Entanglement Of Molecular Chains Research Articles

Low modulus hydrogel-like elastomer sensors with ultra-fast self-healing, underwater self-adhesion, high durability/stability and recyclability for bioelectronics

Flexible sensors simultaneously with property of hydrogel-like low modulus/room temperature ultra-fast self-healing and with elastomer-like durability /environmental stability and underwater adhesion for bioelectronics has not been reported. A low modulus hydrogel-like elastomer that achieves ultrafast self-healing through molecular chain entanglement at room temperature was prepared based on furfuryl alcohol-modified poly(sebacate glyceride) (PGS) prepolymer, furfuryl alcohol-modified poly(ionic liquid) and bismaleimide by Diels-Alder (DA) reaction. The conductive elastomer-based flexible sensors exhibit hydrogel-like properties of low modulus (6.41 kPa) and ultra-fast self-healing (98 % self-healing efficiency within 5 s). The elastomer also possesses rapid subzero and underwater self-healing properties within 5 s. Moreover, PGS-0.2DA-0.2PIL exhibits pressure sensitive adhesive properties and can be adhered/re-adhered in water. The flexible sensor shows elastomer-like high durability, high environmental stability, multiple recyclability and reusability, and it exhibits wide detection ranges, fast response time, low hysteresis, anti-freezing, anti-bacterial and good biocompatibility. The flexible sensors can accurately identify micro-expressions/eye rotation, monitor human movement/health, detect ECG/EMG signals and control robotic arm movements. In conclusion, a new strategy for design of hydrogel-like conductive elastomers via molecular structure design is proposed, and the elastomers-based flexible sensors with low modulus, rapid self-healing and durability/environmental stability show great promising for bioelectronic applications.

Nanoscale phase separation achieved through trace PVDF/PEI blending enhances mechanical and energy storage performance at high temperatures

Due to the development of advanced electronic systems, there is an urgent need for polymer dielectric film capacitors with high breakdown strength (Eb) and high discharge energy density (Ud) at elevated temperatures. Herein, an all-organic blend polymer composite is fabricated by blending polyetherimide (PEI) and a trace amount of Poly(vinylidene fluoride) (PVDF), achieving nanoscale phase separation and forming interfaces between PEI and PVDF grain. The real permittivity (εr) and Eb of blend composites are simultaneously enhanced after PVDF introduction. It is worth noting that increasing the temperature does not reduce the Eb of the PEI/xPVDF blend composite. Our Study shows that optimizing the plasticity and storage modulus of PEI/xPVDF significantly contributes to maintaining Eb at elevated temperatures. Additionally, high temperatures enhance the entanglement of molecular chains at the PVDF-PEI interface, further supporting the preservation of Eb. Finally, a high Eb of 540 MV/m, a high Ud of 5.92 J/cm3 are achieved for the PEI/0.5PVDF blend at 150 °C. This work presents a new approach to enhance the Eb of dielectric polymers by optimizing mechanical properties at high temperature, which providing a different strategy for enhancing the energy storage performance.

Effect of alkaline protease content on the structure and properties of natural rubber

AbstractThe solidification technology of natural rubber exerts a significant impact on the properties of natural rubber. The solidification technology of alkaline protease has been highly valued by researchers at home and abroad because of its good solidification effect, excellent vulcanization performance, and low pollution. In this study, the effects of alkaline protease solidification technology and enzyme dosage on the structure and properties of natural rubber were investigated and compared with those of formic acid solidification technology. The solid‐state NMR results showed that increasing the enzyme dosage increased the molecular chain entanglements in the raw rubber. The gel content test results showed that the natural network structures (i.e. gels) increased after the addition of alkaline protease. The test results of the vulcanization characteristics showed that the addition of alkaline protease significantly shortened the positive vulcanization time. The Mw was the largest at an enzyme dosage of 0.07%. The test results for mechanical properties showed that the mechanical properties were best when the enzyme dosage was 0.07%. In addition, as the alkaline protease dosage increased, the Akron abrasion volume of natural rubber decreased, and the Akron abrasion volume was the lowest at an enzyme dosage of 0.07%.

The influence of low-temperature shear on crystallization of shish-kebab of unimodal/ bimodal C4 short-chain branching polyethylene

The shish crystal, a crucial structure in the formation of shish-kebab crystals, has drawn widespread attention due to its highly oriented chain arrangement, significantly enhancing the mechanical properties of products. This study utilizes polyethylene samples with longer C4 short branches, employing in-situ synchrotron SAXS/WAXD to investigate the influence of short branch length and content on the formation of shish-kebab crystals in unimodal and bimodal polyethylene under low-temperature shear conditions (with supercooling degrees of 13.5 °C and 10.5 °C). The results reveal that the presence of C4 short-chain branching affects system crystallization, but low-temperature shear induces stronger mechanical action on the melt, resulting in better-oriented lamellar crystals compared to high-temperature shear (superheat degrees of 22.5 °C and 19.5 °C), achieving higher orientation. This achieves the control of shish-kebab crystal generation through the stretched network mechanism. Both types of samples with different C4 short-chain branching contents generate shish-kebab crystals during the shear stage, with relatively higher short-chain branching content inducing more shish crystal formation but with less regular structure. The bimodal polyethylene exhibit higher proportions and absolute amounts of final shish crystals compared to the unimodal polyethylene, indicating that high molecular weight portions are conducive to shish crystal generation under shear. The result demonstrates the feasibility of generating shish-kebab crystals during the low-temperature shear process of PE in the presence of C4 branches using the stretched network mechanism under shear flow conditions. Moreover, controlling the degree of entanglement of molecular chains by adjusting shear temperature, branch content, and branch length can modulate two formation mechanisms of shish crystals—coil-stretch transition mechanism at high temperature and stretched network mechanism at low-temperature.

Rheology of polyborazanes with various molecular structures and dynamic transformation process

AbstractThe molecular structure of polymer precursors significantly affects their rheological properties, thermal stability, and ceramic conversion rates. For the first time, we revealed the effects of polyborazane molecular structure on rheology and molecular configuration dynamic transformation process. The systems studied are polyborazane precursors with rigid six‐membered ring structures. We synthesized precursors with different molecular structures, including polyborazanes with varying degrees of branching and molecular chain flexibility, and investigated how molecular structure affects viscosity under different conditions of temperature, time, and shear rates. The results indicate that decreasing the branching degree enhances thermal stability and reduces both zero‐shear viscosity and infinite‐shear viscosity. Increasing the flexibility of molecular chains notably reduces infinite‐shear viscosity, while having minimal impact on zero‐shear viscosity and thermal stability. In conclusion, the ideal molecular structure should aim to increase the flexibility of the molecular chains while maintaining a certain degree of branching, such as a dendritic molecular configuration. By correlating viscosity data with molecular structure, we constructed a dynamic transition process of molecular chain entanglement, disentanglement, and crosslinking. This research is essential for understanding polymer rheology and its applications in industry, particularly in designing and synthesizing precursor structures for producing various ceramic fibers through Polymer‐Derived Ceramics.

Strength and toughness of semicrystalline polymer fibers: Influence of molecular chain entanglement

The mechanical properties of oriented semicrystalline polymers fibers are mainly determined by the semicrystalline morphology in which lamellar crystals and disordered amorphous layers are in staggered arrangement. As a stress transmission channel, amorphous entanglement network can affect the strength and toughness of fiber together with crystalline phase. In this study, the relationship between mechanical properties and amorphous entanglement of oriented poly (l-lactic acid) fibers was clarified by studying the cyclic loading characteristics. Based on the Haward-Thakray model of semi-crystalline polymers, the energy contributions of the crystalline phase and the amorphous phase are separated. During the deformation of oriented fiber, the crystal will be broken under the action of tight entanglement network, and the entanglement network can transfer stress well without failure under the action of straight chain. Therefore, although the crystalline phase and the amorphous phase jointly bear the strength, the toughness and fracture behavior mainly affected by the entangled network of the amorphous phase.

Integrated construction of stretchable supercapacitor with outstanding deformation stability and flame retardancy

The fast development of wearable electronics requires urgently stretchable energy storage devices, but conventional stretchable energy-storage devices suffer from poor dynamic deformation stability. The key is to create a new construction strategy of "electrode/electrolyte interface integration". Herein, we have proposed a clever strategy that combines layer-by-layer electrospinning with a self-selected vapor-phase polymerization (VPP) method to assemble the integrated stretchable supercapacitors (ISSCs). Furthermore, the interface stability enhancement mechanism is revealed through experimental and theoretical simulations, showing that the synergistic effect of molecular chain entanglement and mechanical meshing endows excellent anti-deformation stability of ISSCs. As a result, the as-assembled ISSCs deliver excellent dynamic deformation electrochemical stability with 99.5 % capacitance retention after 500 stretching cycles at strain and outstanding flame retardancy (limiting oxygen index (LOI) up to 48.1 % at a film thickness of only 0.22 mm). The innovative integrated design strategy endows a systematic construction plan for the scalable fabrication of wearable organic energy storage devices.

“Like binding a book”: Interfacial improvement of pre-melted ultrahigh molecular weight polyethylene by pulse vibration molding

Ultrahigh molecular weight polyethylene (UHMWPE) is widely used in industrial, military, and civilian applications owing to its excellent properties. However, the high entanglement degree of UHMWPE melt leads to great difficulties in diffusion and crystallization, which causes poor interfacial strength and mechanical properties of pre-melted UHMWPE, restricting its high-quality processing and high-value recycling. To this end, we propose a rapid interface stitching technology with a pulsed vibration force driving free volume homogenization and chain segment orientation. For the first time, pulse vibration molding (PVM) is applied for the hot-pressing of pre-melted UHMWPE, successfully realizing the interface stitching and product strengthening. Compared with those of the convention molding (CM) samples at 180 °C, the interfacial adhesive fracture toughness of the adhesive samples processed using PVM is increased by 105.9 % and the work of tension of the recycled samples processed using PVM is also increased by 49.09 %, respectively. The fracture strength of the PVM recycled samples at 180 °C reaches 91.77 % of that of the pure samples and the yield strength is also higher, which significantly enhances the recycling of UHMWPE. The characterization results of the interfacial molecular chain entanglement and crystallization show that PVM strengthens the molecular chain diffusion and induces crystallization by promoting the orientation of chain segments, especially at the interface. Consequently, we believe that the proposed technology can play a significant role in the UHMWPE processing methods that involve surface healing.

Effect of rheological behaviors of polyacrylonitrile grafted sericin solution on film structure and mechanical properties

Sericin protein possesses excellent biocompatibility, antioxidation, and processability. Nevertheless, manufacturing large quantities of strong and tough pure regenerated sericin materials remains a significant challenge. Herein, we design a lightweight structural sericin film with high ductility by combining radical chain polymerization reaction and liquid-solid phase inversion method. The resulting polyacrylonitrile grafted sericin films exhibit the ability to switch between high strength and high toughness effortlessly, the maximum tensile strength and Young's modulus values are 21.92 ± 1.51 MPa and 8.14 ± 0.09 MPa, respectively, while the elongation at break and toughness reaches up to 344.10 ± 35.40 % and 10.84 ± 1.02 MJ·m−3, respectively. Our findings suggest that incorporating sericin into regenerated films contributes to the transformation of their mechanical properties through influencing the entanglement of molecular chains within polymerized solutions. Structural analyses conducted using infrared spectroscopy and X-ray diffraction confirm that sericin modulates the mechanical properties by affecting the transition of condensed matter conformation. This work presents a convenient yet effective strategy for simultaneously addressing the recycling of sericin as well as producing regenerated protein-based films that hold potential applications in biomedical, wearable, or food packaging.

Ultrafast-degradable and super-elastic PBAT/polybutylene succinate foam with stable cellular structure and enhanced thermal insulation

PBAT is considered a leading eco-friendly polymer known for its exceptional biodegradability and mechanical properties. However, the production of high-performance PBAT foam remains challenging owing to poor foaming ability and intrinsic shrinkage. Herein, this study presents a flexible approach to prepare super-elastic and ultrafast-degradable PBAT/polybutylene succinate (PBS) foams achieved by microcellular foaming with CO2 & N2 as co-blowing agents. Firstly, the SEM, FTIR, as well as XPS spectra, confirmed a uniform and miscible distribution of PBS. Further, the crystallization kinetics and rheological analysis demonstrated that PBS effectively promoted crystallization and molecular chain entanglement. Thus, the PBAT/PBS foam exhibited significantly refined cellular structure, higher expansion ratio of 20.3, and restricted shrinkage of less than 4 %. More importantly, compared with neat PBAT foam, the compression strength of PBAT/PBS foam was dramatically enhanced by 47.7 %, and the energy loss coefficient was pronouncedly reduced by 58.8 % under the expansion ratio of 15.0. Meanwhile, the PBAT/PBS foam showed a thermal conductivity as low as 35.9 mW/m·K, enhanced hydrophobicity, and an exceptionally rapid degradation ratio. Considering the eco-friendly and flexible characteristics of this process, anti-shrinkage and ultrafast-degradable PBAT/PBS foams with improved mechanical and thermal insulation performance present promising prospects to replace the nondegradable polymer foams.

Characterising the modifying efficiency of polyphosphoric acid to bitumens with different oil sources

ABSTRACT To explore the properties and mechanism of different polyphosphoric acid (PPA)-modified bitumen, this research selected three bitumens with different oil sources and two PPAs with different relative H3PO4 contents (which are 105%, 115%, namely 105 and 115 grade PPA, respectively). A succession of tests and analyses was conducted to explore the performance of the PPA-modified bitumens. The physical performance test results show that PPA improves the high-temperature performance of the bitumens, and it has different modification effects on the three bitumens. When PPA reacted with the bitumen that has a higher content of polar components, the performance variation of the bitumen was higher than the other two kinds of bitumens. Furthermore, the 115-grade PPA seemed to have a better modified efficiency than that of the 105-grade PPA due to the longer molecular chain length. This also leads to the entanglement of molecular chains of PPA-modified bitumen was more significant with the 115-grade PPA. Therefore, the 115-grade PPA-modified bitumen shows a large asphaltene agglomeration in the AFM diagram.

Sprayable oxidized polyvinyl alcohol with improved degradability and sufficient mechanical property for fruit preservation.

Besides their limited preservation capacity and low biosafety, traditional fruit preservation procedures exacerbate "white pollution" because they utilize excessive plastic. Herein, an environmentally friendly one-pot method was developed to obtain degradable polyvinyl alcohol (PVA), where the hydroxyl radicals generated through the reaction between hydrogen peroxide (H2O2) and iron ions functioned to oxidize PVA. The oxidized PVA (OPVA-1.0) with abundant ketone groups, reduced crystallinity, and short molecular chains was completely degraded into H2O and CO2 after being buried in the soil for ∼60 days. An improvement in its degradation rate did not weaken the mechanical properties of OPVA-1.0 compared to other modified PVA films because the adverse effect of decreased crystallinity on its mechanical performance was offset by its ion coordination. Alternatively, the tensile strength or toughness of OPVA-1.0 was enhanced due to its internal multi-level interactions including molecular chain entanglement, hydrogen bonding, and metal coordination bonds. More interestingly, OPVA-1.0 was water-welded into various products in a recyclable way owing to its reversible physical bonds, where it was sprayed, dipped, or brushed conformally onto different perishable fruits to delay their ripening by 5-14 days. Based on the cellular biocompatibility and biosafety evaluations in mice, OPVA-1.0 obtained by the facile oxidation strategy was demonstrated to alleviate "white pollution" and delay the ripening of fruits effectively.

Self-healing coating with the ability to mark damaged locations, based on electrospun photothermal fibers and AIE agents

The anti-corrosion coatings based on core-sheath fibers prepared by electrospinning methods are developed for the indication and repair of large-scale damage to coatings. The cores are the composite fluorescent agents composed of AIE-gens and CHEF-gens, which exhibit strong fluorescence characteristics sensitive to corrosion due to the CHEF and FRET effects. The composite fluorescent agents provided information about the location of damages when the coatings, with the fibers as the core materials, are damaged. The sheaths are photothermal materials, composed of photothermal responsive acid doped polyaniline and shape memory polyurethane. The photothermal properties of acid doped polyaniline, under the irradiation of an infrared laser, contributes to heating in the damaged areas. The softened and activated polyurethane simultaneously lead to interpenetration and entanglement of molecular chains at the closed damage sites, resulting in complete repair of the damaged coatings.

The enhanced physical properties of XLPE insulation for high voltage cable based on LDPE/LLDPE or LDPE/HDPE blends

Exploring methods of improving the performance of high-voltage cable XLPE insulation is a hot issue in high-voltage and insulation technology. This paper presented a new method to improve the physical properties of XLPE by doping low-content polyolefin materials, such as LLDPE or HDPE. The new XLPE insulation has significantly improved high-temperature mechanical properties and slightly improved room-temperature mechanical properties. The optimal thermal elongation properties were achieved with a 1 phr content of HDPE and LLDPE, while DC conductivity, DC breakdown strength, and dielectric properties were stable or slightly improved. The properties mentioned above showed a decreasing trend at higher content. This study demonstrated that adding HDPE or LLDPE to LDPE increases the physical entanglement of XLPE molecular chains, which has a similar effect to crosslinks formed by chemical crosslinking in enhancing the mechanical properties of XLPE insulation. This suggests that there is a potential to reduce the concentration of crosslinking agents during XLPE cable manufacturing while maintaining electrical properties and improving mechanical properties at elevated temperatures. It provides a new idea for improving the properties of XLPE insulation for high-voltage DC cables.

Novel determining technique for the entanglement degree of ultra-high molecular weight polyethylene

A novel method for characterising the degree of entanglement of molecular chains was established based on information obtained using differential scanning calorimetry (DSC). This technique is based on crystal morphology and establishes a correlation with the number of entanglements in rheology. In particular, this method can be implemented to characterise the entanglement of ultra-high-molecular-weight polyethylene molecular chains and was demonstrated to be successful in resolving the problem of obtaining the GN0 value in the testing process of low-molecular-weight polyethylene.

Cardanol derivatives as compatibilizers for strengthening and toughening polylactic acid/bamboo fiber bio‐composites

AbstractThe application of bamboo fibers (BFs) as a reinforcing filler in polylactic acid (PLA) is hindered by their poor compatibility owing to the intrinsic hydrophilia of BFs and the hydrophobicity of PLA. To solve this issue, cardanol (CD) and epoxidized cardanol glycidyl ether (ECGE) were used as compatibilizers to strengthen and toughen PLA/BF bio‐composites, to the best of our knowledge, preparing PLA/BF/CD and PLA/BF/ECGE bio‐composites. The impact strengths of the synthesized bio‐composites increased from 7.75 to 23.75 and 7.75 to 23.95 kJ/m2, respectively, compared with that of a PLA/BF composite without compatibilizer. The investigation of the mechanical properties, crystallization, fractured surface morphology, and solvent stress‐cracking resistance properties revealed that the toughening mechanism of the PLA/BF/CD bio‐composites are mainly based on the plasticization of CD, which results in high impact toughness but low tensile strength. Moreover, the modification with ECGE improves the impact and tensile strengths of the bio‐composite owing to the following factors: (1) the epoxy groups of ECGE generate strong interactions with the BF surface and PLA to form an enhanced interfacial structure; (2) when present at high concentrations, chain extension reaction between ECGE and PLA to increase the molecular chain entanglement of PLA; and (3) upon curing and crosslinking, ECGE forms an entangled network structure that toughens the matrix.

In silico quantification of 3D thermal gradients and voids during fused filament fabrication deposition to enhance mechanical and dimensional stability

Fused filament fabrication (FFF) is one of the most widely used additive manufacturing techniques for polymeric materials. However, the mechanical and dimensional quality of the final printed parts are still deviating from the maximal performance, due to the presence of voids, and incomplete inter- and intralayer bond formation implying suboptimal molecular chain entanglement. The current work puts forward a three-dimensional Ansys Polyflow® computational study in which temperature gradients and void formation are analysed for the deposition of up to eight strands, accounting compared to the state of the art for (i) bond formation at the strand interfaces by material deformation; (ii) non-Newtonian viscosity variations; (iii) measured temperature dependent material properties, including conductivity, specific heat capacity and viscosity; and (iv) convection. Selecting acrylonitrile butadiene styrene (ABS) as polymeric material, it is demonstrated that a dynamic heat transfer is obtained with contributions from the heated bed to layers printed above, and from just printed warmer layers to colder layers printed before in both the vertical and transversal direction. These extra heat transfers renew the interlayer contact between two strands, as the temperature at the weld line can be pushed several times above the glass transition temperature. A tuning of this renewable welding is possible based on a variation of the bed and nozzle temperature; the latter more relevant upon increasing the number of layers printed. It is further highlighted that the void shape and size is different close and away from the bed (2.5-8% void percentage variation). Moreover, a novel computational method is put forward to quantify the surface roughness based on edge analysis (80-120 μm variation).

Polyethylene based on molecular weight design for eco‐friendly asphalt

AbstractPolyethylene (PE) is widely used as a modifier for asphalt due to its low cost. However, PE increases the high‐temperature viscosity of asphalt, leading to higher construction temperatures and harmful emissions. In this study, PE‐modified asphalt with good road performance, energy saving and emission reduction was synthesized by adjusting the molecular weight (Mw) of PE. By studying the effect of PE with different Mw on the viscosity of asphalt, the Mw of PE that can reduce the high‐temperature viscosity of asphalt was concluded and the target product PE‐4 was synthesized. PE reduces the high‐temperature viscosity of asphalt when its Mw is less than the critical molecular weight (Mc) for molecular chain entanglement in the molten state. PE‐4 successfully reduced the high‐temperature viscosity of matrix asphalt. The pavement performance of PE‐4 modified asphalt was characterized. The results showed that PE‐4 reduced the penetration of asphalt, and improved its softening point, ductility, and rutting resistance. PE‐4 modified asphalt is an eco‐friendly asphalt with good road performance. The above data proved that PE with Mw less than Mc makes PE a promising asphalt modifier, which is beneficial to the green utilization of PE.

Adsorption and Assembly of Octenyl Succinic Anhydride Starch/Chitosan Electrostatic Complexes at Oil–Water Interface

Biopolymer electrostatic complexes are popular Pickering stabilizers whose structures greatly affect their interfacial properties. This study comprehensively demonstrated the interfacial adsorption and assembly of dissolved octenyl succinic anhydride (OSA) starch (OSA-D)/chitosan (CS) electrostatic complexes with different structures through complementary characterization methods. We found that compared with single-component systems, OSA-D/CS complexes exhibited significantly increased wetting stability and adsorption rate to the interface, which was reinforced by molecular dynamics simulations. Their soft structures and the entanglement of molecular chains led to the formation of thick and highly viscoelastic multilayer adsorbed films, which greatly resisted deformation against shearing forces. The adsorption and assembly of the complexes were strongly influenced by OSA-D/CS ratios and pH, which could be related to the different interfacial interaction strengths. Overall, the electrostatic complexation, structural characteristics, and interfacial properties of OSA-D/CS complexes were well related, thereby providing valuable information for the regulation of controlled interfaces and bulk system properties.

Enhanced Interfacial Adhesion and Increased Isotropy of 3D Printed Parts with Microcellular Structure Fabricated via a Micro‐Extrusion CO2‐Foaming Process

Compared with the cumbersome traditional manufacturing processes, the fused filament fabrication (FFF) 3D printing technology can freely fabricate complex porous parts, but cannot produce microcellular structures, and suffers from inherent poor interfacial adhesion and anisotropy due to periodic heating. Herein, a novel micro‐extrusion CO2‐foaming process is applied in the FFF process, and foamed 3D printed polyetherimide (PEI) parts with internal microcellular structure are fabricated. The tensile strength of the foamed part with a density of 0.85 g cm−3 is 42.8 MPa, which was significantly higher than 22.6 MPa for the unfoamed counterpart. Moreover, the side length of periodic triangular voids between raster is reduced from 207 to 105 μm, and the degree of anisotropy is reduced from 79.5% to 13.8%. CO2 plasticization leads to a reduction in glass‐transition temperature and viscosity of polymer systems, and the diffusion and entanglement of interfacial molecular chains are facilitated by the increase in contact area and pressure caused by foaming and expansion. The micro‐extrusion CO2 foaming endows the 3D printed parts with lightweight, internal microcellular structure, enhanced interface bonding, and isotropic mechanical properties, which will broaden the application scopes of FFF‐3D printing technology.