Low Crosslinking Research Articles

Nano‐Silica‐Particles Filling Effect on Mechanical Properties of Silicone‐Rubber Composites

ABSTRACTThe mechanical properties of silicone‐rubber composites filled with nano‐ or micro‐silica‐particles are discussed experimentally and theoretically. The matrix rubbers cured under various ratios of the main component to the curing agent are prepared to change the crosslinking density of the matrix rubber. Because the interphase layer made of the matrix rubber in the glassy state is formed around the nano‐particle, the nano‐particle behaves as an apparent single particle together with the interphase layer and the interphase layers apparently increase the nano‐particle volume fraction. The Young's moduli of the nano‐ and micro‐composites with a larger (apparent) particle volume fraction are greater than that of the matrix rubber. However, the proportional limit strains are smaller, although the fracture strains are slightly smaller. The Young's modulus and proportional limit strain can be analyzed theoretically with the (apparent) volume fraction. The fracture toughness of the composites increases as the (apparent) volume fraction increases, but it increases little at the (apparent) volume fraction above 0.2. However, the fracture toughness monotonically increases for the nano‐composites with low crosslinking density of the matrix rubber. Finally, the mechanical properties can be designed by using the matrix rubber with the different crosslinking density and the interphase layer.

Physically cross-linked cellulose nanofiber (LCNF/CNF) hydrogels: impact of the composition on mechanical and swelling properties

Lignocellulose nanofibers (LCNFs) are highly regarded for their ability to significantly enhance the rigidity of formed structures. When integrated into cellulose nanofiber (CNF) hydrogels, they hold substantial promise in augmenting mechanical strength, as well as improving adsorption capacity. Herein, the preparation of hydrogels from an aqueous suspension of CNFs and LCNFs extracted from eucalyptus cellulose pulp through a homogenization process is outlined. Suspensions of different concentrations were prepared to assess the influence of lignin and nanofiber content on the properties of the hydrogels. The hydrogels cellulose nanofibers (HCNF) and lignocellulose nanofibers (HLCNF) were formed through a freeze–thaw process, revealing an enhancement in rigidity with increasing nanofiber concentration. DFT (density functional theory) calculations illustrated the cross-linking mechanism between cellulose chains induced by the crystallization of water molecules, thus, corroborating the postulated hydrogel formation mechanism. Microstructural analysis revealed honeycomb-shaped matrices in longitudinal sections, with HLCNF hydrogels presenting less smooth walls. Studies on water adsorption capacity showed rapid swelling in both hydrogels, correlated with the nanofiber content reaching 8750% and 5500% for HLCNF and HCNF, respectively. HLCNF hydrogels exhibited higher adsorption capacity due to the influence of lignin on cross-linking rates. Mechanical compression tests demonstrated exceptional resilience in all hydrogels. Despite having a lower cross-linking density compared to hydrogels made from 2 wt.% cellulose nanofibers, hydrogels composed of 2 wt.% lignocellulose nanofibers exhibited a Young’s modulus of 2.83 kPa. This underscores the superior mechanical properties of lignin-based hydrogels, highlighting the effect of lignin on the hydrogel matrix.

Structure and Functional Characteristics of Novel Polyurethane/Ferrite Nanocomposites with Antioxidant Properties and Improved Biocompatibility for Vascular Graft Development.

Novel ferrite/polyurethane nanocomposites were synthesized using the in situ polymerization method after the addition of different spinel nanoferrite particles (copper, zinc, and copper-zinc) and examined as potential coatings for medical devices and implants in vascular tissue engineering. The influence of the nanoferrite type on the structure and functional characteristics of the polyurethane composites was investigated by FTIR, SWAXS, AFM, TGA, DSC, nanoindentation, swelling behavior, water contact angle, and water absorption measurements. Biocompatibility was evaluated by examining the cytotoxicity and adhesion of human endothelial cells and fibroblasts onto prepared composites and performing a protein adsorption test. The antioxidant activity was detected by UV-VIS spectroscopy using a 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging assay. Embedding the different types of nanoparticles in the polyurethane matrix increased phase mixing, swelling ability, and DPPH scavenging, decreased surface roughness, and differently affected the stiffness of the prepared materials. The composite with zinc ferrite showed improved mechanical properties, hydrophilicity, cell adhesion, and antioxidant activity with similar thermal stability, but lower surface roughness and crosslinking density compared to the pristine polyurethane matrix. The in vitro biocompatibility evaluation demonstrates that all nanocomposites are non-toxic, exhibit good hemocompatibility, and promote cell adhesion, and recommends their use as biocompatible materials for the development of coatings for vascular implants.

Simultaneous Encapsulation of Probiotic Bacteria (Lactococcus lactis, and Lactiplantibacillus plantarum) in Calcium Alginate Hydrogels.

Encapsulation in alginate hydrogel microspheres is an effective method for protecting and improving the survival of lactic acid bacteria in different environments. This research aims to expand the knowledge about the structure/property relationship of calcium alginate microspheres loaded with a mixture of autochthonous probiotic bacteria (Lactococcus lactis and Lactiplantibacillus plantarum). A novel hydrogel formulation (FORMLAB) was prepared by ionic gelation and the molecular interactions between the FORMLAB constituents, surface morphology, structure, swelling degree, and release profile were characterized. The simultaneous encapsulation of two bacterial cultures in the same compartment does not diminish their viability. The binding of calcium ions to bacterial cells creates favorable conditions for the propagation of the encapsulated bacteria. The molecular interactions between the FORMLAB constituents are complex, involving mainly hydrogen bonds and electrostatic interactions. With a very high degree of swelling followed by low crosslinking, the surface of the microspheres covered with bacterial cells and diffusion through the hydrogel matrix allow for the delivery of probiotics at the right time. The findings suggest that bacterial cells are efficiently delivered from calcium alginate microspheres, offering promising applications in the development of functional foods, especially in cheese production.

Designing from biobased to closed-loop circularity: Flexible dynamic polyimine-amide networks

Dynamic polyimine-amide networks with exceptional properties, including high flexibility, excellent thermal stability and dual closed-loop circularity were designed by combining dynamic covalent imine-functionalities with amide-chemistry. The solvent free up-scalable synthesis started from carboxyl-functionalization of lignin-derivable aldehydes followed by melt polycondensation with a triamine to form two dynamic networks (PIAX1 and PIAX2, respectively). While previously reported vanillin-derived polyimine thermosets were typically non-flexible and brittle, our polyimine-amides are flexible with elongation at break 380 % for PIAX1 and 65 % for PIAX2, where the higher flexibility of PIAX1 is deduced to the lower glass transition temperature and crosslinking density. Both materials illustrate fast stress relaxation even at low temperature, down to 50 °C in the case of PIAX1. Retained and even improved mechanical properties were observed after several cycles of thermal reprocessing, e.g., after three reprocessing cycles by hot pressing, PIAX1 recovered 116 % of original tensile stress and 126 % of original elongation at break, while chemical recycling under acidic conditions at room temperature yielded repolymerizable trialdehydes and triamines. Furthermore, rapid self-healing and shape memory behaviour at low temperature were demonstrated for PIAX1. A promising molecular design, further tuneable by choice of aldehyde and triamine, is demonstrated enabling high performance and dual closed-loop circularity.

3D-printed artificial cornea featuring aligned fibrous structure and enhanced mechanical strength

The global shortage of donor eye bank tissue has significantly impeded advancements in biomaterial for corneal implantation. To address this issue, we have developed a 3D-printed artificial cornea using a composite hydrogel of sodium alginate (SA) and cellulose nanofibers (CNF), crosslinked with poly-L-lysine-co-L-glutamic acid (PLL80GA20, PG) and calcium chloride (CaCl2, CC). The 2 wt% SA/CNF composite hydrogel offers several advantages, including low toxicity, cost-effectiveness, excellent printability, and high mechanical strength, even with low crosslinker concentrations. The PG was synthesized via ring-opening polymerization of L-glutamate N-carboxyl anhydride (BGNCA) and L-lysine N-carboxyl anhydride (CBZNCA). The purity of the monomers was verified through DSC analysis, revealing a melting point of 97 ℃. The molecular weight of the synthesized PG was determined to be 47 kDa. A dual crosslinking strategy was employed, starting with electrostatic crosslinking, followed by ionic crosslinking using varying concentrations of PG and CC at different effective charge concentrations of 6.25 mM, 12.25 mM, and 25 mM. The hydrogel and 3D-printed cornea were comprehensively evaluated for chemical structure, surface functional groups, water content, mechanical strength, orientation, cytotoxicity, biocompatibility, and transparency. Notably, the inclusion of PG significantly enhanced the mechanical properties of the 3D-printed cornea, with the hydrogel achieving a storage modulus of 2,360 kPa at 6.25 mM of PG/CC, while maintaining over 95% water content. The artificial cornea demonstrated 86% transparency, and the cell viability showed 96% viable on Day 7 with degradation rate of 35.9% in 28 days. The superior hydrophilicity, transparency, and mechanical strength of the printed hydrogel highlights its potential for the development of full-thickness corneal structures, making it a promising candidate for future corneal implants.

Solvent-free Acrylate/BCB drop-on-demand (DOD) inkjet dielectric ink for 3D printing

Currently, drop-on-demand (DOD) inkjet-printed dielectric inks used to produce next-generation high-frequency electronic devices fail to meet the requirements of circuit board substrates in terms of thermal, mechanical, and dielectric properties. To address this gap, we synthesized a low-viscosity acrylate monomer featuring an intrinsically low dielectric structure (hexafluorobisphenol A) and multiple cross-linking sites, and a benzocyclobutene monomer with low curing shrinkage and excellent thermomechanical properties. By mixing these monomers with other reactive diluents and verifying them through theoretical calculations and printing, we have developed a range of dielectric inks suitable for inkjet 3D printing. To enhance the overall performance of the cured inks, a sequential UV/thermal curing strategy was employed to form interpenetrating networks (IPNs). The optimal ink formulations met the requirements of circuit board substrates, demonstrating excellent heat resistance (Td5% = 334 °C, Tg = 181 °C), mechanical properties (tensile strength = 85 MPa, elongation at break = 13.5 %), and dielectric properties (Dk = 2.526 and Df = 0.113 at 15 GHz). These formulations meet the performance requirements for circuit board substrates and lead the industry in mechanical and dielectric properties. Furthermore, the feasibility of inkjet printing heterogeneous integrated electronic devices was verified, showing excellent print resolution and continuity of the conductive network. This work provides new insights into the future development of dielectric materials for inkjet 3D printing.

Factor XIII Activation Peptide Residues Play Important Roles in Stability, Activation, and Transglutaminase Activity.

A subunit of factor XIII (FXIII-A) contains a unique activation peptide (AP) that protects the catalytic triad and prevents degradation. In plasma, FXIII is activated proteolytically (FXIII-A*) by thrombin and Ca2+ cleaving AP, while in cytoplasm, it is activated nonproteolytically (FXIII-A°) with increased Ca2+ concentrations. This study aimed to elucidate the role of individual parts of the FXIII-A AP in protein stability, thrombin activation, and transglutaminase activity. Recombinant FXIII-A AP variants were expressed, and SDS-PAGE was used to monitor thrombin hydrolysis at the AP cleavage sites R37-G38. Transglutaminase activities were assessed by cross-linking lysine mimics to Fbg αC (233-425, glutamine-substrate) and monitoring reactions by mass spectrometry and in-gel fluorescence assays. FXIII-A AP variants, S19P, E23K, and D24V, degraded during purification, indicating their vital role in FXIII-A2 stability. Mutation of P36 to L36/F36 abolished the proteolytic cleavage of AP and thus prevented activation. FXIII-A N20S and P27L exhibited slower thrombin activation, likely due to the loss of key interdomain H-bonding interactions. Except N20S and P15L/P16L, all activatable FXIII-A* variants (P15L, P16L, S19A, and P27L) showed similar cross-linking activity to WT. By contrast, FXIII-A° P15L, P16L, and P15L/P16L had significantly lower cross-linking activity than FXIII-A° WT, suggesting that loss of these prolines had a greater structural impact. In conclusion, FXIII-A AP residues that play crucial roles in FXIII-A stability, activation, and activity were identified. The interactions between these AP amino acid residues and other domains control the stability and activity of FXIII.

Soft elasticity enabled adhesion enhancement of liquid crystal elastomers on rough surfaces

The fabrication of pressure-sensitive adhesives (PSA) using liquid crystal elastomers (LCE) that are tolerant to substrate roughness is explored in this work. Traditional soft adhesives are designed by maintaining a balance between their cohesive strength and compliance. However, rough surfaces can significantly affect the adhesion strength of PSAs. Lowering the stiffness of the adhesive by reducing the cross-linking density or using additives can improve contact on rough surfaces. But this also decreases the cohesive strength and affects the overall performance of the adhesive. Additive-free LCE-based adhesives are shown to overcome these challenges due to their unique properties. Soft elasticity of LCE and low cross-link density contribute to their high compliance, while moderate cross-linking provides finite strength. The effect of contact time and substrate roughness on the adhesive performance is evaluated using probe-tack, indentation, lap shear, and static loading experiments. The unique combination of properties offered by LCE can lead to the development of roughness-tolerant adhesives, thereby broadening the application scope of PSAs.

Protocatechualdehyde-based epoxy vitrimer with low dielectric, excellent flame retardancy, and recyclability

Conventional bisphenol A epoxy resins cannot meet the requirements of the new generation of electronic/electrical industries in terms of dielectric properties and flame retardancy and are challenging to reprocess after molding, resulting in waste of resources and environmental hazards. Therefore, a tetrafunctional active ester curing agent (TIE) was successfully synthesized by a one-pot method using biomass protocatechualdehyde as raw materials, followed by curing DGEBA to prepare an epoxy vitrimer (TIE/DGEBA). MHHPA/DGEBA was chosen for comparison since the –OH was also absent after curing. The results showed that TIE/DGEBA had good combinatorial performance, thanks to the unique structure of TIE, including active ester units, siloxane chains, and aromatic Schiff base groups. TIE/DGEBA possessed a lower dielectric constant (2.9 vs. 4.0) compared to MHHPA/DGEBA, which was attributed to the synergistic effect of the less-polar siloxane chain segments, bulky benzene structure, and lower cross-linking density (1971 vs. 733 mol/cm3) of TIE/DGEBA. The aromatic Schiff base not only imparted good thermal stability (T30% = 418.0 vs. 422.2 °C) to TIE/DGEBA but ensured that it allowed for recycling and reprocessing. After solvent recycling, the resin can be remolded without significant change in tensile strength (53.0 vs. 46.3 MPa). TIE/DGEBA displayed better flame retardancy with higher residual weight (28.2 % vs. 5.5 %), lower total heat release (29.6 vs. 43.5 kJ/g), and good resistance to thermal oxidization. The structural and performance characteristics of TIE/DGEBA offer a strategy for designing multifunctional epoxy-based materials in electrical/electronic applications.

FEATURES OF THE INTERACTION AND FORMATION OF NANOSTRUCTURED CHITOSAN SYSTEMS DURING IONOTROPIC GELATION

Bombyx mori chitosan nanoparticles (ChS NPs) were obtained and the kinetic aspects of their size distribution depending on the degree of nonequilibrium of the synthesis by ionotropic gelation using sodium tripolyphosphate (TPP) were studied. The size of ChS NPs was greatly influenced by the ChS concentration, which varied from 0.5 to 10 mg/ml. The size of the NPs increased from 100 to 300 nm when the ChS concentration increased from 0.5 to 10 mg/ml and while maintaining all other parameters of the reaction. An increase in the ChS to-TPP ratio corresponded to a lower cross-linking density and thus ensured slower kinetics for NP formation alongside the formation of large chitosan/TPP aggregates. There was an almost threefold increase in the particle size when the pH of the medium increased from 3.8 to 4.7; thus, the size of ChS NPs depends on the pH of the solution. There was a slight agglomeration of NPs from 363 to 642 nm with an increase in the NP synthesis time from 4 to 24 h. According to calculations, the maximum interaction energy is 50.4 and 69.4 kcal/mol for deprotonated TPP (P3O105-); after adiabatic transfer of the proton, the value decreases to 32.9–33.5 kcal/mol. The maximum interaction energy is –12.8 kcal/mol for the initially protonated TPP (H4P3O10-).

Self-Polymerized Tough and High-Entanglement Zwitterionic Functional Hydrogels.

Zwitterionic hydrogels exhibit great potential in biomedical applications due to their antifouling properties and biocompatibility. However, the single-network structure of pure zwitterionic hydrogels leads to a low toughness and strength, limiting their application in biomedical fields. In this work, a high entanglement sulfobetaine methacrylate-dopamine hydrogel (SBMA-DA-PE) with low cross-linker content and high monomer concentration is prepared by using a dopamine oxidative radical polymerization method. Compared to a regular zwitterionic hydrogel, the SBMA-DA-PE hydrogel exhibits a 5-fold increase in tensile fracture stress and a 10-fold increase in compressive fracture stress. The SBMA-DA-PE hydrogel possesses excellent mechanical properties (the maximum compressive stress ≥4.85MPa, the maximum compressive strain ≥90%). Besides, the non-covalent interactions between catechol or ortho-quinones within the SBMA-DA-PE hydrogel, combined with strong intermolecular electrostatic interactions, endow the SBMA-DA-PE hydrogel with great self-healing capabilities and fatigue resistance. The SBMA-DA-PE hydrogel demonstrates low swellability and possesses good antifouling properties. Furthermore, the good printability and conductivity of the tough SBMA-DA-PE hydrogel endows it with new possibilities for developing biological 3D scaffolds and electronic devices. Overall, this work provides new insights into the preparation of zwitterionic hydrogels with high mechanical strength and multi-functionality for biomedical applications.

Unveiling the Potential of Surface Polymerized Drug Nanocrystals in Targeted Delivery.

Nanocrystals (NCs) have entirely changed the panorama of hydrophobic drug delivery, showing improved biopharmaceutical performance through multiple administration routes. NCs are potential highly loaded nanovectors due to their pure drug composition, standing out from conventional polymers and lipid nanoparticles that have limited drug-loading capacity. However, research in this area is limited. This study introduces the concept of surface modification of drug NCs through single-layer poly(ethylene glycol) (PEG) polymerization as an innovative strategy to boost targeting efficiency. The postpolymerization analysis revealed size and composition alterations, indicating successful surface engineering of NCs of the model drug curcumin of approximately 200 nm. Interestingly, mucosal tissue penetration analysis showed enhanced entry for fully coated and low cross-linked (LCS) PEG NCs, with an increase of 15 μg/cm2 compared to the control NCs. In addition, we found that polymer chemistry variations on the NCs' surface notably impacted mucin binding, with those armored with LCS PEG showing the most significant reduction in interaction with this glycoprotein. We validated this strategy in an in vitro nose-to-brain model, with all of the NCs exhibiting a promising ability to cross a tight monolayer. Furthermore, the metabolic and pro-inflammatory activity revealed clear indications that, despite surface modifications, the efficacy of curcumin remains unaffected. These findings highlight the potential of surface PEGylated NCs in targeted drug delivery. Altogether, this work sets the baseline for further exploration and optimization of surface polymerized NCs for enhanced drug delivery applications, promising more efficient treatments for specific disorders and conditions requiring active targeting.

Eco-friendly and novel tannin-based wood adhesive enhanced with cellulose nanofibrils grafted by hyperbranched polyamides

Tannin-based adhesives, as a natural biobased adhesive, have the potential to expand their application in wood industry as substitutes for traditional adhesives. In this study, cellulose nanofibrils and hyperbranched polyamides (HBPA) were studied to address the challenges associated with the low crosslinking degree and poor water resistance characteristics of condensed tannin-based wood adhesives. The modification strategy focuses on grafting oxidized cellulose nanofibrils with hyperbranched polyamides through the Schiff base reaction. Comprehensive analyses, including FTIR, XPS, XRD, and TG, confirm the successful binding of oxidized cellulose nanofibrils with hyperbranched polyamides, demonstrating their potential to enhance the properties of tannin adhesives. Furthermore, the investigation about bonding strength, and water resistance of tannin adhesives reveal significant improvements in the mechanical and water resistance properties through this modification strategy. In particular, the maximum wet shear strength is 0.7 MPa, meeting the requirements for Class II plywood. This study provides valuable insights into improving the performance of tannin adhesives, offering promising implications for broader applications and contributing to eco-friendly practices in the wood industry.

Shape memory and mechanical properties of ESO modified epoxy/polyurethane semi-interpenetrating polymer networks for smart plaster

While numerous studies have explored the potential of shape memory materials in medical applications, the current research output is not enough for significant productivity in industrial products. In this research, a type of shape memory orthopedic plaster was fabricated by using epoxy/polyurethane interpenetrating networks modified with epoxidized soybean oil (ESO) and then compared with some commercial plasters. Polymer networks that were produced could be tailored to have glass transition temperatures (Tgs) within the range of 70–90 °C by changing the percentage composition of polyurethane and soybean oil. Shape recovery and fixity ratios in all samples were above 95 and 97 %. DMA results showed that IPNs with variable amount of soybean oil had lower glass transition temperature (Tg) and cross-link densities compared to IPNs without soybean oil. Based on the tensile test results, most samples exhibited an elastic modulus in the range of 280–400MPa, a level deemed somewhat acceptable when compared to commercial samples. Light microscope images had shown that the increase of polyurethane led to the phase separation of polymers, which was improved by the addition of soybean oil.

Impact of Annealing Chemistry on the Properties and Performance of Microporous Annealed Particle Hydrogels.

Microporous annealed particle (MAP) hydrogels are a promising class of in situ-forming scaffolds for tissue repair and regeneration. While an expansive toolkit of annealing chemistries has been described, the effects of different annealing chemistries on MAP hydrogel properties and performance have not been studied. In this study, we address this gap through a controlled head-to-head comparison of poly(ethylene glycol) (PEG)-based MAP hydrogels that were annealed using tetrazine-norbornene and thiol-norbornene click chemistry. Characterization of material properties revealed that tetrazine click annealing significantly increases MAP hydrogel shear storage modulus and results in slower in vitro degradation kinetics when microgels with a higher cross-link density are used. However, these effects are muted when the MAP hydrogels are fabricated from microgels with a lower cross-link density. In contrast, in vivo testing in murine critical-sized calvarial defects revealed that these differences in physicochemical properties do not translate to differences in bone volume or calvarial defect healing when growth-factor-loaded MAP hydrogel scaffolds are implanted into mouse calvarial defects. Nonetheless, the impact of tetrazine click annealing could be important in other applications and should be investigated further.

Impact assessment of polymer, cross-linker, and nanoparticles on gelation kinetics and properties of silica nanocomposite hydrogel for water shut-off treatment in harsh reservoir conditions

The study presented the impacts of various parameters like compositional combinations of PHPA (partially hydrolyzed polyacrylamide), organic cross-linker (hydroquinone-HQ and hexamethylenetetramine-HX), and silica nanoparticles (SNP) in addition to the degree of hydrolysis and molecular weight of PHPA on the efficacy of hydrogel for water shut-off jobs. The investigation indicated that the gelation time, gel strength of the gel, tolerance against salinity, and temperature were tuned as required by the field conditions by changing the variables mentioned above. The gelation time was found to vary inversely with the concentration of polymer, cross-linkers, and silica nanoparticles, whereas the gel strength and temperature tolerance followed the reverse trend. SNP was observed to control the gel properties significantly, even at the lower polymer and cross-linker compositions, as evidenced by the stronger network in FESEM, rheological, and other related properties. The hydrogels prepared with the PHPA-LM (low molecular wt) and PHPA-HM (high molecular wt) polymers and HX-HQ cross-linkers showed improved temperature tolerance from 126.49 °C to 131.78 °C and 99.88 °C to 164.34 °C, respectively when improvised with SNP. The gel’s microstructure (FE-SEM image) exhibited significant silica nanoparticle aggregation and evenly distributed compact three-dimensional network structure. The prepared nanohydrogel with optimized composition maintained its stability even at a salinity of 60000 ppm and 120 °C for more than two years. Sand-pack flooding with the nanohydrogel proved very effective, with a permeability reduction of ∼ 90 %. Thus, the prepared nano-hydrogel could be effectively used for high temperature and high salinity conditions with preferred resistance to water flow.

Heterogeneous organo/metal cooperative catalysis: One-pot immobilization of Pd(PPh3)4 and chiral phosphoric acid to hollow mesoporous polystyrene nanospheres for efficient asymmetric α-allylation of aldehydes

The widely used combinations of palladium catalysts and chiral phosphoric acids face with the problems of cooperative catalysis and low-cost immobilization of binary catalysts in heterogeneous catalysis, due to the significant decline in the freedom of anchored catalysts. In this paper, the one-pot immobilization of both chiral phosphoric acid (TRIP) and Pd(PPh3)4 to hollow mesoporous polystyrene nanospheres (HMPNs) via Friedel-Crafts alkylation is developed to fabricate HMPNs-supported dual organo/metal catalysts (Pd(PPh3)4#TRIP@HMPNs) at a low cost. The efficient cooperative catalysis of anchored TRIP and Pd(PPh3)4 with good to excellent yields (8993 %) and enantioselectivities (8087 % ee) is achieved in the direct asymmetric α-allylation of aldehydes with allylic alcohols. The higher molar ratio of TRIP to Pd(PPh3)4 and a lower crosslinking degree of HMPNs are beneficial to the cooperative catalysis of the anchored catalysts. Overall, this paper showcases a success in solving the key problems in heterogeneous asymmetric metal/oragano catalysis.

Preparation and performance analysis of nano‐crosslinking agent for sulphonated guar gum fracturing fluid

AbstractIn order to solve the problems of poor temperature resistance and low crosslinking efficiency of crosslinking agent for sulphonated guar gum fracturing fluid, in this paper, nano‐silica was reacted with 3‐aminopropyltriethoxysilane to obtain surface‐modified nano‐silica, which was then reacted with boric acid and n‐butyl titanate to obtain nano‐silica‐based boron‐titanium composite crosslinking agent. Its physical properties and structure were characterized by infrared (IR), laser particle size analysis, X‐ray diffraction (XRD), and atomic force microscopy (AFM). The sulphonated hydroxypropyl guar gum fracturing fluids formed by nano‐crosslinking agent were analyzed: When the temperature was uniformly increased from 25 to 120°C and the shear rate was 170 s−1, the viscosity was finally constant at about 50 mPa · s, which indicated that the temperature and shear resistance were good; the system had a better filtration‐loss reduction performance; the average sedimentation rate of ceramic grains in the fracturing fluid system was 0.00872 cm · min−1, indicating that the system had good sand carrying performance; the damage rate of fracturing fluid filtrate to the core was 23.33%; the gel breaking performance test showed that the fracturing fluid had good gel breaking performance. By analyzing the performance of the fracturing fluid, it can be seen that the nano‐crosslinking agent has the advantages of good temperature resistance and high cross‐linking efficiency compared with the traditional boron and titanium cross‐linking agents.

Molecular Dynamics Simulations of Gas Transport Properties in Cross-Linked Polyamide Membranes: Tracing the Morphology and Addition of Silicate Nanotubes.

This study employs molecular dynamics (MD) simulations to fundamentally provide insight into the role of cross-link density in the CO2 separation properties of interfacially polymerized polyamide (PA) membranes. For this purpose, two atomistic models of pure polyamide membranes with different cross-link densities are constructed by MD simulations to conceptually determine how the fractional free volume of polyamide affects the gas separation performance of the membrane. The PA membrane with a lower cross-link density (LCPA) shows a higher gas diffusion coefficient, a lower gas solubility coefficient, and a higher gas permeability than the PA membrane with a higher cross-link density (HCPA). Moreover, the pristine and modified silicate nanotubes (SNTs) as the fast gas transport channels are incorporated into the polyamide membranes to assess the effect of the SNT/PA interface chemistry on the CO2 separation properties of the membranes. SNTs are systematically modified by three modifying agents with different CO2-philic groups and different interfacial interaction energies with the polyamide matrix. The results of MD simulations demonstrate that the incorporation of silicate nanotubes into the PA matrix increases the gas diffusivity and permeability and decreases the CO2/gas selectivity. Moreover, the membranes containing modified SNTs possessing high CO2-philicity and high SNTs/PA interfacial interactions show a high CO2 separation performance.