关键词： Acrylic resins   Biopolymers   Biocomposites   Phosphate ion release   Mechanical properties  

摘要： Background: The denture-base acrylic resins used by partially edentulous patients can cause local demineralization of teeth. Alkali ions released from the bioactive materials that were added to acrylic resins can increase the pH of the oral environment and slow down the demineralization process. Aim of the study: This study aimed to create a new denture-base acrylic resin that can release ions. Materials and methods: A total of 222 samples with different fillers (calcium hydrogen phosphate, hydroxyapatite, two kinds of bioactive glasses, and a product obtained by reaction between bioactive glass formed from glass ionomer cement and polyacrylic acid) were prepared for the study. All the materials were tested for mechanical properties and their use as phosphate donors for 3 weeks. The measurements were presented as mean +/- SD error of the mean. Data were analyzed by two-way analysis of variance, with a p-value of < 0.05 as statistically significant. Results: Acrylic resins obtained after the addition of a small quantity of bioactive materials (2.5-5%) showed similar mechanical properties (such as flexural strength and Izod impact resistance) as non-filled material. However, the hardness of the modified materials was higher compared to pure poly (methyl methacrylate). Samples modified with materials released phosphate ions for a short period. The materials that were identified to be most promising as an ion source were samples containing 5% calcium hydrogen phosphate (p < 0.01). Conclusions: Based on the results, it can be concluded that denture-base acrylic resins resulting after the addition of different bioactive precursors have improved mechanical properties and can release ions to the oral environment for a short period. (C) 2021 The Author. Production and hosting by Elsevier B.V. on behalf of King Saud University.

关键词： polymer synthesis   expanding monomer   UV-curing kinetics   volume shrinkage   3D printing  

摘要： Spiroorthocarbonates (SOCs) exhibit good shrinkage resistance with ring-opening polymerization initiated by a cationic photoinitiator, with potential application in reducing the volume shrinkage by C=C double bond polymerization on three-dimensional (3D) printing. However, SOCs as an additive dealing with volume shrinkage in 3D printing are rarely reported. Moreover, little progress has been made in the kinetics study on its ring-opening polymerization. In this study, we presented an effective strategy to reduce 3D printing volume shrinkage based on SOCs chemistry and systematically studied the ring-opening photopolymerization kinetics. 3,9-diethyl-3,9-bis(allyloxymethyl)-1,5,7,11-tetraoxastetraoxaspiro undecane (DB-TOSU), one kind of SOCs, was adopted as an expanding monomer. Initiated by cationic photoinitiator with sensitizer under 405 nm LED light, the maximum conversion of DB-TOSU is up to 84%. As a volume-control agent for 3D printing, volume shrinkage reduction is 71.2% when adding DB-TOSU into 3D printing resin based on SOCs chemistry. Moreover, the toughness of resin was enhanced. In the 3D printing application test, DB-TOSU displayed a good application prospect owing to its good compatibility with the printing resin and printing accuracy after volume expansion.

关键词： Optical and Electronic Materials   Characterization and Evaluation of Materials  

摘要： The single crystal of barium ion-doped gamma-Glycine (BGG) has been synthesized by slow evaporation technique. The grown crystal was subjected to the characterization studies such as XRD, nucleation Kinetics, UV, FTIR, micro-hardness, SEM with EDAX, SHG analysis, NMR, and thermal Studies. The cell parameters a = b = 7.210, c = 5.845, alpha = beta = 90 degrees, and gamma = 120 degrees revealed that BGG belongs to the hexagonal crystal system with P3(1) space group. The nucleation kinetic parameters were derived from nucleation studies and an agreement between the experimental and theoretical values of interfacial surface energy has been established. Optical transparency of the grown crystal was investigated by UV spectrum. The lower optical cutoff wavelength and the band gap values have been found to be at 328 nm and 3.5 eV, respectively. The vibrational frequencies of various functional groups in the crystal have been derived from FTIR spectrum and further employed to identify the molecular structure of the crystal. Microhardness mechanical studies carried out by Vickers microhardness method showed that hardness number (H-V) increases with load for BGG crystal. Surface morphology of the grown crystal has been examined through SEM with EDAX. Kurtz Perry technique has been adopted to measure the Second harmonic generation (SHG) efficiency of the title crystal and has been found to be 1.16 times as that of standard KDP. The chemical structure and the molecular arrangement position of the grown crystal were established by C-13 and H-1 NMR spectrum. The thermogravimetric and differential thermal analysis showed that BGG is thermally stable up to 320.43 degrees C. The results of the aforementioned characterizations attested that the grown BGG crystal can be used as a potential fabrication material in nonlinear optical devices.

关键词： Molecular dynamics   Silane coupling agents   Polymer nanocomposites   ReaxFF  

摘要： Various factors that affect nanoparticles' (NP) strength and dispersion in silica-Styrene Butadiene Rubber (SBR) nanocomposites are determined using ReaxFF molecular dynamics simulations. Factors such as the size of silica NP, type of Silane Coupling Agent (SCA), surface occupancy of SCA at the silica surface and spatial distribution of sulphur cross-links at a molecular scale are considered. Various parameters like peak normal traction, strength modulus, interface energy, radius of gyration, and distance between NP of different systems were monitored to determine which factors significantly influence NP's strength and dispersion. It was found that the strength increased with both the size and volume fraction of the NP. The size of the NP or the type of the SCA did not affect the dispersion at all. The dispersion of NP was found to depend on the surface occupancy of a given SCA significantly. Furthermore, it was observed that the introduction of sulphur cross-links farther from the NP increased the tensile strength of the nanocomposite than if they were closer to the NP. This result indicates that controlling the distribution of sulphur cross-links may significantly influence the strength of the nanocomposite.

关键词： Laminates   Curing kinetics   Stacking methods   Thermomechanical property   Mechanical properties  

摘要： A carbon fiber/epoxy resin prepreg was tested by DSC, and the phenomenological nth-order and autocatalytic reaction curing kinetic models of the prepreg were established. On this basis, the optimum curing process of the prepreg was obtained. In addition, in order to explore the effect of ply parameters on the mechanical properties of the laminates, the thermomechanical and mechanical properties of the laminates of [0](10), [+ 45/ - 45](5s) and [0/90](5s), prepared by compression molding, were investigated. The results show that the autocatalytic reaction model agrees well with the DSC curves obtained from the experimental data. The curing process of the carbon fiber/epoxy resin prepreg is 130 degrees C /60 + 160 degrees C/30 min. The flexural and impact strength of [0](10) laminates are higher than that of [+ 45/ - 45](5s) and [0/90](5s) laminates. The glass transition temperature (T-g) of the laminates is 142-146 degrees C, and the loss factor of [0](10) laminate is significantly higher than that of [+ 45/ - 45](5s) and [0/90](5 s) laminates. The great differences in the mechanical properties of the laminates are mainly due to the different amounts of 0 degrees fibers, which lead to the different bearing and deformation capacity of the laminates under external force. Graphic abstract

关键词： Alumina microrods   Growth kinetics   Ostwald ripening   Oriented growth   LaMer theory  

摘要： Understanding the growth kinetics and mechanism of alumina microrods is of great importance for controllable synthesis. In this work, alumina microrods with controllable morphology are hydrothermally synthesized to investigate the influence of reaction conditions on the growth mechanism which is supported by the reaction kinetics. The evolution kinetics of gel nucleation are established by tracing the change in the Al(OH)(4) ligand and AlOOH monomer concentrations. The driving force of the axial growth of alumina microrods is primarily affected by the reaction temperature and reaction time, and the aspect ratio is regulated by reactant concentration. The oriented growth from Al(OH)(4) ligands to alumina microrods and Ostwald ripening from small boehmite spherical particles on the microrod surface successively control the perfection of the crystal surface. It verifies that the nucleation kinetics of microrods are driven by the supersaturation of the gel ligands and improves the LaMer theory with specific kinetic equations. (C) 2021 Elsevier Ltd. All rights reserved.

关键词： Conductive drying   Drying kinetics   Interfacial thermal resistance   Mechanical compression   Sewage sludge  

摘要： Improving sludge drying efficiency is of tremendous importance for public health, subsequent treatment, and comprehensive utilization. The interfacial thermal resistance between sludge and hot wall greatly limits the con-ductive drying performance. This study employed mechanical compression to decrease the interfacial thermal re-sistance. The drying kinetics and interfacial heat transfer behavior were investigated at mechanical loads of 25 to 200 kPa, temperatures of 120 to 210 degrees C, and sludge thicknesses of 1.0 to 3.0 mm, and were compared to those in the conventional drying process without mechanical load. The increase of temperature and mechanical load and the decrease of thickness improved drying rates. The drying experienced one warm-up period and two falling rate periods. The breakthrough of interfacial vapor film was responsible for the rapid rise in drying rates initially. At the thickness of 3.0 mm, 210 degrees C, and 100 kPa, the effective moisture diffusivity was increased by 2.5 times, and the apparent activation energy was reduced by 34% compared to the traditional process in the first falling rate period, implying that mechanical compression facilitated moisture migration and bound water desorption. The effective moisture diffusivity in the first falling rate period was increased by 35% compared to the diffusivity in the second falling rate period because of the pressure-driven flow. The decrease in drying rates was due to the transformation from the pressure-driven flow to vapor diffusion-limited flow in the first falling rate period. Additionally, this study provided essential information on developing a new sludge treatment method and estab-lishing the drying model. (c) 2021 Published by Elsevier B.V.

关键词： Carbon tetrachloride (CCl4)   Sonochemistry   Acoustic bubbles   Reactive chlorine species (RCS)   (OH)-O-center dot radicals   Computational analysis  

摘要： In spite of the great number of experimental works conducted on CCl4 sono-degradation, several controversies are observed, these including the main species generated upon CCl4 decomposition and the mechanism by which CCl4 accelerated the sonolytic removal of nonvolatile contaminants. In this paper, a new mechanism of carbon tetrachloride pyrolysis inside an argon bubble is proposed. In this model, the effects of heat exchange, mass transport and the chemical reactions heat on the bubble dynamics are taken into account. This model was used to explain the formation of the different species created by the pyrolytic decomposition of CCl4 inside the bubble at 355 kHz for various acoustic intensities (In = 0.7, 1 and 1.5 W/cm(2)), where the whole range of CCl4 concentration in the bulk solution is covered (from 0 to 5.2 x 10(-3) mol/L, at 20 degrees C). It has been found that the increase of CCl4 mole fraction inside the bubble decreases its maximal temperature. However, the chemical bubble yield increases proportionally with the increase of CCl4 mole fraction. It has been demonstrated that CCl4 enhances the sonolytic degradation of nonvolatile contaminants through the formation of reactive chlorine species (RCS: (CCl3)-C-center dot, :CCl2 and Cl-center dot and HOCl) coupled with an increase of (OH)-O-center dot radicals yield when sonolysis is performed in the presence of CCl4. Besides, the contributing effect of (OH)-O-center dot radicals and HOCl is lower than that of the other RCS. For the acoustic intensity of 1.5 W/cm(2) and CCl4 mole fractions within the bubble lower than similar to 0.007 (CCl4 concentration <= 10(-4) mol/L in the bulk solution), the amounts of RCS and (OH)-O-center dot radicals are approximately in the same range. However, for higher CCl4 mole fractions (>0.007), the production of RCS becomes dominant. On the other hand, for the acoustic intensity of 1 W/cm(2), the yield of RCS is dominant whatever the initial mole fraction of CCl4 inside the bubb

关键词： Titanium nitride MXenes   Titanium carbide MXenes   Mechanical behavior   Molecular dynamics  

摘要： MXenes have recently witnessed significant evolution and advances in terms of their applications in different areas such as flexible electronics, energy storage devices, and coatings. Here, the mechanical properties of both pristine and functionalized Tin+1CnO2 and Tin+1NnO2 (n = 1, 2) are investigated utilizing classical molecular dynamics simulations. For eight different MXene structures, the stress-strain curves are calculated including Young's modulus, strength, and fracture strain. It is found that Ti2N holds the highest Young's modulus with the value of 517 GPa while Ti3C2 has the lowest one with the amount of 133 GPa. In addition, the strongest MXene structure is Ti2N while the weakest strength belongs to the TiC3O2 structure. It is also found that oxidation, as a possible effect in experiments, enhances Young's modulus in Titanium Carbide MXenes, while it turns opposite for the Titanium Nitride ones. Both groups of structures however experience an increase in their fracture stress. Moreover, the effect of vacancy is probed on Young's modulus and a linear correlation is presented versus the defect concentration for Ti2N structure. These results provide a benchmark to analyze the mechanical properties of MXenes for their potential applications in a wide range of nanoelectronics and nanomechanics.

关键词： mucus   rheology   dynamic light scattering   stress relaxation   microscopic dynamics  

摘要： Mucus is a biological gel covering the surface of several tissues and ensuring key biological functions, including as a protective barrier against dehydration, pathogen penetration, or gastric acids. Mucus biological functioning requires a finely tuned balance between solid-like and fluid-like mechanical response, ensured reversible bonds between mucins, the glycoproteins that form the gel. In living organisms, mucus is subject to various kinds mechanical stresses, e.g., due to osmosis, bacterial penetration, coughing, and gastric peristalsis. However, our knowledge of the effects of stress on mucus is still rudimentary and mostly limited to macroscopic rheological measurements, with no insight into the relevant microscopic mechanisms. Here, we run mechanical tests simultaneously to measurements of the microscopic dynamics pig gastric mucus. Strikingly, we find that a modest shear stress, within the macroscopic rheological linear regime, dramatically enhances mucus reorganization at the microscopic level, as sig-naled by a transient acceleration of the microscopic dynamics, by up to 2 orders of magnitude. We rationalize these findings by proposing a simple, yet general, model for the dynamics physical gels under strain and validate its assumptions through numerical simulations of spring networks. These results shed light on the rearrangement dynamics of mucus at the microscopic scale, with potential implications in phenomena ranging from mucus clearance to bacterial and drug penetration.