Uniform Si-Infused UiO-66 as a Robust Catalyst Host for Efficient CO2 Hydrogenation to Methanol

Due to the weak nature of organic coordination bonds, metal–organic frameworks (MOFs) can hardly retain their intrinsic physicochemical properties and structural integrity when functioning in harsh heterogeneous reactions. Herein, a post-synthetic strategy to reinforce the MOF structure by inserting siliceous linkers inside is proposed, according to which a Si-infused UiO-66 (s-UiO-66) with well-developed porosity and exceptional thermal/structural stability is fabricated. This monodispersed Si-infused matrix with enlarged nanopores is then utilized as the catalyst host, and is highly conductive to confining ultrafine CuO nanoparticles with uniform dispersion. Targeting CO₂ hydrogenation to methanol reaction, the Cu-loaded s-UiO-66 (CuO/s-UiO-66) delivers a remarkable and efficient methanol production rate outperforming other Cu/ZrO₂-based catalysts and the commercial catalyst. Moreover, the robust structure of CuO/s-UiO-66 prevents both copper phase and host material from aggregation during the catalyst preparation procedure and the reaction. In addition to material-oriented studies, in situ characterization techniques are employed to identify the active Cu component and key intermediates formed during the CO₂ hydrogenation reaction, separately. It is envisioned that this Si infusion strategy can be applied to construct stable host materials with boundary-defined structures from the pristine MOFs for broadened applications under extreme circumstances.     

3D-Printed Soft and Hard Meta-Structures with Supreme Energy Absorption and Dissipation Capacities in Cyclic Loading Conditions

The main objective of this article is to introduce novel 3D bio-inspired auxetic meta-structures printed with soft/hard polymers for energy absorption/dissipation applications under single and cyclic loading–unloading. Meta-structures are developed based on understanding the hyper-elastic feature of thermoplastic polyurethane (TPU) polymers, elastoplastic behavior of polyamide 12 (PA 12), and snowflake inspired design, derived from theory and experiments. The 3D meta-structures are fabricated by multi-jet fusion 3D printing technology. The feasibility and mechanical performance of different meta-structures are assessed experimentally and numerically. Computational finite element models (FEMs) for the meta-structures are developed and verified by the experiments. Mechanical compression tests on TPU auxetics show unique features like large recoverable deformations, stress softening, mechanical hysteresis characterized by non-coincident compressive loading–unloading curve, Mullins effect, cyclic stress softening, and high energy absorption/dissipation capacity. Mechanical testing on PA 12 meta-structures also reveals their elastoplastic behavior with residual strains and high energy absorption/dissipation performance. It is shown that the developed FEMs can replicate the main features observed in the experiments with a high accuracy. The material-structural model, conceptual design, and results are expected to be instrumental in 3D printing tunable soft and hard meta-devices with high energy absorption/dissipation features for applications like lightweight drones and unmanned aerial vehicles (UAVs).     

Optimization of nanofiber-caproate/laurate esters synthesis,their characterization,and usage as emulsifier in o/w emulsion

The aim of this study is to optimize the esterification of nanofibers with caproyl/lauroyl chlorides at different substitution degrees' (DS) and to investigate the usage of nanofiber derivatives in model emulsions. First, cellulosic material was obtained and milled into nanofibers using a micro-fluidizer. Then, these nanofibers were esterified with caproyl/lauroyl chlorides in a solvent of DMAc/LiCl with DMAP as an acid scavenger. The esterification of nanofibers with caproyl/lauroyl chlorides was optimized for fatty acid chloride mole and reaction time. Esterification reactions were carried out at 80°C with various molar ratios of acyl chlorides (3–15 moles) versus anhydroglucose unit of nanofibers and for various time durations (30–360 min). The hydrophobic derivatives with DS in the range of 0.34–2.77 were successfully obtained. Using the data obtained as a result of the optimization, nanofiber-fatty acid esters with different DS (0.50–2.75) were produced and characterized. Analyzes showed that the esterification process was successful and as the degree of esterification increased, the crystallinity index and thermal stability of the derivatives decreased. Then, the nanofiber-caproate/laurate esters with different DS were used as emulsifier (0.5 wt%) in an oil-in-water model emulsion containing 25 wt% oil and the emulsions were analyzed. The nanofiber caproate/laurate esters with a DS of 0.50–1.25 were suitable for o/w emulsions, while samples with a DS of 2.00 and above were not found suitable. Emulsions prepared by using nanofiber derivatives with 1.25 DS had higher G′ and G″ and viscosity values and lower droplet sizes than those of other group.     

Effects of inorganic fillers on the performance of the water-based intumescent fire-retardant coating

The purpose of this research was to evaluate the influences of filler type and its content on the performance of a water-based intumescent fire-retardant coating. Three fillers (vermiculite, celite, and aluminum hydroxide) were added to the intumescent paint formulation. The thermal and fire protective properties were studied with thermogravimetric analysis (TGA), torch test, electrical furnace, scanning electron microscopy (SEM), and Fourier transform infrared analysis (FTIR). The results showed that adding fillers into coatings up to 3% could improve the intumescent coating's behavior and increase its endurance against flames. Of the three fillers used, vermiculite showed a better performance in the torch test, attributed to its chemical and physical structure. Vermiculite has low thermal conductivity and is considered an appropriate filler for heat-insulation. The final back-plate temperatures in the torch test for the vermiculite-containing samples were around 100°C–150°C lower than that of other samples. Moreover, vermiculite's addition improved the coating's expansion by 10% compared with the control sample's. The vermiculite sample's char layer morphology showed a uniform cell size distribution, indicating structural robustness. The coating samples successfully transformed polypropylene flammability from highly flammable to V0 level in the UL 94 vertical burning test standard. The results showed that vermiculite could improve intumescent paint's fire resistance and be used as an enhancer in intumescent coating formulations.     

Investigation of the Reaction Kinetics of Poly(butylene terephthalate) and Epoxide Chain Extender

Polyesters, such as poly (butylene terephthalate) (PBT), owe a rather low melt strength, which is considered as not beneficial for foaming. To overcome this issue, a typical attempt is the incorporation of chemical modifications—so-called chain extenders (CE)—in the reactive extrusion process. In this study, the reaction kinetic variables are investigated depending on the material and process parameters. For this purpose, different series of experiments are performed with varying PBT with different molecular weights and the commonly used CE, Joncryl ADR4468, on a micro compounder. The screw force is recorded and analyzed using an Avrami and an Arrhenius plot. First, the amount of CE is systematically varied. To study the course of the reaction in more detail, the reaction is stopped in a series of measurements (10, 30, 60, and 90 s after complete filling). Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), and Raman spectra are recorded. In the second series, the effect of processing temperatures between 250 and 270 °C is investigated, and finally, in the third series, the average molecular weight of PBT is varied. It could be shown that the activation energy seems to be dependent on the initial molecular weight; lower molecular weights result in lower activation energy.     

Chaos prediction in trolling mode atomic force microscopy: analytical approach

Microsystem Technologies - Recently a novel mode of AFM called Trolling-mode AFM (TR-AFM) was developed with the ability to operate in liquid environments with an intrinsically high-quality factor....     

Conflict management techniques for model merging: a systematic mapping review

Software and Systems Modeling - Model merging conflicts occur when different stakeholders aim to integrate their contradicting changes that are applied concurrently to update software models. We...     

Effects of molecular weight,stereo configuration of PLA,and processing on the dispersion of multiwalled carbon nanotubes and properties of corresponding nanocomposites

Multiwalled carbon nanotubes (MWCNTs) were dispersed and distributed via a co-rotating twin-screw extruder (TSE) in high (h)- and low (l)-molecular-weight amorphous and semicrystalline polylactides (PLAs) (aPLA and scPLA, respectively). Effects of PLA molecular weight and D-lactic acid equivalents content (D-content), as well as processing parameters, were examined on the MWCNT dispersion quality in PLA. The effectiveness of the MWCNT dispersion in various PLA matrices was investigated using scanning electron microscopy (SEM) and small-amplitude oscillatory and transient shear flow rheometry in the molten state. The results showed a better dispersion of MWCNTs in the low-molecular-weight PLA grades (aPLAl and scPLAl). In addition, better MWCNT dispersion was observed in aPLA grades when processed at a higher temperature of 190°C than at 150°C. At 150°C, while MWCNT bundles in aPLAl could be broken down, a good dispersion could not be achieved in aPLAh due to the lower molecular mobility at such a temperature. The electrical conductivity of the samples was also shown to increase as the MWCNT dispersion was improved. The existence of crystallites in scPLA-based nanocomposites, however, disrupted the connectivity of the MWCNTs and decreased the final electrical conductivity. The lower molecular weight aPLAl prepared at 190°C showed the highest electrical conductivity (~10⁻⁵ S/m) at a low loading of 0.5 wt.% MWCNTs.