Deposition patterns formed by the evaporation of linear diblock copolymer solution nanodroplets on solid surfaces.

The evaporation-induced deposition pattern of the linear diblock copolymer solution has attracted attention in recent years. Given its critical applications, we study deposition patterns of the linear diblock copolymer solution nanodroplet on a solid surface (the wall) by molecular dynamics simulations. This study focuses on the influence of the nonbonded interaction strength, including the interaction between the wall and polymer blocks (ɛAW and ɛBW), the interaction between the solvent and the wall (ɛSW), and the interaction between polymer blocks (ɛAB). Conditions leading to diverse deposition patterns are explored, including the coffee-ring and the volcano-like structures. The formation of the coffee-ring structure is attributed to receding interfaces, the heterogeneity inside the droplet, and the self-assembly of polymer chains. This study contributes to the establishment of guidelines for designing deposition patterns of the linear diblock copolymer solution nanodroplet, which facilitates practical applications such as inkjet printing.

Lignin Derived Ultrathin All-Solid Polymer Electrolytes with 3D Single-Ion Nanofiber Ionic Bridge Framework for High Performance Lithium Batteries.

The lignin derived ultrathin all-solid composite polymer electrolyte (CPE) with a thickness of only 13.2 µm, which possess 3D nanofiber ionic bridge networks composed of single-ion lignin-based lithium salt (L-Li) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as the framework, and poly(ethylene oxide)/lithium bis(trifluoromethanesulfonyl)imide (PEO/LiTFSI) as the filler, is obtained through electrospinning/spraying and hot-pressing. t. The Li-symmetric cell assembled with the CPE can stably cycle more than 6000 h under 0.5 mA cm-2 with little Li dendrites growth. Moreover, the assembled Li||CPE||LiFePO4 cells can stably cycle over 700 cycles at 0.2 C with a super high initial discharge capacity of 158.5 mAh g-1 at room temperature, and a favorable capacity of 123 mAh g-1 at -20 °C for 250 cycles. The excellent electrochemical performance is mainly attributed to the reason that the nanofiber ionic bridge network can afford uniformly dispersed single-ion L-Li through electrospinning, which synergizes with the LiTFSI well dispersed in PEO to form abundant and efficient 3D Li+ transfer channels. The ultrathin CPE induces uniform deposition of Li+ at the interface, and effectively inhibit the lithium dendrites. This work provides a promising strategy to achieve ultrathin biobased electrolytes for solid-state lithium ion batteries.

Structural heterogeneity in tetra-armed gels revealed by computer simulation: Evidence from a graph theory assisted characterization.

Designing homogeneous networks is considered one typical strategy for solving the problem of strength and toughness conflict of polymer network materials. Experimentalists have proposed the hypothesis of obtaining a structurally homogeneous hydrogel by crosslinking tetra-armed polymers, whose homogeneity was claimed to be verified by scattering characterization and other methods. Nevertheless, it is highly desirable to further evaluate this issue from other perspectives. In this study, a coarse-grained molecular dynamics simulation coupled with a stochastic reaction model is applied to reveal the topological structure of a polymer network synthesized by tetra-armed monomers as precursors. Two different scenarios, distinguished by whether internal cross-linking is allowed, are considered. We introduce the Dijkstra algorithm from graph theory to precisely characterize the network structure. The microscopic features of the network structure, e.g., loop size, dispersity, and size distribution, are obtained via the Dijkstra algorithm. By comparing the two reaction scenarios, Scenario II exhibits an overall more idealized structure. Our results demonstrate the feasibility of the Dijkstra algorithm for precisely characterizing the polymer network structure. We expect this work will provide a new insight for the evaluation and description of gel networks and further help to reveal the dynamic process of network formation.

Functionalized lignin nanoparticles assembled with MXene reinforced polypropylene with favorable UV-aging resistance, electromagnetic shielding effects and superior fire-safety.

Deterioration in mechanical performances and aging resistance due to the introduction of flame retardants is a major obstacle for bio-based fire-safety polypropylene (PP). Herein, we reported a kind of functionalized lignin nanoparticles assembled with MXene (MX@LNP), and applied it to construct the flame-retardant PP composites (PP-MA) with superior fire safety, excellent mechanical performance, electromagnetic shielding effects and aging resistance. Specifically, the PP-MA doped with only 18 wt% flame-retardant additives (PP-MA18) achieved the UL-94 V-0 rating. In comparison to pure PP, PP-MA18 presented a greatly decreased peak of heat release rate (pHRR), total heat rate (THR), and peak smoke production rate (pSPR) by 79.7 %, 69.0 % and 75.8 %, respectively, and satisfactory decrease in total flammable and toxic volatiles evolved. The formed fine solid microstructure of carbon residuals effectively promoted the compactness of char layers. More importantly, the nano-effect and the strong interface interaction between the complexed MX@LNP and PP enhanced the tensile strength (45.78 MPa) and elongation at break (725.95 %) of PP-MA. Additionally, the significant ultraviolet absorption and electromagnetic wave dissipation performance of MXene and lignin enabled excellent aging resistance and electromagnetic shielding effects of PP-MA compared with PP. This achieved MX@LNP afforded a novel approach for developing flame retardant materials with excellent application performance.

PolyNC: a natural and chemical language model for the prediction of unified polymer properties.

Language models exhibit a profound aptitude for addressing multimodal and multidomain challenges, a competency that eludes the majority of off-the-shelf machine learning models. Consequently, language models hold great potential for comprehending the intricate interplay between material compositions and diverse properties, thereby accelerating material design, particularly in the realm of polymers. While past limitations in polymer data hindered the use of data-intensive language models, the growing availability of standardized polymer data and effective data augmentation techniques now opens doors to previously uncharted territories. Here, we present a revolutionary model to enable rapid and precise prediction of Polymer properties via the power of Natural language and Chemical language (PolyNC). To showcase the efficacy of PolyNC, we have meticulously curated a labeled prompt-structure-property corpus encompassing 22 970 polymer data points on a series of essential polymer properties. Through the use of natural language prompts, PolyNC gains a comprehensive understanding of polymer properties, while employing chemical language (SMILES) to describe polymer structures. In a unified text-to-text manner, PolyNC consistently demonstrates exceptional performance on both regression tasks (such as property prediction) and the classification task (polymer classification). Simultaneous and interactive multitask learning enables PolyNC to holistically grasp the structure-property relationships of polymers. Through a combination of experiments and characterizations, the generalization ability of PolyNC has been demonstrated, with attention analysis further indicating that PolyNC effectively learns structural information about polymers from multimodal inputs. This work provides compelling evidence of the potential for deploying end-to-end language models in polymer research, representing a significant advancement in the AI community's dedicated pursuit of advancing polymer science.

Exploring mechanical properties and failure mechanisms of aramid and PBO crystals through molecular dynamics simulations.

Molecular dynamics simulations were used to analyze the mechanical properties and failure processes of poly(p-phenylene-terephthalamide) (PPTA), poly(p-phenylene-benzimidazole-terephthalamide) (PBIA), PBIA-PPTA (formed by 1:1 copolymerization of PPTA and PBIA), and poly(p-phenylene-benzobisoxazole) (PBO) crystals at different strain rates and temperatures. The failure stress and strain were found to be linear with the temperature and logarithmic strain rate. Moreover, based on the kinetic theory of fracture and the comprehensive simulation results, we formulated a model that describes the failure stress of the aforementioned crystals under varying strain rates and temperatures. Through the analysis of the failure process, we found that in PPTA, PBIA, and PBIA-PPTA crystals, the bond failure probability is correlated with the strain rate and temperature. The examination of bond lengths and angles unveiled that bonds with larger initial aligning angles are more susceptible to failure during the strain process. Intriguingly, the stretching process induced a conformational change in the PBO molecular chain, leading to a deviation from the linear relation in its stress-strain curve.

Helical structures of achiral liquid crystals under cylindrical confinement.

Confined liquid crystals (LCs) exhibit complex and intriguing structures, which are fascinating fundamental problems in soft matter. The helical structure of cylindrical cavities is of great importance in LC studies, particularly for their application in optical devices. In this study, we employ molecular dynamics simulations to explore the behavior of achiral smectic-B LCs confined in narrow cylindrical cavities, where geometric frustration plays an important role. By increasing the cylinder size, LCs exhibit a transition from multi-helical to layered structures. Notably, we observe two stable structures, namely the helical structure and the layered structure, at moderate cylinder size. We also investigate the effects of the arrangement of cylindrical wall particles (hexagonal or square array) and anchoring strength on the LC structure. Our findings reveal that both the hexagonal array and strong anchoring strength promote the formation of helical structures. Our study provides novel insights into the confinement physics of LCs and highlights the potential for achieving helical structures in achiral LCs, which will expand the future applications of LCs.

The design of highly conductive and stretchable polymer conductors with low-load nanoparticles.

Highly conductive and stretchable polymer conductors fabricated from conductive fillers and stretchable polymers are urgently needed in flexible electronics, implants, soft robotics, etc. However, polymer conductors encounter the conductivity-stretchability dilemma, in which high-load fillers needed for high conductivity always result in the stiffness of materials. Herein, we propose a new design of highly conductive and stretchable polymer conductors with low-load nanoparticles (NPs). The design is achieved by the self-assembly of surface-modified NPs to efficiently form robust conductive pathways. We employ computer simulations to elucidate the self-assembly of the NPs in the polymer matrices under equilibrium and tensile states. The conductive pathways retain 100% percolation probability even though the loading of the NPs is lowered to ∼2% volume. When the tensile strain reaches 400%, the percolation probability of the ∼2% NP system is still greater than 25%. The theoretical prediction suggests a way for advancing flexible conductive materials.

Single-Ion Polymer Electrolyte Based on Lithium-Rich Imidazole Anionic Porous Aromatic Framework for High Performance Lithium-Ion Batteries.

The low ionic conductivity and Li+ transference number ( t L i + ${t}_{L{i}^ + }$ ) of solid polymer electrolytes (SPEs) seriously hinder their application in lithium-ion batteries (LIBs). In this study, a novel single-ion lithium-rich imidazole anionic porous aromatic framework (PAF-220-Li) is designed. The abundant pores in PAF-220-Li are conducive to the Li+ transfer. Imidazole anion has low binding force with Li+ . The conjugation of imidazole and benzene ring can further reduce the binding energy between Li+ and anions. Thus, only Li+ moved freely in the SPEs, remarkably reducing the concentration polarization and inhibiting lithium dendrite growth. PAF-220-quasi-solid polymer electrolyte (PAF-220-QSPE) is prepared through solution casting of Bis(trifluoromethane)sulfonimide lithium (LiTFSI) infused PAF-220-Li and Poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP), and possessed excellent electrochemical performance. The electrochemical property are further improved by preparing all-solid polymer electrolyte (PAF-220-ASPE) via pressing-disc method, which has a high Li+ conductivity of 0.501 mS cm-1 and t L i + ${t}_{L{i}^ + }$ of 0.93. The discharge specific capacity at 0.2 C of Li//PAF-220-ASPE//LFP reached 164 mAh g-1 , and the capacity retention rate is 90% after 180 cycles. This study provided a promising strategy for SPE with single-ion PAFs to achieve high-performance solid-state LIBs.

Automatic Multiscale Method of Building up a Cross-linked Polymer Reaction System: Bridging SMILES to the Multiscale Molecular Dynamics Simulation.

An automatic method is introduced to generate the initial configuration and input file from SMILES for multiscale molecular dynamics (MD) simulation of cross-linked polymer reaction systems. Inputs are a modified version of SMILES of all the components and conditions of coarse-grained (CG) and all-atom (AA) simulations. The overall process comprises the following steps: (1) Modified SMILES inputs of all the components are converted to 3-dimensional coordinates of molecular structures. (2) Molecular structures are mapped to the coarse-grained scale, followed by a CG reaction simulation. (3) CG beads are backmapped to the atomic scale after the CG reaction. (4) An AA productive run is finally performed to analyze volume shrinkage, glass transition, and atomic detail of network structure. The method is applied to two common epoxy resin reactions, that is, the cross-linking process of DGEVA (diglycidyl ether of vanillyl alcohol) and DHAVA (dihydroxyaminopropane of vanillyl alcohol) and that of DGEBA (diglycidyl ether of bisphenol A) and DETA (diethylenetriamine). These components form network structures after the CG cross-linking reaction and are then backmapped to calculate properties in the atomic scale. The result demonstrates that the method can accurately predict volume shrinkage, glass transition, and all-atom structure of cross-linked polymers. The method bridges from SMILES to MD simulation trajectories in an automatic way, which shortens the time of building up cross-linked polymer reaction model and suitable for high-throughput computations.

Defect transition of smectic liquid crystals confined in spherical cavities.

The formation and transformation of defects in confined liquid crystals are fascinating fundamental problems in soft matter. Here, we use molecular dynamics (MD) simulations to study ellipsoidal liquid crystals (LCs) confined in a spherical cavity, which significantly affects the orientation and translation of LC molecules near the surface. The liquid-crystal droplet can present the isotropic to smectic-B phase transition through the smectic-A phase, as the number density of the LC molecules increases. We further find the change of LC structure from bipolar to watermelon-striped during the phase transition from smectic-A (SmA) to smectic-B (SmB) phases. Our results reveal the transition from bipolar defects to the inhomogeneous structures with the coexistence of nematic and smectic phases in smectic liquid-crystal droplets. We also study the influence of the sphere size in the range of 10σ0 ≤ Rsphere ≤ 50σ0 on the structural inhomogeneities. It shows a weak dependence on the sphere size. We further focus on how the structures can be affected by the interaction strength εGB-LJ. Interestingly, we find the watermelon-striped structure can be changed into a configuration with four defects at the vertices of a tetrahedron upon increasing the interaction strength. The liquid crystals at a strong interaction strength of εGB-LJ = 10.0ε0 show the two-dimensional nematic phase at the surface. We further present an explanation for the origin of the striped-pattern formation. Our results highlight the potential for using confinement to control these defects and their associated nanostructural heterogeneity.

Single-Ion Gel Polymer Electrolyte based on In-Situ UV Irradiation Cross-Linked Polyimide Complexed with PEO for Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) have become the research focus of energy storage products. Due to the combination of Li+ and the Lewis basic sites of polymer chains, anions move more than five times faster, which do not participate in the electrode reaction during the discharge cycles, leading to concentration polarization, voltage losses, and high internal resistance. To solve this phenomenon, in this work, a polymer network structure of single-ion polymer electrolyte-based polyimide (DPI-SIGPE) with plasticizer ethylene carbonate (EC)/dimethyl carbonate (DMC) is formed by in-situ cross-linking double bond polyimide, 4-styrene sulfonyl (benzenesulfonyl) imide, and cross-linking agent pentaerythritol tetra(2-thiol acetate) under UV irradiation. By incorporating the anion as a part of the polymer chain, DPI-SIGPE exhibits high lithium-ion conductivity of 2.7 × 10-4 S cm-1 at 30 °C and transference number of 0.87. Typical lithium stripping/plating cycling of 900 h demonstrates uniform lithium deposition impacted by DPI-SIGPE. Meanwhile, it has good dimensional thermal stability with no obvious shrinkage at 200 °C for 0.5 h and wide electrochemical window of 4.6 V. Thus, the polyimide-based cross-linked single-ion gel polymer electrolyte has the promising potential for application in LIBs.

External field induced defect transformation in circular confined Gay-Berne liquid crystals.

Normally, defects in two-dimensional, circular, confined liquid crystals can be classified into four types based on the position of singularities formed by liquid crystal molecules, i.e., the singularities located inside the circle, at the boundary, outside the circle, and outside the circle at infinity. However, it is considered difficult for small aspect ratio liquid crystals to generate all these four types of defects. In this study, we use molecular dynamics simulation to investigate the defect formed in Gay-Berne, ellipsoidal liquid crystals, with small aspect ratios confined in a circular cavity. As expected, we only find two types of defects (inside the circle and at the boundary) in circular, confined, Gay-Berne ellipsoids under static conditions at various densities, aspect ratios, and interactions between the wall and liquid crystals. However, when introducing an external field to the system, four types of defects can be observed. With increasing the strength of the external field, the singularities in the circular, confined system change from the inside to the boundary and the outside, and the farthest position that the singularities can reach depends on the strength of the external field. We further introduce an alternating, triangular wave, external field to the system to check if we can observe the transformation of different defects within an oscillating period. We find that the position of the singularities greatly depends on the oscillating intensity and oscillating period. By changing the oscillating intensity and oscillating period of the external field, the defect types can be adjusted, and the transformation between different defects can be easily observed. This provides a feasible way to modulate liquid crystal defects and investigate the transformation between different defects.

Lithium-Rich Porous Aromatic Framework-Based Quasi-Solid Polymer Electrolyte for High-Performance Lithium Ion Batteries.

The development of solid polymer electrolytes (SPEs) with high ionic conductivity, wide electrochemical window, and high mechanical strength is the key factor to realize high-energy-density solid lithium ion batteries (SLIBs). Porous aromatic frameworks (PAFs) have the advantages of high porosity, easily functionalized molecular structure, and rigid stable framework, which fully meet the requirements of solid polymer electrolytes with high Li+ capacity, fast Li+ transport, and safety. Herein, a lithium-rich amidoxime (AO)-modified porous aromatic framework (PAF-170-AO) was obtained through the absorption of LiTFSI by amidoxime groups and abundant pores and then compounded with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to prepare a PAF-based quasi-solid polymer electrolyte (PAF-QSPE) with only tiny amounts of plasticizer (∼12 µL). The amidoxime groups of PAF-170-AO restricted the movement of the anions of LiTFSI through hydrogen bonding, which effectively promoted the dissociation and migration number of Li+ (tLi+), reduced the concentration polarization, and inhibited the growth of lithium dendrites. The PAF-QSPE exhibited a high ionic conductivity of 1.75 × 10-4 S cm-1 and tLi+ of 0.55 at room temperature. The activation energy was as low as 0.136 eV. Furthermore, the assembled SLIBs with the PAF-QSPE presented a discharge capacity of 163 mAh g-1 at 0.2 C and a capacity retention rate of 96% after 350 cycles, illustrating a stable cycling performance. This work demonstrated the great application potential of lithium-rich PAFs in QSPEs.

The advantages of nanoparticle surfactants over Janus nanoparticles on structuring liquids.

The nanoparticle (NP) surfactants generated in situ by binding NPs and polymers can assemble into an elastic NP monolayer at the interface of two immiscible liquids, structuring the liquids. Janus NPs can be more strongly bound to the interface than the NP surfactants, but they are unable to structure liquids into complex shapes due to the difficulty of assembling the jamming arrays. By molecular dynamics simulations, we give an insight into the better performance of NP surfactants than Janus NPs on dynamically structuring liquids. The high energy binding of Janus NPs to the interface will drive the Janus NPs to assemble into micelles in binary liquids. The micelles are stabilized in one liquid by encapsulating a little of the other liquid, hindering interfacial adsorption when the interface is marginally extended upon liquid deformation. In contrast, the in situ formed NP surfactants can rapidly fill the enlarged interfacial area to arrest the consecutive shape changes of the liquids. Moreover, NP surfactants can be designed with an appropriate coverage ratio (≤50%) of NP surface bearing host-guest sites to avoid dissolution and impart a desirable mechanical elasticity to their assembly.

Colloidal cubic diamond photonic crystals through cooperative self-assembly.

Colloidal cubic diamond crystals with low-coordinated and staggered structures could display a wide photonic bandgap at low refractive index contrasts, which makes them extremely valuable for photonic applications. However, self-assembly of cubic diamond crystals using simple colloidal building blocks is still considerably challenging, due to their low packing fraction and mechanical instability. Here we propose a new strategy for constructing colloidal cubic diamond crystals through cooperative self-assembly of surface-anisotropic triblock Janus colloids and isotropic colloidal spheres into superlattices. In self-assembly, cooperativity is achieved by tuning the interaction and particle size ratio of colloidal building blocks. The pyrochlore lattice formed by self-assembly of triblock Janus colloids acts as a soft template to direct the packing of colloidal spheres into cubic diamond lattices. Numerical simulations show that this cooperative self-assembly strategy works well in a large range of particle size ratio of these two species. Moreover, photonic band structure calculations reveal that the resulting cubic diamond lattices exhibit wide and complete photonic bandgaps and the width and frequency of the bandgaps can also be easily adjusted by tuning the particle size ratio. Our work will open up a promising avenue toward photonic bandgap materials by cooperative self-assembly employing surface-anisotropic Janus or patchy colloids as a soft template.

A chiral smectic phase induced by an alternating external field.

Using simple achiral building blocks modulated by an external field to achieve chiral liquid crystal phases remains a challenge. In this study, a chiral helix liquid crystal phase is obtained for a simple Gay-Berne ellipsoid model under an alternating external field by using molecular dynamics simulations. Our results show that the chiral helix liquid crystal phase can be observed in a wide range of external field strengths when the oscillation period is smaller than the rotational characteristic diffusion timescale of ellipsoids. In addition, we find that the pitch and tilt angle of the helix structure can also be adjusted by changing the strength and oscillation period of the applied alternating external field. This may provide a feasible route for the regulation of chiral liquid crystal phases by an alternating external field.

Multiple 2D crystal structures in bilayered lamellae from the direct self-assembly of 3D systems of soft Janus particles.

Numerous crystals and Frank-Kasper phases in two-dimensional (2D) systems of soft particles have been presented by theoretical investigations. How to realize 2D crystals or Frank-Kasper phases via the direct self-assembly of three-dimensional (3D) systems remains an important issue. Here, through numerical simulations, we report the surprising finding of multiple 2D crystal structures in bilayered lamellae from the direct self-assembly of 3D systems of soft Janus particles. With varying the patch size and particle density, soft Janus particles, which exhibit very similar self-assembly behavior to giant amphiphiles, spontaneously form ordered bilayered lamellae. Within each layer of the bilayered lamellae, we find abundant highly-ordered 2D crystals including the Frank-Kasper σ phase and open kagome lattice. The kinetic mechanisms of the formation of these 2D crystals within the layers are revealed, and include a classical one-step nucleation mechanism and a two-step nucleation mechanism. Our findings suggest a simple route towards 2D crystals via the direct self-assembly of 3D systems of amphiphilic Janus building blocks.

Transition kinetics of defect patterns in confined two-dimensional smectic liquid crystals.

Topological defects in liquid crystals under confined geometries have attracted extensive research interests. Here, we perform molecular dynamics simulations to investigate the formation and transition of defect patterns in two-dimensional smectic Gay-Berne liquid crystals with a simple rectangular confinement boundary. Two typical types of defect patterns, bridge and diagonal defect patterns, are observed, which can be transformable continuously between each other over time. The transition usually starts from the line or point defect regions, and the competition between neighboring and opposite boundary effects induces the continuous realignments of the smectic layers to connect the neighboring or opposite walls. The relative stability of these two defect patterns can be controlled by changing the confinement conditions. These results deepen our understanding of transition kinetics of defect patterns in confined liquid crystals.

Flow-driven competition between two capsules passing through a narrow pore.

By incorporating a distance function into the finite element simulation, we investigate the flow-driven competition between two soft capsules passing through a narrow pore, employing the arbitrary Lagrangian-Eulerian formulation to satisfy the boundary conditions for fluid flow and capsule deformation. In our simulations, the motion and deformation of the capsules can be described in an intuitive manner, and the order in which capsules of different sizes pass through a pore can be clearly determined. Meanwhile, when the capsules are near the narrow pore, the change of the flow field is also very interesting and can be expressed intuitively. It is shown that, driven by the Poiseuille flow, the larger capsule has a stronger tendency to pass through the pore than the small one, which can be attributed to the greater resistance and the volume advantage of the larger capsule. In addition, we demonstrate that this tendency can be reversed by changing the inlet velocity and setting the initial position of the smaller capsule closer to the axis of the pore. And as long as the large one passes through first, the small one will offset the axis to the same orientation as the initial, while the large one always moves along the axis.