Geometry-based cross-linking algorithm for modeling resorcinol resins through united-atom molecular dynamics simulations

High-temperature resistance and hydrophobic polysiloxane-based polyurethane films with cross-linked structure prepared by the sol-gel process

Low hydrogen permeability and high durability proton exchange membrane with three-dimensional acid-base crosslink structure for water electrolysis

Associating molecular structure and mechanical properties is important for silicone rubber design. Although silicone rubbers are widely used due to their odourless, non-toxic, and high- and low-temperature resistance advantages, their application and development are still limited by their poor mechanical properties. The mechanical properties of silicone rubbers can be regulated by designing the cross-link density and cross-linking structure, and altering the molar contents of vinyl in the side groups of methyl vinyl silicone rubber (MVQ) leads to different cross-linking structures and cross-linking densities in the vulcanized rubber. Therefore, this study investigated the differences in molecular parameters and molecular chain structures of unprocessed MVQ rubbers with different vinyl contents. The results showed that MVQ rubbers with high vinyl contents were branched polymers, better facilitating the cross-linking reaction than MVQ rubbers with low vinyl contents. In addition, silicone rubbers with different vinyl contents were co-cross-linked to introduce an inhomogeneous cross-linked network in the silicone rubber to improve its mechanical properties. The cross-linked network properties were analysed by the Flory-Rehner model and Mooney-Rivlin plots, and it was found that the long chains in the sparsely cross-linked domains of the network favoured high elongation at break and the short chains in the densely cross-linked domains contributed to high modulus, which could satisfy the functions of reinforcing and toughening the rubber materials at the same time. It was also found by analysing the filler network and aggregate morphology that the inhomogeneous cross-linked network led to an improvement in the dispersion of silica in the rubber and a significant improvement in the mechanical properties of silicone rubber.

Reusable polycaprolactone based sorbents with different cross-linking densities for the removal of organic pollutants

Shear-induced structuring of particulate whey protein gels

Silk fibroin/Ag nanowire-based multifunctional sensor for wearable self-powered wireless multi-sensing microsystems

A refractive index (RI) tunable polysiloxane coating was fabricated based on the cross-linked network structure embedded with mesoporous silica nanoparticles (MSNs), in which the MSNs were utilized to modulate the RI as well as to support the interior structure of the polysiloxane coating. The Si–O–Si inorganic backbone structure in combination with characteristics from the photopolymerization of active bonds produced the main cross-linked network structure, and controllable embedding of MSNs constructed the network-sphere structure. This approach eliminated the high-temperature post-treatment that was needed to remove the template, which ensures the safe application for temperature-sensitive laser crystal substrates and avoids coating structure collapse. In addition, degradation of the resulting coating can be minimized due to the similar chemical formation between MSN and polysiloxane coating. Hereby, a polysiloxane coating with expected spectral and laser damage-resistant properties can be obtained. This will facilitate the fabrication and application of a laser component with both high-transmission and high-flux capability for a high-power laser system.

Acrylamide polymers were widely used as oilfield chemical treatment agents because of their wide viscosity range and versatile functions. However, with the increased formation complexity, their shortcomings such as poor solubility and low resistance to temperature, salt, and calcium were gradually exposed. In this paper, acrylamide (AM)/2-acrylamide-2-methyl-1-propane sulfonic acid (AMPS) copolymers were synthesized by aqueous solution polymerization and inverse emulsion polymerization, respectively. The aqueous polymer (W-AM/AMPS) and the inverse emulsion polymer (E-AM/AMPS) were characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (1H NMR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and particle size analysis. The rheological properties, filtration properties, and sodium ion (Na+) and calcium ion (Ca2+) resistance were investigated. The results showed that E-AM/AMPS not only had a dissolution speed 4 times faster than that of W-AM/AMPS but also had superior shear-thinning performance both before and after aging. The filtration property of the bentonite system containing 2 wt % E-AM/AMPS was also better than that of the bentonite system containing 2 wt % W-AM/AMPS. In addition, E-AM/AMPS also exhibited extremely high tolerance for Na+ and Ca2+. The huge difference between rheological and filtration properties of E-AM/AMPS and W-AM/AMPS in drilling fluid can be attributed to the differences in the polymer microstructure caused by the two polymerization methods. Both FTIR and 1H NMR results showed that more hydrogen bonds were formed between E-AM/AMPS molecular groups and molecular chains, which led to a cross-linked network structure of E-AM/AMPS which was observed by TEM. It was this cross-linked network structure that made E-AM/AMPS have a high viscosity and allowed it to be better adsorbed on bentonite particles, thus exhibiting excellent rheological and filtration behavior. In addition, E-AM/AMPS powder had a high specific surface area so that it can be dissolved in water faster, greatly reducing the time and difficulty of configuring drilling fluid.

Cross-linked elastomers are stretchable materials that typically are not recyclable or biodegradable. Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) are soft and ductile, making these bio-based polymers good candidates for biodegradable elastomers. Elasticity is commonly imparted by a cross-linked network structure, and covalent adaptable networks have emerged as a solution to prepare recyclable thermosets via triggered rearrangement of dynamic covalent bonds. Here, we develop biodegradable and recyclable elastomers by chemically installing the covalent adaptable network within biologically produced mcl-PHAs. Specifically, an engineered strain of Pseudomonas putida was used to produce mcl-PHAs containing pendent terminal alkenes as chemical handles for postfunctionalization. Thiol-ene chemistry was used to incorporate boronic ester (BE) cross-links, resulting in PHA-based vitrimers. mcl-PHAs cross-linked with BE at low density (<6 mole %) affords a soft, elastomeric material that demonstrates thermal reprocessability, biodegradability, and denetworking at end of life. The mechanical properties show potential for applications including adhesives and soft, biodegradable robotics and electronics.

In this study, the cross-linked network structures, dynamic mechanical properties and Po、PRI of microbe coagulated natural rubber (NR) samples were analyzed. And mechanical properties of the corresponding NR vulcanizates were further determined by universal testing machines. The results show that the NR of aging resistance increased with the cycle of hanging.When hanged 14 days,the PRI and P0 were 85 and 36.6. With the cycle of hanging rising, NR raw rubber of cross-linked density increased,and had good dynamic mechanical properties as compared with that hanged 0 days.

Poly (vinyl alcohol) (PVA) hydrogel membrane has transport properties because of their cross-linked network structure, which had been used in soilless cultivation of plants. This work revealed the permeability and diffusion ability of nutrient ions in the PVA hydrogel membrane, such as K+, Na+, Ca2+, and Mg2+, which were based on the solution–diffusion model and free volume theory. The microstructure of the membrane was confirmed by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction, and scanning electron microscopy. From experimental results, the process of ion diffusion was a steady-state diffusion. With the increase in temperature and concentration, ion permeability was enhanced. However, compared with divalent ions, permeability increase for monovalent ions is more pronounced due to its smaller hydrated radius. At the concentration of 0.01 mol/L, the permeability coefficient of K+ was 3.5 × 10−7 cm2/s at 30 °C, which was nearly three times of Mg2+. The nutrient ion permeability coefficient was more strongly dependent on the temperature than the ion concentration. For the permeability of K+, the temperature increases from 20 to 50 °C, the permeability coefficient changes from 1.54 to 8.64 × 10−7 cm2/s, and when the concentration increases from 0.01 to 0.08 mol/L, the permeability coefficient changes from 4.53 to 6.8 × 10−7 cm2/s.

The green synthesis of iron nanoparticles (FeNPs) doped and silver nanoparticles (AgNPs) loaded reduced graphene oxide (rGO) (Fe-Ag@rGO) nanocomposite and its applications in methylene blue (MB), malachite green (MG), rhodamine B (RB) degradation were reported. Initially, AgNPs loaded rGO (Ag@rGO) nanocomposites were synthesised simultaneously by an ecological method using Tamarindus indica shell extract as a green reducing agent. Then, the doping of FeNPs into rGO@Ag nanocomposites afforded Fe-Ag@rGO nanocomposite. Interestingly, the finding of this study confirmed that the Fe-Ag@rGO nanocomposites exhibited countless stupendous features in terms of dye degradation. Briefly, the UV-visible spectroscopy and Fourier-transform infrared spectroscopy (FTIR) study confirmed the synthesis of Fe-Ag@rGO nanocomposite. The scanning electron microscopy (SEM) images showed the spherical shape with cross-linked network structures that confirmed the surface modification and synthesis of Fe-Ag@rGO nanocomposite. Finally, the dye degradation potential of the photocatalyst was found to be 97.20%, 98.43%, and 97.33%, for MB, MG, RB, respectively. Herein, the improved photocatalytic performance of the Fe-Ag@rGO was found due to the larger surface area, porous nature, high electron mobility, and synergistic effect of the Fe-Ag@rGO nanocomposite. Additionally, the effective interfacial hybridisation of ‘Ag’, and doping of ‘Fe’ on the rGO sheet extended the duration of the photogenerated electron (e-) hole pairs that can also be contributing to dye degradation. Conclusively, the present experiment provides the new Fe-Ag@rGO nanocomposite to the dye degradation, which could be improved environmental remediation.

Preparation and properties of novel cross-linked sulfonated poly(arylene ether ketone) for direct methanol fuel cell application

Radical copolymerization of two monomers, one of them being bi— functional, has been widely used for the synthesis of polymer networks. However, the actual structure of such networks is still controversial, and it has never been related accurately with the copolymerization parameters. It has been assumed that large fluctuations of the length of the elastic chain originate, at least in part, from the fact that the consumption of the two monomers follow different rate laws. It occured to us that the decisive factor in that respect is not the consumption of the bifunctional monomer, but it is the ability of the pendant double bonds to undergo reaction with growing radicals and to form the actual branch points. This is clearly evidenced by recent works carried out on the system styrene—divinylbenzene in which it was shown that, once the gel point has been reached, cross— linking goes on; more links between individual chains are formed, whereby the crosslink density increases and the average length of the elastically effective network chain decreases. A kinetic investigation of the radical copolymerization was carried out on several systems of this type: styrene—divinylbenzene, styrene—diisopropenyl— benzene, styrene—ethylene dimethacrylate, methylmethacrylate—ethylene di— methacrylate. In some cases, a chain transfer agent was added to the system to delay the occurence of network formation. From the conversion curves of each individual monomer — that were obtained from vapor phase chromatography taken at regular time intervals — the instantaneous composition of the co— polymers formed were determined. Thus, the values of the radical reactivity ratios of the two monomers involved could be calculated. It was confirmed that the bifunctional monomer is more reactive and therefore more readily consumed than the monofunctional monomer. In addition, it was shown that the rate of polymerization of styrene is enhanced noticeably in the presence of a small amount of divinylbenzene. Also it was established that the rate of crosslinking does not parallel the rate of consumption of the divinyl monomer. To give account of all results it has to be assumed that in the early stages of the reaction most of the bifunctional monomer reacted gives yield to pendant double bonds (and, perhaps, to a much lesser extent, to cyclization). The reactivity of these pendant unsaturations is far lower than that of the monomers involved, consequently the pendant double bonds are still numerous, once the gel point has been reached. As these double bonds are slowly consumed in the later stages of the reaction (when not much monomer is left over), the network becomes tighter, its swelling ratio decreases and its modulus increases. These findings throw new light into the problem of the structural homogeneity of network synthesized by radical copolymerization. It cannot be stated anymore that the crosslink density is bound to be inhomogeneous in such networks, nor that once the bifunctional monomer is consumed pendant chains are formed solely. In fact it appears that these species are far more homogeneous in structure that it had been assumed previously, and the crosslink density can be related with the composition of the monomer mixture, provided the reaction was pursued until all double bonds have been consumed. INTRODUCTION Polymer networks are commonly obtained by radical copolymerization of two monomers, one of them being bifunctional (Ref. 1—3). It is a method of great industrial interest, which was applied to a large number of systems. However, even in the absence of syneresis (solvent expulsion during the

Section 4 - General theory of gel preparation