Crosslinking Density Research Articles

Facile supramolecular processing of recyclable adaptive polymer composites for highly reproducible sensory materials

Dynamic polymer networks (DPNs), when cross-linked, can display chemical and physical adaptiveness due to their dynamic connections and associated phase transitions. However, the reliable preparation of these conductive composites and achieving consistent performance through recycling remain challenging, primarily due to a lack of systematic approaches. Herein, we describe synergistic association of supramolecular gel and high density dynamic crosslinking using vinylogous urethane (VU) bond that enable highly reliable sensitivity and reproducibility after recycling to high performance adaptive dynamic polymer networks containing conductive fillers. We introduce a straightforward method to create DPNs-single-walled carbon nanotube (SWCNT) composites. This involves facile grinding a random copolymer in a supramolecular eutectic liquid, resulting in a supramolecular gel. Subsequently, dynamic cross-linking is applied. The resulting dynamic polymer-SWCNT (DPC) composites, incorporating a supramolecular gel, demonstrate adjustable electrical conductivity and high sensitivities to various mechanical motions and irradiations, including specific light and heat. Significantly, the DPC exhibits excellent recyclability, along with enhanced reproducibility and sensitivity as a strain sensor compared to other recyclable sensors. Furthermore, we establish a strong correlation between the sensitivity and stiffness of the DPC composite with dynamic cross-linking density. These findings highlight the promising potential of adaptive gel-based processing of DPNs for highly sensitive, recyclable sensory materials with excellent reproducibility.

The Importance of Adhesion in Solid-State Batteries

Solid-state batteries are one of the key technologies to expedite the electrification of the economy. Compared with traditional liquid electrolytes, solid-state electrolytes are intrinsically safer and can enable high-energy designs by pairing with high-capacity cathodes and lithium metal anodes. However, maintaining the solid/solid contact between electrode and electrolyte during electrochemical cycling is non-trivial and the main challenge for all-solid-state batteries. The common strategy for combatting the contact issue is applying stack pressure, which is a sort of scientific shortcut that masks the real challenges of maintaining good contact between the different electrodes and electrolytes. Improving the adhesion between different battery components is a more effective and commercially viable strategy. We hypothesized that increasing the adhesion between electrode and electrolyte will improve electrode integrity, mitigate contact loss, and increase Coulombic efficiency and cycle life.There are very few studies on the adhesion of battery materials. This is primarily due to limited techniques to measure adhesion at the nanometer and micrometer scales relevant to the battery operation. In this work, we proposed to use atomic force microscopy (AFM) with customized probes to investigate adhesion between a model solid polymer electrolyte (SPE) consisting of crosslinked poly(ethylene oxide) (xPEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and a model cathode active material, LiNi0.6Mn0.2Co0.2O2 (NMC622). We showed that a two-fold increase in polymer stiffness (storage shear modulus, G’) from increasing the crosslinking density, leads to a 40% reduction in the bulk ionic conductivity in the SPE. However, we show evidence that this trade-off relationship between stiffness and ionic conductivity does not significantly impact the battery performance. In drastic contrast, it leads to a decrease in the work of adhesion at the electrolyte|cathode interface, which has a profound impact on the resulting discharge capacity of the battery. How the crosslinking density of the polymer affects the NMC-xPEO adhesion at the microscale and how this affects battery performance remain open questions, which the authors wish to gain insight into from the discussions.

Unmatched resilience and fatigue resistance in a novel cellulose-derived ionic gel with hierarchical superstructured synergy for advanced human-computer interaction

Unlike traditional hydrogels, solvent-free ionic gels eliminate leakage and solvent volatilization, making them suitable for applications in electronic skin, sensing, and other fields due to their excellent conductivity and flexibility. However, designing solvent-free ionic gels with exceptional fatigue resistance, high ionic conductivity, and toughness remains a significant challenge. We address this challenge by employing small molecule/polymer heating self-assembly to regulate the synergistic effects of various components on the hierarchical superstructure. A multi-stage network was formed through the free radical polymerization of 3-Ethyl-1-vinyl-1H-imidazol-3-ium bromide ([C2VIm]Br), lipoic acid (LA), acrylic acid (AA), and hydroxypropyl cellulose (HPC), stabilized by dense hydrogen bonding and polymer chain entanglement. The resulting HPC/LA/AA/iLs (HLAI) ionic gel exhibits exceptional properties: excellent flexibility (with an elongation at break of 4222 %), toughness (1.03 MJ/m3), high ionic conductivity (3.29 × 10−2 S/m), and outstanding fatigue resistance (with a resilience of 91.9 % after 1000 load-unloading cycles at 50 % strain). Additionally, it shows low sensitivity to crack propagation (50 % notched sample can be stretched to 9 times without breaking) and good environmental stability, demonstrating excellent sensing sensitivity and stability (GF=3.23). The conductive ionic gel features a sophisticated hierarchical superstructure that synergistically enhances its properties at the molecular level. The integration of dynamic disulfide bonds, achieved through the polymerization of Lipoic acid, imparts remarkable self-healing capabilities and superior fatigue resistance. Additionally, the incorporation of a rigid HPC structure with dense cross-linking points bolsters elasticity, fracture resistance, and resilience. The gel’s ionic conductivity and sensing sensitivity are significantly enhanced by the inclusion of ionic liquids with polymerizable double bonds, making it an ideal material for applications requiring both flexibility and conductivity. This work presents a novel strategy for designing high-performance multi-stage network solvent-free ionic gels, opening up exciting possibilities for biomimetic electronic skin applications.

Thermomechanical properties of multifunctional polymer hybrid nanocomposites based on carbon nanotubes and nanosilica

AbstractNanocomposites containing low wt% of oxidized multi‐walled carbon nanotubes (MWCNT‐OXI), nanosilica (NS), and its hybrid (MWCNT‐OXI/NS) in epoxy resin were produced and evaluated. The used nanoparticles were studied by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Raman spectroscopy while the nanocomposites were investigated in relation to its morphology, thermal, and mechanical properties. The results demonstrated significant improvements in the storage modulus (E′), glass transition temperature (Tg), and cross link density (CD), for the produced nanocomposites. Increases in thermal conductivity (TC) of up to 85% at 90°C were observed for the nanocomposites containing 1.0 wt% of the hybrid MWCNT‐OXI + NS nanofiller, when compared with neat polymer. It was also verified increases in the resistance to plastic deformation for the nanocomposites, maintained the polymer thermal stability with the addition of these nanoparticles. Finally, the use of MWCNT‐OXI and NS, combined or not, significantly improved the thermal and mechanical properties of polymer, showing multifunctional characteristics for the produced nanocomposites.

Injectable Dual Fenton/Enzymatically Cross-Linked Double-Network Hydrogels Based on Acrylic/Phenolic Polymers with Highly Reinforced and Tunable Mechanical Properties.

Injectable hydrogels have been extensively used as promising therapeutic scaffolds for a wide range of biomedical applications, such as tissue regeneration and drug delivery. However, their low fracture toughness and brittleness often limit their scope of application. Double-network (DN) hydrogel, which is composed of independently cross-linked rigid and ductile polymer networks, has been proposed as an alternative technique to compensate for the weak mechanical properties of hydrogels. Nevertheless, some challenges still remain, such as the complicated and time-consuming process for DN formation, and the difficulty in controlling the mechanical properties of DN hydrogels. In this study, we introduce a simple, rapid, and controllable method to prepare in situ cross-linkable injectable DN hydrogels composed of acrylamide (AAm) and 4-arm-PPO-PEO-tyramine (TTA) via dual Fenton- and enzyme-mediated reactions. By varying the concentration of Fenton's reagent, the DN hydrogels were rapidly formed with controllable gelation rate. Importantly, the DN hydrogels showed a 13-fold increase in compressive strength and a 14-fold increase in tensile strength, compared to the single network hydrogels. The mechanical properties, elasticity, and plasticity of DN hydrogels could also be modulated by simply varying the preparation conditions, including the cross-linking density and reagent concentrations. At low cross-linker concentration (<0.05 wt %), the plastic DN hydrogel stretched to over 6,500%, whereas high cross-linker concentration (≥0.05 wt %) induced fully elastic hydrogels, without hysteresis. Besides, DN hydrogels were endowed with rapid self-recovery and highly enhanced adhesion, which can be further applied to wearable devices. Moreover, human dermal fibroblasts treated with DN hydrogels retained viability, demonstrating the biocompatibility of the cross-linking system. Therefore, we expect that the dual Fenton-/enzyme-mediated cross-linkable DN hydrogels offer great potential as advanced biomaterials applied for hard tissue regeneration and replacement.

Flame retarded lignin-based epoxy resin with excellent antibacterial and anti-corrosion properties modified by coordinated phospho-nitrogen flame retardant

In this paper, epoxidized lignin (HL) and sebacic acid (HSA) were used as the hard and soft segments, respectively, and a kind of reactive coordinated phosphorous-nitrogen flame retardants (DTZ) was designed and synthesized via Zn2+ coordination to fabricate a multifunctional non-bisphenol A lignin based epoxy (EP) composite. The swelling behavior and morphological analysis demonstrated that the crosslinking density of EP increased significantly after adding HL and DTZ. The existence of coordination sacrificial bond of DTZ dissipated more energy when it was subjected to external forces, thereby making 80HSA/14HL/6DTZ maintained a high tensile strength (10.65 MPa) while having little damage to the elongation at break (30.74 %). The limiting oxygen index (LOI) of 80HSA/14HL/6DTZ was significantly higher than that of 100HSA (22.3 %), reaching 36.6 %, and the vertical combustion test (UL-94) reached V-0 level. The morphology of carbon layer and residual carbon analysis showed that HL and DTZ had synergistic effect, and the flame retardancy mechanism of gas phase and condensed phase existed in the combustion process. Simultaneously, the addition of HL and DTZ also endowed the EP composite with excellent corrosion resistance and antibacterial properties.

In Situ-Forming, Bioorthogonally Cross-linked, Nanocluster-Reinforced Hydrogel for the Regeneration of Corneal Defects.

Corneal defects can lead to stromal scarring and vision loss, which is currently only treatable with a cadaveric corneal transplant. Although in situ-forming hydrogels have been shown to foster regeneration of the cornea in the setting of stromal defects, the cross-linking, biomechanical, and compositional parameters that optimize healing have not yet been established. This, Corneal defects are also almost universally inflamed, and their rapid closure without fibrosis are critical to preserving vision. Here, an in situ forming, bioorthogonally cross-linked, nanocluster (NC)-reinforced collagen and hyaluronic acid hydrogel (NCColHA hydrogel) with enhanced structural integrity and both pro-regenerative and anti-inflammatory effects was developed and tested within a corneal defect model in vivo. The NCs serve as bioorthogonal nanocross-linkers, providing higher cross-linking density than polymer-based alternatives. The NCs also serve as delivery vehicles for prednisolone (PRD) and the hepatocyte growth factor (HGF). NCColHA hydrogels rapidly gel within a few minutes upon administration and exhibit robust rheological properties, excellent transparency, and negligible swelling/deswelling behavior. The hydrogel's biocompatibility and capacity to support cell growth were assessed using primary human corneal epithelial cells. Re-epithelialization on the NCColHA hydrogel was clearly observed in rabbit eyes, both ex vivo and in vivo, with expression of normal epithelial biomarkers, including CD44, CK12, CK14, α-SMA, Tuj-1, and ZO-1, and stratified, multilayered morphology. The applied hydrogel maintained its structural integrity for at least 14 days and remodeled into a transparent stroma by 56 days.

Superior Enhancement in Mechanical Properties of Polyurethane‐Based Multifunctional GAP Partially Grafted with Fluorinated Polyether via Catalyst‐Free Click Reaction

AbstractDifunctional glycidyl azide polymer (GAP) is an energetic binder promising for propellant formulations. The multifunctional fluorine‐containing GAP has been synthesized to enhance its mechanical properties. This work outlined multifunctional GAP partially grafted with 1,2,3‐triazole‐5‐(α‐hydroxyl)‐fluorinated polyether (GAP‐g‐3F) synthesized by thermal and catalyst‐free azide‐alkyne cycloaddition reaction, in which the azide groups were from GAP and electron‐deficient alkynes from β‐propargyl‐α‐hydroxyl poly (tri‐fluoropropane glycidyl ether) (PHP3F). PHP3F was synthesized via the typical cationic ring‐opening polymerization of 2‐((2,2,2‐trifluoroethoxy) methyl) oxirane and propargyl alcohol as the initiator. The chemical structures, molecular weight, and thermal properties were characterized by FTIR, NMR, GPC, DSC, and TGA, respectively. HNMR results showed that 8 % of total azide groups in GAP were grafted. GAP‐g‐3F had a slightly higher glass transition temperature than that of GAP. The results of TGA showed that GAP‐g‐3F had suitable thermal decomposition resistance up to 200 °C. The thermal properties, mechanical properties, cross‐linking network structures, and microstructures of the polyurethane networks cured with hexamethylene diisocyanate trimer as a crosslinking agent were determined and compared by TGA, universal tensile test, swelling measurement, and SEM, respectively. The initial decomposition temperature of GAP‐g‐3F‐based polyurethane networks (GAP‐g‐3F‐PU) was around 220 °C, thus meeting the requirements for propellants. In addition, GAP‐g‐3F‐PU exhibited superior mechanical properties, showing an almost twelvefold increase in tensile strength to 16.9 MPa compared with difunctional GAP‐PU with 1.4 MPa tensile strength. The results of the swelling measurement revealed that the GAP‐g‐3F‐PU sample showed a higher crosslinking density in comparison to the GAP‐PU sample. SEM results indicated that the multifunctional fluorine‐containing GAP could enhance compatibility between the soft and hard segments of polyurethanes, leading to a decrease in their separation degree. This finding showed that the synthesis of a multifunctional GAP partially grafted with fluorinated polyether via a triazole ring may be a promising solution to decrease the separation degree increase of PUs, thereby improving the mechanical properties.

Capsaicin mimic-based antifouling and antibacterial polyester nanofiltration membranes with tunable crosslinked structures

Polyester thin-film composite (PE TFC) nanofiltration membranes based on the interfacial polymerization (IP) of polyols/polyphenols and acyl chloride continue to attract considerable attention for textile wastewater treatment due to their excellent antifouling properties. Herein, N-(5-methyl acrylamide-2,3,4 hydroxy benzyl) acrylamide (AMTHBA), a polyphenol-inspired capsaicin derivative, was first utilized as an aqueous monomer for the preparation of antifouling and antibacterial PE TFC membranes via the IP process. The moderate reactivity of AMTHBA and its unique solubility enabled a rational control of the crosslinking density of PE membranes, allowing the formation of structures from loose to dense through an adjustment of the AMTHBA concentration. The densely crosslinked AM-TMC PE membrane exhibited favorable desalination performance, with a water permeance of 21.8 L m−2 h−1 bar−1 and a Na2SO4 rejection of 83.8 %. The loosely crosslinked AM-TMC PE membrane exhibited excellent dye/salt separation performance, with high dye rejections (e.g., 98.5 % for MB) and low salt rejections (e.g., 4.0 % for NaCl), as well as high water permeance (30.4 L m−2 h−1 bar−1). In contrast, the capsaicin-containing PE TFC membranes also demonstrated markedly enhanced resistance to bacterial growth and organic fouling. These findings indicate that AM-TMC PE membranes present novel avenues for the advancement of task-specific separation membranes.

Shape Memory Polymers with Patternable Recovery Onset Regulated by Light.

Shape memory polymers (SMPs) show attractive prospects in emerging fields such as soft robots and biomedical devices. Although their typical trigger-responsive character offers the essential shape-changing controllability, having to access external stimulation is a major bottleneck toward many applications. Recently emerged autonomous SMPs exhibit unique stimuli-free shape-shifting behavior with its controllability achieved via a delayed and programmable recovery onset. Achieving multi-shape morphing in an arbitrary fashion, however, is infeasible. In this work, a molecular design that allows to spatio-temporally define the recovery onset of an autonomous shape memory hydrogel (SMH) is reported. By introducing nitrocinnamate groups onto an SMH, its crosslinking density can be adjusted by light. This affects greatly the phase separation kinetics, which is the basis for the autonomous shape memory behavior. Consequently, the recovery onset can be regulated between 0 to 85min. With masked light, multiple recovery onsets in an arbitrarily defined pattern which correspondingly enable multi-shape morphing can be realized. This ability to achieve highly sophisticated morphing without relying on any external stimulation greatly extends the versatility of SMPs.

Tribomechanical Properties of PVA/Nomex® Composite Hydrogels for Articular Cartilage Repair.

Due to the increasing prevalence of articular cartilage diseases and limitations faced by current therapeutic methodologies, there is an unmet need for new materials to replace damaged cartilage. In this work, poly(vinyl alcohol) (PVA) hydrogels were reinforced with different amounts of Nomex® (known for its high mechanical toughness, flexibility, and resilience) and sterilized by gamma irradiation. Samples were studied concerning morphology, chemical structure, thermal behavior, water content, wettability, mechanical properties, and rheological and tribological behavior. Overall, it was found that the incorporation of aramid nanostructures improved the hydrogel's mechanical performance, likely due to the reinforcement's intrinsic strength and hydrogen bonding to PVA chains. Additionally, the sterilization of the materials also led to superior mechanical properties, possibly related to the increased crosslinking density through the hydrogen bonding caused by the irradiation. The water content, wettability, and tribological performance of PVA hydrogels were not compromised by either the reinforcement or the sterilization process. The best-performing composite, containing 1.5% wt. of Nomex®, did not induce cytotoxicity in human chondrocytes. Plugs of this hydrogel were inserted in porcine femoral heads and tested in an anatomical hip simulator. No significant changes were observed in the hydrogel or cartilage, demonstrating the material's potential to be used in cartilage replacement.

Nanostructure-transportation relation to PEMFCs activity and durability degradation

The Proton exchange membrane (PEM) is a crucial component in the membrane electrode assembly (MEA), playing a vital role in providing a channel for water transport and acting as a bridge for proton conduction. However, during the long-term operation of fuel cells, PEM is susceptible to attack from metal ions such as Cr3+ originating from the corrosion of metallic bipolar plates, leading to changes in its transport properties. Here, we report on the impact of Cr3+ on the microstructure and mechanical properties of PEM and then correlate it with changes in water uptake and proton conductivity, studying the effect of Cr3+ contamination on fuel cell performance and durability. The study reveals that Cr3+ forms a dense cross-linking structure with sulfonic acid groups inside the ionomer, resulting in an increase in storage modulus due to the larger ion radius and higher valence state, leading to a decrease in water uptake and proton conductivity. The membrane transport properties are primarily dependent on its water content. It is observed that Cr3+ contamination reduced the fuel cell voltage and maximum power density by 47.6 % and 57.1 %, respectively, with a voltage attenuation rate up to 2.9 mV/h, nearly 14 times that of the uncontaminated condition (0.21 mV/h). These findings provide valuable insights for developing high-transmission PEMs and aid in predicting the degradation and lifespan of fuel cells under actual operating conditions.

A super-toughened polyethylene naphthalene (PEN) enabled by polyacrylate elastomer with low crosslink density and reactivity

In elastomer toughening of polyester plastics, both the particle size distribution of the elastomer and the interfacial strength between the elastomer and matrix are key factors for toughness. In this work, bi-functional polyacrylate elastomers with controllable crosslinking density and reactivity were designed for enhancing the toughness of polyethylene naphthalene (PEN) matrix. Firstly, the elastomers with crosslinked structure possess increased melt viscosity and endowed wide particle size distribution, which contribute to the construct of thin matrix ligament and make PEN matrix more susceptible to shear-yield. Secondly, the high interfacial strength between elastomer and matrix can facilitate the transfer of external stress from PEN matrix to the elastomer, protecting the matrix from destroying. The resulted PEN blends exhibit an excellent impact resistance of 45.20 kJ/m2 and a high tensile toughness of 3.586 MJ/m3, which are 21.73 times and 47.81 times higher, respectively, than the virgin PEN. The present work may provide an effective approach for designing polyester blends with enhanced impact resistance and tensile toughness.

Characterization of silicon-based chromium (VI) replacement coatings by using time-of-flight secondary ion mass spectrometry and salt spray tests

This paper proposes an innovative approach in characterization of silicon-based chromium (VI) replacement coatings on an Al substrate by using, salt spray tests and time-of-flight secondary ion mass spectrometry (ToF-SIMS) performed in profile mode by a gas cluster ion beam source (GCIB). While salt spray tests highlight the difference in anticorrosion behaviour, ToF-SIMS provides molecular information on the entire coating and even down to the interface with the Al substrate. ToF-SIMS revealed Si2O2+ and SiOAl + fragments which both contribute to understanding the differences in the anticorrosion performance which are found in the salt spray tests. Si2O2+ moieties relate to the cross-linking density of the coating and subsequently determines the barrier properties. SiOAl+ originates from the interface and characterizes the actual “conversion” of Al at the interface by the deposited layer. The differences in the profile of Si2O2+ and SiOAl + explained the respective anticorrosion performance. From the tested coatings PCT161 showed the highest intensity for both Si2O2+ and SiOAl + while simultaneously performing the best results in the salt spray test. These observations highlight that Si2O2+ and SiOAl + fragments are good indicators of anticorrosion performance and are confirmed by salt spray tests. Moreover, PCT161 and PCT146 are true conversion coatings capable of replacing chromium-based systems.

The Effect of Crosslinking Density on the Dynamic Behavior of Thermo‐Responsive Poly(N‐Isopropylacrylamide) Hydrogels

AbstractStimuli‐responsive hydrogels are of great interest in many biomedical applications, from drug delivery to tissue engineering. In this work, thermo‐responsive poly(N‐isopropylacrylamide) (PNIPAM) hydrogels are prepared by adding different amounts of crosslinking agent (N,N′‐methylenebisacrylamide, BIS) in a two‐step‐freezing polymerization method, which is simple and potentially able to reduce fabrication times and costs. The hydrogel swelling behavior and the temporal evolution of the volume variation in response to temperature changes are investigated. Results demonstrate how the thermo‐responsive behavior of these materials is related to the content of the BIS crosslinking agent, which is helpful to guide the synthesis of dynamic hydrogels with tunable functional properties.

One facile route to prepare high‐performance radiation resistant EPDM rubber composites through graphite modification technology

AbstractModification and improvement of aging resistance in nuclear power environment for the ethylene‐propylene‐diene (EPDM) rubber has been attracting the attention of scientists. In this article, graphite modified EPDM composites (ultrafine graphite [UG]/EPDM) were prepared, and effect of graphite with sizes of 13, 2.6, and 1.3 μm on the processability, vulcanization parameters, mechanical properties, stability of radiation aging of EPDM composites were investigated, respectively. The results showed that EPDM rubber was an irradiated crosslinked polymer. The Mooney viscosity and crosslinking density of EPDM gradually increased with increasing graphite content under the effect of physical and chemical cross‐linking of graphite. The lamellar structure of graphite particles in the rubber matrix is beneficial to improvement of the mechanical properties and aging resistance of the EPDM composites and play a reinforcing role, and the sp2 hybrid structure of graphite can trap and quench free radicals, delayed the irradiation aging of EPDM. UG/EPDM composites irradiation stability was improved with increasing graphite dispersion in EPDM matrix. Under the cumulative irradiation dose of 1000 kGy, the tensile strength of blank sample and UG‐2.6 μm−10 decreased by 51.1% and 17.7%, respectively, and the hardness increased by 8.7% and 4.9%, respectively. The energy storage modulus and the corresponding glass transition temperature (Tg) of UG/EPDM composites enhanced with graphite, while the thermal stability of the composites was improved.

Influence of monomer structure and catalyst concentration on topological transition and dynamic properties of dicarboxylic acid‐epoxy vitrimers

AbstractThis study delineates the dependence of thermophysical behavior of acid‐epoxy vitrimers on their formulation. The stress relaxation due to the bond exchange reaction and the glass transition temperature of acid epoxy vitrimers are investigated, with respect to the influence of catalyst content and acid chain length. This is carried out for a range of dicarboxylic acids and catalyst concentrations formulated and characterized using calorimetry and dynamic mechanical analysis. The influence of acid chain length on the bond exchange rate, topological transition, and glass transition temperatures of the vitrimers is found to be significant. The activation energy of the exchange reaction varies over a wide range from 73 to 104 kJ/mol and the topology freezing temperature from 66 to 136°C with the behavior governed by the interplay between crosslinking density, network flexibility and density and distance of functional groups, with an increase of catalyst concentration leading to lower topological transition temperature and the dependence on chain length showing non‐monotonic behavior. The glass transition decreases by about 30°C as the carbon chain length increases from 6 to 14 carbons due to enhanced monomer flexibility and is not affected by the concentration of catalyst.

Preparation and characterization of UV-curable coatings based on waterborne polyurethane acrylate/g-C3N4 co-crosslinked network for wood materials

Wood materials are often damaged due to exposure to environmental factors including humidity changes, temperature fluctuations, and ultraviolet radiation, resulting in surface aging, deformation, and cracking. Therefore, developing a new wood coating with good mechanical properties and weather resistance is conducive to improving the usability and service life of wood as an outdoor material. In this study, graphitic carbon nitride (g-C3N4) with a characteristic crystal structure was synthesized using melamine as raw material. By constructing a g-C3N4 /polyurethane acrylate co-crosslinked network, a UV-curable wood coating with excellent interfacial adhesion was prepared, which retained the natural aesthetic texture of the wood and imparted good wear resistance, anti-wetting property, and aging resistance to the wood material. Subsequently, the formation process and cross-linking reaction mechanism of the coating were revealed by XRD, FTIR and XPS measurements. Compared with untreated samples, coatings with a cross-linked network structure exhibited enhanced resistance to external environmental changes. As the content of the g-C3N4 increased (>1.0 %), the mechanical properties were significantly improved, with the mass loss rate and damaged area decreasing by 56.9 % and 60.0 %. Meanwhile, with the increased cross-link density of the coating, the water and heat resistance of the wood increased by 22.77 % and 260 %, respectively. After a seven-day UV aging resistance test, the ΔE values only changed by 10.28 %, showing good weathering resistance. This design and synthesis of wood coating provides an effective technology for the long-term use of outdoor wood material.

Influence of a cross-linker agent on mechanical and other properties of polysiloxane based scintillators

Polysiloxane scintillators (PSS) are of great interest due to their neutron and gamma-ray (n/γ) discrimination capability and excellent radiation hardness. However, one major drawback is their low mechanical hardness. To address this issue, we present a cross-linking agent, 1,3-diethenyl-1,3-dimethyl-1,3-diphenyldisiloxane (DS), incorporated into PSS to study its effects on various physical properties. It was found that the enhanced inter-chain entanglement of covalently bonded polymer chains by the DS cross-linker significantly improved the mechanical hardness and optical properties. Gravimetric analysis (TGA) indicated a slightl improvement in stability during thermal degradation. This cross-linker at 0-17 wt% concentrations has also slightly positive impact on the PSD performance as demonstrated by measurements of pulse shape discrimination (PSD) using a 238Pu-Be neutron source. The improved cross-linking density helped prevent both the generation of free molecule radicals and diffusion of fluorophore dyes. Consequently, the cross-linked samples remained transparent with no dye precipitation, even after 12 months of storage.

Tangential flow filtration facilitated fractionation of polymerized human serum albumin: Insights into the effects of molecular size on biophysical properties.

Human serum albumin (HSA) is currently used as a plasma expander (PE) to increase blood volume during hypovolemic conditions, such as blood loss. However, its effectiveness is suboptimal in septic shock and burn patients due to their enhanced endothelial permeability, resulting in HSA extravasation into the tissue space leading to edema, and deposition of toxic HSA-bound metabolites. Hence, to expand HSA's applicability toward treating patients with compromised endothelial permeability, HSA has been previously polymerized to increase its molecular size thus compartmentalizing the polymerized HSA (PolyHSA) molecules in the vascular space. Previous studies bracketed PolyHSA between 100 kDa and 0.2 μm. In this research, PolyHSA was synthesized at two cross-link densities 43:1 and 60:1 (i.e., molar ratios of glutaraldehyde to HSA) and subsequently fractionated via tangential flow filtration (TFF) into two narrower brackets: bracket A (500 kDa and 0.2 μm) and bracket B (50-500 kDa). PolyHSA within the same size bracket at different cross-link densities exhibited similar solution viscosity, zeta potential, and osmolality but differed in hydrodynamic diameter. At the same cross-link density, the PolyHSA A bracket showed higher viscosity, lowered zeta potential, and a larger hydrodynamic diameter compared with the PolyHSA B bracket while maintaining osmolality. Interestingly, PolyHSA 43:1 B, PolyHSA 60:1 A, and PolyHSA 60:1 B brackets exhibited colloid osmotic pressure similar to HSA, indicating their potential to serve as PEs.