Chinese Journal of Polymer Science最新文献

Wood, a readily available and sustainable natural resource, has found widespread use in construction and furniture. However, its inherent flammability poses a potential fire risk. Although intumescent fire-retardant coatings effectively mitigate this risk, achieving high transparency in such coatings presents a significant challenge. In our approach, we employed a cross-linked network of phytic acid anion and N-[3-(trimethoxysilyl) propyl]-N,N,N-trimethylammonium cation to create a transparent “three-in-one” intumescent coating. The collaborative P/N/Si flame-retardant effect markedly improved the intumescent char-forming capability, preventing the wood from rapid decomposition. This resulted in a substantial reduction in heat release (13.9% decrease in THR) and an increased limiting oxygen index (LOI) value of 35.5%. Crucially, the high transparency of the coating ensured minimal impact on the wood’s appearance, allowing the natural wood grains to remain clearly visible. This innovative approach provides a straightforward method for developing transparent intumescent flame-retardant coatings suitable for wooden substrates. The potential applications extend to preserving ancient buildings and heritage conservation efforts.

Understanding how supercoiled DNA releases intramolecular stress is essential for its functional realization. However, the molecular mechanism underlying the relaxation process remains insufficiently explored. Here we employed MD simulations based on the oxDNA2 model to investigate the relaxation process of a 336-base pair supercoiled minicircular DNA under double-strand breaks with two fixed endpoints. Our simulations show that the conformational changes in the DNA occur continuously, with intramolecular stress release happening abruptly only when the DNA chain traverses the breakage site. The relaxation process is influenced not only by the separation distance between the fixed ends but also their angle. Importantly, we observe an inhibitory effect on the relaxation characterized by small angles, where short terminal loops impede DNA conformational adjustments, preserving the supercoiled structure. These findings elucidate the intricate interplay between DNA conformational change, DNA motion and intramolecular stress release, shedding light on the mechanisms governing the relaxation of supercoiled DNA at the molecular level.

Polyampholyte gels, which have hierarchical structures, exhibit excellent self-healing properties and have great promise for biomaterials and bioengineering. We investigated the relationship between microscopic structures and macroscopic viscoelastic properties of polyampholyte gels and found three factors influencing their viscoelastic properties, including the chemical crosslinking bonds, topological entanglements controlled by monomer concentration, and the ionic bonds. Ionic strength plays a major role on the strength of ionic bonds. A crossover point of elastic modulus and loss modulus was observed in the dynamic frequency sweeps at low monomer concentration or low chemical crosslinking density for gels with intermediate strength of ionic bonds. The solid-liquid transition signaled by the crossover point is a typical feature of dynamic associated gels, representing the dynamical association-dissociation of the ionic bonds and full relaxation of the topological entanglements in the gel network. While the crossover point disappears when the ionic bonds are too weak or too strong to form “permanent” bonds. Consistently, in the non-linear yielding measurement, gels with intermediate strength of the ionic bonds are ductile and yield at very large shear strain due to the self-healing properties and the dynamic association-dissociation of the ionic bonds. But the self-healing properties disappear when the ionic bond strength is too weak or too strong. Our work reveals the mechanism of how the dynamic association-dissociation of ionic bonds influences both the linear and non-linear viscoelastic properties of the polyampholyte gels.

The injection of a polymer chain into a small circular cavity under tangential self-propelled force is studied by using Langevin dynamics simulation. Results indicate that the injection dynamics of the active polymer shows strong correlation with the polymer conformation inside the cavity depending on the polymer rigidity (k_b). The injection time τ varies nonmonotonously with increasing k_b, and reaches its minimum at k_b*. When k_b is small (k_b ≪ k_b*), the polymer is nearly random coil in the cavity, and spends a long time at the final stage of the injection process due to the large repulsion between monomers inside the cavity. When k_b is moderate (k_b ∼ k_b*), the part of polymer inside the cavity forms spiral configuration under the tangential active force, and the whole polymer moves synchronously with a constant velocity during the injection process, leading to a small injection time. When k_b is large (k_b ≫ k_b*), the polymer is nearly straight at the initial stage of the injection process, and takes a long time to bend itself, leading to a large injection time.

Effective thermal transport across solid-solid interfaces, essential in thermal interface materials (TIMs), necessitates both optimal thixotropy and high thermal conductivity. The role of filler surface modification, a fundamental aspect of TIM fabrication, in influencing these properties is not fully understood. This study employs the use of a silane coupling agent (SCA) to modify alumina, integrating experimental approaches with molecular dynamics simulations, to elucidate the interface effects on thixotropy and thermal conductivity in polydimethylsiloxane (PDMS)-based TIMs. Our findings reveal that varying SCAs modify both interface binding energy and transition layer thickness. The interface binding energy restricts macromolecular segmental relaxation near the interface, hindering desirable thixotropy and bond line thickness. Conversely, the transition layer thickness at the interface positively influences thermal conductivity, facilitating phonon transport between the polymer and filler. Consequently, selecting an optimal SCA enables a balance between traditionally conflicting goals of high thermal conductivity and minimal bond line thickness, achieving an impressively low interface thermal resistance of just 2.45–4.29 K·mm²·W⁻¹ at 40 psi.

For a polymer/polymer dismissible blend with two crystallizable components, the crystallization behavior of different components and the reciprocal influences between different crystals are interesting and important, but did not investigate in detail. In this study, the L-poly(lactic acid)/polypropylene (PLLA/PP) blends with different weight ratios were prepared by melt mixing and the crystallization behavior of the blends were investigated. Results showed that the crystalline structures of PLLA and PP were not altered by the composition. For the crystallization of PLLA, both the diffusion of chain segments and crystallization rate were enhanced under the existence of PP crystals. For the crystallization of PP, its crystallization rate was depressed under the existence of amorphous PLLA molecular chains. When the PP crystallized from the existence of PLLA crystals, although the diffusion rate of PP was reduced by PLLA crystals, the nucleation positions were obviously enhanced, which accelerated the formation of PP crystals. This investigation would supply more basic data for the application of PLLA/PP blend.

The mechanical behavior of polymer networks is intrinsically correlated with the local chain topology and chain connectivity. In this study, we delve into this relationship through the lens of coarse-grained molecular dynamics (CG-MD) simulations. Our aim is to illuminate the intricate interplay between local topology and stress distribution within polymer monomers, cross-linkers, and various components with distinct cross-link connections, thereby elucidating their collective impact on the mechanical properties of polymer networks. We mainly focus on how specific local structures contribute to the overall mechanical response of the network. In particular, we employ local stress analysis to unravel the mechanics of these structures. Our findings reveal the diverse responses of individual components, such as junctions, strands, cross-linkers between junctions, and dangling chain ends, when subjected to stretching. Notably, we observe that these components exhibit varying degrees of deformation tolerance, underscoring the significance of their roles in determining the mechanical characteristics of the network. Our investigations highlight junctions as primary contributors to stress accumulation, and particles with higher local stress showing a stronger correlation between stress and Voronoi volume. Moreover, our results indicate that both strands and cross-linkers between junctions exhibit heightened stress levels as strand lengths decrease. This study enhances our understanding of the multifaceted factors governing the mechanical attributes of cross-linked polymer systems at the microstructural level.

Abstract

Regulation of phase structure has been recognized as one of the most effective ways to fabricate self-healing polymers with high mechanical strength. The mechanical properties of the resultant polymers are certainly affected by the size of separated phase domain. However, the study on this aspect is absence, because it can hardly exclude the influence of variation in monomer proportion required for tuning the separated phase size. Here, we report the first study on tuning the phase size through reversible addition-fragmentation chain transfer (RAFT) polymerization without changing the proportion of monomers. As expected, the size of separated phase has been successfully mediated from 15 nm to 9 nm by tuning the molecular weight of the chain transfer agent. It is found that the mechanical strength and the self-healing efficiency of the resultant polymers increase simultaneously with the decrease of phase size. The study on the formation kinetics of hydrogen bonds reveals that the decrease of phase size can facilitate the re-bonding rate of hydrogen bonds, even if the migration of polymer chains is restricted.

Various sectors of the industry are searching for new materials with specific requirements, providing improved properties. The study presents novel composite materials based on polylactide that have been modified with the organosilicon compound, (3-thiopropyl) polysilsesquioxane (SSQ-SH). The SSQ-SH compound is a mixture of cage structures and not fully condensed random structures. The composite materials were obtained through injection moulding. The study includes a comprehensive characterization of the new materials that analyze their functional properties, such as rheology (MFR), mechanical strength (tensile strength, Charpy impact strength), and thermal properties. SEM microscopic photos were also taken to analyze the microstructure of the samples. The addition of a 5% by-weight organosilicon compound to polylactide resulted in a significant increase in MFR by 73.8% compared to the neat polymer. The greatest improvement in impact strength was achieved for the 5% SSQ-SH/PLA composite, increasing it by 32.0 kJ/m² compared to PLA, which represents an increase of up to 187%. The conducted research confirms the possibility of modifying the properties of the polymer by employing organosilicon compounds.

Abstract

The liquid-liquid phase separation of biopolymers in living cells contains multiple interactions and occurs in a dynamic environment. Resolving the regulation mechanism is still a challenge. In this work, we designed a series of peptides (XXLY)₆SSSGSS and studied their complexation and coacervation behavior with single-stranded oligonucleotides. The “X” and “Y” are varied to combine known amounts of charged and non-charged amino acids, together with the introduction of secondary structures and pH responsiveness. Results show that the electrostatic interaction, which is described as charge density, controls both the strength of complexation and the degree of chain relaxation, and thus determines the growth and size of the coacervates. The hydrophobic interaction is prominent when the charges are neutralized. Interestingly, the secondary structures of peptides exhibit profound effect on the morphology of the phases, such as solid phase to liquid phase transition. Our study gains insight into the phase separation under physiological conditions. It is also helpful to create coacervates with desirable structures and functions.