Quinoxaline derivatives as long wavelength photosensitizers in photoinitiated cationic polymerization of diaryliodonium salts

The present paper is focused on visible light initiated cationic polymerizations. Photoinitiated polymerization of representative vinyl ether and oxirane monomers using two quinoxaline derivatives; namely (2-(2,3-dihydrobenzo [b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b]-[1,4]dioxin-7-yl)-5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-7yl) quinoxaline) (DBQEd) and 2,3,5,8-tetra(thiophen-2-yl)quinoxaline (TTQ) are studied. Novel dyes based on the quinoxaline skeleton are employed as efficient photosensitizers in cationic photopolymerizations. Polymerizations were initiated at room temperature upon irradiation with long-wavelength UV and visible lights in the presence of diphenyliodonium hexafluorophosphate (Ph₂I⁺PF₆^?). The progress of the polymerizations was monitored by optical pyrometry (OP). Solar irradiation is also employed to carry out the cationic polymerization of a diepoxide monomer in the presence of air.     

Study of Physically Transient Insulating Materials as a Potential Platform for Transient Electronics and Bioelectronics

Controlled degradation and transiency of materials is of significant importance in the design and fabrication of degradable and transient biomedical and electronic devices and platforms. Here, the synthesis of programmable biodegradable and transient insulating polymer films is reported, which have sufficient physical and chemical properties to be used as substrates for the construction of transient electronics. The composite structure can be used as a means to control the dissolution and transiency rate of the polymer composite film. Experimental and computational studies demonstrate that the addition of gelatin or sucrose to a PVA polymer matrix can be used as a means to program and either slow or enhance the transiency of the composite. The dissolution of the polymer composites are fitted with inverse exponential functions of different time constants; the lower time constants are an indication of faster transiency of the polymer composite. The addition of gelatin results in larger time constants, whereas the addition of sucrose generally results in smaller time constants.     

Synthesis, characterization and electrochromic properties of a conducting copolymer of pyrrole functionalized polystyrene with pyrrole

A well-defined polystyrene (PSt) based polymer containing at one end-chain 3,5-dibromobenzene moiety, prepared by atom transfer radical polymerization (ATRP), was modified in two reaction steps. First one constitutes a Suzuki coupling reaction between aromatic dibromine functional polymer and 3-aminophenylboronic acid, when a diamino-containing intermediate was obtained. The second step is a condensation reaction between the diamino functional polystyrene and 2-pyrrole aldehyde. Thus, a polymer containing a conjugated sequence having pyrollyl groups at the extremities was synthesized. The presence of oxidable pyrrole groups in the structure of the polymer permitted further electropolymerization. The structures of intermediate polymers were analyzed by spectral methods (¹H NMR, FTIR). Electrochemical copolymerization of pyrrole functionalized polymer (PStPy) with pyrrole was carried out in acetonitrile (ACN)-tetrabutylammonium tetrafluoroborate (TBAFB) solvent electrolyte couple. Characterization of the resulting copolymer were performed via Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), spectroelectrochemical analysis, and kinetic study. Spectroelectrochemical analysis show that the copolymer of PStPy with Py has an electronic band gap (due to π-π* transition) of 2.4 eV at 393 nm, with a yellow color in the fully reduced form and a blue color in the fully oxidized form. Via kinetic studies, the optical contrast %ΔT was found to be 20% for P(PStPy-co-Py). Results showed that the time required to reach 95% of the ultimate T was 1.7 s for the P(PStPy-co-Py).     

Influence of Laser Peening With and Without Coating on the Surface Properties and Stress Corrosion Cracking Behavior of Laser-Welded 304 Stainless Steel

Metallurgical and Materials Transactions A - This study aims to investigate the effect of laser peening with (LP) and without coating (LPwC) process on subsurface microstructural evolution,...     

MXene Composite and Coaxial Fibers with High Stretchability and Conductivity for Wearable Strain Sensing Textiles

The integration of nanomaterials with high conductivity into stretchable polymer fibers can achieve novel functionalities such as sensing physical deformations. With a metallic conductivity that exceeds other solution‐processed nanomaterials, 2D titanium carbide MXene is an attractive material to produce conducting and stretchable fibers. Here, a scalable wet‐spinning technique is used to produce Ti₃C₂T_x MXene/polyurethane (PU) composite fibers that show both conductivity and high stretchability. The conductivity at a very low percolation threshold of ≈1 wt% is demonstrated, which is lower than the previously reported values for MXene‐based polymer composites. When used as a strain sensor, the MXene/PU composite fibers show a high gauge factor of ≈12900 (≈238 at 50% strain) and a large sensing strain of ≈152%. The cyclic strain sensing performance is further improved by producing fibers with MXene/PU sheath and pure PU core using a coaxial wet‐spinning process. Using a commercial‐scale knitting machine, MXene/PU fibers are knitted into a one‐piece elbow sleeve, which can track various movements of the wearer's elbow. This study establishes fundamental insights into the behavior of MXene in elastomeric composites and presents strategies to achieve MXene‐based fibers and textiles with strain sensing properties suitable for applications in health, sports, and entertainment.     

Additive-Free Aqueous MXene Inks for Thermal Inkjet Printing on Textiles

Direct printing of functional inks onto flexible substrates allows for scalable fabrication of wearable electronics. However, existing ink formulations for inkjet printing require toxic solvents and additives, which make device fabrication more complex, limit substrate compatibility, and hinder device performance. Even water-based carbon or metal nanoparticle inks require supplemental surfactants, binders, and cosolvents to produce jettable colloidal suspensions. Here, a general approach is demonstrated for formulating conductive inkjet printable, additive-free aqueous Ti₃C₂T_x MXene inks for direct printing on various substrates. The rheological properties of the MXene inks are tuned by controlling the Ti₃C₂T_x flake size and concentration. Ti₃C₂T_x-based electrical conduits and microsupercapacitors (MSCs) are printed on textile and paper substrates by optimizing the nozzle geometry for high-resolution inkjet printing. The chemical stability and electrical properties of the printed devices are also studied after storing the devices for six months under ambient conditions. Current collector-free, textile-based MSCs show areal capacitance values up to 294 mF cm⁻² (2 mV s⁻¹) in poly(vinyl alcohol)/sulfuric acid gel electrolyte, surpassing reported printed MXene-based MSCs and inkjet-printed MSCs using other 2D nanomaterials. This work is an important step toward increasing the functional capacity of conductive inks and simplifying the fabrication of wearable textile-based electronics.     

Biogenic Amine Content of Beers Consumed in Turkey and Influence of Storage Conditions on Biogenic Amine Formation

The biogenic amine content of beers available in Turkey, both domestic production and imported products, was investigated. A total of 17 domestic and 13 imported beers were evaluated in terms of 8 different biogenic amines (histamine, tyramine, spermine, spermidine, 2‐phenylethylamine, putrescine, tryptamine and cadaverine). HPLC methodology with pre‐column derivatization and photodiode array detection after derivatization with dansyl chloride was used for quantification. In addition, the evolution of important amines such as histamine, tyramine, putrescine and cadaverine were investigated during different storage conditions by response surface methodology. The results indicated that both storage temperature and storage time were important factors affecting biogenic amine content. Histamine and putrescine increased during storage, but then decreased after reaching a maximum level after six weeks. With the biogenic amines tyramine and cadaverine, the amounts increased during the entire storage period. At higher storage temperatures, the formation of biogenic amines increased.     

Eating patterns of Turkish adolescents: a cross-sectional survey

Background  

Adolescence is a crucial period for development of dietary behaviors that continue into adulthood and influence the risk of chronic diseases later in life. The aim of this study was to determine the eating patterns of adolescents' and their compliance with the Food Guide Pyramid.     

The effect of changes in π-conjugated terthienyl systems using thienyl and ethylenedioxybenzene functionalized thieno[3,4-b]pyrazine precursors: Multicolored low band gap polymers

New classes of thieno[3,4-b]pyrazines containing thienyl and ethylenedioxy phenyl units on electron-withdrawing moieties of π-conjugated terthienyl were synthesized. The effect of structural differences on electrochemical and optoelectronic properties of the resulting polymers was investigated. Changes in the electronic nature of the functional groups enable to tune the electrochemical properties of the π-conjugated terthienyl monomers by lowering oxidation potential from 0.62 V (DTTP) to 0.56 V (DBTP). Spectroelectrochemical analyses revealed that the neutral polymer (PDBTP) is dark green in its neutral state revealing π-π* transitions in two well-separated bands at 410 and 751 nm. The electronic band gap of polymer, defined as the onset of the π-π* transition, is found to be 1.0 eV. Using the thienyl unit instead of ethylenedioxy phenyl, a red shift in the band gap (0.95 eV) is observed. The polymer, PDTTP, exhibits multicolor electrochromism and can be switched between a dark yellow neutral state, a green intermediate state, and a brown oxidized state. PDBTP also shows a multicolored electrochromic behavior with three distinct states: dark green at the neutral state, a brown intermediate state, and a brown-violet oxidized state.     

Tuning of the neutral state color of the π-conjugated donor-acceptor-donor type polymer from blue to green via changing the donor strength on the polymer

Two donor-acceptor-donor types of π-conjugated monomers were synthesized using Stille coupling reaction. Both monomers were found to produce electroactive polymers upon electrochemical oxidation. The effects of different donor substituents on the polymers' electrochemical and spectroelectrochemical properties were examined. Optical characterization revealed that the band gaps of poly(2-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-7-yl)-5,8-di(thiophen-2-yl)quinoxaline) (PDBQTh) and poly(2-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-7-yl)-5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)quinoxaline) (PDBQEd) were 1.5 eV and 1.3 eV, respectively. PDBQEd reveals two distinct absorption bands as expected for this type of donor-acceptor-donor polymer at 423 and 738 nm, while PDBQTh has a single absorption band at 630 nm. The colorimetry analysis revealed that while PDBQTh has a blue color, PDBQEd showed a green color in the neutral state. PDBQEd revealed reversible n-doping.