Tortuous Path Research Articles

Poly(lactic acid)/Poly(butylene succinate) (PLA/PBS) Layered Composite Gas Barrier Membranes by Anisotropic Janus Nanosheets Compartibilizers.

Poly(lactic acid) (PLA), one of the most promising biodegradable polymer products, has achieved wide applications for its relatively good mechanical properties and moderate degradability. Here we report an environment-friendly filler, the organic-inorganic composite Janus nanosheets (PLA/PBS JNs), which can jam at the interface of the PLA/PBS blend with a low threshold as the compatibilizer and can simultaneously toughen the composites and improve the gas barrier performance due to better interfacial interaction and tortuous path effect. With 0.3 wt % of PLA/PBS JNs added, the tensile strength and elongation at break of the PLA/PBS blend can be improved by 37% and 224%, respectively. After a further hot-pressing process, the barrier performance of the PLA/PBS composite membranes can be significantly enhanced since PLA, PLA/PBS JNs, and PBS are arranged in a nearly lamellar structure with oxygen permeability of 0.63 × 10-15 cm3 cm·cm-2 s-1 Pa-1 with only 0.5 wt % of PLA/PBS JNs.

Thickness effect on threshold electric field of ZnO microvaristors/silicone rubber composite with nonlinear conductivity

As a functional material, ZnO microvaristors/silicone rubber composite, with nonlinear conductivity, will be manufactured to different thicknesses for different applications. However, few study focuses on the thickness effect of the composite. In this paper, ZnO/SiR composites with thickness from 50 μm to 2800 μm were prepared. The conductivity results show that the threshold electric field (Eb) of the composites increases from 40 V/mm to a stable value (more than 1000 V/mm) as the thickness increases. A simulation model based on the Voronoi network was carried out to explore the mechanism. For the thickness close to the diameter of fillers, the key element determining Eb is the microstructural nonuniformity of electrical characteristics of microvaristors. As the sample becomes thick, the increasingly tortuous conduction path is considered to trigger off the increase of Eb. The thickness effect discussed in this paper will be helpful in designing electrostatic discharge elements in electronic devices.

Coefficient of thermal expansion and mechanical properties of modified fiber-reinforced boron phenolic composites

Abstract Boron phenolic resin is widely used in the aerospace field because of its excellent thermal properties. In this article, nitrile rubber powder was added to phenolic resin to modify fiber-reinforced phenolic resin composites. The results showed that the tensile strength continued to decrease; the elongation ratio increased from 20.01% to 32.04%; and flexural strength and flexural modulus reached the highest values of 188 and 9,401 MPa, respectively. Thermal analysis showed that rubber had little effect on the heat resistance at low temperatures, especially below 350°C. Furthermore, the coefficient of thermal expansion of the composites increased from 8.9 × 10−6 to 1.5 × 10−5 K−1, increasing by nearly 70%. The electron microscopy images showed a tortuous fracture path in modified composites, which indicated that rubber powder–modified phenolic composites had a ductile fracture.

Elucidating the Rate-Limiting Processes in High-Temperature Sodium-Metal Chloride Batteries.

Sodium‐metal chloride batteries are considered a sustainable and safe alternative to lithium‐ion batteries for large‐scale stationary electricity storage, but exhibit disadvantages in rate capability. Several studies identify metal‐ion migration through the metal chloride conversion layer on the positive electrode as the rate‐limiting step, limiting charge and discharge rates in sodium‐metal chloride batteries. Here the authors present electrochemical nickel and iron chlorination with planar model electrodes in molten sodium tetrachloroaluminate electrolyte at 300 °C. It is discovered that, instead of metal‐ion migration through the metal chloride conversion layer, it is metal‐ion diffusion in sodium tetrachloroaluminate which limits chlorination of both the nickel and iron electrodes. Upon charge, chlorination of the nickel electrode proceeds via uniform oxidation of nickel and the formation of NiCl2 platelets on the surface of the electrode. In contrast, the oxidation of the iron electrodes proceeds via localized corrosion attacks, resulting in nonuniform iron oxidation and pulverization of the iron electrode. The transition from planar model electrodes to porous high‐capacity electrodes, where sodium‐ion migration along the tortuous path in the porous electrode can become rate limiting, is further discussed. These mechanistic insights are important for the design of competitive next‐generation sodium‐metal chloride batteries with improved rate performance.

3D hollow CoNi-LDH nanocages based MMMs with low resistance and CO2-philic transport channel to boost CO2 capture

Layered double hydroxide (LDH) bearing numerous hydroxyl groups shows high affinity with CO2 and is promising in mixed matrix membranes (MMMs) based CO2 capture. However, its non-porous structure limits the further improvement of CO2 permeability. In this work, 3D hollow CoNi-LDH nanocages were developed to construct low-resistance and CO2-philic transport channel in MMM by in-situ etching of ZIF-67 template. The resultant material exhibits hollow structure with cavity size of about 500 nm, mesopores and micropores from LDH stacking and ZIF-67 template. The outer layered CoNi-LDH nanosheets can attract more CO2 molecules by their abundant hydroxyl groups, resulting in an improvement in dissolution selectivity of CO2 over N2. Meanwhile, the tortuous gas diffusion paths originated from 2D nanosheet stacking can further enhance the CO2 selectivity over N2. Moreover, the hollow nanocages provide CO2 molecules with fast transport path, resulting in high CO2 permeability. As a result, compared with pure Pebax membrane and 2D LDH/Pebax MMM, all the 3D hollow CoNi-LDH/Pebax MMMs present enhanced CO2 permeability. The 3D hollow CoNi-LDH-2h/Pebax MMM performs the highest CO2 permeability of 135.49 Barrer, which are increased by 141.95% and 71.50% than those of the above two membranes, respectively. The selectivity of 3D hollow CoNi-LDH-2h/Pebax MMM is about 26.30% higher than that of the pure Pebax membrane. The present membrane presents comparable CO2 capture capacity in contrast with most reported Pebax based MMMs and surpasses the Robeson upper bond. Together with the good long-term stability, the 3D hollow CoNi-LDH nanocages are believed to be a promising candidate for MMMs to improve CO2 capture.

Moisture absorption and spectroscopic studies of epoxy clay nanocomposite

Epoxy resins are prone to serious moisture absorption inspite of their inherent advantages, which can be mitigated by the incorporation of montmorillonite nanoclay that provide tortuous path to flow of moisture. Moisture absorption studies of epoxy clay nanocomposites is carried out, to analyse the effect of nanoclay content, immersion media and immersion temperature. Nanocomposites prepared in 0.5, 1 and 1.5 wt% using magnetic stirring and ultrasonication and neat epoxy specimen were immersed in distilled water and artificial seawater maintained at 28 and 38 °C till saturation. Fick’s and Langmuir’s models were applied to calculate the kinetic parameters from the water absorption graphs. Atomic force microscopy (AFM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope with energy dispersive X-ray (SEM–EDX) characterizations were performed. Diffusivity is least for nanocomposite containing 0.5 wt% nanoclay at both temperatures in both medium. However, it is least when the medium is distilled water. As the temperature of immersion medium increases, the diffusivity also increases. Saturation moisture uptake increased with increase in nanoclay content, because of the residual hydrophilic nature of nanoclay. AFM and XRD analysis revealed better dispersion and exfoliated structure of nanoclay respectively at 0.5 wt% loading. FTIR spectroscopy was applied to identify the chemical bonds that helped in proposing the reaction mechanism of the nanocomposite synthesis. Spectra comparison of dry and wet specimens complimented the moisture absorption data by showing lower infrared transmittance in wet specimens. With Increase in nanoclay content, the transmittance decreased corresponding to increase in saturation moisture uptake for distilled water immersed specimens. SEM–EDX analysis distinguished between the cations entered from the artificial seawater and cations that were still present in the nanoclay.

Evaluation of the cementite morphology influence on the hydrogen induced crack nucleation and propagation path in carbon steels

The effect of cementite morphology on the crack initiation and growth path was studied using in situ electrochem-ical micro-cantilever bending (ECCB) technique under hydrogen (H) charging. Two carbon steels with lamellar cementite morphology (pearlitic microstructure) and spherical or broken lamellas cementite morphology (spheroidite microstructure), both with approximately the same carbon equivalent, were used in this study. The ECCB tests were performed in H-free and two H charging steps with −1050 mV and −1550 mV charging potential versus Ag/AgCl reference electrode. The results show that both materials are resistant to crack initiation in the H-free condition while under −1050 mV charging, crack propagates through the grain boundaries in a tortuous path in spheroidite mi-crostructure and the lamellar microstructure displayed a higher strength with small cracks propagating through both the grain boundaries and the lamellas. A drastic load decrease in the load-displacement (L-D) curve happened under −1550 mV charging for both microstructures accompanied by a straight crack growth path in spheroidite microstruc-ture, independent of grain boundaries or ferrite-cementite interfaces while a competition between the shear crack growth mechanism and the interfacial cracking determines the crack growth path in the lamellar microstructure.

Stress driven micron- and nano-scale wrinkles as a new class of transport pathways of two-dimensional laminar membranes towards molecular separation

Narrow and tortuous interstitial paths through parallelly oriented interlayer spacings hinder the practical viability of 2D laminar membranes due to the limited membrane permeance. Ubiquitous stress involved wrinkling morphologies of biological tissues inspire us to exploit spontaneously formed wrinkles for facilitating transmembrane molecular transport. Herein, a stress driven wrinkle engineering methodology is proposed for manipulating micron- and nano-scale wrinkles as a new class of transport pathways of GO membranes. Micron-scale wrinkles of GO laminates are initiated by capillary stress via good solvents evaporation, while nano-scale wrinkles of GO nanosheets are induced by entropy stress via poor solvents resolvation. The deliberately tailored GO membranes possess nanoarchitectures with both high porous volume and low defective degree, thus achieving remarkable molecular separation performances (water permeance of ∼69.2 L m−2 h−1 bar−1and dye rejection of >98%). This work offers a straightforward experimental strategy for designing high-performance 2D laminar membranes via rational wrinkle manipulations.

Nanocomposite Coatings Based on Polyvinyl Alcohol and Montmorillonite for High-Barrier Food Packaging.

Materials with high barrier properties against oxygen are required for the packaging of many sensitive foods. Since commodity polymers lack these properties, additional barrier materials are used in plastic-based barrier packaging. These are usually more expensive than commodity polymers and, in higher fractions, also make recycling more difficult. Current developments, therefore, aim at barrier layers that are as thin as possible but retain the barrier properties. One approach is to incorporate nanoparticles into these layers. In this study, the barrier properties of nanocomposite coatings, consisting of unmodified polyvinyl alcohol (PVA), and dispersed stick-shaped halloysite (Hal) or platelet-shaped montmorillonite (MMT) silicate nanoparticles, were investigated. The PVA was dissolved in aqueous nanoparticle dispersions, which were prepared by mechanical shearing, to produce the so-called “nanolacquer.” Nanolacquers with nanoparticle concentrations of 7, 30, and 47 vol% with respect to PVA were applied in a single process step with k-bar on a polypropylene substrate film. The integration of 30 vol% platelet-shaped MMT enhances the barrier performance in comparison to pure PVA by a factor of 12 and 17 for oxygen and helium, respectively. Scanning electron microscopy (SEM) shows a homogeneous distribution and a parallel alignment of the nanoparticles within the coated layer. An increase in the crystallinity of PVA was observed due to the nanoparticle integration as demonstrated by x-ray diffraction (XRD) measurements. The investigation by Fourier transform infrared (FTIR) spectroscopy and the activation energy of the permeation coefficient indicate an interaction between the nanoparticles and the PVA. The theoretically calculated values for barrier enhancement accord well with the experimental values, which emphasizes that the gas barrier improvement for oxygen and helium is mainly dominated by the tortuous path effect.

On the design of particle filters inspired by animal noses.

Passive filtering is a common strategy to reduce airborne disease transmission and particulate contaminants across scales spanning orders of magnitude. The engineering of high-performance filters with relatively low flow resistance but high virus- or particle-blocking efficiency is a non-trivial problem of paramount relevance, as evidenced in the variety of industrial filtration systems and face masks. Next-generation industrial filters and masks should retain sufficiently small droplets and aerosols while having low resistance. We introduce a novel 3D-printable particle filter inspired by animals' complex nasal anatomy. Unlike standard random-media-based filters, the proposed concept relies on equally spaced channels with tortuous airflow paths. These two strategies induce distinct effects: a reduced resistance and a high likelihood of particle trapping by altering their trajectories with tortuous paths and induced local flow instability. The structures are tested for pressure drop and particle filtering efficiency over different airflow rates. We have also cross-validated the observed efficiency through numerical simulations. We found that the designed filters exhibit a lower pressure drop, compared to commercial masks and filters, while capturing particles bigger than approximately 10 μm. Our findings could facilitate a novel and scalable filter concept inspired by animal noses.

Diversity of intergranular corrosion and stress corrosion cracking for 5083 Al alloy with different grain sizes

5083 Al alloy sheets with different grain sizes (8.7−79.2 μm) were obtained by cold rolling and annealing. Their microstructures, intergranular corrosion (IGC), stress corrosion cracking (SCC), and crack propagation behaviors were investigated. The results showed that samples with coarse grains exhibit better IGC resistance with a corrosion depth of 15 μm. The slow strain rate test results revealed that fine-grained samples exhibit better SCC resistance with a susceptibility index (ISSRT) of 11.2%. Furthermore, based on the crack propagation mechanism, grain refinement can improve the SCC resistance by increasing the number of grain boundaries to induce the corrosion crack propagation along a tortuous path. The grains with {011} orientation could hinder crack propagation by orientating it toward the low-angle grain boundary region. The crack in the fine-grained material slowly propagates due to the tortuous path, and low H+ and Cl− concentrations.

Energy dissipation in composites with hybrid nacre-like helicoidal microstructures

Natural ceramic composites present complex microstructures that lead to tortuous crack paths and confer them high toughness. Current microreinforced composites do not yet reach the same level of complexity in their microstructures, resulting in poorer properties. To achieve complex microstructuration, magnetically-assisted slip casting (MASC) was conducted using a setup with 4 degrees of freedom. Among all possible microstructures, a hybrid design between nacre-like and helicoidal arrangements was selected due to its ability to tilt and twist the crack path. The hybrid microstructured specimen fabricated, consisting of aluminum oxide micro platelets in a silicone matrix, were tested under compression and their mechanical performance compared. Although nacre-like composites exhibited the highest strength and toughness, helicoidal hybrids could show some ductility and higher stiffness. The fabrication strategy proposed here could thus be a simple route to study more complex microstructures in view of increasing the toughness of microplatelet reinforced composites.

Evaluating cementation factor for bioturbated sandstones, Bhuj Formation, Kachchh Basin, India: a novel approach using triple-porosity model

Cementation factor has a crucial role in evaluating volumetric reserves for heterogeneous clastic reservoir. Bioturbation is a prominent source of heterogeneity existing in hydrocarbon-bearing formation across the world. The effect of bioturbation on the petrophysical properties of the clastic has not been comprehensively understood yet, especially its effect on cementation factor estimation. The precise description of such properties is beneficial in developing better volumetric estimates and optimizing field development planning. The present work discusses an approach to characterize cementation factor in bioturbated clastic Bhuj Formation, Kachchh Basin, India. In order to ascertain the cementation exponent for bioturbated media, an improved triple-porosity model is proposed by quantifying the total porous volume into three components, namely matrix 1, matrix 2 and bioturbated region. An equivalent resistance model is then developed by identifying the series and parallel relation between the two matrix components and the burrow. The experimental observations of electrical response indicated large variation in resistivity in vertical cores compared to horizontal cores. The decreased resistivity is due to the vertically aligned burrow which due to their enhanced porosity provides less tortuous path for current to flow. The triple-porosity model is validated with different porosity value of matrix 1, matrix 2 and burrow, and a cementation factor of 2.8 for higher bioturbated samples and 3 for lower bioturbated samples is obtained. This validates the previous understanding of enhanced flow and storage property and thereby produces a consistent way to evaluate total cementation factor. The correct estimation of cementation factor helps in precise evaluation of water saturation in bioturbated reservoirs.

Effect of microstructure and crystallographic orientation characteristics on low temperature toughness and fracture behavior of pipeline steels

In order to elucidate the relationship among microstructure, crystallographic orientation characteristics and fracture behavior of pipeline steels at low temperature, three pipeline steels with different microstructures were fabricated by varying the cooling rate. Different characteristics of the three microstructures, such as high angle grain boundaries(HAGBs), crystallographic orientation and brittle fracture characteristics were investigated. The study showed that HAGBs had a considerable possibility to make the cracks deviate greatly from the original direction and were a decisive factor in determining the features of fracture and impact toughness. The AF(acicular ferrite) microstructures of steels C2 and C3 had the stronger arrestability to cracks because of their high density of HAGBs, which was reflected from more tortuous crack propagation paths and smaller cleavage fracture units on the fracture surface. In addition, the maximum content of {001} cleavage planes parallel to the fracture surface in steel C1 also led to the highest DBTT (ductile–brittle transition temperature). Compared with steel C2, steel C3 had more {100} cleavage planes parallel to the surface of the V-notch, resulting in larger and more secondary cracks which could significantly alleviate the stress concentration at the tip of the primary crack during impact test. Steel C3 also exhibited higher intensities around the {332}<113> components than steel C2. Therefore, the impact absorbed energy of steel C3 was higher than that of steel C2. Moreover, a modified equation can be used to quantitatively predict the DBTT of PF(polygonal ferrite), however, it can be only used for an approximate prediction for AF due to its complex microstructure.

Fracture mechanism of alumina-spinel castables containing ZrO2 by wedge splitting test and digital image correlation technique

To clarify the fracture mechanism of alumina-spinel castables, two kinds of alumina-spinel castables with or without fused zirconia-alumina (FZA) were prepared. The full-field strains and crack propagation process in the region of interest (ROI) of alumina-spinel castables were investigated by wedge splitting test (WST) and digital image correlation (DIC) technique. Fractographic methods were used to analyze the crack propagation path of the castables after the WST. The results indicated that the load-displacement curve of alumina-spinel castables containing FZA exhibits a non-linear fracture, demonstrated typical ductile fracture; while that of alumina-spinel castables without FZA is linear, showed typical brittle fracture. The characteristic length reaches to 258.9 mm in FZA containing castables, more than 4 times that of the castables without FZA. In contrast, castables containing FZA has longer and more tortuous crack propagation path, larger damage zone length, which results in the increase of the dissipated energy. Crack branching can be observed around the main crack in castables containing FZA, meaning that microcracks toughening is the main mechanism for flexibility improvement of the alumina-spinel castables containing FZA, formation of micro-cracks can be attributed to the martensitic transformation of zirconia.

Experimental study of heat transfer between fluid flowing through fracture surface with tortuous seepage path

Under the dual challenges of energy demand and environmental protection, geothermal energy has broad application prospects because of their cleanliness and huge reserves. Understanding the flow and heat transfer process of fluid flowing through fractured rock is of importance for the utilization of geothermal resources. A more practical calculation equation for convective heat transfer coefficient is derived based on Newton's cooling equation and previous research. Samples with different seepage paths were prepared through 3D printing technology and cement mortar pouring method. The effect of seepage path tortuosity, aperture, and initial temperature on the characteristics of heat transfer were analyzed and discussed by conducting the seepage and heat transfer test. The experimental results show that the overall convective heat transfer coefficient of sample with seepage path are lower than those of sample with smooth fractures. The greater the tortuosity of seepage path, the greater the overall convective heat transfer coefficient. In addition, the correlation of tortuosity and C, n in the characteristic number equation is proposed, providing significant parameters for the study of hydraulic-mechanical-thermal coupling when fluid flowing through rock mass with high temperature.

Experimental study on fracture mechanics of cementitious materials reinforced by graphene oxide–silica nanocomposites

This study aims to improve the fracture properties of cementitious materials by adding graphene oxide (GO) and graphene oxide–silica nanocomposites (GO-nanoSiO2). The pristine GO was coated with nano-silica to form GO-nanoSiO2 composites. Based on the three-point bending test, the fracture toughness and fracture energy of cementitious materials were calculated to provide comprehensive fracture mechanics characterization. The fracture surface morphology and the crack development in mortar were detected by ultra-depth microscopy and scanning electron microscopy. The results demonstrate that the addition of GO-nanoSiO2 is more beneficial to improve the fracture properties of cementitious materials than pristine GO and the amount of nano-silica grafted on GO surface affects its enhancement effect. The initial fracture toughness, unstable fracture toughness and fracture energy of mortar reinforced by GO-nanoSiO2 (0.05 wt% GO and the mass ratio of nano-SiO2/GO is 2.8) are increased by 92.2%, 64.7% and 77.5%, respectively. GO-nanoSiO2 improves the roughness of mortar fracture surface, changes the propagation mode of cracks, and makes the crack propagate along a more tortuous path which contributes to energy dissipation.

Sound absorption in Hilbert fractal and coiled acoustic metamaterials

We describe here a class of acoustic metamaterials with fractal Hilbert space-filling and coiled geometry with equal tortuosity for noise mitigation. Experiments are performed using a four-microphone impedance tube and benchmarked against non-viscous and viscothermal finite element models related to configurations spanning up to five fractal/geometry orders. We show that the acoustic absorption can be predicted by the resonance of the cavities associated with the tortuous paths. For a given fractal/geometry order, the acoustic absorption at specific frequencies is also enhanced by maximizing the difference between the minimum and maximum fluid particle velocity of the air inside the patterns. These principles can be used to design high-performance acoustic metamaterials for sound absorption over broad frequency ranges.

Solid state infiltration of porous steel with aluminium by the forcefill process

Abstract We report first results on producing a metal – metal composite by forcing solid aluminium to fill a porous steel preform. This process is akin to forcefill used for filling of vias when producing metallic interconnects in microelectronics. Using scanning electron microscopy with energy-dispersive X-ray spectroscopy, it was shown that for nominal pore size as small as 100 μm, the pores could be filled with aluminium throughout the entire preform used, thus demonstrating the viability of the process. An interesting aspect of this solid state ‘infiltration’ is that the tortuous random paths taken by the plastically flowing Al involve numerous kinks. Some of them may induce large localised shear deformation similar to that produced by equal channel angular pressing, which is used to fabricate bulk ultra-fine-grained materials. It is, therefore, conjectured that towards the exit end of the channels the infiltrating material may develop an ultra-fine grain structure and exhibit enhanced strength. It is suggested that the process described can be used to produce metal– metal (or ceramic – metal) composites with unusual mechanical properties. Thin fibres of the material that has percolated through the porous preform can be expected to have a sub-micron grain structure and to possess improved mechanical properties.

Saturation evaluation of microporous low resistivity carbonate oil pays in Rub Al Khali Basin in the Middle East

To solve the problem that it is difficult to identify carbonate low resistivity pays (LRPs) by conventional logging methods in the Rub Al Khali Basin, the Middle East, the variation of fluid distribution and rock conductivity during displacement were analyzed by displacement resistivity experiments simulating the process of reservoir formation and production, together with the data from thin sections, mercury injection and nuclear magnetic resonance experiments. In combination with geological understandings, the genetic mechanisms of LRPs were revealed, then the saturation interpretation model was selected, the variation laws and distribution range of the model parameters were defined, and finally an updated comprehensive saturation interpretation technique for the LRPs has been proposed. In the study area, the LRPs have resistivity values of less than 1 Ω·m, similar to or even slightly lower than that of the water layers. Geological research reveals that the LRPs were developed in low-energy depositional environment and their reservoir spaces are controlled by micro-scale pore throats, with an average radius of less than 0.7 μm, so they are typical microporous LRPs. Different from LRPs of sandstone and mudstone, they have less tortuous conductive paths than conventional reservoirs, and thus lower resistivity value under the same saturation. Archie's formula is applicable to the saturation interpretation of LRPs with a cementation index value of 1.77—1.93 and a saturation index value of 1.82—2.03 that are 0.2—0.4 lower than conventional reservoirs respectively. By using interpretation parameters determined by classification statistics of petrophysical groups (PGs), oil saturations of the LRPs were calculated at bout 30%—50%, 15% higher than the results by conventional methods, and basically consistent with the data of Dean Stark, RST, oil testing and production. The 15 wells of oil testing and production proved that the coincidence rate of saturation interpretation is over 90% and the feasibility of this method has been further verified.