Mobility Of Molecular Chains Research Articles

UV aging resistance improvement of SBS modified asphalt binder by organic layered double hydroxide and naphthenic oil: Its preparation, properties and mechanism

To enhance the UV aging resistance of SBS modified asphalt, LDHs and naphthenic oil were selected to modify it compositely. Firstly, organic treatment for LDHs was carried out through the combination of surface modification method and intercalation modification method to improve its compatibility with asphalt, and effectiveness of organic treatment was evaluated through the microscopic testing methods. Then, organic LDHs/SBS modified asphalt binders were developed by melt blending method, on this basis, appropriate naphthenic oil was added for composite modification. Subsequently, the conventional physical properties, storage stability and rheological properties tests were carried out to evaluate the comprehensive properties of the prepared modified asphalt containing LDHs and naphthenic oil. On this basis, TOPSIS method was conducted for multi-index optimization to determine the optimal dosages of LDHs and naphthenic oil. Finally, UV aging resistance of the developed modified asphalt was also evaluated, and reaction mechanism was explored with FTIR and FM. Test results show that stearic acid (SA) was successfully absorbed on the surface of LDHs, and -SO32- in ultraviolet light absorber (UVT) has successfully entered the interlayer galleries of LDHs, thus achieving the organic treatment for LDHs. Organic LDHs can significantly improve the high temperature properties and storage stability of SBS modified asphalt, and naphthenic oil can also improve the storage stability of SBS modified asphalt at the proper dosage. In addition, the two modifiers can both effectively improve the UV aging resistance of SBS modified asphalt. Based on the multi-index optimization results, it is recommended that the optimal dosages of LDHs and naphthenic oil are 2 % and 2.5 %, respectively, and at this conditions, comprehensive properties of the prepared modified asphalt can achieve the best. Microstructure characterization tests results reveal that LDHs and naphthenic oil are only simply dispersed in asphalt and do not cause the structural damage of SBS modified asphalt. Meanwhile, the special layered structure of LDHs can hinder the mobility of asphalt molecular chains, which enhances the interaction force between asphalt molecular chains and SBS modifier molecular chains, thus improving the road properties of SBS modified asphalt.

Viscoelastic Performance of Bagasse/Glass Fiber Hybrid Epoxy Composites: Effects of Fiber Hybridization on Storage Modulus, Loss Modulus, and Damping Behavior

Abstract This study aimed to investigate the viscoelastic properties of bagasse/glass fiber multilayered hybrid reinforced epoxy composites, focusing on how fiber hybridization affects dynamic mechanical performance. Epoxy composites with various layering sequences, including all-glass (AG), all-bagasse (AB), bagasse-glass-bagasse (BGB), and glass-bagasse-glass (GBG), were fabricated and analyzed using dynamic mechanical analysis (DMA) to measure storage modulus (E'), loss modulus (E''), and damping factor (tan δ). The results showed that hybrid composites (GBG and BGB) experienced a decrease in storage modulus by approximately 25% compared to AG, indicating enhanced polymer molecular chain mobility and improved interfacial adhesion between bagasse fibers and the epoxy matrix. The glass transition temperature (Tg) was slightly lower in hybrid composites, with GBG at 61 °C and BGB at 60 °C, compared to 62 °C for AG. In terms of energy dissipation, AG exhibited the highest loss modulus peak at 62 °C, while AB showed the lowest with a Tg at 53 °C. The damping factor analysis revealed that AB had the highest damping peak (tan δ = 0.9) at 61 °C, although this occurred at a lower temperature than the AG composite (tan δ = 0.7 at 76 °C). These findings suggest that bagasse and glass fiber hybrid composites offer tailored viscoelastic properties, making them suitable for applications in automotive components, aerospace structures, and sports equipment.

The relationship between the structure of stearic acid diamide lubricants and the lubrication properties in acrylonitrile-butadiene-styrene resins

Although amide lubricants are commonly used as lubricants for acrylonitrile-butadiene-styrene (ABS) resins, the relationship between their structure and lubricating properties remains unclear. In this paper, a series of stearic acid diamide lubricants for ABS resins were synthesized through an amidation reaction with the stearic acid and aliphatic diamines. The chemical structure was characterized by FTIR and 1H NMR. A detailed evaluation of the lubrication effect of the lubricant was carried out by dynamic mechanical analysis, rotational rheometry, contact angle measurements, and so on. The results showed that the complex viscosity, glass transition temperature and diamine's alkyl chain length of stearic acid diamides were positively correlated, while the elongation at break displayed a negative correlation. Compared to ethylenediamine bis stearate acid (EBA), 1,8-diaminooctane bis stearate acid (OBA) exhibited a 37.8 % increase in the complex viscosity at 0.1 rad/s, along with a 4.6 % rise in the glass transition temperature. It was indicated that the lubrication effect of stearic acid diamides deteriorated with the increase of the alkyl chain lengths of diamines. The lubrication mechanism was further validated by molecular dynamics simulations. As the alkyl chain lengths of diamines increased, the mean square displacement and interaction energy of the system exhibited a tendency to become lower and higher, respectively. This meant that the longer alkyl chains of the diamines in the lubricants were not advantageous to the free mobility of the matrix molecular chains. These findings provided insightful guidance for the sensible design of lubricants for ABS resins.

Unlocking the Potential of Liquid Plasma Polymer Films: Characterizing Aging Effects and Their Impact on the Wrinkling Phenomenon.

Here, we present the study of the intricate dynamics between the physicochemical properties of liquid propanethiol plasma polymer films (PPFs) and the formation of wrinkles in PPF/Al bilayers. The study investigates the effect of liquid PPF aging in the air before top Al layer deposition by magnetron sputtering on the wrinkling phenomenon for 4 days. Thanks to atomic force microscopy, the wrinkle dimensions were found to decrease by approximately 55% in amplitude and 66% in wavelength, correlated with an increase in the viscosity of the PPF over the aging duration (i.e., from less than 107 to 1010 Pa·s). This behavior is not linked to alterations in cross-linking degree as evidenced by time-of-flight secondary ion mass spectrometry experiments but rather to network densification driven by the inherent molecular chain mobility due to the viscous state of the PPF. X-ray photoelectron spectroscopy measurements emphasizing the absence of oxidation of the PPF over the aging duration support this, revealing a unique aging mechanism distinct from other plasma polymer families. Overall, this study offers valuable insights into the design and application of mechanically responsive PPFs involved in bilayer systems, paving the way for advancements in nanotechnology and related fields.

Barrier Properties of Biodegradable Aliphatic–Aromatic Copolyesters (PBXT Series)

AbstractIn this study, a series of biodegradable poly(butylene alkylene carboxylate‐co‐terephthalate) copolymers with varying methylene numbers in the alkylene units (0, 2, 4, and 8) are synthesized. These copolymers, namely, poly(butylene oxalate‐co‐terephthalate) (PBOT), poly(butylene succinate‐co‐terephthalate) (PBST), poly(butylene adipate‐co‐terephthalate) (PBAT), and poly(butylene sebacate‐co‐terephthalate) (PBSeT), are prepared with nearly identical structural and molar compositions. The objective of this study is to comprehensively examine the impact of alkylene unit length on the barrier properties of the materials, delving into aspects such as crystallinity, free volume, molecular chain mobility, as well as adsorption and diffusion of gases within the materials. The findings indicate a decrease in crystallinity from 17.2% for PBOT to 10.2% for PBSeT as the alkylene chain length increases, while maintaining the same chemical composition. Concurrently, the fractional free volume increases from 0.9% to 2.6%, and the melt flow activation energy decreases from 106.6 to 52.1 kJ mol−1. Importantly, theoretical calculations are performed, demonstrating that the predominant site for gas adsorption and diffusion is within the material's free volume. These combined observations indicate a gradual decrease in barrier properties as the number of methylene groups increases.

In sight the behavior of natural Bletilla striata polysaccharide hydrocolloids by molecular dynamics method

Plant polysaccharides, distinguished by diverse glycosidic bonds and various cyclic sugar units, constitute a subclass of primary metabolites ubiquitously found in nature. Contrary to common understanding, plant polysaccharides typically form hydrocolloids upon dissolution in water, even though both excessively high and low temperatures impede this process. Bletilla striata polysaccharides (BSP), chosen for this kinetic study due to their regular repeating units, help elucidate the relationship between polysaccharide gelation and temperature. It is suggested that elevated temperatures enhance the mobility of BSP molecular chains, resulting in a notable acceleration of hydrogen bond breakage between BSP and water molecules and consequently, compromising the conformational stability of BSPs to some extent. This study unveils the unique relationship between polysaccharide dissolution processes and temperature from a kinetics perspective. Consequently, the conclusion provides a dynamical basis for comprehending the extraction and preparation of natural plant polysaccharide hydrocolloids, pharmaceuticals and related fields.

4D Printing of Mechanically Ultrastretchable and Ultrastrength Liquid‐Free Ionoelastomers with Rapid Responsiveness

Abstract4D printing has attracted widespread attention due to its ability to fabricate complex structures capable of responding to specific stimuli. However, existing smart materials used for 4D printing, such as conventional hydrogels, liquid crystal elastomers, and shape‐memory polymers, are constrained in their ability to fulfill both mechanical ultrastrength and ultrastretchability requirements simultaneously due to their water saturation or uneven network structures. This study presents 4D printing of liquid‐free ionic elastomers (LFIEs) that is achieved through photopolymerization of the acrylic acid‐tetramethylammonium chloride‐polymerizable deep eutectic solvent. The transition temperature (Tt) of the high‐fracture‐strength LFIEs is adjusted by introducing phenylphosphoric acid, harboring multiple hydrogen‐bonds, leading to improved molecular chain mobility through softening of the chains. Consequently, the 4D‐printed LFIEs retain their high strength while achieving ultrastretchable properties even under elevated temperatures during heating. Moreover, the 4D‐printed LFIEs demonstrate both a swift response time and a high fixation rate even after undergoing repeated transformation cycles. These outstanding capabilities exhibit by LFIEs present a reliable strategy for advancing their applications in diverse fields, such as smart furniture, robotics, and intelligent manufacturing with remote monitoring, and beyond.

Chitinous Bioplastic Enabled by Noncovalent Assembly.

Natural polymeric-based bioplastics usually lack good mechanical or processing performance. It is still challenging to achieve simultaneous improvement for these two usual trade-off features. Here, we demonstrate a full noncovalent mediated self-assembly design for simultaneously improving the chitinous bioplastic processing and mechanical properties via plane hot-pressing. Tannic acid (TA) is chosen as the noncovalent mediator to (i) increase the noncovalent cross-link intensity for obtaining the tough noncovalent network and (ii) afford the dynamic noncovalent cross-links to enable the mobility of chitin molecular chains for benefiting chitinous bioplastic nanostructure rearrangement during the shaping procedure. The multiple noncovalent mediated network (chitin-TA and chitin-chitin cross-links) and the pressure-induced orientation nanofibers structure endow the chitinous bioplastics with robust mechanical properties. The relatively weak chitin-TA noncovalent interactions serve as water mediation switches to enhance the molecular mobility for endowing the chitin/TA bioplastic with hydroplastic processing properties, rendering them readily programmable into versatile 2D/3D shapes. Moreover, the fully natural resourced chitinous bioplastic exhibits superior weld, solvent resistance, and biodegradability, enabling the potential for diverse applications. The full physical cross-linking mechanism highlights an effective design concept for balancing the trade-off of the mechanical properties and processability for the polymeric materials.

Manufacture of biaxially oriented high-density polyethylene membranes with tunable properties via “structuring” processing strategy

Polyethylene (PE) is the most widely used thermoplastic resin in the world now. Among the endless number of PE products, films constitute over 50% of the consumer market and are applied in optical, packing and filtration areas according to distinct condensed structures. In this work, we prepared high-density polyethylene (HDPE)/liquid paraffin (LP) precursor films with various condensed structures by adjusting the LP content. Subsequently, we delved into the mechanism behind structural evolution during the uniaxial stretching process. Our findings reveal that an increase in LP content can increase the mobility of molecular chains, fostering the transformation of lamellae into an oriented microfiber structure during uniaxial stretching process. This improvement contributes to the enhanced stretchability of the films. Finally, we fabricated biaxially oriented membranes with distinct properties. These properties span from non-porous packaging films with exceptional optical characteristics to porous films suitable for specialized separation applications, achieved through the manipulation of the LP content. In summary, we manufacture different kinds of PE films through the strategy of “structure→ processing→ property”, which provides efficient access to design a given polymer material with desired structure and tunable properties via “structuring” processing.

3D-Printable Sustainable Bioplastics from Gluten and Keratin.

Bioplastic films comprising both plant- and animal-derived proteins have the potential to integrate the optimal characteristics inherent to the specific domain, which offers enormous potential to develop polymer alternatives to petroleum-based plastic. Herein, we present a facile strategy to develop hybrid films comprised of both wheat gluten and wool keratin proteins for the first time, employing a ruthenium-based photocrosslinking strategy. This approach addresses the demand for sustainable materials, reducing the environmental impact by using proteins from renewable and biodegradable sources. Gluten film was fabricated from an alcohol-water mixture soluble fraction, largely comprised of gliadin proteins. Co-crosslinking hydrolyzed low-molecular-weight keratin with gluten enhanced its hydrophilic properties and enabled the tuning of its physicochemical properties. Furthermore, the hierarchical structure of the fabricated films was studied using neutron scattering techniques, which revealed the presence of both hydrophobic and hydrophilic nanodomains, gliadin nanoclusters, and interconnected micropores in the matrix. The films exhibited a largely (>40%) β-sheet secondary structure, with diminishing gliadin aggregate intensity and increasing micropore size (from 1.2 to 2.2 µm) with an increase in keratin content. The hybrid films displayed improved molecular chain mobility, as evidenced by the decrease in the glass-transition temperature from ~179.7 °C to ~173.5 °C. Amongst the fabricated films, the G14K6 hybrid sample showed superior water uptake (6.80% after 30 days) compared to the pristine G20 sample (1.04%). The suitability of the developed system for multilayer 3D printing has also been demonstrated, with the 10-layer 3D-printed film exhibiting >92% accuracy, which has the potential for use in packaging, agricultural, and biomedical applications.

The novel mechanical and recovery behaviors of 3D printed EVA under cyclic tensile loading

In this study for the first time, the cyclic mechanical properties and shape recovery behavior of 3D printed EVA were investigated. EVA with high elastic capability was successfully printed by direct material extrusion method and then a novel cyclic shape recovery test was conducted in which the tensile test was performed at three different strain levels (250, 500 and 1000%) in six cycles and after the end of each cycle by heating the samples, their recovery was measured. The results showed that in all strain levels and tensile cycles, the full recovery is observed, which is completed in two steps after unloading and after heating the sample. Upon exposure to hot water, the disruption of intermolecular forces facilitated the recovery of the material's original shape through increased molecular mobility and rearrangement of polymer chains. However, it was observed that with increasing strain levels (from 250% to 1000%), the recovery process became less effective, leading to a decline in mechanical properties. Also, by increasing the number of tensile cycles, the tensile stress value at the desired strain level and the rate of change decreases and after the second cycle, the cyclic behavior under tensile loading almost reaches a constant trend.

Effect of cross-link density on the performance of polyimine/epoxy vitrimers

Vitrimers are polymers rich in dynamic covalent bonds in cross-link networks. When the dynamic covalent bonds are not activated, the vitrimers show the performance stability of the traditional thermosetting polymer. When the dynamic covalent bonds are activated, the vitrimers can show some novel and unique properties, such as stress relaxation, self-healing and reprocessing. This new type of polymer has attracted wide attention because of its unique properties. As thermoset materials, the degree of cross-link and cross-link density of the materials are very important for the performance of vitrimers. In order to find out the effects of cross-link density on the properties of vitrimers, a series of dynamic polyimine/epoxy cross-link networks with different cross-link densities were designed and prepared, and their properties were characterized. The materials with higher cross-link density show higher thermal properties, mechanical properties and shape fixation ratio. However, due to the increase of cross-link density, the mobility of molecular chain and the exchange of dynamic bonds are limited, so the healing efficiency, shape recovery ratio and shape recovery rate will decrease to a certain extent. This study provides important insights into a deeper understanding of this new type of polymer.

A comprehensive study on the effect of molecular chain flexibility on the low-temperature curing ability of polyimides

As stringent demands for PI materials with low-temperature curable properties have increased in the high-frequency communication era, the introduction of flexible structures has gained prominence for enhancing molecular chain mobility.

Crystallization and heat resistance properties of poly(glycolic acid) reinforced poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends

In this study, poly(lactic acid) and poly(butylene adipate-co-terephthalate) (PLA/PBAT 70/30) were melt blended in the presence with varying amounts of poly (glycolic acid) PGA. SEM, DSC, XRD, and POM were utilized to study the crystallization behavior of the PLA/PBAT/PGA blends. The results clearly demonstrated that PGA played a significant role in enhancing PLA's molecular chain mobility and improving neat PLA's crystalline properties. Notably, POM observations indicated the addition of PGA increased the density of spherulite nucleation, while WAXD integral data showed a reduction in the crystallite dimensions of PLA due to PGA. The tensile test revealed the mechanical properties of the PLA/PBAT/PGA blends were significantly improved by the addition of PGA. Moreover, the presence of PGA led to a notable increase in the heat deformation temperature (HDT) of the PLA/PBAT/PGA blends by increasing crystallinity.

Hardening mechanism of waste polyolefin mixtures in the presence of modified bentonite clay

The aim of the work is to obtain and study polymer composite materials based on mixtures of secondary polyolefins and modified polydisperse bentonite clay. The formation features of the structure of mixtures of waste polyolefins in the presence of this-type filler are studied. The data on the changes in the mechanical strength of mixed composites, as well as the results of physico-chemical studies are presented. Mixtures based on waste polymers in the presence of highly dispersed particles of modified polydisperse bentonite are characterized by the improvement of the strength of composites due to increased interfacial interaction in them and by the formation of structure uniformity of the material. This to some extent compensates for the loss of cohesive strength of secondary polymers due to thermal degradation processes. The following conclusions are made: at the phase boundaries, the molecular mobility of polymer chains decreases, which leads to changing the crystallization conditions and to appearing a nonequilibrium stress state; introducing bentonite increases crystalline due to the initiation of physico-chemical interaction; the strength grows due to increased interfacial interaction and structure uniformity; the formation mechanism of a complex of properties of composites consists of two-level adsorption – a modifier on filler particles and active polymer groups on the modified filler surface.

Design of sustainable 3D printable polylactic acid composites with high lignin content

In this study, we report the development of a sustainable polymer system with 50 wt% lignin content, suitable for additive manufacturing and high value-added utilization of lignin. The plasticized polylactic acid (PLA) was incorporated with lignin to develop the bendable and malleable green composites with excellent 3D printing adaptability. The biocomposites exhibit increases of 765.54 % and 125.27 % in both elongation and toughness, respectively. The plasticizer enhances the dispersion of lignin and the molecular mobility of the PLA chains. The good dispersion of lignin particles within the structure and the reduction of chemical cross-linking promote the local relaxation of the polymer chains. The good local relaxation of the polymer chains and the high flexibility allow to obtain a better integration between the printed layers with good printability. This research demonstrates the promising potential of this composite system for sustainable manufacturing and provides insights into novel material design for high-value applications of lignin.

Preferential formation of stereocomplex crystals in poly(L-lactic acid)/poly(D-lactic acid) blends by a fullerene nucleator

Selective formation of stereocomplex (sc) crystallization in enantiomeric poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA) blends is considered as one of the most effective and promising way to improve the mechanical and thermal properties of polylactide (PLA) materials. However, homocrystallization (hc) prevails over sc crystallization in high-molecular-weight (HMW) PLLA/PDLA blends. Herein, we propose a simple and straightforward approach for fabricating sc crystallization and suppress hc crystallization for HMW PLLA/PDLA blends through the addition of C70 as a nucleator. Non-isothermal crystallization and wide-angel X-ray diffraction studies demonstrate that, the incorporation of 1 wt% C70 overwhelmingly leads to the formation of sc crystallites, while preventing the formation of hc crystallites. Isothermal crystallization experiments at 140 °C reveal a significant reduction in the half-crystallization period of the PLLA/PDLA blend upon the addition of C70. Fourier-transformed infrared spectroscopy suggests that, the improved intermolecular interactions between PLLA and PDLA chains, as well as the inhibition of molecular chain diffusion and mobility, contribute to the accelerated formation of sc facilitated by C70. The enhanced sc crystallization results in a 15.5 °C higher thermal stability in the as-prepared PLLA/PDLA blend with 1 wt% C70 compared to the neat counterpart.

Unraveling Tribochemistry and Self-Lubrication Mechanism of Polytetrafluoroethylene by Reactive Coarse-Grained Molecular Dynamics Simulations.

Lubrication of polymeric materials generally involves processes of atomic-scale chemical bond forming/breaking at the interface and mesoscale chain reorientation, disentanglement, and so forth. However, it is difficult to describe the important aspects of tribochemical reactions by conventional coarse-grained molecular dynamics (CGMD) simulations. Here, reactive CGMD simulations were conducted based on the ReaxFF force field to study the tribochemical interactions between polytetrafluoroethylene (PTFE) and iron. The chemical bond forming/breaking between the molecular chain and countersurface was fitted through the bond dissociation energies of specific reaction sites from all-atom ReaxFF-MD simulations. This enabled a quantitative description of tribochemical reactions in a macromolecule system. First, the number of anchoring bonds between PTFE molecules and the countersurface showed a strong correlation with the friction coefficient. The shearing process induced breaking of the interfacial anchoring bonds as well as chain disentanglement in the matrix, which consequently led to ordering reorientation of molecular chains toward sliding direction and hence decrease of friction. Second, two competitive factors were clarified to affect polymer friction with varying temperatures. The decrease of interfacial anchoring reactivity and molecular chain mobility at low temperature prohibited reorientation of molecular chains and increased the friction coefficient. On the other hand, the hardening of PTFE and the reduction in effective contact area at low temperatures decreased the friction coefficient. This led to a turning point with a maximum friction coefficient around 100 K. These results shed light on the essential role of tribochemical reactions on polymer lubrication, especially under low temperatures, which provides design guidance of polymeric lubrication systems for engineering applications.

Novel Strategy to Improve the Performance of Poly(l-lactide): The Synergistic Effect of Disentanglement and Strong Shear Field

As a biobased and biodegradable material that can replace traditional petrochemical-based polymers, poly(l-lactide) (PLLA) shows great application potential. However, its widespread application still faces some obstacles, mainly associated with the poor thermal resistance, because the molecular chains of PLLA are semirigid and of poor regularity. Therefore, the crystallization rate is low, making it difficult to crystallize during the molding process, and the finally obtained PLLA is almost amorphous. In this work, the entanglement density of molecular chains was reduced to promote the molecular chain mobility. Then, PLLA was processed in combination with a strong shear field provided by the vibration injection molding technology. The results show that the synergistic effect of disentanglement and strong shear field can significantly accelerate the crystallization kinetics of PLLA. In addition, due to the better mobility, molecular chains of PLLA tend to be more regularly arranged along the flow direction under strong shear field, resulting in thicker shear layers as well as the generation of denser and more perfect shish-kebab structures. As a result, PLLA material with enhanced performance is obtained, which favors to broaden the application range of PLLA.

Toward Highly Matching the Dura Mater: A Polyurethane Integrating Biocompatible, Leak-Proof, and Self-Healing Properties.

The dura mater is the final barrier against cerebrospinal fluid leakage and plays a crucial role in protecting and supporting the brain and spinal cord. Head trauma, tumor resection and other traumas damage it, requiring artificial dura mater for repair. However, surgical tears are often unavoidable. To address these issues, the ideal artificial dura mater should have biocompatibility, anti-leakage, and self-healing properties. Herein, this work has used biocompatible polycaprolactone diol as the soft segment and introduced dynamic disulfide bonds into the hard segment, achieving a multifunctional polyurethane (LSPU-2), which integrated the above mentioned properties required in surgery.In particular, LSPU-2 matches the mechanical properties of the dura mater and the biocompatibility tests with neuronal cells demonstrate extremely low cytotoxicity and do not cause any negative skin lesions. In addition, the anti-leakage properties of the LSPU-2 are confirmed by the water permeability tester and the 900mm H2 O static pressure test with artificial cerebrospinal fluid. Due to the disulfide bond exchange and molecular chain mobility, LSPU-2 could be completely self-healed within 115min at human body temperature. Thus, LSPU-2 comprises one of the most promising potential artificial dura materials, which is essential for the advancement of artificial dura mater and brain surgery.