In this work, the single-chain elasticity of polyformaldehyde (POM) is studied, for the first time, by employing atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS). We find that the single-chain elasticity of POM in a nonpolar organic solvent (nonane) can be described well by a theoretical model (QM-FRC model), when the rotating unit length is 0.144 nm (C―O bond length). After comparison, POM is more flexible than polystyrene (a typical polymer with C―C backbone) at the single-chain level, which is reasonable since the C―O bond has a lower rotation barrier than C―C bond. This result indicates that the flexibility of a polymer chain can be tuned by the C―O bond proportion in backbone, which casts new light on the rational design of new synthetic polymers in the future.

Two-dimensional covalent organic frameworks (COFs) with specific morphologies including nanofibers and nanoplates are highly desired in both nanoscience research and practical applications. Thus far, however, morphology engineering for COFs remains challenging because the mechanism underlying the morphology formation and evolution of COFs is not well understood. Herein, we propose a strategy of surfactant mediation coupled with acid adjustment to engineer the morphology of a β-ketoenamine-linked COF, TpPa, during solvothermal synthesis. The surfactants function as stabilizers that can encapsulate monomers and prepolymers to create micelles, enabling the formation of fiber-like and plate-like morphologies of TpPa rather than irregularly shaped aggregates. It is also found that acetic acid is important in regulating such morphologies, as the amino groups inside the prepolymers can be precisely protonated by acid adjustment, leading to an inhibited ripening process for the creation of specific morphologies. Benefitting from the synergistic enhancement of surfactant mediation and acid adjustment, TpPa nanofibers with a diameter down to ~20 nm along with a length of up to a few microns and TpPa nanoplates with a thickness of ~18 nm are created. Our work sheds light on the mechanism underlying the morphology formation and evolution of TpPa, providing some guidance for exquisite control over the growth of COFs, which is of great significance for their practical applications.

With the wide applications of lithium-ion batteries (LIBs) in electronic devices and electric vehicles, it is of great importance to improve their safety and electrochemical performance. Herein, soluble polyimides (PI) containing carboxyl groups (―COOH) were synthesized by a simple one-step method and PI separators with sponge-like, interpenetrating porous structures were prepared via non-solvent induced phase separation (NIPS). The obtained PI separators exhibited excellent thermal stability and fire-resistance properties, with the electrolyte uptake of 344% and good dimensional integrity in air at 200 °C. The results showed that the lithium-ion transference number of the obtained PI separator could reach 0.48, which was much higher than that of the Celgard-2400 separator (0.38). The Li/LiFePO₄ half-cell with the PI separator showed excellent cycle capability and high-rate performance with a high capacity of 121.80 mA·h·g^–1 at 5 C, which was better than that of the cell with the Celgard-2400 separator (54.3 mA·h·g^–1), demonstrating the promising applications of this PI separators in LIBs.

High-performance ambipolar charge transport materials can reduce the manufacturing cost of OFET and OPV devices, and simplify circuit design and device structure. In order to obtain ambipolar donor-acceptor (D-A) polymer, many efforts have been made through different donor and acceptor combination, halogenation or heteroatom substitution. However, the influencing factor for charge transport polarity is still much complicated. Based on intra-chain super-exchange mechanism for D-A polymer, we found that the energy alignment of donor and acceptor moiety has large impact on charge transport polarity. When the HOMO-LUMO (H-L) gap of the acceptor moiety is narrow, its HOMO/LUMO energy level both lie between the HOMO and LUMO of the donor moiety (sandwich-type energy alignment), and the corresponding D-A copolymers will be more likely ambipolar transport. And thus, take a narrow H-L gap thiazoleisoindigo (TzIID) acceptor as an example, we demonstrated that a series of TzIID based copolymers combined with wide H-L gap donor moieties can reveal ambipolar transport. We further predict several high performance ambipolar D-A copolymers (TzIID-TT etc.) with balanced electron and hole transport, whose effective mass (m_e^*=0.146 and m_h^*=0.128) is one of the smallest effective masses among ambipolar materials.

Biocompostable poly(glycolic acid) (PGA) crystallizes slowly under fast cooling condition, leading to poor mechanical performance of the final products. In this work, a self-nucleation (SN) route was carried out to promote the crystallization of PGA by regulating only the thermal procedure without any extra nucleating agents. When self-nucleation temperature (T_s) decreased from 250 °C to 227 °C, the nuclei density was increased, and the non-isothermal crystallization temperature (T_c) of PGA was increased from 156 °C to 197 °C and the half-life time (t_0.5) of isothermal crystallization at 207 °C was decreased by 89%. Consequently, the tensile strength and the elongation at break of the PGA were increased by 12% and 189%, respectively. According to the change of T_c as a function of T_s, a three-stage temperature domain map (Domain I, II and III) was protracted and the viscoelastic behavior of the self-nucleation melt and the homogeneous melt was studied. The results indicated that interaction among PGA chains was remained in Domain IIb, which can act as pre-ordered structure to accelerate the overall crystallization rate. This work utilizes a simple and effective SN method to regulate the crystallization behavior and the mechanical properties of PGA, which may broaden the application range of resulting materials.

Macromolecule nanocrystal network and strong interfacial interaction are always beneficial to enhance the mechanical property of polymer-based nanocomposites. Poly(vinyl alcohol) (PVA), a typical biocompatible semicrystalline polymer, is an ideal candidate for preparing high performance polymer-based nanocomposites. However, the rich hydrogen bonds between PVA matrix and graphene oxide (GO) can disrupt the formation of PVA nanocrystal network. Thus, it remains a great challenge to achieve both strong and tough PVA-GO nanocomposites. Herein, by introducing a novel Janus-like amphiphilic graphene oxide (JGO), both hydrogen bonding and interfacial crystallization have been constructed between JGO sheets and PVA matrix. Benefiting from amphiphilic interfacial interaction and the enhanced crystal network, both PVA-JGO dried films and their swollen hydrogel films show superior mechanical properties than those of traditional PVA-GO nanocomposites. PVA-JGO dried films exhibit a 264% improvement of toughness at a JGO loading of 1 wt%. Meanwhile, the corresponding PVA-JGO swollen hydrogel films display simultaneous improvement of nearly 8 times increase of tensile strength and 20 times increase of toughness compared to traditional PVA-GO nanocomposite. This work indicates multiple interfacial interactions and macromolecule crystal networks can be concurrent in PVA nanocomposites by innovative modification of nanofillers, providing a new strategy to construct PVA nanocomposites with high strength and high toughness. The integration of outstanding mechanical and swelling resistance properties on PVA-JGO nanocomposite films render their promising applications, such as packaging and toughening hydrogel materials.

Flexible electronic devices based on reversible bonds for self-curing capabilities arouses extensive interest. However, most of the composite conductive elastomers have the problems of poor mechanical properties and slow recovery of mechanical properties during multiple stretching, which hinder their stability in continuous operation. In this study, hyperbranched-MWCNTs/hyperbranched-PDMS self-healable conductive elastomers inspired by cephalopods were successfully developed. The prepared conductive elastomer exhibited good self-healing ability (91%) at room temperature excited by multiple reversible interactions. The prepared elastomer showed outstanding mechanical properties and anti-fatigue ability, so that it can cope with more arduous tasks. Moreover, the elastomer was sensitive to the change of stress states and can be used as a stable strain sensor. Therefore, the self-repairing conductive elastomer has potential practicability in the fields of human-computer interaction, motion monitoring, soft robot and so on.

Interfacial crystallization of polyoxymethylene/poly(butylene succinate) blends induced by the polyamide 6 (PA6) fiber was investigated. Due to strong heterogeneous nucleating ability, dense nuclei were generated on the surface of the PA6 fiber, which compelled the growth of twisted lamellae perpendicular to the PA6 fiber. As a result, unique interfacial banded transcrystallization was formed, which is rarely found before. Crystallization temperature was dominant in determining the nucleation activity of the PA6 fiber, further affecting the architecture of banded transcrystallization. With the increase of crystallization temperature, the nucleation density decreased to give more growth space for the twisted lamellae around the fiber. The wave-like banded stripes were transformed into fan-like stripes. Accordingly, band spacing and eccentricity respectively showed positive and negative correlation with crystallization temperature. These meaningful results shed light on regulating the architecture of banded crystals in polymer composites.

Due to the mechanical stability of the PP layer, the oriented PP/PE double-layer film with a row-nucleated crystalline structure can be annealed at a higher temperature than the PE monolayer film. In this work, the effects of annealing temperature within the melting range of PE on the crystalline structure and properties of PP/PE double-layer films were studied. When the annealing temperature is between 100 and 130 °C, below the melting point of PE, the crystallinity, the long period, lateral dimension and orientation of the lamellae in the PE layer increase with the annealing temperature due to the melting of thin lamellae and the self-nucleated effect of partially-melted melts during annealing. With the annealing temperature further increasing to 138 °C, near the melting ending point of PE, since the lamellae melt completely and the melt memory becomes weak during annealing, some spherulite structures are formed in the annealed sample, resulting in a decrease of orientation. In contrast, the annealing only causes the appearance of a low-temperature endothermic plateau in the PP layer. The improved size and orientation of lamellar structure in the PE layer increase the pore arrangement and porosity of the stretched PP/PE microporous membrane. This study successfully applies the self-nucleation effect of partially-melted polymer melt into the practical annealing process, which is helpful to guide the production of high-performance PP/PE/PP lithium batteries separator and the annealing process of other multilayer products.

A new lattice model is designed to be suitable for simulating low-molecular-weight block copolymer (BCP) melts currently used in experiments to achieve sub-10 nm domain sizes (i.e., having an invariant degree of polymerization between 10² and 10³). It gives an isothermal compressibility comparable to real polymers such as polystyrene and poly(methyl methacrylate), high Monte Carlo simulation efficiency, and the fluctuation effects important for the low-molecular-weight BCPs. With its high lattice coordination number, the model can also be readily used for branched chains such as star BCPs.

Immiscible polymer blends are an important family of polymer materials. The interfacial thickness between different phases is a very important parameter that dictates, to a great extent, the morphology and properties of such a blend. This work explores and optimizes an up-to-date atomic force microscopy (AFM) of type NanoIR2^TM system in order to quantitatively measure the interfacial thickness of immiscible polymer blends. This system is equipped with two nano-probes capable of detecting the response of a material to an infrared pulse called AFM-infrared spectroscopy mode (AFM-IR) or conducting resonance called AFM-Lorentz Contact Resonance mode (AFM-LCR), respectively. Its potential for quantitatively measuring the interfacial thickness of immiscible polymer blends is evaluated using blends composed of polyamide 6 (PA6) and polyolefin elastomer (POE) in the presence or absence of a POE containing maleic anhydride (POE-g-MAH) as a compatibilizer. Surface roughness affects adversely the signal intensity and consequently an accurate measurement of the interfacial thickness. Optimum sample surface preparation procedures are proposed.