Different Degrees Of Crosslinking Research Articles

Experimental Tensile Strength Analysis of Different Manufacturer Oring

Importance and Purpose of Tensile Testing on ORings The tensile test on rings and especially on O-rings is primarily carried out for quality assurance reasons. The tensile test provides information about the formulation quality (evaluation of the absolute values, strength of the material, and determination of formulation changes). For example, it is not possible to detect an exchange of the polymer of compounds with different molecular weights and/or a different molecular weight distribution (e.g. highviscosity press mix by low-viscosity spray mix) by infrared spectroscopy (IR), but only by tensile testing and possibly by long-term compression set tests. Furthermore, the tensile test provides information on subsequent changes compared to the prototype condition. The Influence of Processing In the case of some O-rings, due to poor processing, it is not the strength value of the material that is determined, but the lower strength of the joining line (= confluence point of the rubber compound in the production of the O-ring in the injection mold) at which the O-ring tears. This problem depends on the material (e.g. certain acrylate rubbers), the tool and the process parameters. The joining line can usually be detected in advance by a visual and strain test or by relatively large scatter in a tensile test. Typical for the scatter in tensile tests of O-rings are 5-10%-points standard deviation related to the mean value of the elongation at break or the tensile strength. An important characteristic of good processing is the achievement of the optimum degree of vulcanization. However, there is no generally valid optimum, but this must be determined depending on the intended application of the elastomeric component. If, for example, the tear resistance is the most important material parameter for the finished product, a different degree of crosslinking or a different cross linking density must be aimed for than if, for example, a low

Real and In Silico Microgels Show Comparable Bulk Moduli Below and Above the Volume Phase Transition.

The compressibility of soft colloids influences their phase behavior and flow properties, especially in concentrated suspensions. Particle compressibility, which is proportional to the reciprocal of the bulk modulus K, is a key parameter for soft polymer-based particles that can be compressed in crowded environments. Here, microgels with different degrees of cross-linking, i.e.,softness, are investigated below and above their volume phase transition temperature (VPTT). By combining molecular dynamics simulations with small-angle neutron scattering with contrast variation, a change in the particle bulk moduli of two orders of magnitude is observed. The degree of cross-linking has a significant impact on the bulk modulus of the swollen microgel, while above the VPTT the values of K are almost independent of the cross-linking density. The excellent agreement between experimental results and simulations also highlight that the model microgels from computer simulationspossess both the internal architecture and the elastic properties of real polymeric networks. This paves the way to a systematic use of simulations to investigate the behavior of dense microgelsuspensions below and above their VPTT.

Influence of Crosslink Density on Electrical Performance and Rheological Properties of Crosslinked Polyethylene.

To investigate the influence of the crosslinked polyethylene (XLPE) structure on electrical performance, various analytical methods were employed to study polyethylene structures with different degrees of crosslinking. Dynamic rheological analysis was conducted to determine material shear viscosity, dynamic viscosity, storage modulus (G'), loss modulus (G″), and other rheological parameters. Additionally, the electrical performance of the material was analyzed by studying the phenomenon of space charge accumulation under direct current voltage. The results indicate that with an increasing mass fraction of the crosslinking agent, the crosslink density of crosslinked polyethylene initially increases and then decreases. When the dicumyl peroxide (DCP) content exceeds 1.0 wt.%, there is an accumulation of like-polarity space charges. The best rheological processing performance of crosslinked polyethylene is observed when the DCP content is in the range of 1.0-1.5 wt.%.

Thermomechanical response of liquid crystal elastomers: role of crosslinker density

In this work thermomechanical properties of main-chain liquid crystal elastomers (MC-LCEs) with different degrees of crosslinking were investigated, and gradual loss of thermomechanical response was observed on repetitive measurements. Specifically, six samples of MC-LCEs were prepared, with crosslinker-to-mesogen relative concentration ranging from 5% to 10% in steps of 1%. The obtained results were then compared to thermomechanical response of side-chain liquid crystal elastomers (SC-LCEs). Additionally, thermomechanical response of polymer dispersed main-chain liquid crystal elastomers (MC-PDLCEs) was investigated. Results indicate that in MC-LCEs the concentration of crosslinker defines thermomechanical response and affects stability of the system. The loss of thermomechanical response is negligible in the case of crosslinker to mesogen ratio being the smallest, namely in 5% sample, and it is unaffected by glasslike to nematic phase transition. SC-LCEs do not show any sign of such behaviour and remain stable after several cycles of thermomechanical measurements.

Elution Behavior of Carbohydrates Using Core-Shell Ion-Exchange Resin St-70 with Different Degrees of Cross-Linking in the Porous Shell

Elution Behavior of Carbohydrates Using Core-Shell Ion-Exchange Resin St-70 with Different Degrees of Cross-Linking in the Porous Shell

Molecular simulation on the rheological properties of phenolic resins during crosslinking

In this paper, the variations in the viscosity and molecular weight of phenol–formaldehyde resin (PF) before gelation were simulated by the molecular dynamics simulation (MD) method, and a new mathematical model was developed to describe the rheological properties of PF. The modeling of PFs with different degrees of crosslinking was developed by using a new crosslinking program. The simulation results show that the gel point for the PF model is at 54% degree of crosslinking. The mathematical model shows that the higher the temperature of the system is, the lower the initial viscosity of the model. This study provides a new rheological model for controlling the curing process and the final performance of thermosetting resins.

Efficacy of co-loading Ag nanoparticles and metronidazole in PEG–gelatin-based sponges for the treatment of chronic wounds

Polymer-based sponges loaded with antibacterial agents are potential wound dressings ideal for treating bacteria-infected wounds. Gelatin/poly (ethylene glycol) (PEG) sponge-based wound dressings loaded with metronidazole and Ag nanoparticles with different degrees of cross-linking were prepared, and their capability to treat infected wounds in vitro was evaluated. The degree of cross-linking of the sponges varied, and the porosity of the sponges was in the range of 15.64–91.10%. The amount of gelatin used to prepare the sponges influenced the porosity of the sponges. The sponges displayed an initial burst drug release of metronidazole followed by a sustained release profile. The sponges exhibited considerable antibacterial activity against Gram-positive and Gram-negative bacteria. The % cell viability of the sponges was in the range of 71.17–86.10%, indicating distinguished biocompatibility. The in vitro experiment showed that the sponge loaded with metronidazole, SAM2%, displayed a significant reduction of 66.68% in the scratch area compared to the sponge loaded with a combination of silver nanoparticles and metronidazole with a closure rate of 46.61% at 96 h. The promising features of the sponges indicate that they are potential wound dressings for treating infected wounds.

Modeling the viscoelastic behavior in the frequency domain of crosslinked polystyrene with different degrees of crosslinking from the perspective of relaxation

Modeling the viscoelastic behavior in the frequency domain of crosslinked polystyrene with different degrees of crosslinking from the perspective of relaxation

Thermal Conductivities of Uniform and Random Sulfur Crosslinking in Polybutadiene by Molecular Dynamic Simulation.

Thermal conductivities of polybutadiene crosslinked with sulfur as a function of the heat flux autocorrelation function by using an equilibrium molecular dynamic (EMD) simulation were investigated. The Green-Kubo method was used to calculate thermal conductivities. All simulations were performed by applying the LAMMPS software (version 3 Mar 2020) package. The united-atom force field (OPLS-UA) from the Moltemplate software (version 2.20.3) was applied in the simulations. The influence of uniform and random distributions of sulfur in polybutadiene on the final value of thermal conductivities was studied by polymeric model structures with similar and variable degrees of crosslinking. The results showed that for identical degrees of crosslinking, the distribution of crosslinkers in the polymeric model structures significantly influenced the final value of thermal conductivity. Moreover, the influence of the crosslinking degree on the final value of thermal conductivity was studied by considering polymeric model structures with different degrees of crosslinking. The results demonstrate that by having a random distribution of sulfur, the thermal conductivity will be enhanced. However, by increasing the degree of crosslinking to the higher percentage in random crosslinked model structures, the value of thermal conductivity drops significantly due to possible higher crystallization of the model structures, which decrease the degree of freedom for phonon contributions.

ACTIVE-BAPO - A Versatile Transfer Agent for Photoactive Bis(acyl)phosphane Oxide Units.

A N-hydroxy succinimide (NHS) ester substituted bis(acyl)phosphane oxide (ACTIVE-BAPO) was prepared by phospha-Michael addition and used for an easy one-step BAPO ligation with substrates containing primary amino groups, such as amino acids, proteins, and poly(amidoamine) (PAMAM) dendrimers. Thereby, a range of new molecular and polymeric photoinitators was obtained. Real-time photo-rheology experiments demonstrated the outstanding efficiency of the PAMAM BAPOs as photoinitiators for free radical polymerization. Remarkably, it is found that PAMAM BAPOs also act as crosslinking agents to convert monofunctional methacrylate monomers into thermosetting networks without any further additives. Depending on the number of the attached BAPOs, thermosets with a different degree of crosslinking and swelling capability in water were obtained.

The compression of deformed microgels at an air/water interface.

The compression of deformed hydrogel microspheres (microgels) at air/water interfaces was investigated using a Langmuir-Blodgett trough with simultaneous in situ visualization of the process using a fluorescent microscope. The relationship between the structure of the microgel arrays and the compression behavior was clarified using microgels with different degrees of crosslinking.

Elution Behavior of Carbohydrates for Core-Shell Ion-Exchange Resin St-60 with Different Degrees of Cross-Linking in the Porous Shell

Elution Behavior of Carbohydrates for Core-Shell Ion-Exchange Resin St-60 with Different Degrees of Cross-Linking in the Porous Shell

Novel Gemini Surfactant for Binding Eu(III)-Polyoxometalate into Hydrogels and Polymer Latexes.

The incorporation of rare-earth ions into polymer matrices can lead to useful materials in various fields such as biomarkers, lasers, luminescent devices, optical storage materials, and so on. Methods of incorporation are either extremely simple, such as mixing the polymer and the ion of interest in adequate solvents, or more sophisticated such as synthesizing predesigned monomers that contain the rare-earth ion or binding the ion on an already formed polymer chain. Cationic gemini surfactants represent a class of surfactants that can be used to incorporate metal-oxygen cluster compounds by means of strong electrostatic interactions. In this study, first, a novel cationic gemini surfactant having double bonds on both side chains was designed and prepared. After characterization, the surfactant was used to synthesize hydrogels with different degrees of crosslinking and also as a surfmer in emulsion polymerization of methyl methacrylate. The resulted polymer matrices were able to bind europium-polyoxometalate Na9[EuW10O36].32H2O. In case of luminescent lanthanide ions, changing the microenvironment around the metal ion also changes the intensity of some emission peaks as well as other luminescent parameters. Investigation of emission spectra of Eu3+ indicates a decrease in the symmetry of the microenvironment, when the polyanions pass from water to latex, to surfactant solution, and to hydrogel.

Correlation between frictional heat and triboelectric charge: In operando temperature measurement during metal-polymer physical contact

In operando techniques have emerged to elucidate the fundamental mechanism of triboelectrification via relevant physical quantity measurement during the physical contact of two materials. Here, a correlation between frictional heat and triboelectric charge is reported in a metal-polymer triboelectric nanogenerator through the in operando temperature measurement. Fluorine-doped tin oxide (FTO) metal is slid back-and-forth under different contact pressures across polydimethylsiloxane (PDMS) polymers having different degrees of crosslinking, i.e., mixing ratio. Both the triboelectric charge and temperature variation increase and become saturated with different time-constants. Notably, the saturated triboelectric charge increases, while the saturated temperature decreases, with increasing mixing ratio. In contrast, both saturated triboelectric charge and temperature increase with increasing contact pressure. X-ray photoemission spectroscopy reveals that chemical bonds are modified inhomogeneously at the surface, and that charged materials are transferred from PDMS to FTO in accordance with the mixing ratio- and sliding time-dependent triboelectric charges. Frictional heat plays a distributive role in bond rupture and temperature variation, depending on the activation energy and frictional coefficient of PDMS. In operando temperature variation measurement provides important information on the specific bonds for triboelectrification and detailed charge-transfer process during physical contact.

Birefringence effect studies of collagen formed by nonenzymatic glycation using dual-retarder Mueller polarimetry.

.Significance: Nonenzymatic glycation of collagen covalently attaches an addition of sugar molecules that initially were involved in a reversibly reaction with amino groups on the protein. Due to the ultimate formation of stable irreversible advanced glycation end products, the process of glycation leads to abnormal irreversible cross-linking, which ultimately accumulates with age and/or diabetes in the extracellular matrix, altering its organization.Aim: We report the use of dual-retarder Mueller polarimetry in conjunction with phase retardance to differentiate collagen cross-linking in a normal collagen gel matrix from that in tissues with nonenzymatic cross-linking.Approach: A dual-liquid crystal-based Mueller polarimetry system that involves electronic modulation of polarization state generators (PSGs) was employed to produce all types of polarization states without moving any part and enable detection of the signal directly using a Stokes polarimeter. The linear phase retardance response was obtained for the characterization of the solution and gel forms of collagen using differential Mueller matrix analysis.Results: We found that linear phase retardance measurements via differential Mueller matrix polarimetry successfully differentiated collagen gel matrices with different degrees of cross-linking formed by a nonenzymatic glycation process and demonstrated that this technology constitutes a quick and simple modality.Conclusions: This approach has high sensitivity for studying differences in fibrillar cross-linking in glycated collagen. Further, our work suggests that this method of structural analysis has potential clinical diagnostic value owing to its noninvasive and cost-efficient nature.

Layer-by-Layer Fabrication of PAH/PAMAM/Nano-CaCO3 Composite Films and Characterization for Enhanced Biocompatibility.

Nanoparticle production and functionalization for various biomedical uses are still challenging. Polymer composites constituted of poly(amidoamine) (PAMAM), polyallylamine hydrochloride (PAH), and calcium carbonate (CaCO3) nanoparticles have good biocompatibility with physiological tissue and fluids, making them excellent candidates for biomedical applications. This study investigated the characteristics of polymeric/nano-CaCO3 composite films based on a PAH/PAMAM matrix, which were fabricated through layer-by-layer synthesis on quartz glass substrates. It was found that the as-prepared elastic moduli of the resultant (PAH/PAMAM)n-CaCO3 (where n represents the number of bilayers) composite films varied from 1.40 to 23.70 GPa for different degrees of cross-linking when 0.1 M nano-CaCO3 particles were incorporated into the polymer matrix. The highly cross-linked (PAH/PAMAM)15-CaCO3 composite film had the highest recorded elastic modulus of 23.70 GPa, while it was observed that for all the composite films fabricated for the present study, the addition of the nano-CaCO3 particles approximately doubled the elastic modulus regardless of the degree of polymerization. Live/Dead assays were used to determine whether the produced composite films were compatible with human lung fibroblast cells. The findings indicate that the (PAH/PAMAM)7.5-CaCO3 composite film had the most positive effect on cell growth and proliferation, with the (PAH/PAMAM)15-CaCO3 composite film demonstrating significant ion transport behavior with low impedance, which was considered good for in vivo rapid cell-to-cell communication. Therefore, the (PAH/PAMAM)7.5-CaCO3 and (PAH/PAMAM)15-CaCO3 composite films are potential tissue engineering biomaterials, but further studies are essential to generate more data to evaluate the suitability of these composites for this and other biomedical functions.

The effect of peroxide cross-linking on the thermal conductivity and crystallinity of low-density polyethylene

In this work, the thermal conductivity of a series of low-density polyethylene (LDPE) with different degrees of cross-linking was measured by the transient hot-wire method at different temperatures. It was found that the thermal conductivity of LDPE samples with different degrees of cross-linking decreased smoothly with increasing temperature at temperatures ranging from ‐20 to 80°C. The higher the degree of cross-linking, the smaller the negative temperature dependence of the cross-linked LDPE samples. The decrease of negative temperature dependence of LDPE was explained by the thermal vibration of molecular chains. Meanwhile, the crystallinity and melting point of a series of LDPE samples with different degrees of cross-linking were determined by differential scanning calorimetry (DSC), and the crystallization process of LDPE samples with different degrees of cross-linking was investigated using the Jeziorny method with a modification of the Avrami equation. The results show that the thermal conductivity of cross-linked LDPE is directly proportional to the crystallinity and inversely proportional to the gel content. This work provides a basis for the future design of semi-crystalline polymers with no temperature dependence of thermal conductivity.

Preparation of Vanillin Derivatives Based on Schiff Base Reaction

This study introduced the aldehyde monomer derived from vanillin (4,4-[(1,4-phenylenedimethylene) dioxy] -bis (3-methoxybenzaldehyde), BA), followed by reaction with tris (2-aminoethyl) amine (TA) and diamine (DA) to prepare a series of polyimine films (BADT-X). By adjusting the ratio of TA and DA, BADT-X with different degrees of cross-linking can be obtained, thereby the performance of the film could be tuned. The physical results show that with the increase of TA content, the mechanical performance of BADT-X has been improved from 31.20 to 45.95MPa, furthernore, the degradation temperature (Td5%) increased from 166.66 to 272.80 °C, and the char yield of all BADT-x was more than 45% at 600 °C. Meanwhile, the quick reshape properties of this polyimine film can be accomplished without any external catalyst in 5 mins at elevated temperature.

Precipitation-based microscale enzyme reactors coupled with porous and adhesive elastomer for effective bacterial decontamination and membrane antifouling on-demand

Bacterial contamination of water environments can cause various troubles in various areas. As one of potential solutions, we develop enzyme-immobilized elastomer, and demonstrate the uses of enzyme reactions on-demand for effective microbial decontamination and antifouling. Asymmetrically-structured elastomer is prepared by combining two polydimethylsiloxane (PDMS) layers with different degrees of crosslinking: highly-crosslinked and lightly-crosslinked PDMS layers. At the surface of highly-crosslinked PDMS layer, porous structure with average diameter of 842 nm is formed by dissolving pre-packed and entrapped latex beads. Lightly-crosslinked PDMS on the other side, due to its adhesive nature, enables iterative attachments on various materials under either dry or wet condition. Glucose oxidase (GOx) is immobilized by using the pores at the surface of highly-crosslinked PDMS matrix via a ship-in-a-bottle protocol of precipitation-based microscale enzyme reactor (p-MER), which consists of GOx adsorption, precipitation and chemical crosslinking (EAPC). As a result, crosslinked enzyme aggregates (CLEAs) of GOx not only are well entrapped within many pores of highly-crosslinked PDMS layer (ship-in-bottle) but also cover the external surface of matrix, both of which are well connected together. Highly-interconnected network of CLEAs themselves effectively prevents enzyme leaching, which shows the 25% residual activity of GOx under shaking at 200 rpm for 156 days after 48% initial drop of loosely-bound p-MER after 4 days. In presence of glucose, the underwater attachment of biocatalytic elastomer demonstrates the generation of hydrogen peroxide via p-MER-catalyzed glucose oxidation, exhibiting effective biocidal activities against both gram-positive S. aureus and gram-negative E. coli. Adhesion-induced GOx-catalyzed reaction also alleviates the biofouling of membrane, suggesting its extendibility to various engineering systems being suffered by biofouling. This study of biocatalytic elastomer has demonstrated its new opportunities for the facile and on-demand enzyme-catalyzed reactions in various environmental applications, such as bactericidal treatment, water treatment/purification, and pollutant degradation.

Uncoupling bacterial attachment on and detachment from polydimethylsiloxane surfaces through empirical and simulation studies

Bacterial infections related to medical devices can cause severe problems, whose solution requires in-depth understanding of the interactions between bacteria and surfaces. This work investigates the influence of surface physicochemistry on bacterial attachment and detachment under flow through both empirical and simulation studies. We employed polydimethylsiloxane (PDMS) substrates having different degrees of crosslinking as the model material and the extended Derjaguin − Landau − Verwey − Overbeek model as the simulation method. Experimentally, the different PDMS materials led to similar numbers of attached bacteria, which can be rationalized by the identical energy barriers simulated between bacteria and the different materials. However, different numbers of residual bacteria after detachment were observed, which was suggested by simulation that the detachment process is determined by the interfacial physicochemistry rather than the mechanical property of a material. This finding is further supported by analyzing the bacteria detachment from PDMS substrates from which non-crosslinked polymer chains had been removed: similar numbers of residual bacteria were found on the extracted PDMS substrates. The knowledge gained in this work can facilitate the projection of bacterial colonization on a given surface.