Identification of Molecular Fluorophore as a Component of Carbon Dots able to Induce Gelation in a Fluorescent Multivalent-Metal-Ion-Free Alginate Hydrogel

We introduce a simple approach to fabricate fluorescent multivalent metal ion-free alginate hydrogels, which can be produced using carbon dots accessible from natural sources (citric acid and L-cysteine). Molecular fluorophore 5-oxo-2,3-dihydro-5H-[1,3]-thiazolo[3,2-a] pyridine-3,7-dicarboxylic acid (TPDCA), which is formed during the synthesis of carbon dots, is identified as a key segment for the crosslinking of hydrogels. The crosslinking happens through dynamic complexation of carboxylic acid groups of TPDCA and alginate cages along with sodium ions. The TPDCA derived hydrogels are investigated regarding to their thermal, rheological and optical properties, and found to exhibit characteristic fluorescence of this aggregated molecular fluorophore. Moreover, gradient hydrogels with tunable mechanical and optical properties and controlled release are obtained upon immersion of the hydrogel reactors in solutions of divalent metal ions (Ca2+, Cu2+, and Ni2+) with a higher affinity to alginate. - 2019, The Author(s).This contribution was made possible by the NPRP award [8–878–1–172] from Qatar National Research Fund (a member of Qatar foundation), Qatar University grant QUCG-CAM-19/20-2 and by a grant from the Germany/ Hong Kong Joint Research Scheme sponsored by the Research Grants Council of Hong Kong and the Germany Academic Exchange Service of Germany (Reference No.: G-CityU103/16). M.D. thanks the VEGA Scientific Grant Agency for support through project no. 2/0158/17.Scopu

Mussel-mimicking sulfobetaine-based copolymer with metal tunable gelation, self-healing and antibacterial capability

In the present study, the sulfobetaine-based copolymer bearing a dopamine functionality showed gel formation adjusted by the application of metal salts for gelation and various values of pH. Normally, the liquid-like solution of the sulfobetaine-based copolymer and metal cross-linkers is transformed to a gel-like state upon increasing the pH values in the presence of Fe3+ and Ti3+. Metal-induced coordination is reversible by means of the application of EDTA as a chelating agent. In the case of Ag+ ions, the gel is formed through a redox process accompanied with the oxidative coupling of the dopamine moieties and Ag0 particle formation. Mussel-mimicking and metal-dependent viscoelastic properties were observed for Fe3+, Ti3+, and Ag+ cross-linking agents, with additionally enhanced self-healing behavior in comparison with the covalently cross-linked IO4 ? analogues. Antibacterial properties can be achieved both in solution and on the surface using the proper concentration of Ag+ ions used for gelation; thus, a tunable amount of the Ag0 particles are formed in the hydrogel. The cytotoxicity was elucidated by the both MTT assay on the NIH/3T3 fibroblast cell line and direct contact method using human dermal fibroblast cell (F121) and shows the non-toxic character of the synthesized copolymer.P.K. gratefully acknowledge Qatar University internal grant QUUG-CAM-2017-1. This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic ? Program NPU I (LO1504). This work was also supported by the Maersk Oil R&TC Qatar project. This work was also made possible by NPRP grant # 9 ? 219-2-105 from the Qatar National Research Fund (A Member of The Qatar Foundation). The finding achieved herein is solely the responsibility of the authors.Scopu

The Influence of Incorporating Plastic within Concrete and the Potential Use of Microwave Curing; A Review

In recent decades, researchers have used plastic to replace natural aggregates (NAs), or as filler and fibre within the concrete. This particular paper puts forward a review that gives comprehensive consideration to the properties and drawbacks, of concrete that contains plastic. As such, it may be hypothesised that poor bond capacity and higher air content due to inclusion of plastic aggregate (PA) within concrete are the predominant factors that reduce the properties in terms of mechanics and durability. In that regard, this study has put forward a new method of curing using microwave irradiation for improvement with respect to those factors. So, that there can be further improvement with regard to overall durability with respect to advanced chemical and hydrophobic resistivity and enhanced performance for conventional concrete with respect to bonding and ductility

Improved flexible, controlled dielectric constant material from recycled LDPE polymer composites

In this study, recycled low density polyethylene (RLDPE) is developed with the addition of aluminum oxide (Al2O3) to have new polymer composites. The following wt% were used of the filler (1, 4 and 6 wt%). Tensile properties, Hardness, scanning electron microscopy (SEM) thermo gravimetric analysis, differential scanning calorimetry and dielectric properties were studied for these composites. 4 wt% Al2O3/RLDPE composites showed the optimum values of 15.52, 180.8 and 59.72 MPa for the tensile strength, tensile modulus and hardness were reported. Increasing the filler % decreased the mechanical properties of the composites due to agglomeration and poor surface contact with the polymer matrix. This is confirmed by SEM studies. Al2O3 filler increased the melting and crystallization temperature of RLDPE. Furthermore, it showed that Al2O3 filler improved the thermal stability of RLDPE with increasing the % of filler. Relative permittivity, dielectric loss factor and AC electrical conductivity were increased with increasing the amount of the AL2O3. The relative permittivity reached a value of 4.9 at 1 kHz frequency, which is a good value for a flexible composite prepared from recycled material and it can be used in electrical devices and electronic packaging.This work was made possible by NPRP Grant No. NPRP5-039-2-014 from the Qatar National Research Fund (A Member of The Qatar Foundation)

Electrospun PVDF graphene oxide composite fibre mats with tunable physical properties.

This article is aimed at a basic physical characterization of electrospun PVDF/graphene oxide (GO) composite non-woven fibre mats. The morphological characterization of the prepared fabrics was performed via SEM investigations. Introduction of the GO during the electrospinning process caused significant changes in the crystalline structure of PVDF, and a transformation from α- to β-crystalline phases was achieved. Addition of the GO particles into PVDF did not only improve the thermal stability of the polymer, but also acted as a reinforcing filler, giving rise to improved dynamic moduli and tensile strength. The dielectric properties were evaluated over a broad frequency range, and it was confirmed that the presence of small amounts of GO had little effect on the dielectric properties of the PVDF, since the GO has a dielectric character similar to that of the PVDF

Investigation of the physico-mechanical properties of electrospun PVDF/cellulose nanofibers.

The electro-activity and mechanical properties of PVDF depends mainly on the b-phase content and degree of crystallinity. In this study, cellulose fibers were used to improve these characteristics. This could be achieved because the hydroxyl groups on cellulose would force the fluorine atoms in PVDF to be in the trans-conformation, and the cellulose particles could act as nucleation centers. Electrospinning was used to prepare the PVDF/cellulose (nano)fibrous films, and this improved the total crystallinity and the formation of b-crystals. However, the presence and amount of cellulose in PVDF were found to have little influence on the b-phase content and on the total crystallinity of PVDF. Improvements in the extent of crystallinity and the b-phase content were primarily brought about by the chain- and crystal orientation as a result of electrospinning. The thermal stability of PVDF in the composites slightly increased with increasing cellulose content in the composites up to 1.0 wt %, while the modulus and tensile strength significantly increased up to the same filler level. The dielectric storage permittivity also increased with increasing cellulose content, but the presence of cellulose had no influence on the dynamics of the c- and b-relaxations of the PVDF

Electrospun Copolyamide Mats Modified by Functionalized Multiwall Carbon Nanotubes

In this article, we report the preparation and properties of electro-conductive mats based on the commercial copolyamide (Vestamelt X1010) and multiwall carbon nanotubes functionalized by amino groups. Vestamelt X1010 is easily soluble in n-propanol at room temperature up to a concentration of 18 wt%. This is a significant advantage of this system because n-propanol is considered to be a safe and relatively environmentally friendly solvent compared with the organic solvents and acids frequently used for electrospinning of common synthetic polymers. The co-polyamide nanofibers were modified by multiwall carbon nanotubes grafted by amino groups to enhance their electrical conductivity at low filler content. The percolation threshold was found to be 0.33 vol%. Some applications of these mats were demonstrated such as the capability for sensing a selected vapor (acetone) and for oil/water separation. It was shown that neat Vestamelt X1010 mats remove around 85 wt% of oil (100 ppm of vegetable oil dispersed in water), whereas the addition of 1 wt% of CNTs enhances this ability up to 95 wt%. POLYM. COMPOS., 40:E1451-E1460, 2019.This work was made possible by NPRP grant No.: 7-1724-3-438 from the Qatar National Research Fund (A Member of the Qatar Foundation).Scopu

Foamy phase change materials based on linear low-density polyethylene and paraffin wax blends

Foamy phase-change materials (FPCMs) based on linear low-density polyethylene (LLDPE) blended with 30 wt.% of paraffin wax (W) were successfully prepared for the first time. The advantage of these materials is their double functionality. First, they serve as standard thermal insulators, and second, the paraffin wax acts as a phase change component that absorbs thermal energy (the latent heat) during melting if the temperature increases above its melting point, which ensures better heat protection of buildings, for instance, against overheating. The density of the porous fabricated FPCM was 0.2898 g/cm3 with pore content 69 vol.% and gel portion achieved 27.5 wt.%. The thermal conductivity of the LLDPE/W foam was 0.09 W/m.K, whereas the thermal conductivity of the neat LLDPE foam prepared under the same conditions was 0.06 W/m.K, which caused a higher porosity of approximately 92 vol.%. The FPCM absorbed or released approximately 22–23 J/g during melting or cooling, respectively, and the material was stable under thermal and mechanical cycling. © 2018, Springer International Publishing AG, part of Springer Nature.This work was made possible by the NPRP grant No: 4 - 465 - 2 - 173 from the Qatar National Research Fund (a member of the Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu