Understanding Local and Macroscopic Electron Mobilities in the Fullerene Network of Conjugated Polymer‐based Solar Cells: Time‐Resolved Microwave Conductivity and Theory

The efficiency of bulk heterojunction (BHJ) organic photovoltaics is sensitive to the morphology of the fullerene network that transports electrons through the device. This sensitivity makes it difficult to distinguish the contrasting roles of local electron mobility (how easily electrons can transfer between neighboring fullerene molecules) and macroscopic electron mobility (how well‐connected is the fullerene network on device length scales) in solar cell performance. In this work, a combination of density functional theory (DFT) calculations, flash‐photolysis time‐resolved microwave conductivity (TRMC) experiments, and space‐charge‐limit current (SCLC) mobility estimates are used to examine the roles of local and macroscopic electron mobility in conjugated polymer/fullerene BHJ photovoltaics. The local mobility of different pentaaryl fullerene derivatives (so‐called ‘shuttlecock’ molecules) is similar, so that differences in solar cell efficiency and SCLC mobilities result directly from the different propensities of these molecules to self‐assemble on macroscopic length scales. These experiments and calculations also demonstrate that the local mobility of phenyl‐C₆₀ butyl methyl ester (PCBM) is an order of magnitude higher than that of other fullerene derivatives, explaining why PCBM has been the acceptor of choice for conjugated polymer BHJ devices even though it does not form an optimal macroscopic network. The DFT calculations indicate that PCBM's superior local mobility comes from the near‐spherical nature of its molecular orbitals, which allow strong electronic coupling between adjacent molecules. In combination, DFT and TRMC techniques provide a tool for screening new fullerene derivatives for good local mobility when designing new molecules that can improve on the macroscopic electron mobility offered by PCBM.     

Enhancing ionic conductivity and flexibility in solid polymer electrolytes with rainforest honey as a green plasticizer

Solid polymer electrolytes (SPEs) play a pivotal role in advancing electrochemical devices, such as proton batteries and supercapacitors, owing to their potential for enhancing safety and flexibility. In this work, employs a solution casting technique to prepare SPEs, utilizing chitosan-dextran blends as the polymer matrix. Ammonium thiocyanate (NH₄SCN) is incorporated as a charge carrier, while honey is introduced as a plasticizer. The interaction between these materials is confirmed through Fourier transform infrared (FTIR) analysis. X-ray diffraction (XRD) analysis reveals that the addition of 10 wt.% honey (H10) to the polymer blend results in the lowest degree of crystallinity (15.24%), emphasizing the pivotal role of plasticizers in modulating the structural properties of SPEs. Furthermore, by incorporating 40 wt.% NH₄SCN (SN40) into the plasticizer-polymer host (H10), the ambient temperature conductivity obtains its maximum value of (1.08 ± 0.19 × 10⁻³ S cm⁻¹) with the lowest degree of crystallinity of 10.44%, verify it is the most amorphous electrolyte. The observed trend in conductivity is influenced by the diffusion coefficient (D), ion density (n), and mobility of the ions (μ). Complementing these findings, field emission scanning electron microscopy (FESEM) is employed to investigate the surface morphology and cross section of the SPEs, providing a comprehensive understanding of their structural characteristics. From linear sweep voltammetry (LSV), SN40 is electrochemically stable up to 2.2 V and the t_ion is 0.97 indicating that the ions are the dominant charge carriers.     

Plasma welding of thin plate

The plasma arc has a large arc force (regarded as the plasma force) and keyhole welding is generally performed by the formation of a small hole at the weld pool of a butt joint by making use of this plasma force. Under these circumstances, due to the small footprint area of the plasma heat source and welding by the formation of a keyhole, there is little melting at the joint zone and welding with a narrow bead width becomes feasible. Recently, a new type of plasma welding process has been proposed such that the welding tungsten electrode tip is brought close to the tip of the cooling chip and keyholeless welding is performed, similarly to TIG welding and this process has been made practicable.¹ This process solves the disadvantages of keyhole welding while retaining the advantages of plasma welding and is capable of meeting the requirements of high speed welding. However, it is difficult to apply either method to fillet joints where keyhole formation is difficult due to the problems of the large plasma force and the torch structure. In either case, the large plasma force due to the plasma passing through the cooling chip small hole is surmised to be intimately associated with the weld morphology due to plasma welding.     

Is HLA-DRW13 (W6) associated with juvenile myoclonic epilepsy in Arab patients?

In a study of 32 unrelated Arab patients with juvenile myoclonic epilepsy (JME), we compared the frequencies of human leukocyte antigen (HLA) class I and II alleles with those of unrelated healthy controls. A significant difference between the phenotypic frequencies in JME patients and controls was observed for DRW13, the split of DRW6 (37.5 vs 11% of controls). The strength of association as measured by the relative risk was 4.85 for this antigen (p = 0.002). The possible association of JME with HLA-DRW6 recently reported in Caucasians was confirmed in this study. This finding speaks for the homogeneity of the disease among Arabic and Caucasian JME patients. The existence of this association is evidence of a locus in the HLA region that influences expression of JME.     

Irradiation of poly(vinyl chloride) with H2 plasma. I

A system has been designed to serve as a plasma source and has the advantage of producing plasma of known energy and controlled intensity. Poly(vinyl chloride) films were irradiated with hydrogen plasma for different intervals of time. The effect of irradiation time and storing on the extent of crosslinking was investigated. The viscosity of the soluble part decreased at the initial stage of irradiation, then increased. The crosslinking extent was observed by measuring the swelling ratio of the irradiated samples. Spectral analysis indicated the formation of carbonyl groups and polyene structure in the irradiated PVC. The mechanisms of dehydrochlorination and crosslinking are discussed.     

Modelling the leaching of Pb, Cd, As, and Cr from cementitious waste using PHREEQC

A leaching model was developed using the United States Geological Survey public domain PHREEQC geochemical package to simulate the leaching of Pb, Cd, As, and Cr from cementitious wastes. The model utilises both kinetic terms and equilibrium thermodynamics of key compounds and provides information on leachate and precipitate speciation. The model was able to predict the leaching of Pb, Cd, As, and Cr from cement in the presence of both simple (0.1 and 0.6M acetic acid) and complex municipal landfill leachates. Heavy metal complexation by the municipal landfill leachate was accounted for by the introduction of a monoprotic organic species into the model. The model indicated Pb and As were predominantly incorporated within the calcium silicate hydrate matrix while a greater portion of Cd was seen to exist as discrete particles in the cement pores and Cr (VI) existed mostly as free CrO4(2-) ions. Precipitation was found to be the dominant mechanism controlling heavy metal solubility with carbonate and silicate species governing the solubility of Pb and carbonate, silicate and hydroxide species governing the solubility of Cd. In the presence of acetic acid, at low pH values Pb and Cd acetate complexes were predominant whereas, at high pH values, hydroxide species dominated. At high pH values, the concentration of As in the leachate was governed by the solubility of Ca3(AsO4)2 with the presence of carbonate alkalinity competing with arsenate for Ca ions. In the presence of municipal landfill leachate, Pb and Cd organic complexes dominated the heavy metal species in solution. The reduction of As and Cr in municipal landfill leachate was crucial for determining aqueous speciation, with typical municipal landfill conditions providing the reduced forms of As and Cr.     

Utility-based adaptive radio resource allocation in OFDM wireless networks with traffic prioritization

In this letter, a joint transmit scheduling and dynamic sub-carrier and power allocation method is proposed to exploit multi-user diversity in downlink packet transmission in an OFDM wireless network with mixed real-time and non-real-time traffic patterns. To balance efficiency and fairness and to satisfy the QoS requirements of real-time users, we utilize a utility-based framework and propose a polynomial-time heuristic algorithm to solve the formulated optimization problem. The distinguishing feature of the proposed method is that it gives in one shot, the transmission scheduling, the sub-carriers assigned to each user, and the power allocated to each sub-carrier, based on a fair and efficient framework while satisfying the delay requirements of real-time users.     

Synthesis and characterization of chitosan-coated magnetite nanoparticles using a modified wet method for drug delivery applications

Abstract

Immobilizing various chemical functionalities on the surfaces of magnetite nanoparticles extends these applications without affecting the overall magnetic properties of the coated nanoparticles. In this study, magnetite nanoparticles have been prepared in the presence of chitosan using a simple modified wet method. Composition, morphology and magnetic properties of the chitosan-coated nanoparticles were investigated. Results showed the formation of coating with various thicknesses on the surfaces of the superparamagnetic nanoparticles. This in turn reduced the magnetization of the nanoparticles to some extent. The least particle size obtained in the presence of chitosan was 10?nm.