Movement Of Molecular Chains Research Articles

Tribological properties of polyimide coating filled with solvent-free covalent carbon quantum dots nanofluids

Novel organic coatings were developed by incorporating solvent-free covalent carbon quantum dots nanofluids (CQDs NFs) into a polyimide (PI) matrix. The tribological properties of CQDs NFs/PI composite coatings were tested using a ball-on-disk tribometer, revealing that even a low loading of CQDs NFs significantly improved tribological performance of PI. Molecular dynamics (MD) simulations and nanoindentation tests showed that CQDs NFs restricted PI molecular chain movement, enhancing mechanical properties. Additionally, CQDs NFs promoted the formation of stable transfer films on steel surfaces, improving wear resistance. This study confirms CQDs NFs' effectiveness in modifying PI composite coatings' friction and wear properties.

Exploring the wear resistance of EPDM‐PAE/SWCNTs composites with a novel perspective of micro‐network structure

AbstractThe effect of single‐walled carbon nanotubes (SWCNTs) on the crosslinking network structure of Ethylene Propylene Diene Monomers (EPDM)—Polyamide elastomers (PAE) is investigated in detail using Hansen Solubility Parameter (HSP) theory. Rheological method and scanning electron microscopy (SEM) are used to investigate the effect of SWCNTs on the molecular chain movement and their interaction with the filler network of EPDM‐PAE. The DIN abrasion test is conducted to obtain the effect of SWCNTs on the wear characteristics of EPDM‐PAE/SWCNTs composites. The linear synergistic relationship between crosslinking density and wear volume indicates that the change in wear properties is contributed by the micro‐network structure. The addition of SWCNTs increases the chemical crosslinking density and improves the wear properties of EPDM‐PAE. However, the decrease in the physical crosslinking density leads to an increase in the degree of internal friction within the network structure, resulting in a decrease in the wear performance. Changes in wear resistance can be related to the micro‐network structure, which provides a novel approach to studying the wear characteristics of high‐performance elastomers. It is also an innovative work based on the network structure to guide the preparation of new wear‐resistant elastomeric materials.

Interface Structure and Properties of Polypropylene/Wood Flour Composites Reinforced with Grafted Polypropylene Compatibilizer

AbstractIn this work, a new compatibilizer, ternary monomer grafted polypropylene (hereafter shorted as: G‐PP), was successfully synthesized by solid phase grafting of maleic anhydride, methyl methacrylate, and butyl‐acrylate onto polypropylene. For all developed polypropylene matrix composites, the prepared G‐PP evidently showed enhancing mechanical properties on PP/wood flour (WF) composites, which is obviously superior to those from maleic anhydride grafted polypropylene (W‐PP) and virgin polypropylene (C‐PP). In particular, the wettability of G‐PP was greatly improved, while the melting temperature and β crystal phase amounts of the WF composites with G‐PP are much higher when compared to that of W‐PP and C‐PP. This can be reasonably explained by the formation of continuous micropores and filaments in WF composites containing G‐PP, as verified by hot stage polarizing optical microscope (POM). Meanwhile, the G‐PP effectively reduced movement of molecular chains of WPC and formed a better interface layer with WF, which contributed to penetrate more deeply and form micro‐crosslinking in the WF layer. We believe that the results reported in this work will increase the added value of polypropylene based wood plastics composites (WPC) and allow WPC to participate in lightweight and environmentally friendly products.

Flexural properties of moso bamboo induced by hydrothermal treatment

The superior flexural properties of bamboo make it widely used in the field of bamboo furniture. However, thick bamboo strips are more susceptible to fracture in bending due to their significant fiber gradient variation, especially the nodes. In this study, the eco-friendly hydrothermal treatment was employed to augment the flexural properties of bamboo and mitigate the fracture. The results showed that the flexural strength, flexural modulus, flexural toughness, and flexural radius of curvature increased with the increase of strip thickness. The strip thickness was positively correlated with vascular bundle content. The structure of bamboo became more uniform after hydrothermal treatment and the nodes were no longer the susceptible fracture point. The moisture content was a pivotal factor influencing the flexural properties, which increased as hydrothermal treatment time and temperature increased. Furthermore, hydrothermal treatment increased bamboo's flexibility by softening it through moisture absorption and the facilitating molecular chain movement within the fibers. The optimal moisture content for bamboo strips when manufacturing curved components was around the fiber saturation point. These findings contributed to the refinement of the green manufacturing techniques for bamboo curved furniture components, aiming to foster sustainable environmental development.

Preparation of ultraviolet‐cured silicone elastomer reinforced by SH‐POSS crosslinker for light emitting diode encapsulant

AbstractStable silicone encapsulants are essential for protecting high‐power light‐emitting diodes (LED) from dust and moisture and extending their service life. Herein, by incorporating thiol‐functionalized polyhedral oligomeric silsesquioxane (SH‐POSS) as a crosslinker into ultraviolet‐curable silicone elastomer (UVSE), a series of new UV‐cured silicone encapsulants (SH‐POSS/UVSE) have been developed through thiol‐ene click chemistry. It was found that SH‐POSS effectively enhanced the mechanical properties of SH‐POSS/UVSE. When 30 mol% SH‐POSS was added, the tensile strength and elongation at break reached 1.01 MPa and 422%, respectively, 2.1 and 1.6 times higher than pure UVSE. This could be ascribed to the more concentrated crosslinking network and the improved interfacial interactions between SH‐POSS and UVSE than physical blending. Moreover, the steric effect of branched and rigid SH‐POSS restricted the movement of UVSE molecular chains. Incorporating SH‐POSS also suppressed UVSE degradation and improved its thermal stability. Additionally, when the LED sample encapsulated by SH‐POSS/UVSE‐30 was immersed in boiling red ink for 2 h, no crack or stain was observed, indicating that SH‐POSS/UVSE‐30 possessed good adhesion to the LED lead frame. This work provides a new approach to fabricating high‐strength and stable silicone composites, which are promising candidates as LED encapsulants.

Dynamics of the Davydov’s soliton in external oscillating magnetic field

The influence of an external oscillating in time magnetic field on the dynamics of the Davydov’s soliton is studied. It is shown that soliton parameters depend on the amplitude and frequency of the magnetic field, as well as on the field orientation with respect to the molecular chain axis. Electron dynamics in the parallel magnetic field is a composition of the “free” soliton coherent propagation along the molecular chain and oscillatory movement in the transverse direction. The latter is described by the functions of the harmonic oscillator with the cyclotron frequency depending on the field frequency. In a perpendicular field the soliton dynamics is a superposition of (i) the free electron plane wave in the plane perpendicular to the molecular chain, and (ii) propagation along the chain which is described by the modified Nonlinear Schrödinger equation with an extra term depending on the field. This equation is solved using the nonlinear perturbation theory. It is shown that the soliton velocity and phase are given by expressions which include the terms oscillating in time with the frequency of the main harmonic, given by the external field frequency, and higher multiple harmonics. Such complex effects of external time-depending magnetic fields on the dynamics of solitons modify the charge transport in low-dimensional molecular systems, which in its turn, can affect the functioning of the devices based on such compounds. These results suggest also the physical mechanism of therapeutic effects of oscillating magnetic fields, based on the field influence on the dynamics of solitons which provide charge transport through biological macromolecules in the redox processes.

High‐temperature energy storage performance of polyetherimide all‐organic composites enhanced by hindering charge hopping and molecular motion

AbstractDielectric capacitors are widely used in aerospace, power systems, and other fields. Working environments with ever‐increasing temperatures pose a new challenge to energy storage performance. Polyetherimide (PEI) has gained extensive research for its good high‐temperature properties. In order to further improve its energy storage performance at high temperatures, many researchers have worked on PEI all‐organic composites doping with molecular semiconductors. Previous studies generally only considered the effect of introduced deep traps on macroscopic properties such as electrical conductivity, electrical breakdown, and energy storage performance. It has been shown that only qualitative analyses can be performed from the perspective of charge trapping, and it is difficult to obtain quantitative results. Therefore, this work proposes to study the macroscopic properties of polymer dielectrics by combining charge trapping with molecular displacement. A comprehensive conduction‐breakdown‐energy storage model was established to explain the influence mechanism of molecular semiconductors on the improved energy storage performance of PEI composites at high temperatures. The molecular semiconductor fillers increase the coefficient of friction between molecular chains, which restricts the movement of molecular chains and also limits charge hopping. Therefore, the dielectrics have higher breakdown strengths and smaller conduction losses, which synergistically enhance the energy storage performance.

Improved high temperature energy storage density and efficiency of polyimide nanocomposites via hindering charge and molecular motions

Electric vehicles and renewable energy consumption have huge demands for high-performance polymer dielectric capacitors. However, the resistivity and breakdown strength of existing polymer dielectrics deteriorate significantly at high temperatures, reducing the energy storage density and charge-discharge efficiency of capacitors below service requirements. The charge transport and molecular chain motion characteristics in linear polymers determine their conductivity, breakdown, and energy storage properties, but the quantitative relationship between them is not clear. An in-situ polymerization method was used to prepare polyimide/Al2O3 nanocomposites (PI/Al2O3 PNCs). Experimental results show that the resistivity, breakdown strength, energy storage density, and charge-discharge efficiency of PNCs increase initially and then decrease with increasing doping content, peaking at 3 wt%. The discharged energy density of PI/Al2O3-3 wt% PNCs at 180°C is 207.52 % higher than pure PI. A conductance-breakdown-energy storage co-simulation model based on charge transport and molecular chain displacement was used to simulate the voltage-current, breakdown, and energy storage characteristics of PNCs. The simulation results are consistent with the experiments. Comparative studies between simulation and experiments show that the independent interface zone between nanofillers and PI hinders charge transport and molecular chain movement, reducing electric field distortion and molecular chain spacing, thereby improving high-temperature breakdown and energy storage performance of PNCs.

Effects of Modified Silicon Carbide on The Physical Properties of Bioplastic Blends

The study’s goal is to improve the physical properties of biodegradable plastics by mixing poly(lactic acid) (PLA), polybutylene succinate (PBS), and silicon carbide (SiC) to make composites that could be used as filaments for 3D printing. Polymer blends and composites were fabricated using an internal mixer. The fraction of SiC was varied from 10 to 40 phr and filled in PLA/PBS blends with a retained ratio of 80/20 wt.%. Then, the mechanical properties, thermal properties, melt flow rate and morphology of PLA/PBS/SiC composites were investigated. Field emission scanning electron microscope images present a uniform dispersion of silane-treated SiC particles throughout the PLA/PBS matrix. The morphology showed better adhesion between PLA/PBS and treated SiC particles. Therefore, this was also the reason for the improvement of Young’s modulus and impact strength when the SiC fraction was increased, which were improved by 33% and 104%, respectively, compared to neat PLA. Furthermore, the melt flow rate increased with an increasing SiC fraction. This might be because adding SiC reduces the viscosity of the composites, which affects the molecular chain movement of the PLA/PBS and the crystallinity of PLA, therefore decreasing the ΔHm of PLA and Xc,PLA. However, Tg and Tm of PLA and PBS remained relatively stable with an increasing fraction of SiC particles.

Preparation of Graphene Oxide/Polymer Hybrid Microcapsules via Photopolymerization for Double Self-Healing Anticorrosion Coatings.

In this work, graphene oxide (GO)/polymer hybrid microcapsule-loaded self-healing agents were prepared via the combination of the emulsion template method and photopolymerization technology. The incorporation of GO in the microcapsule shell not only improved the impermeability, mechanical property, and solvent resistance property of the microcapsules significantly but also endowed the microcapsules with photothermal conversion property. By incorporating GO/polymer hybrid microcapsules in water-borne epoxy resin, a novel kind of anticorrosion coating with a double self-healing property was successfully fabricated. When the coating was scratched, the linseed oil (LO) encapsulated in the microcapsules could fill the crack, and the photothermal conversion property of GO could promote the molecular chain movement of the damaged area under near-infrared (NIR) irradiation to realize the close of the crack. Based on the filling of LO and photothermal conversion-induced scratch narrowing, the "filling" and "close" double self-healing effect can be realized under temporal NIR irradiation, which could lead to the complete recovery of the scratched coating. The |Z|f=0.1Hz value of the damaged coating with GO/polymer microcapsules after double healing was comparable to that of the intact coating, which was about 4 orders of magnitude higher than that of the scratched blank coating and single self-healing coating. As to the neutral salt spray test, the scratched blank coating failed in protection after 100 h, while the healed composite coating did not show any corrosion after 300 h.

Impact of Sacrificial Hydrogen Bonds on the Structure and Properties of Rubber Materials: Insights from All-Atom Molecular Dynamics Simulations.

The inclusion of sacrificial hydrogen bonds is crucial for advancing high-performance rubber materials. However, the molecular mechanisms governing the impact of these bonds on material properties remain unclear, hindering progress in advanced rubber material research. This study employed all-atom molecular dynamics simulations to thoroughly investigate how hydrogen bonds affect the structure, dynamics, mechanics, and linear viscoelasticity of rubber materials. As the modified repeating unit ratio (β) increased, both interchain and intrachain hydrogen bond content rose, with interchain bonds playing a predominant role. This physical cross-linking network formed through interchain hydrogen bonds restricts molecular chain movement and relaxation and raises the glass transition temperature of rubber. Within a certain content of hydrogen bonds, the mechanical strength increases with increasing β. However, further increasing β leads to a subsequent decrease in the mechanical performance. Optimal mechanical properties were observed at β = 6%. On the other hand, a higher β value yields an elevated stress relaxation modulus and an extended stress relaxation plateau, signifying a more complex hydrogen-bond cross-linking network. Additionally, higher β increases the storage modulus, loss modulus, and complex viscosity while reducing the loss factor. In summary, this study successfully established the relationship between the structure and properties of natural rubber containing hydrogen bonds, providing a scientific foundation for the design of high-performance rubber materials.

High temperature electrical breakdown and energy storage performance improved by hindering molecular motion in polyetherimide nanocomposites

Polyetherimide (PEI) is widely used as a material for high temperature and high power energy storage capacitors in new energy vehicles and other fields. However, as the temperature increases, the electrical conductivity increases and the breakdown strength decreases, which greatly reduces the energy storage density of the capacitor and limits the application range. In order to clarify the influence mechanism of high temperature on the breakdown and energy storage performance of dielectrics, this paper established a charge capture and molecular displacement (CTMD) breakdown model based on the expansion motion of molecular segments to study the charge transport and molecular chain motion process of PEI nanocomposites (PNCs) at high temperature. The results show that at 100 °C, compared with pure PEI, the internal maximum molecular displacement of PEI PNCs with appropriate doping content (3 wt%) is reduced by 28.79 %, and the breakdown strength is increased by 11.20 %. Appropriate nano-doping can effectively increase the movement difficulty of molecular chains and reduce the activation volume that provides energy for charge transport. Thus, charge transport is inhibited, current density is reduced, and Joule heat accumulation is avoided. Finally, the high temperature breakdown and energy storage performance are improved.

Dynamics and Internal Structure Evolution during the Glass Transition of the Ethylene-Cyclic Olefin Copolymers: A Molecular Dynamics Simulation.

Amorphous ethylene-cyclic olefin copolymers (COCs) which can be used in cell phone lenses and prefilled syringes have attracted increasing attention due to their excellent and tunable thermal properties. In order to better explain the influence of COC microstructure (cyclic olefin types and content) on the glass transition mechanism, we used molecular dynamics (MD) simulations to track the evolution of free volume, diffusion coefficients, atomic mobility, trans conformation probabilities, and characteristic parameters of α-relaxation kinetics during the quenching process. MD results show that for the classic COC E-co-NB (ethylene-norbornene copolymer), an increase in cyclic olefin content from 25 to 50 mol % reduces atomic mobility, limiting the molecular chain movement at higher temperatures and improving Tg. Compared to NB, the more rigid rings in tricyclopentadiene (TCPD) and exo-1,4,4a,9,9a,10-hexahydro-9,10(1',2')-bridged phenylidene-1,4-bridged methylideneanthracene (HBM) have the following effects: (1) reducing the thermal expansion coefficient and overall chain mobility; (2) enhancing the diffusion energy barrier; (3) promoting the formation of local ordered structures; (4) accelerating α-relaxation dynamics at high temperatures and improving the dynamic fragility m. These lead to an upward shift in the temperature region where chain movement is limited and thus improve Tg and high-temperature dimensional stability. In this simulation, the correlation equation between Tg, m, and the microstructural parameters of COCs is established, which is of great significance for the development of COCs with high performance.

Self-Healing Polyurethane Elastomers with Superior Tensile Strength and Elastic Recovery Based on Dynamic Oxime-Carbamate and Hydrogen Bond Interactions.

The preparation of self-healing polyurethane elastomers (PUEs) incorporating dynamic bonds is of considerable practical significance. However, developing a PUE with outstanding mechanical properties and high self-healing efficiency poses a significant challenge. Herein, this work has successfully developed a series of self-healing PUEs with various outstanding properties through rational molecular design. These PUEs incorporate m-xylylene diisocyanate and reversible dimethylglyoxime as hard segment, along with polytetramethylene ether glycol as soft segment. A significant amount of dynamic oxime-carbamate and hydrogen bonds are formed in hard segment. The microphase separated structure of the PUEs enables them to be colorless with a transparency of >90%. Owing to the chemical composition and multiple dynamic interactions, the PUEs are endowed with ultra-high tensile strength of 34.5MPa, satisfactory toughness of 53.9MJ m-3, and great elastic recovery both at low and high strains. The movement of polymer molecular chains and the dynamic reversible interactions render a self-healing efficiency of 101% at 70°C. In addition, this self-healing polyurethane could still maintain high mechanical properties after recycling. This study provides a design strategy for the preparation of a comprehensive polyurethane with superior overall performance, which holds wide application prospects in the fields of flexible displays and solar cells.

Polyurethane combining preeminent toughness, puncture-resistance, and self-healing capabilities by multiple repair options based on dual dynamic covalent bonds

The development of self-healing materials has enabled the production of more reliable and intelligent materials. However, resolving the conflict between mechanical strength and self-healing efficiency as well as limited repair options of the self-healing materials is still the most pressing scientific challenge. In this study, a self-healing polyurethane with multiple repair methods is prepared by introducing disulfide bonds into thermo-reversible imine bonds-based polyurethane. The resultant polyurethane exhibits impressive comprehensive mechanical properties and preeminent repair capabilities. More importantly, damages can be repaired through various routes such as room temperature, moderate temperature, hair dryer blowing, and ethylenediamine assistance treatments. The superior mechanical properties, repetitive self-healing performance, and multiple options for repair is attributed to the cooperation of thermally reversible imine and disulfide exchanges, thermal motion of molecular chains, and dissociation/regeneration of hydrogen bonds. So this research provides numerous ideal options for repairing cracks and other damages in materials used in construction industry under different usage environments. Consequently, high-quality repairs, improved efficiency, and extended service life of construction engineering materials can be ensured.

Preparation and properties of acrylate/polyvinyl alcohol self-healing hydrogels based on hydrogen bonds and coordination bonds

Abstract Despite the widespread attention garnered by self-healing hydrogels in various fields, achieving a balance between high mechanical strength and self-healing capability remains a challenge. Particularly, the addition of fillers in the fabrication of spray-coated waterproof materials hinders the movement of molecular chains. Simultaneously, the self-repair of metal ions is hindered by issues such as a prolonged required time and low repair rate. Therefore, we introduce a polyvinyl alcohol (PVA) solution subjected to freeze–thaw cycles into the acrylic acid magnesium/calcium hydrogel system, creating a self-healing hydrogel with an interpenetrating polymer network (IPN). Due to the abundance of hydroxyl groups on the PVA molecular chains, during the freezing process, some PVA chains form microcrystals that do not dissolve upon thawing at room temperature. These microcrystals act as cross-linking points, connecting PVA chains into a 3D network. Consequently, the hydrogel, under the dual effects of hydrogen bonds and coordination bonds, exhibits excellent mechanical properties and the ability to self-heal at room temperature. Furthermore, by adjusting the concentration of the PVA solution, the mechanical properties and healing ability of the hydrogel can be tailored to meet various construction requirements.

The Effect of SiO2 Particle Size on Crystallization Behavior and Space Charge Properties for SiO2/MMT/LDPE Composites.

The matrix material used in this paper was low-density polyethene (LDPE), and the added particles selected were silicon oxide (SiO2) particles and montmorillonite (MMT) particles. The sizes of the SiO2 particles were 1 µm, 30 nm, and 100 nm, respectively; three kinds of SiO2/MMT/LDPE multi-component composites were prepared based on MMT/LDPE composites doped with MMT particles. The effect of the SiO2 particle size on the crystallization behavior and space charge properties of SiO2/MMT/LDPE composites was studied. The crystalline behaviors and crystallinity of the materials were analyzed. At the same time, the changes in the relative dielectric constant εr and loss factor tanδ for each material with the influence of frequency were studied, and the space charge accumulation, residual characteristics, and apparent charge mobility of each material were explored. The results show that the smaller the size of the added particles, the smaller the grain size and the clearer the grain outline for the multi-composite material. After adding 30 nm SiO2 particles, the crystallinity of the material increases significantly. The microstructure formed by the addition of 100 nm SiO2 particles effectively restricts molecular chain movement and makes it difficult to establish the polarization of the composite. The incorporation of large-size particles can reduce the proportion of the crystalline structure for the material as a whole, resulting in the formation of a new structure to promote charge transfer. Among the three kinds of SiO2 particles, the addition of 30 nm SiO2 particles can effectively suppress the space charge, and the composite material has the lowest residual space charge after depolarization. The addition of 100 nm SiO2 particles can cause the accumulation of many homopolar charges near the anode.

Tribological Properties of Polyimide Composites Modified with Diamondoid Metal-Organic Frameworks.

In this work, diamondoid metal-organic frameworks (MOFs) were efficiently prepared by sonochemical synthesis and grown on polyimide (PI), aiming to improve the anti-wear performance of the PI matrix. By introducing MOFs into the PI matrix, the free movement of PI molecular chains were restricted, and its hardness and elastic modulus were improved. It was found that the wear rate of the 3 wt.% MOFs/PI composites was reduced by 72.6% compared to pure PI at a load of 4 N after tribological testing by using a ball-on-disk tribometer. This can be attributed to the excellent load-bearing and shear resistance of the fourfold-interpenetrated diamondoid networks, in which the transition metal elements can favor the formation of transfer films. It is worth noting that the 3 wt.% MOFs/PI composites still exhibited great tribological properties under high loads or high speeds. The findings of the present study indicate that diamondoid metal-organic frameworks can be used as efficient modifiers to enhance the tribological properties of PI.

Improving the dielectric properties of polypropylene for metallised film capacitors based on cyclic olefin copolymer blending

AbstractHigh conductivity loss and low breakdown strength of traditional polypropylene (PP) film in the high‐temperature environment are the key factors limiting the application of metallised film capacitors (MFCs). The effect of cyclic olefin copolymers (COCs) with different glass transition temperatures (Tgs) on the dielectric performance of PP/COC composites at high temperature are studied. The results showed that the addition of COC enhanced the intermolecular interaction force, which led to the reduction of defects in the films. In addition, COC with high Tg inhibits the movement of molecular chains and enhances the thermal stability of the film, which limits the transport of carriers at high temperatures. The conductivity and breakdown strength of the modified films (with a Tg of 134°C for COC) at 125°C are 91.6% lower and 45.7% higher, respectively, than that of pure PP. This method shows great potential in improving the dielectric properties of PP at high temperatures.

Effect of Thermal and Electric Fields on Thermal Stability and Dielectric Properties of SiO2/Cellulose Composite Materials

Molecular simulation techniques are widely used to study transformer insulation material characteristics and nano-modification mechanism. However, there are numerous researches on the thermal stability and dielectric properties of nano-modified cellulose insulation paper, and few studies have combined nano-modification with the process of electrical-thermal aging. This study established SiO2/Cellulose models with different weight percentages to calculate their average number of hydrogen bonds (AHB), glass transition temperature (Tg ) and relative permittivity (RP) under electro-thermal coupling. The study indicates that the 5wt% SiO2/Cellulose model exhibits the best modification effect. Temperature is the primary factor causing aging of the cellulose insulation paper, and the introduction of an electric field accelerates the thermal aging of the cellulose insulation paper. Increasing hydrogen bond quantity and restricting molecular chain movement are key factors that enhance insulation materials anti-aging performance.