Preparation and characterization of new electrically conductive composites based on expanded graphite with potential use as remote environmental detectors

The presented paper is focused on studying electrically conductive composites based on an elastomeric matrix and expanded graphite as the filler. A potential application as an environmental remote detector was studied. The influence of filler particle size, film thickness, detector length, temperature, and the amount of oil on the detector response rate were explored. Peel tests were performed in order to investigate the adhesion of prepared detector films to different materials. Expanded graphite with average particle size 5 µm was chosen for the experiments due to its fastest response. Decreasing the detector film thickness has caused an increase in the response rate but also a decrease in the signal measured. The response rate of the detector system was in a practical range even for lower temperatures. From the obtained data, the proposed detector seems to be suitable for a practical application

Effect of waste wax and chain structure on the mechanical and physical properties of polyethylene

The influence of adding waste wax, produced as a by-product of the low density polyethylene manufacturing process, on the thermal and mechanical properties of three types of polyethylene (PE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE), with 10, 20, 30 and 40wt.% was investigated. Polymer–wax mixing was effective with no apparent leakage of the wax during sample preparation, which was evident from the agreement between the theoretical and experimental values of enthalpy for all types of PE.The wax dispersion in the matrix strongly depends on the percentage of wax added to the polymer and the molecular structure of the polymer. It was found that increasing the wax content enhances the phase separation. LDPE undergoes less phase separation due to its highly branched structure composed of a network of short and long chain branches. The wax has no pronounced plasticising effect on the polymer. This is clearly manifested in LDPE as no change in the melting temperature occurred. LLDPE and HDPE were slightly affected by a high concentration of wax (30% and 40%). This is due to the non-uniform distribution of short chain branching along the LLDPE and HDPE main chains, which can interact with the wax structure.NPRP 4 – 465 – 2 – 173 from Qatar National Research Fund (a member of Qatar Foundation). Open Access funding from King Saud University

Alginate-halloysite nanocomposite aerogel: Preparation, structure, and oil/water separation applications

Environmental remediation using green approaches for addressing various pollution-related issues, especially water pollution, is in high demand. Here, we designed an environmentally friendly, low-cost, and stable sodium alginate-halloysite clay composite aerogel (SAHA) for oil/water separation via a two-step synthesis procedure, including ionic crosslinking and freeze-drying. The as-prepared SAHA aerogels were characterized in detail by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and Fourier transformation infrared (FT-IR) spectroscopy. Characterization of the SAHA aerogels revealed a three-dimensional porous microstructure with uniformly dispersed halloysite nanotubes (HA) within the alginate matrix. The elemental composition of the hydrogels investigated using energy dispersive X-ray spectrometry (EDX) revealed the presence of minerals, such as magnesium, sodium, aluminum, and silicon in the SAHA aerogels. The presence of a hydrophilic alginate matrix combined with these unique morphological characteristics resulted in SAHA aerogels with underwater oleophobicity and excellent oil/water separation efficiency (up to 99.7%). The ease of fabrication, excellent oil/water separation, and multiple performances make the SAHA aerogel an interesting candidate for practical applications in water recycling.Funding: This research was funded by Qatar University through Qatar University Collaborative Grant QUCG-CAM-19/20-2.Scopu

Modification of polyethylene by RF plasma in different/mixture gases

Herein, low-density polyethylene (LDPE) films were treated using radio-frequency plasma discharge in the presence of air, nitrogen, oxygen, argon, and their mixtures to introduce new chemical functionalities. The surface properties of treated LDPE were qualitatively and quantitatively characterized using various analytical and microscopic techniques. It was found that the optimum plasma treatment for LDPE occurs in the presence of air plasma at an exposure time of 120 s and 80 W of nominal power. The plasma formed layer had tendency to increasing thickness with increasing treatment time up to 60 s using air and oxygen and even more with inert gases. An aging study of plasma-treated LDPE samples stored in ambient air or water medium revealed the partial hydrophobic recovery.Funding: This publication was made possible by an Award JSREP07-022-3-010 from the Qatar National Research Fund (a member of The Qatar Foundation).Scopu

Highly conductive phase change composites based on paraffin-infiltrated graphite panels for photo/electrothermal conversion and storage

The extensive utilization of phase change materials (PCMs) for thermal energy harvesting, storage, and thermal management is often constrained by their inadequate thermal and electrical conductivity, form instability, and lack of photoabsorbance. To overcome these challenges, a phase change composite was prepared by vacuum infiltration of paraffin wax (PW) into a highly conductive scaffold of graphite panel (GP). Various PW grades with different phase change temperatures were tested to study their suitability for a wide range of applications. Graphite-based skeleton ensured high thermal and electrical conductivity and impeded liquid PW leakage in all composites. The composite thermal conductivity was enhanced up to 677 and 22 times that of PW in the axial and radial directions, respectively. The latent heat capacity of the composites varied between 88.5 and 102.7 J/g, depending on the PW grade. The composites are capable of harvesting thermal energy either by applying a small voltage of 1.8 V with a high electrothermal conversion efficiency of up to 71.1 % or by simulated sunlight with an excellent photothermal conversion efficiency of up to 76.5 %. The simple fabricating technique, a broad range of applications with different PW grades, and their efficient thermal properties meet the requirements for widespread utilization in thermal energy harvesting, storage, and thermal management of electronics, buildings, etc. 2023 The AuthorsSEM was accomplished in the Central Laboratories Unit, Qatar University. The authors greatly acknowledge Dr. Zubair Ahmad (Qatar University) for providing the solar simulator. Authors thank Dr. Patrik Sobolciak and Abdul Jaleel (Qatar University) for their assistance in the experiments. This research was funded by the Qatar National Research Fund (a member of The Qatar Foundation), grant number NPRP13S-0127-200177.Scopu

Separation of water/oil emulsions by an electrospun copolyamide mat covered with a 2D Ti3C2Tx MXene

Purpose: Copolyamide 6,10 (coPA) electrospun mats were covered with multilayered (ML) and single-layered (SL) MXene (Ti3C2Tx) as a membrane for the separation of water/vegetable oil emulsions. Methods: Prepared membranes were characterized by atomic force microscopy (AFM), profilometry, the contact angle measurements of various liquids in air, and the underwater contact angle of vegetable oil. The separation efficiency was evaluated by measuring the UV transmittance of stock solutions compared to the UV transmittance of the filtrate. Results: The MXene coating onto coPA mats led to changes in the permeability, hydrophilicity, and roughness of the membranes and enhanced the separation efficiency of the water/vegetable oil emulsions containing 10, 100, and 1000 ppm of sunflower vegetable oil. It was found that membranes were highly oleophobic (>124°) under water, unlike in air, where the membranes showed high oleophobicity (<5°). The separation efficiency of water/oil emulsions for both types of covered membranes reached over 99%, with a surface coverage of 3.2 mg/cm2 Ti3C2Tx (for ML-Ti3C2Tx) and 2.9 mg/cm2 (for SL-Ti3C2Tx). Conclusions: The separation efficiency was greater than 98% for membranes covered with 2.65 mg/cm2 of ML-Ti3C2Tx, whereas the separation efficiency for membranes containing 1.89 and 0.77 mg/cm2 was less than 90% for all studied emulsion concentrations.This publication was supported by the Qatar University Collaborative Grant QUCG-CAM-19/20-2. The findings achieved herein are solely the responsibility of the authors. The publication of this article was funded by the Qatar National Library.Scopu

Light-controllable viscoelastic properties of a photolabile carboxybetaine ester-based polymer with mucus and cellulose sulfate

In this study, the interaction of a photoswitchable carboxybetaine ester-based polymer with mucus and cellulose sulfate was elucidated, showing light-controllable viscoelastic properties. This polymer contains photolabile o-nitrobenzyl ester moieties, allowing transformation from its polycationic form to a charge-balanced nontoxic polyzwitterionic form upon photolysis by irradiation at 365 nm. Rheological studies revealed that the polycationic form of the polymer interacts with mucus and cellulose sulfate to create a physically crosslinked hydrogel based primarily on polyionic complexation and partially on hydrogen bonding. In these cases, a dramatic change in the rheological synergism was confirmed for mucus-based and cellulose sulfate-based systems. Rheological synergism with the polycationic carboxybetaine ester sample reached nearly 4 and 3.8, while it decreased with the charge-balanced zwitterionic sample to 0.3 and 0.7 after irradiation of the mucus-based and cellulose sulfate-based systems, respectively. Disruption of the interaction during light-induced transformation was on-line monitored and showed a 3 and 3.3 times decrease in the elastic modulus for the mucus-based and cellulose sulfate-based systems, respectively. These properties suggest possible biomedical applications, such as spatially controlled drug release or laparoscopic utilization.Qatar National Research Fund, QNRF; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Qatar University, QU: 7 - 1724 - 3 - 438, QUUG-CAM-2017-

Electrically conductive, transparent polymeric nanocomposites modified by 2D Ti3C2Tx (MXene)

The electrically conductive, transparent, and flexible self-standing thin nanocomposite films based on copolyamide matrix (coPA:Vestamelt X1010) modified with 2D Ti3C2Tx (MXene) nanosheets were prepared by casting and their electrical, mechanical and optical properties and then, were investigated. The percolation threshold of the MXene filler within the coPA matrix was found to be 0.05 vol. %, and the highest determined electrical conductivity was 1.4 x 10(-2) Scm(-1) for the composite filled with 5 wt. % (1.8 vol. %) of MXene. The electrical conductivity of the as-prepared MXene was 9.1 Scm(-1), and the electrical conductivity of the MAX phase (the precursor for MXene preparation) was 172 Scm(-1). The transparency of the prepared composite films exceeded 75%, even for samples containing 5 wt. % of MXene, as confirmed by UV spectroscopy. The dynamic mechanical analysis confirmed the improved mechanical properties, such as the storage modulus, which improved with the increasing MXene content. Moreover, all the composite films were very flexible and did not break under repeated twisting. The combination of the relatively high electrical conductivity of the composites filled with low filler content, an appropriate transparency, and good mechanical properties make these materials promising for applications in flexible electronics.Qatar University Collaborative High Impact Grant [QUHI-CENG-18/19-1

Advanced Thermal Energy Systems Based On Paraffin Waxes Applicable In Building Industry

Thermal energy storage systems are crucial for reducing dependency on fossil fuels and minimizing CO2 emissions. The building sector is a major sector responsible for producing high levels of CO2 in most countries (including Qatar). Thermal energy storage can be accomplished either by using sensible heat storage or latent heat storage components. Latent heat storage is more attractive than sensible heat storage because of its high storage density with smaller temperature fluctuations.[1] The materials able to utilize latent heat which can undergo phase changes (usually solid to liquid changes) at relatively low temperatures, while absorbing or releasing high amounts of energy are called phase change materials (PCMs).[2] Most promising PCMs are paraffin waxes which contain saturated hydrocarbon mixtures. They are frequently used due to their numerous advantages such as high latent heat of fusion, negligible super-cooling, and chemical inertness.[3,4] In this contribution, thermal properties of the PCMs based on linear low density polyethylene (LLDPE), different types of paraffin waxes with melting points, 25 oC and 42 oC, and expanded graphite (EG) were characterized by unique transient guarded hot plate technique (TGHPT), which allow to identified thermal properties of large sized samples[5] in comparison with commonly used ifferential scanning calorimetry (DSC). It was confirmed that all prepared PCMs were able to store and release huge amount of thermal energy. The 25 % increase of capacity to store and release a thermal energy was observed by PCMs contains paraffin wax with melting point 25 oC in comparison with paraffin wax with melting point 42 oC. Also reproducibility of storage and release heat of the PCMs by repeating of heating and cooling process has been demonstrated. Moreover, the increase of the EG content in the PCMs led to the increase of thermal conductivity from 0.24 W/mK for PCMs without EG to 1.3 W/mK for PCMs contain 15 wt.% of EG. Additionally, life cycle assessment of prepared PCMs has been demonstrated to identify the effects of these new materials on the Qatar environment. Our results indicate that using of PCMs in building industry can reduce emission of CO2 up to 10%.qscienc

Piezoresponse, mechanical, and electrical characteristics of synthetic spider silk nanofibers

This work presents electrospun nanofibers from synthetic spider silk protein, and their application as both a mechanical vibration and humidity sensor. Spider silk solution was synthesized from minor ampullate silk protein (MaSp) and then electrospun into nanofibers with a mean diameter of less than 100 nm. Then, mechanical vibrations were detected through piezoelectric characteristics analysis using a piezo force microscope and a dynamic mechanical analyzer with a voltage probe. The piezoelectric coefficient (d33) was determined to be 3.62 pC/N. During humidity sensing, both mechanical and electric resistance properties of spider silk nanofibers were evaluated at varying high-level humidity, beyond a relative humidity of 70%. The mechanical characterizations of the nanofibers show promising results, with Young’s modulus and maximum strain of up to 4.32 MPa and 40.90%, respectively. One more interesting feature is the electric resistivity of the spider silk nanofibers, which were observed to be decaying with humidity over time, showing a cyclic effect in both the absence and presence of humidity due to the cyclic shrinkage/expansion of the protein chains. The synthesized nanocomposite can be useful for further biomedical applications, such as nerve cell regrowth and drug delivery. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.NPRP from the Qatar National Research Fund (Qatar Foundation) [NPRP 7-1724-3-438