Wide Size Distribution Research Articles

On the effect of axial inlet angle on the droplet size distribution and mixing uniformity for swirl jet mixer at high phase ratios

The “short pass” problem of liquid-liquid two-phase mixing at high phase ratios limited the development and applications of jet mixer in industrial process. In this study, the effect of the axial inlet angle on the mixing characteristics of a swirl jet mixer was investigated through laser particle size analysis and computational fluid mechanics (CFD) coupled with population balance model (PBM). The result was shown that as the axial inlet angle increased, the dispersed phase droplet sizes decreased, and the droplet size distribution was widened for the fixed mixer configuration. At Re ≤ 3.000×104, tangential inlet was more conducive to improving mixing uniformity. Conversely, the axial inlet angle of 90° was optimal at Re ≥ 3.750×104. Numerical simulations revealed that the tangential inlet effectively intensified liquid-liquid interactions, including streamlines extension, increased vorticity, improved droplet size uniformity. Additionally, the increase of the axial inlet angle resulted in increased turbulence stress and shortened decay period, the reduction in droplet size, and a wide droplet size distribution. The research findings can serve as theoretical basis for the hydraulic design and promoted applications of swirl jet mixers.

Pd-N-doped carbons for chemoselective hydrogenation of cinnamaldehyde: Unravelling the influence of particle size and support in multiphase batch and continuous-flow systems

The chemoselective hydrogenation of the CC bond of cinnamaldehyde (CAL) was investigated under batch and continuous flow conditions, by comparing the performance of two ad-hoc prepared palladium-based catalysts supported on N-doped carbons to that of a commercial Pd/C system. An impregnation (I) and a solution-mediated (S) protocols were used for the synthesis of the catalytic materials, Pd-N/Ci and Pd-N/Cs, respectively, in the presence of chitin as a precursor of the support. The S method afforded palladium nanoparticles of 2.0±0.5 nm, while by impregnation, a wider size distribution was achieved with particles mostly belonging to two groups displaying a mean radius of 3.0±0.5 nm and 8.4±0.5 nm, respectively. A parametric analysis of the hydrogenation reaction showed that both the reaction conditions and the nature of the catalysts played a role to steer the selectivity towards the formation of the desired product, 3-phenylpropanal (hydrocinnamaldehyde, HCAL). At 50 °C and 1 bar H2, in a triphasic (liquid-liquid-liquid) batch reactor where the catalyst was compartmentalized in an ionic liquid layer, Pd-N/Ci and commercial Pd/C were almost equally active and allowed to obtain HCAL in a 90–96 % selectivity at complete conversion. On the other hand, at the same T and p (50 °C/1 bar), Pd-N/Cs was more effective in the continuous-flow mode: the process was quantitative yielding HCAL with a selectivity and a productivity of 91 % of 16 mmol (gcat h)−1, respectively, while the catalyst proved highly stable showing no loss of activity over 300 min of time on-stream. The reaction environment, the size and dispersion of the metal active sites, and the nature of the catalyst support were major contributors to such results, acting synergistically to each other to tune the energetics of adsorption/desorption of reactants/products, of the interfacial interactions/ barriers, and in the last analysis, of the process kinetics/selectivity.

Assessment of the opportunities of demolition waste using as a building material of the future in Ukraine

The object of research is the potential of secondary use of waste from the destruction of buildings and structures, which were formed as a result of the military aggression of the Russian Federation on the territory of Ukraine. For Ukraine, the issue of demolition waste is critical at the level of environmental safety and ensuring the demand for building materials for the reclamation of Ukraine according to the principles of the circular economy. To date, there are no official methods that would allow to determine the exact amount of destruction and the quality of the material formed, which complicates the development of mechanisms for its utilization in production. The key industry considered during the research for disposal of demolition waste is the industry of construction materials production. In the course of research, it was determined that most of the generated waste is waste from the destruction of buildings and structures made of precast concrete, however, considering that these wastes are generated by the action of explosions from shells. It is very difficult to ensure their compliance with the requirements of current standards due to the inclusion that such waste can contain. Therefore, the problem considered by this study is the determination of the nature of waste from the destruction of buildings and structures, their physical, mechanical and chemical characteristics, in the context of the final applications of products based on them. The results of the study showed that when reproducing the concrete mix for tared concrete for civil purposes, which do not have high requirements for stability in aggressive operating conditions, when replacing natural aggregate crushed to a fraction of 5 to 20 mm, the requirements for concrete strength are achieved in the level of C40/50 strength class. But the rheological characteristics deteriorate due to the high absorption of water from the concrete mixture by the studied material. Research has shown that for further use in the production of ready-mixed concrete and precast concrete products, it is necessary to prepare demolition waste with a wide particle size distribution and low dust content. This can ensure a high level of recycling and meet the demand for concrete in the reconstruction of Ukraine. The fine aggregate from the demolition waste crushing process can be considered as secondary cementitious material for cement production.

Hyaluronic Acid Nanoparticles with Parameters Required for In Vivo Applications: From Synthesis to Parametrization.

Hyaluronic acid is an excellent biocompatible material for in vivo applications. Its ability to bind CD44, a cell receptor involved in numerous biological processes, predetermines HA-based nanomaterials as unique carrier for therapeutic and theranostic applications. Although numerous methods for the synthesis of hyaluronic acid nanoparticles (HANPs) are available today, their low reproducibility and wide size distribution hinder the precise assessment of the effect on the organism. A robust and reproducible approach for producing HANPs that meet strict criteria for in vivo applications (e.g., to lung parenchyma) remains challenging. We designed and evaluated four protocols for the preparation of HANPs with those required parameters. The HA molecule was cross-linked by novel combinations of carbodiimide, and four different amine-containing compounds resulted in monodisperse HANPs with a low polydispersity index. By a complex postsynthetic characterization, we confirmed that the prepared HANPs meet the criteria for inhaled therapeutic delivery and other in vivo applications.

Evaluation of the Effect of Different Extraction Temperatures on the Synthesis of Silver Nanoparticles from Ocimum basilicum (Basil) Plant

The eco-friendly green synthesis of silver nanoparticles (AgNPs) using Ocimum basilicum (basil) extract at varying extraction temperatures (40°C, 60°C, 80°C, 100°C) was investigated to determine the optimal conditions for nanoparticle formation. Analysis methods such UV-Vis spectrophotometry, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and TransmissionElectron Microscopy (TEM) confirmed the crystalline, spherical nature of AgNPs and identified phytochemicals acting as capping and reducing agents. Notably, the extraction temperature was found to influence both the DPPH radical scavenging activity and the structural properties of AgNPs. According to TEM analysis results, it was observed that high extraction temperatures increased the nanoparticle formation efficiency but created a wide size distribution. The crystallite sizes, calculated using the Scherrer equation, for AgNPs synthesized at different extraction temperatures, were determined to be 12.45 nm, 18.77 nm, 17.76 nm, and 16.03 nm, respectively. The hydrodynamic sizes of the AgNPs were found to range between 158.1 and 333.7 nm. The study highlights the critical role of extraction temperature in the synthesis process, suggesting 40°C as the optimal temperature for achieving efficient and environmentally friendly synthesis of AgNPs with enhanced biological activities.

An application of hierarchical MgAl hydrotalcite in the highly efficient treatment of oilfield macromolecular contaminants.

In this work, salicylic acid (SA) was used to induce the self-assembly of octadecyl trimethyl ammonium chloride (OTAC), a cationic surfactant, into three-dimensional wormlike micelle aggregates. These aggregates act as a soft template for hierarchical MgAl hydrotalcite (LDH) to create a multi-level pore structure adsorption material. Scanning electron microscopy characterization showed that the surface of the hierarchical hydrotalcite exhibited a dense layered structure, unlike the monolayer structure of ordinary hydrotalcite. Furthermore, the hierarchical MgAl-LDH possesses a significantly larger specific surface area (113.94 m2/g) and wide pore size distribution ranging more extensively from 2 to 80nm, which significantly has an impressive adsorption effect on sulfonated lignite (SL), with a maximum adsorption capacity of 192.7mg/g at pH = 7. Extensive research has been conducted on the adsorption mechanism of hierarchical MgAl-LDH, attributing it to surface adsorption due to the unique multi-level structure of the adsorbent. After two cycles of regeneration experiments, the adsorption capacity of the adsorbent remained at a high level of 179.1mg/g, demonstrating the excellent renewability of hierarchical MgAl-LDH. Moreover, the hierarchical hydrotalcite showed high adsorption capacity in the adsorption of sulfonated lignite, which was attributed to its larger specific surface area and superior pore structure to expose more active sites.

Bio‐inspired hierarchical bamboo‐based air filters for efficient removal of particulate matter and toxic gases

AbstractAir pollution is caused by the perilous accumulation of particulate matter (PM) and harmful gas molecules of different sizes. There is an urgent need to develop highly efficient air filtration systems capable of removing particles with a wide size distribution. However, the efficiency of current air filters is compromised by controlling their hierarchical pore size. Inspired by the graded filtration mechanisms in the human respiratory system, microporous ZIF‐67 is in situ synthesized on a 3D interconnected network of bamboo cellulose fibers (BCFs) to fabricate a multiscale porous filter with a comprehensive pore size distribution. The macropores between the BCFs, mesopores formed by the BCF microfibers, and micropores within the ZIF‐67 synergistically facilitate the removal of particulates of different sizes. The filtration capabilities of PM2.5 and PM0.3 could reach 99.3% and 98.6%, respectively, whereas the adsorption of formaldehyde is 88.7% within 30 min. In addition, the filter exhibits excellent antibacterial properties (99.9%), biodegradability (80.1% degradation after 14 days), thermal stability, and skin‐friendly properties (0 irritation). This study may inspire the research of using natural features of renewable resources to design high‐performance air‐filtration materials for various applications.

Mesophase pitch-derived porous carbon constructed by template/activation synchronous pore-forming technology for electrochemical energy storage

Porous carbon materials with high specific surface area and wide pore size distribution play a crucial role in the energy storage process. In this paper, a mixed sol-gel system of carbon source, chemical activator and salt template agent was constructed using raw pitch, o-xylene soluble substance and their mesophase as carbon source, NaCl as template agent and KOH as activator. After one step process of high temperature treatment, porous carbon materials with high specific surface area (SBET 1969 m2/g) and wide nanopore distribution (0.4–6 nm) were obtained. The electrochemical properties of the prepared mesophase porous carbon materials were tested. At a charge-discharge rate of 80 mA/g, a specific capacitance of 102.5 F/g can be achieved for porous carbon materials obtained from the o-xylene soluble mesophase, indicating the feasibility of preparing porous carbon electrode materials by o-xylene soluble mesophase. The development of template/activation synchronous pore-forming technology can integrate the advantages of the two kinds of pore-forming technologies, reduce the demand for pore size control in porous carbon materials, and promote the one-step realization of porous carbon materials with high specific surface area, wide pore size distribution and controllable pore size.

Densification and rheological behaviors of 8YSZ powders for Vat photopolymerization-based additive manufacturing

Vat photopolymerization additive manufacturing technology allows the shaping of ceramic structures with limitless opportunities in terms of design freedom, structural resolution, and improving processing speed while reducing cost and wastage. The quality of a final product is influenced by the raw materials and processing routes. The particle size distribution of ceramic powders significantly affects ceramic slurry's rheology and cure behaviour as well as the densification process during sintering. This work studies the rheological properties of slurries prepared from 8 mol.% yttria-stabilized zirconia powders with various particle size distributions and densification of green bodies prepared from these suspensions. The suspension with a narrow particle size distribution showed a non-Newtonian behavior with a viscosity of >1 Pa s at a solid loading above 29 vol%, and a significant densification at a sintering temperature of 1400 °C. The viscosity of a suspension prepared from a powder with a wide particle size distribution was <1 Pa s in a solid loading range of 29–37 vol%. The higher cure depth at a lower exposure energy for slurry with coarse particles allowed a reduction of the printing time, while suspension with fine particles can be used for high-resolution printing with longer exposure time.

Engineering Long‐Releasing Hollow‐like or Condensed Progesterone Hormone Microcrystals with Controlled Polymorphism

Progesterone is an endogenous steroid hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. Progesterone crystallization techniques have previously reported. Among these techniques, solvent crystallization and different solvent:anti‐solvent systems are considered. Herein, the selective development of either hollow‐like or condensed progesterone microcrystals in elevated yield with controlled polymorphism, habit, and release is described for the first time. For the hollow microcrystals, isopropyl alcohol (IPA) and double‐deionized water (DDW) system is developed as solvent:anti‐solvent, while acetonitrile (AcN) and DDW system are developed for the condensed microcrystals. The microcrystals obtained from both developed crystallization systems are thoroughly investigated with varied microscopic techniques, including brightfield and scanning electron microscopy (SEM), thermal analysis by differential scanning calorimetry (DSC), and crystallography by powder X‐ray diffraction (PXRD) and single XRD, and have been compared. Results show that the crystals of the IPA:DDW crystallization system are hollow and exhibit several habits, whereas the microcrystals of the AcN:DDW crystallization system are more condensed. However, both systems are found to have a wide crystal size distribution of one stable polymorph and are thus highly useful for tunable release. More importantly, these microcrystals exhibit elongated and slow release for 14 days under an expedited release conditions model, indicating suitability for long‐term and potential localized release applications.

Numerical Simulation of Rainfall-Induced Erosion on Infiltration and Slope Stability

In slopes where a mixture of coarse and fine particles is present, the infiltration of rainfall can cause the migration of fine particles. This migration alters the hydraulic properties of the soil and has implications for slope stability. In this study, the slope under investigation is a tailings dam composed of loosely consolidated soil with a wide particle size distribution. Due to rainfall infiltration, fine particles tend to migrate within the voids of the coarse particle framework, leading to changes in hydraulic properties and inducing slope instability. The classical internal erosion constitutive model, known as the Cividini and Gioda erosion criterion, is commonly used to predict the behavior and effects of fine particle erosion in geotechnical engineering. However, certain parameters in this erosion criterion equation, such as long-term density, are challenging to obtain through experiments. To investigate the coupled evolution of seepage and erosion within landfill slopes under the influence of rainfall infiltration and to understand the mechanisms of slope instability, this research assumes the erosion of fine particle suspension and adopts the Worman and Olafsdottir erosion criterion to establish a coupled model of unsaturated seepage and internal erosion. The developed model simulates the coupled response of seepage and erosion in unsaturated landfill slopes under three different rainfall intensities. It is then combined with the infinite slope model to quantitatively analyze the impact of fine particle migration on soil permeability and slope stability. The numerical simulations provide the following findings: The Worman and Olafsdottir erosion criterion, unlike the Cividini and Gioda erosion criterion, only requires the determination of the soil’s gradation curve to estimate the erosion rate. Internal erosion primarily occurs within the leading edge of moisture penetration, accelerating the advancement of the wetting front and reducing slope stability. When the rainfall intensity is lower than the saturated permeability coefficient, the influence of internal erosion can be disregarded. However, under rainfall intensities equal to or greater than the saturated permeability coefficient, considering internal erosion results in a difference in the depth of the wetting front of up to 34.2 cm after 6 h in the R2 scenario. The safety factor without considering internal erosion is 1.12, whereas considering internal erosion yields safety factors between 1.08 and 1.09. In the R3 scenario, the difference in the depth of the wetting front reaches 53.8 cm after 6 h, with a safety factor of 1.12 without considering internal erosion and safety factors between 1.06 and 1.07 when considering internal erosion.

Construction of Hydrogels with Highly Salt-Resistant Honeycomb Porous Structures for Solar Desalination and Steam Generation.

Interfacial solar desalination is a method for desalinating seawater using solar energy, and the long-term use of this technology requires a stable evaporation rate and some ability to prevent salt crystallization. To address these issues, carbonized polydopamine-coated bentonite (C@PBT), poly(vinyl alcohol), and cellulose nanofibers were used to construct a three-dimensional oriented hydrogel evaporator with a multilayered honeycomb porous structure for long-term desalination. Carbon nanoparticles transferred between the layers of the bentonite, which increases the spacing of the layers and confers a more effective solar light trapping ability. The evaporation rate was 2.26 kg m-2 h-1 in 20 wt % NaCl solution, and no salt crystals were precipitated from the surface of the evaporator in 12 h of continuous operation. This phenomenon occurs due to the wide distribution of pore sizes and the large size of the pores within the evaporator, which create ample space for salt ions to move freely. Furthermore, after undergoing 300 cycles of compression, its internal pore structure remains intact, and the rate of evaporation remains stable. It ensures the evaporator stability during outdoor cycles. The research work provides an effective method to solve the salt accumulation problem and shows its great potential for application.

Thiourea crystal growth kinetics, mechanism and process optimization during cooling crystallization

In the cooling crystallization process of thiourea, a significant issue is the excessively wide crystal size distribution (CSD) and the abundance of fine crystals. This investigation delves into the growth kinetics and mechanisms governing thiourea crystals during the cooling crystallization process. The fitting results indicate that the crystal growth rate coefficient, kg, falls within the range of 10–7 to 10–8 m·s–1. Moreover, with decreasing crystallization temperature, the growth process undergoes a transition from diffusion-controlled to surface reaction-controlled, with temperature primarily influencing the surface reaction process and having limited impact on the diffusion process. Comparing the crystal growth rate, G, and the diffusion-limited growth rate, Gd, at different temperatures, it is observed that the crystal growth process can be broadly divided into two stages. At temperatures above 25 °C, 1/qd approaches 1, indicating the predominance of diffusion control. Conversely, at temperatures below 25°C, 1/qd increases rapidly, signifying the dominance of surface reaction control. To address these findings, process optimization was conducted. During the high-temperature phase (35–25 °C), agitation was increased to reduce the limitations posed by bulk-phase diffusion in the crystallization process. In the low-temperature phase (25–15 °C), agitation was reduced to minimize crystal breakage. The optimized process resulted in a thiourea crystal product with a particle size distribution predominantly ranging from 0.7 to 0.9 mm, accounting for 84% of the total. This study provides valuable insights into resolving the issue of excessive fine crystals in the thiourea crystallization process.

Fabrication, characterization and application of Pickering emulsion gels stabilized by defatted grape seed powder

The feasibility of defatted grape seed powder (DGSP) stabilizing Pickering emulsion gels as butter substitute was investigated. The Pickering emulsion gel was constructed using DGSP through high-speed homogenization, and the effects of particle concentration (c) and oil-phase (Medium chain triglyceride) volume fraction (φ) on its structure and properties were investigated. Its application as a butter substitute was also evaluated. The results showed that DGSP had various particle shapes, a wide particle size distribution (3–130 μm), and a three-phase contact angle of 128.9 ± 2.3°. The O/W Pickering emulsion gels with φ ≥ 60% could be obtained at c ≥ 2%. The droplet diameter was negatively correlated with c and positively correlated with φ, while the gel strength was positively related to c and φ. The resulting emulsion gel demonstrated solid-like viscoelastic behavior and pseudoplasticity, and had the potential to serve as a butter substitute. The results can promote the application of grape seeds in food.

Ultramicroporous cardo-pendant polyamide nanofilms for enhanced organic solvent nanofiltration

Permeable, selective, and stable polymeric membranes are essential for efficient molecular separation in organic solvents. Polymers of intrinsic microporosity (PIMs) with rigid and twisted chain structures offer abundant pores for high solvent permeability and are emerging as an ideal membrane material. However, guaranteeing high separation selectivity and stability is challenging owing to the wide pore size distribution and low swelling resistance in organic solvents. In this work, we developed intrinsically ultramicroporous polyamides (PAs) with cardo-pendant groups to create crosslinking, ultrathin, and defect-free nanofilms for organic solvent nanofiltration. The molecular simulation confirmed the pivotal role of cardo-pendant group structures in the amine monomers and exhibited their effect in creating pore channel structures within the PAs. Distinctive rigid fluorenyl-based cardo-pendant groups were introduced in amine monomers to finely tailor the packing of PA chains for high ultramicroporosity and a finely tuned pore size. We further achieved the growth of such PAs using a cyclic deposition strategy, in-situ generating highly crosslinking nanofilms with an ultralow thickness of 23–36 nm without structure relaxation. As such, the typically-designed PA membranes demonstrated high and stable solvent permeance (e.g., 18 L m−2 h−1 bar−1 for methanol) and high solute rejection (up to 95 % rejection of 306 Da Azure I), which is superior to its counterparts and current PIM membranes, presenting a new perspective for efficient organic solvent nanofiltration.

Fluid entrapment during forced imbibition in a multidepth microfluidic chip with complex porous geometry

Understanding and controlling fluid entrapment during forced imbibition in porous media is crucial for many natural and industrial applications. However, the microscale physics and macroscopic consequences of fluid entrapment in these geometric-confined porous media remain poorly understood. Here, we introduce a novel multidepth microfluidic chip, which can mitigate the depth confinement of traditional two-dimensional (2-D) microfluidic chips and mimic the wide pore size distribution as natural-occurring three-dimensional (3-D) porous media. Based on microfluidic experiments and direct numerical simulations, we observe the fluid-entrapment scenarios and elucidate the underlying complex interaction between geometric confinement, capillary number and wettability. Increasing depth variation can promote fluid entrapment, whereas increasing capillary number and contact angle yield the opposite effect, which seemingly contradicts conventional expectations in traditional 2-D microfluidic chips. The fluid-entrapment scenario in depth-variable microfluidic chips stems from microscopic interfacial phenomena, classified as snap-off and bypass events. We provide theoretical analyses of these pore-scale events and validate corresponding phase diagrams numerically. It is shown that increasing depth variation triggers snap-off and bypass events. Conversely, a higher capillary number suppresses snap-off events under strong imbibition, and an increased contact angle inhibits bypass events under imbibition. These macroscopic imbibition patterns in microfluidic porous media can be linked with these pore-scale events by improved dynamic pore-network models. Our findings bridge the understanding of forced imbibition between 2-D and 3-D porous media and provide design principles for newly engineered porous media with respect to their desired imbibition behaviours.

Effect of hydroxy propyl cellulose grade and foam quality on foam granulation of a high drug load formulation

Foam granulation is a relatively newer wet granulation process whereby foamed binder solutions are added to the powders in the mixer to reduce localized over-wetting encountered during the wet granulation. This study is the first to investigate the effect of binder grade and foam quality on foam granulation process and granule properties of a high drug load formulation. Two different HPC grades, HPC LF (two times more viscous) and HPC EXF at an equivalent 7.4%w/w solution concentration, and foam quality of 50%, 90% and binder solution dripped were added to a high drug load (81%w/w) formulation for wet granulation. The granules were evaluated for compactibility and resultant compact strengths. The 50% foam quality of either HPC LF and HPC EXF resulted in lowest impeller power reading and water activity compared to 90% foam quality or dripped HPC solution. Granules prepared with 50% foam quality also exhibited smaller granule size, wider size distribution and higher specific surface area, resulting in higher compactibility. Whilst the granules prepared with different foamed HPC grades were not significantly different in compression behavior, they were higher in compact strengths, suggesting that foam mixing was more efficient in binder distribution compared to binder liquid penetration and distribution.

Microalgae polyphosphate nanoparticles deliver bioavailable calcium against phytate antagonism: Ex vivo and in vivo studies

Biogenic nanoparticles are promising carriers to deliver essential minerals. Here, calcium-enriched polyphosphate nanoparticles (CaPNPs) with a Ca/P molar ratio > 0.5 were produced by Synechococcus sp. PCC 7002 in the growth medium containing 1.08 g/L CaCl2, and had nearly spherical morphologies with a wide size distribution of 5–75 nm and strongly anionic surface properties with an average ζ-potential of –39 mV, according to dynamic light-scattering analysis, transmission and scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The ex-vivo ligated mouse ileal loop assays found that calcium in CaPNPs was readily available to intestinal absorption via both ion channel-mediated and endocytic pathways, specifically invoking macropinocytic internalization, lysosomal degradation, and transcytosis. Rat oral pharmacokinetics revealed that CaPNPs had a calcium bioavailability approximately 100 % relative to that of CaCl2 and more than 1.6 times of that of CaCO3. CaPNPs corrected the retinoic acid-induced increase in serum calcium, phosphorus, and bone-specific alkaline phosphatase, and decrease in serum osteocalcin, bone mineral content/density, and femoral geometric parameters with an efficacy equivalent to CaCl2 and markedly greater than CaCO3. In contrast to CaCl2, CaPNPs possessed desirable resistance against phytate’s antagonistic action on calcium absorption in these ex vivo and in vivo studies. Overall, CaPNPs are attractive as a candidate agent for calcium supplementation, especially to populations on high-phytate diets.

Monodispersed Bubble Generation Using Hydrophobic Orifices: The Extended Tate's Law.

The use of submerged orifices for bubble generation is ubiquitous in industries with wettability known to influence the bubble departure diameter. In this study, we investigated bubble generation and departure from the orifices (0.3-2 mm) drilled on hydrophobic perfluoroalkoxy (PFA) tubes in water. By varying the gas inflow rate (33 to 200 mL/min), we found that the Sauter mean diameter closely matched those generated by hydrophilic quartz orifices. However, monodispersed bubbles were formed on the PFA tube compared to those on quartz with much wider size distributions. By examining the dynamic bubbling process, we confirmed its agreement with Tate's law, which was originally developed for quasi-steady conditions and emphasizes a balance between capillary and buoyancy forces. However, it should be noted that dynamic conditions lead to an increase in bubble volume compared to the quasi-steady condition despite following the same principle, which is explained by the continuous gas inflow when the bubble departs from the orifice at a necking stage. The above understandings enable generation of monodispersed bubbles under dynamic conditions, benefiting industries requiring precise control on bubble size, such as the bubble assisted wet etching and cleaning processes in semiconductor fabrication.

Failure of an effective stress approach in polydisperse wet granular materials

In this Letter, the effective stress principle (ESP)—originally developed for granular materials saturated with water and recently extended to unsaturated ones via simulations—is shown to fail once the material presents wide grain size distributions. We demonstrate that the current ESP approaches cannot capture the Mohr-Coulomb strength parameters as soon as the grain size span exceeds dmax/dmin∼4. This failure is attributed to significant differences in the fabric generated by solid interactions in the wet material, which are supposedly capable of matching the characteristics of the dry material. We show that a generalization of the ESP requires not only macroscopic considerations but also direct attention to the nature of contact and force networks. Published by the American Physical Society 2024