Computational Study on Radical-Mediated Thiol-Epoxy Reactions.

Radical-mediated thiol-epoxy reactions were elucidated for analyzing the overlap problem of the thiol-ene/thiol-epoxy systems using computational approaches. Nine epoxy model molecules were evaluated to mimic the chemical structures and reactivity of some industrial epoxy molecules. Modeling reaction mechanisms was conducted through density functional theory (DFT) calculations using the M06-2X/6-31+G(d,p) level at 1.0 atm and 298.15 K. An analog thiol-ene mechanism was proposed for radical-mediated thiol-epoxide reactions. Unlike the thiol-ene reactions, the addition reaction to epoxides is relatively slow (rate constants <10-4 M-1 s-1). However, the chain transfer, which paves the way for the overlapping of dual curing systems, is quite fast (rate constants >101 M-1 s-1). High stability of thiyl radicals, epoxy ring strain, and the instability of formed alkoxy radical from addition reaction were emphasized as the main driving forces for the reaction energetics and kinetics. Control of temperature and using certain thiols are strongly recommended to avoid curing step overlap based on the findings in this study.

Photo-crosslinked lignin/PAN electrospun separator for safe lithium-ion batteries.

A novel crosslinked electrospun nanofibrous membrane with maleated lignin (ML) and poly(acrylonitrile) (PAN) is presented as a separator for lithium-ion batteries (LIBs). Alkali lignin was treated with an esterification agent of maleic anhydride, resulting in a substantial hydroxyl group conversion to enhance the reactivity and mechanical properties of the final nanofiber membranes. The maleated lignin (ML) was subsequently mixed with UV-curable formulations (up to 30% wt) containing polyethylene glycol diacrylate (PEGDA), hydrolyzed 3-(Trimethoxysilyl)propyl methacrylate (HMEMO) as crosslinkers, and poly(acrylonitrile) (PAN) as a precursor polymer. UV-electrospinning was used to fabricate PAN/ML/HMEMO/PEGDA (PMHP) crosslinked membranes. PMHP membranes made of electrospun nanofibers feature a three-dimensional (3D) porous structure with interconnected voids between the fibers. The mechanical strength of PMHP membranes with a thickness of 25 µm was enhanced by the variation of the cross-linkable formulations. The cell assembled with PMHP2 membrane (20 wt% of ML) showed the maximum ionic conductivity value of 2.79*10-3 S cm-1, which is significantly higher than that of the same cell with the liquid electrolyte and commercial Celgard 2400 (6.5*10-4 S cm-1). The enhanced LIB efficiency with PMHP2 membrane can be attributed to its high porosity, which allows better electrolyte uptake and demonstrates higher ionic conductivity. As a result, the cell assembled with LiFePO4 cathode, Li metal anode, and PMHP2 membrane had a high initial discharge specific capacity of 147 mAh g-1 at 0.1 C and exhibited outstanding rate performance. Also, it effectively limits the formation of Li dendrites over 1000 h. PMHP separators have improved chemical and physical properties, including porosity, thermal, mechanical, and electrochemical characteristics, compared with the commercial ones.

A novel polymeric fluorescence sensor based on acrylated citric acid for detection of melamine adulteration: Application in milk powder.

Melamine selective acrylate citric acid (ACA) based polymeric membrane sensor was prepared by radical polymerization method and the sensor was characterized. The sensor showed a selective fluorescent response to melamine (λex/λem = 388/425 nm). The sensor response is linear in the concentration range of 3.96 × 10-9 to 7.93 × 10-8 mol L-1, the optimum pH value is 6.0 and response time is less than 1 min. Limit of detection (LOD) and limit of quantification (LOQ) were calculated as 2.32 × 10-10 mol L-1 and as 7.74 × 10-10 mol L-1, respectively. The sensor showed great selectivity towards melamine in the presence of a large number of molecules and ions. The performance of sensor was also confirmed by determining of melamine in milk powder sample and the results were compared with HPLC results and acceptable results were obtained. As a conclusion, the results revealed that the proposed sensor is an interesting alternative for melamine determination.

Optimizing the immobilization conditions of ß-galactosidase on UV-cured epoxy-based polymeric film using response surface methodology.

UV-cured epoxy-based polymeric film was prepared from glycidyl methacrylate, trimethylolpropane triacrylate, and poly(ethylene glycol) methylether acrylate. 2-hydroxy-2- methylpropiophenone was used as photo initiator. Covalent binding through epoxy groups was employed to immobilize ß-galactosidase from Escherichia coli onto this film, and immobilization conditions were optimized by the response surface methodology. ATR-Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) analysis was carried out to characterize the epoxy-based polymeric film. Immobilization yield of ß-galactosidase on the material was calculated as 3.57 mg/g and the highest enzyme activity for the immobilized enzyme recorded at pH 6.5°C and 60°C. The immobilized enzyme preserved 51% of its activity at the end of 12 runs. Free and immobilized enzyme hydrolyzed 163.8 and 172.3 µM lactose from 1% lactose, respectively. Kinetic parameters of both free and immobilized ß-galactosidase were also investigated, and Km values were determined to be 0.647 and 0.7263 mM, respectively. PRACTICAL APPLICATIONS: In our study we prepared a UV-cured epoxy-based polymeric film and optimized the immobilization conditions of ß-galactosidase from Escherichia coli onto this polymeric film by using response surface methodology (RSM). For this purpose, three-level and three-factor Box-Behnken design, which is an independent, rotatable or nearly rotatable, quadratic design, was applied. Optimal levels of three variables, namely, the amount of enzyme, immobilization time, and pH were determined using Box-Behnken experimental design. Lactose hydrolysis studies were performed from milk and lactose samples using free and immobilized enzyme. In addition, kinetic parameters, storage stability, and re-usability of immobilized ß-galactosidase were examined.

Fabrication of UV-Crosslinked Flexible Solid Polymer Electrolyte with PDMS for Li-Ion Batteries.

Conventional carbonate-based liquid electrolytes have safety issues related to their high flammability and easy leakage. Therefore, it is essential to develop alternative electrolytes for lithium-ion batteries (LIBs). As a potential candidate, solid-polymer electrolytes (SPEs) offer enhanced safety characteristics, while to be widely applied their performance still has to be improved. Here, we have prepared a series of UV-photocrosslinked flexible SPEs comprising poly(ethylene glycol) diacrylate (PEGDA), trimethylolpropane ethoxylate triacrylate (ETPTA), and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) salt, with the addition of polydimethylsiloxane with acrylated terminal groups (acryl-PDMS) to diminish the crystallinity of the poly(ethylene glycol) chain. Polysiloxanes have gained interest for the fabrication of SPEs due to their unique features, such as decrement of glass transition temperature (Tg), and the ability to improve flexibility and facilitate lithium-ion transport. Freestanding, transparent SPEs with excellent flexibility and mechanical properties were achieved without any supporting backbone, despite the high content of lithium salt, which was enabled by their networked structure, the presence of polar functional groups, and their amorphous structure. The highest ionic conductivity for the developed cross-linked SPEs was 1.75 × 10-6 S cm-1 at room temperature and 1.07 × 10-4 S cm-1 at 80 °C. The SPEs demonstrated stable Li plating/stripping ability and excellent compatibility toward metallic lithium, and exhibited high electrochemical stability in a wide range of potentials, which enables application in high-voltage lithium-ion batteries.

Electrospun 3D Structured Carbon Current Collector for Li/S Batteries.

Light weight carbon nanofibers (CNF) fabricated by a simple electrospinning method and used as a 3D structured current collector for a sulfur cathode. Along with a light weight, this 3D current collector allowed us to accommodate a higher amount of sulfur composite, which led to a remarkable increase of the electrode capacity from 200 to 500 mAh per 1 g of the electrode including the mass of the current collector. Varying the electrospinning solution concentration enabled obtaining carbonized nanofibers of uniform structure and controllable diameter from several hundred nanometers to several micrometers. The electrochemical performance of the cathode deposited on carbonized PAN nanofibers at 800 °C was investigated. An initial specific capacity of 1620 mAh g-1 was achieved with a carbonized PAN nanofiber (cPAN) current collector. It exhibited stable cycling over 100 cycles maintaining a reversible capacity of 1104 mAh g-1 at the 100th cycle, while the same composite on the Al foil delivered only 872 mAh g-1. At the same time, 3D structured CNFs with a highly developed surface have a very low areal density of 0.85 mg cm-2 (thickness of ~25 µm), which is lower for almost ten times than the commercial Al current collector with the same thickness (7.33 mg cm-2).

Antimicrobial agent-free hybrid cationic starch/sodium alginate polyelectrolyte films for food packaging materials.

This study aimed to develop polyelectrolyte structured antimicrobial food packaging materials that do not contain any antimicrobial agents. Cationic starch was synthesized and characterized by FT-IR spectroscopy and 1H NMR spectroscopy. Its nitrogen content was determined by Kjeldahl method. Polyelectrolyte structured antimicrobial food packaging materials were prepared using starch, cationic starch and sodium alginate. Antimicrobial activity of materials was defined by inhibition zone method (disc diffusion method). Thermal stability of samples was evaluated by TGA and DSC. Hydrophobicity of samples was determined by contact angle measurements. Surface morphology of samples was investigated by SEM. Moreover, gel contents of samples were determined. The obtained results prove that produced food packaging materials have good thermal, antimicrobial and surface properties, and they can be used as food packaging material in many industries.

Reusable fluorescent photocrosslinked polymeric sensor for determining lead ions in aqueous media.

In this study, 1-vinylimidazole units bearing photocured films were prepared as fluorescent sensors towards Pb(2+) in aqueous solutions. The influence of experimental parameters such as pH, time and foreign ion concentrations were investigated. Sensor response was linear over a concentration range of 4.83×10(-8) to 4.83×10(-7) mol L(-1). The sensor was highly sensitive with a detection limit as low as 1.87×10(-8)molL(-1), and having a selectivity of over four thousand fold. The response time of the sensor was found to be 5 min. When stored in a desiccator at room temperature the sensor showed good stability after a 5 month period. The fluorescence sensors were successful in the determination of Pb(2+) in water samples as well as in the determination of the quantitative amount of lead and the results were satisfying. Compared with previously reported literature, the prepared new sensor is highly sensitive and selective.

Photocured thiol-ene based optical fluorescence sensor for determination of gold(III).

This study describes the preparation and the characterization of a new thiol-ene based polymeric fluorescence sensor by photo initiated polymerization of trimethylolpropane tris(3-mercaptopropionate), 2-hydroxyethylacrylate, and 2,4,6-triallyloxy-1,3,5-triazine which are used as monomers and also a photo initiator (2,2-dimethoxy-2-phenylacetophenone) for its usage as optical sensor for gold ions. The thiol-ene based polymeric membrane sensor was characterized by using attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM). The response characteristics of the sensors including dynamic range, pH effect, response time, and the effect of foreign ions were investigated. Fluorescence spectra showed that the excitation/emission maxima of the membrane were at 379/425 nm, respectively.

Alpha-amylase immobilization on epoxy containing thiol-ene photocurable materials.

Thiol-ene polymerization is a versatile tool for several applications. Here we report the preparation of epoxide groups containing thiol-ene photocurable polymeric support and the covalent immobilization of alpha-amylase onto these polymeric materials. The morphology of the polymeric support was characterized by scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) coupled with SEM was used to explore the chemical composition. The polymeric support and the immobilization of the enzyme were characterized by FTIR analysis. SEM-EDS and FTIR results showed that the enzyme was successfully covalently attached to the polymeric support. The immobilization efficiency and enzyme activity of alpha-amylase were examined at various pH (5.0-8.0) and temperature (30-80 degrees C) values. The storage stability and reusability of immobilized alpha-amylase were investigated. The immobilization yield was 276 +/- 1.6 mg per gram of polymeric support. Enzyme assays demonstrated that the immobilized enzyme exhibited better thermostability than the free one. The storage stability and reusability were improved by the immobilization on this enzyme support. Free enzyme lost its activity completely within 15 days. On the other hand, the immobilized enzyme retained 86.7% of its activity after 30 days. These results confirm that alpha-amylase was successfully immobilized and gained a more stable character compared with the free one.