Poly(p-xylene disulfide) and poly(p-xylene tetrasulfide): synthesis,cure and investigation of mechanical and thermophysical properties

Abstract

In this work, two polysulfide polymers were synthesized using aromatic organic monomer (α,α′-dichloro-p-xylene) and sodium disulfide (Na₂S₂) and sodium tetrasulfide (Na₂S₄) aqueous monomers. Then, the curing process of the polymers was carried out at 170° C using a rheometer. The structural characteristics of synthesized and cured samples were identified by Raman and Fourier transform infrared (FT-IR) spectroscopies. Also, morphological and thermophysical properties of samples were studied by using the X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Moreover, the molecular weight of the synthesized samples was determined by proton nuclear magnetic resonance (¹H NMR). Furthermore, the mechanical properties and hardness of the samples were investigated by tensile test and Shore A. The results showed that in the noncured samples during the increase of sulfur in the polymer structure, solubility was increased whereas it decreased the hardness, melting point (T_m ) and glass transition temperature (T_g ) of polymers. But in cured samples, hardness and T_g increase by increasing sulfur and the mechanical properties also improved. This is due to the increase in crosslinks. Also, Tm and solubility are not observed due to the formation of crosslinks.     

Conformational study of a strained tolanophane by dynamic 1H NMR spectroscopy and computational methods

The existence of a short C–H ⋯ π (alkyl–alkyne) interaction in the structure of a strained and relatively rigid tolanophane is expected to hinder the rotation about the C–C sp³ single bond. Variable-temperature NMR experiments (performed in three solvents, CDCl₃, THF-d₈, and acetone-d₆) and ab initio density functional calculations were carried out to investigate its dynamic nature. An energy barrier of 48.6 kJ/mol is determined at coalescence (210 K) with acetone-d₆ which is in good agreement with calculation result (54 kJ/mol). Correspondence: Hossein Reza Darabi, Chemistry and Chemical Engineering Research Center of Iran, Pajoohesh Blvd., km 17, Karaj Hwy, 14968-13151 Tehran, Iran.     

A Potentiometric Sensor for Cd2+ Based on Carbon Nanotube Paste Electrode Constructed from Room Temperature Ionic Liquid,Ionophore and Silica Nanoparticles

A novel and effective potentiometric sensor for the rapid determination of Cd²⁺ based on carbon paste electrode consisting of the room temperature ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate, multiwalled carbon nanotubes, silica nanoparticles and ionophore was constructed. The prepared composite has a low potential drift, high selectivity and fast response time, which leads to a more stable potential signal. A linear dynamic range of 4.50×10^?9–1.00×10^?1 mol L^?1 with a detection limit of 2.00×10^?9 mol L^?1 was obtained. The modified electrode was successfully applied to the accurate determination of trace amounts of Cd²⁺ in environmental and biological samples.     

Developing a novel packed in‐tube solid‐phase extraction method for determination ∆9‐tetrahydrocannabinol in biological samples and cannabis leaves

A novel plate‐like nano‐sorbent based on copper/cobalt/chromium layered double hydroxide was synthesized by a simple coprecipitation method. The synthesized nanoparticels were introduced into a stainless steel cartridge using a dry packing method. Then, the packed cartridge was introduced as a novel on‐line “packed in‐tube” configuration and followed by high performance liquid chromatography for the determination of trace amounts of ^?9‐tetrahydrocannabinol from biological samples and cannabis leaves. The as‐prepared sorbent exhibited long lifetime, good chemical stability, and high anion‐exchange capacity. Several important factors affecting the extraction efficiency, such as extraction and desorption times, pH of the sample solution and flow rates of the sample and eluent solutions, were investigated and optimized. Under optimized conditions, this method showed good linearity for ^?9‐tetrahydrocannabinol in the ranges of 0.09–500, 0.3–500, and 0.4–500 µg/L with coefficients of determination of 0.9999, 0.9991, and 0.9994 in water, serum and plasma samples, respectively. The inter‐ and intra‐assay precisions (n = 3) were respectively in the ranges of 1.8–4.6% and 1.9–4.0% at three concentration levels of 10, 50, and 100 µg/L. The limits of detection were also in the range of 0.02–0.1 µg/L.     

Design of Furan-Based Acceptors for Organic Photovoltaics

We explore a series of furan-based non-fullerene acceptors and report their optoelectronic properties, solid-state packing, photodegradation mechanism and application in photovoltaic devices. Incorporating furan building blocks leads to the expected enhanced backbone planarity, reduced band gap and red-shifted absorption of these acceptors. Still, their position in the molecule is critical for stability and device performance. We found that the photodegradation of these acceptors originates from two distinct pathways: electrocyclic photoisomerization and Diels–Alder cycloaddition of singlet oxygen. These mechanisms are of general significance to most non-fullerene acceptors, and the photostability depends strongly on the molecular structure. Placement of furans next to the acceptor termini leads to better photostability, well-balanced hole/electron transport, and significantly improved device performance. Methylfuran as the linker offers the best photostability and power conversion efficiency (>14 %), outperforming all furan-based acceptors reported to date and all indacenodithiophene-based acceptors. Our findings show the possibility of photostable furan-based alternatives to the currently omnipresent thiophene-based photovoltaic materials.     

On-line electrochemically controlled in-tube solid phase microextraction of inorganic selenium followed by hydride generation atomic absorption spectrometry

In this work, for the first time, a rapid, simple and sensitive microextraction procedure is demonstrated for the matrix separation, preconcentration and determination of inorganic selenium species in water samples using an electrochemically controlled in-tube solid phase microextraction (EC-in-tube SPME) followed by hydride generation atomic absorption spectrometry (HG-AAS). In this approach, in which EC-in-tube SPME and HG-AAS system were combined, the total analysis time, was decreased and the accuracy, repeatability and sensitivity were increased. In addition, to increases extraction efficiency, a novel nanostructured composite coating consisting of polypyrrole (PPy) doped with ethyleneglycol dimethacrylate (EGDMA) was prepared on the inner surface of a stainless-steel tube by a facile electrodeposition method. To evaluate the offered setup and the new PPy-EGDMA coating, it was used to extract inorganic selenium species in water samples. Extraction of inorganic selenium species was carried out by applying a positive potential through the inner surface of coated in-tube under flow conditions. Under the optimized conditions, selenium was detected in amounts as small as 4.0 parts per trillion. The method showed good linearity in the range of 0.012–200 ng mL⁻¹, with coefficients of determination better than 0.9996. The intra- and inter-assay precisions (RSD%, n = 5) were in the range of 2.0–2.5% and 2.7–3.2%, respectively. The validated method was successfully applied for the analysis of inorganic selenium species in some water samples and satisfactory results were obtained.     

Ultrasound-assisted liquid-phase microextraction based on a nanostructured supramolecular solvent

Novel ultrasonically enhanced supramolecular solvent microextraction (USESSM) then high-performance liquid chromatography with ultraviolet detection have been used for extraction and determination of phthalates in water and cosmetics. Coacervates consisting of decanoic acid-based nano-structured aggregates, specifically reverse micelles, have been used the first time as solvents for ultrasound-assisted emulsification microextraction (USAEME). Sonication accelerated mass transfer of the target analytes into the nano-structured solvent from the aqueous sample, thus reducing extraction time. Several conditions affecting extraction efficiency, for example the concentrations of major components of the supramolecular solvent (tetrahydrofuran and decanoic acid), sample solution pH, salt addition, and ultrasonication time, were investigated and optimized. Under the optimum conditions, preconcentration of the analytes ranged from 176 to 412-fold and the linear range was 0.5–100 μg?L^?1, with correlation coefficients (R ²)?≥?0.9984. The detection sensitivity of the method was excellent, with limits of detection (LOD, S/N?=?3) in the range 0.10–0.70 μg?L^?1 and precision in the range 4.1–11.7 % (RSD, n?=?5). This method was successfully used for analysis of phthalates in water and cosmetics, with good recovery of spiked phthalates (91.0–108.5 %).     

Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@PPy–MWCNT nanocomposite and its application for extraction of ultra-trace amounts of PAHs from various samples

In the present study, multi-walled carbon nanotube oxide was immobilized on the pyrrole magnetic nanoparticles. Application of the synthesized material was investigated for the magnetic solid-phase extraction (MSPE) of polycyclic aromatic hydrocarbons (PAHs), from the environmental samples. Determinations of the analytes were performed with gas chromatography–mass spectrometry. The structure and morphology of Fe₃O₄@PPy–MWCNT were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermal gravimetric analysis, and vibrating sample magnetometer. Performance of MSPE is mainly affected by extraction time, sorbent amount, sample solution volume, and eluent type and volume. In this study, the best possible performance of MSPE has been achieved using a combination of central composite design and Bayesian regularized artificial neural network technique. Under the optimum extraction conditions, linear range between 0.5 and 250 µg L^?1 (R ² > 0.994), preconcentration factors from 232 to 403 and limits of detection ranging from 0.1 to 0.3 µg L^?1 were obtained. Relative standard deviations for intra-day and inter-day precision were 3.3–5.1% and 3.7–5.6%, respectively. In addition, feasibility of the method was demonstrated by extraction and determination of PAHs from some real samples containing tap water, hookah water as well as soil samples, and relative recovery in the range of 85.4–106.8% was obtained. This MSPE method provides several advantages, such as high extraction efficiency, minimum sorbent for extraction of the analytes from high sample volumes, convenient extraction procedure, and short analysis times.     

Electrochemical Biosensors for Cancer Biomarkers Detection: Recent Advances and Challenges

Biomarkers are described as characteristics that provide information about biological conditions whether normal or pathological. Detection of biomarkers at the earliest stage of the cancer is of utmost importance for clinical diagnosis. Electrochemical biosensors allow detecting the low levels of specific analytes in blood, urine or saliva and providing a sensitive approach for direct measurement for cancer biomarker detection. Moreover, the integration of electrochemical devices with nanomaterials, such as carbon nanotubes, gold and magnetic particles offer amplification and multiplexing capabilities for simultaneous measurements of cancer biomarkers very sensitively. This review summarizes the recent developments of electrochemical biosensors systems for the detection of cancer biomarkers with emphasis on voltammetric, amperometric and impedimetric biosensors. A special attention is paid to aptamers and miRNAs that are very promising for the ultra‐sensitive and specific cancer biomarker detection.