight (Mw ≥ 6 × 10(5)) and fully-acylated curdlan was obtained with relatively high yield (>70%). Thermal stability of curdlan was greatly improved by esterification. Crystallization was observed for curdlan esters with C2-C6 side chains. Both Tg (170 → 50 °C) and Tm (290 → 170 °C) of curdlan esters decreased with increasing the side-chain length. By the increase in the side-chain carbon number, curdlan esters showed lower Young's modulus and tensile strength, and larger elongation at break. Thus, material properties of curdlan esters can be controlled by changing the side-chain length. It was found that the increase of the side-chain length resulted in the decrease of crystallinity and the change of crystal structures.

Guest-induced crystal-to-crystal transitions of poly(L-lactide) complexes.

In this study, we systematically investigated various crystal-to-crystal transitions relating to poly(L-lactide) (PLLA) cocrystallized with low-molecular-weight compounds using wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. First, the solvent exchange and the resultant crystal transition of solvent complexes were investigated. Basically, the solvent exchange treatments at -25 °C became successful, although some specific phenomena depending on solvent species were seen. The ratio of the α-form in the crystalline region increased by an increase in the solvent exchange temperature. Second, the crystal transition behavior between CO(2) and solvent complexes was investigated. The complete transition from solvent complex to CO(2) complex was observed for all solvent complexes. In contrast, it was found that types of solvents and the surrounding temperature have a great effect on the transition behavior from CO(2) to solvent complexes. Finally, the guest-induced transitions of noncomplex crystals (α-, α'-, and α″-forms) were examined. As a result, it was revealed that the guest-induced transition behavior of noncomplex crystals was much influenced by the order of crystal (chain conformation and packing) of noncomplexes (α, α', and α″) as well as kinds of guests.

Atomic Force Microscopy Observation of Polylactide Stereocomplex Edge-On Crystals in Thin Films: Effects of Molecular Weight on Lamellar Curvature.

The shapes of the edge-on lamellar crystals of equiweight poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) stereocomplexes with various combinations of molecular weights were investigated by using atomic force microscopy. In the cases of the PLLA/PDLA blends with equivalent molecular weights, the straight-shaped edge-on lamellae were observed. On the other hand, the curved edge-on crystals were able to be seen for the PLLA/PDLA stereocomplexes with nonequivalent molecular weights. It was revealed that the direction of lamellar curvature in the polylactide (PLA) stereocomplexes with nonequivalent molecular weights is the same as that of PLA having lower molecular weight. In addition to the PLLA/PDLA blending ratio, the incidence of chain folding, which is strongly influenced by molecular weight, was considered to have a crucial effect on the lamellar curvature in the edge-on crystals of PLA stereocomplexes.