Compact Particles Research Articles

Modeling of a screw extruder 3D printer using pellets or crushed polymer waste as the raw material

In this article, the process of moving polymer material in the screw extruder of a 3D printer, which uses granules or crushed polymer waste as raw materials, is chosen as the object of mathematical modeling. It is noted that the modeling of screw extruders is a highly relevant task, as it is an essential tool for optimizing production processes in the polymer industry and other industries where they are used. It allows you to study and optimize the material cylinder's processes thoroughly. It is noted that the modeling of screw extruders for 3D printers, which use granules or shredded plastic waste, is a critical factor in supporting innovation, increasing production efficiency, improving product quality, and developing new technological solutions in various industries. It was noted that during the movement of the material along the channel of the extruder screw, several of its states continuously changed from a solid at the entrance of the channel to a viscous liquid at the exit. In the feed zone, the polymer is solid and moves along the material cylinder due to friction. A physical model was used in the simulation, in which compacted polymer particles do not move relative to each other during movement through the channel. This is because the internal friction forces in the polymer greatly outweigh the friction of the polymer on the steel, and the particles move as a single elastic compressible medium due to the balance of dry friction between the cylinder wall and the screw. The geometrical parameters of the extruder in the feed zone are shown. A diagram of the expanded extruder channel for calculating productivity is given. A diagram of the movement of material in it was drawn up to determine the productivity of the extruder feed zone. A mathematical model of productivity was obtained depending on the diameter of the screw, the frequency of rotation, the depth of the screw channel, and the angle of elevation of the screw line of the screw cutting. The pressure in the extruder channel was calculated. A scheme for calculating the forces acting on the material in the feeding zone is given. A formula was obtained for determining the pressure in the material loading zone from the hopper, which connects the characteristics of the polymer material and the geometric parameters of the loading hopper. Keywords: 3D printer, screw extruder, modeling; polymer material; loading area; bunker; productivity; pressure.

Main Results from the ISSI International Team “Characterization of 67P Cometary Activity”

The ESA/Rosetta mission accompanied the Jupiter Family Comet 67P/Churyumov-Gerasimenko and provided a huge amount of data which are providing important results about cometary activity mechanisms. We summarize the results obtained within the ISSI International Team Characterization of 67P cometary activity, which studied dust and gas ejection in different stages of the comet’s orbit, by means of a data fusion between instruments onboard the Rosetta orbiter, i.e., the OSIRIS camera, the VIRTIS imaging spectrometer, the GIADA dust detector, the MIDAS atomic force microscope, the COSIMA dust mass spectrometer, and the ROSINA gas mass spectrometer, supported by numerical models and experimental work. The team reconstructed the motion of the dust particles ejected from the comet surface, finding a correlation between dust ejection and solar illumination as well as larger occurrence of fluffy (pristine) particles in less processed and more pebble-rich terrains. Dust activity is larger in ice-rich terrains, indicating that water sublimation is the dominant activity process during the perihelion phase. The comparison of dust fluxes of different particle size suggests a link between dust morphology and ejection speed, generation of micrometric dust from fragmentation of millimetric dust, and homogeneity of physical properties of compact dust particles across the 67P surface. The comparison of fluxes of refractory and ice particles suggests the occurrence of a small amount of ice in fluffy particles, which is released when they are fragmented. A new model of cometary activity has been finally developed, according to which the comet nucleus includes Water-Ice-Enriched Blocks (WEBs), that, when exposed by CO2 activity, are the main sources of water sublimation and dust ejection.

Preparation and characterization of egg white protein film incorporated with epigallocatechin gallate and its application on pork preservation.

The aim of this study was to develop the composite films with antioxidant and biodegradable activity based on egg white protein (EWP) and epigallocatechin gallate (EGCG). Water susceptibility, light transmittance, microstructure and antioxidant properties of the composite films without and with EGCG were fully characterized. It was noted that the addition of EGCG might decrease the moisture content, water solubility and swelling capacity. SEM micrographs revealed that discontinuous blocks and rough surfaces were caused by increasing concentration of EGCG, whereas compact and homogeneous particles appeared when the concentration of EGCG reached to 80μmol/L. Moreover, the biodegradability of the composite films was demonstrated by the soil degradation properties that they can be almost completely degraded within ten days. Experimental results on the application in chilled fresh pork showed that the EWP-based films could play an antioxidant role when incorporated with EGCG, indicating their great potential for food packaging.

Evaluation of Millability and Recyclability of Asphalt with Paving Interlayers

Abstract Reclaimed asphalt pavement (RAP) has been widely incorporated into roadway base and surface courses, as they provide economic and environmental benefits that lead to sustainable construction practices. However, because of the increasing use of paving interlayers (e.g., geotextiles, geogrids, and geocomposites) during roadway rehabilitation, the likelihood of milling projects involving asphalt layers with paving interlayers (referred to as GRAP) has significantly increased. Consequently, the assessment of potential GRAP reuse in geotechnical and pavement applications becomes essential. This research study aims at evaluating the millability and recyclability of asphalt layers with paving interlayers. Specifically, sections with and without paving interlayers were first milled to evaluate the millability of asphalt layers with paving interlayers. Subsequently, the recyclability of GRAP for the base and surface course of pavements was assessed by quantifying the geotechnical characteristics of millings collected from asphalt layers with paving interlayers, referred herein as geosynthetic RAP or GRAP, and those without paving interlayers (RAP). The evaluation of RAP and GRAP materials for road base suitability included blending them with virgin aggregates and investigating these blends via determination of particle size distribution, binder content, compaction characteristics, abrasion resistance, hydraulic conductivity, and resilient modulus. The evaluation of RAP and GRAP materials for surface course suitability involved preparing asphalt mixtures that incorporated RAP and GRAP and quantifying their particle size distribution, indirect tensile strength, and moisture susceptibility. Comparison of the results obtained from five different base course blends and five different asphalt mixtures demonstrated that the base course blends and asphalt mixtures with GRAP exhibited properties similar to those with RAP. Also, the results of this investigation indicate that asphalt mixtures (surface course) and granular base courses can incorporate up to 30 % and 50 % GRAP, respectively, thus leading to sustainable roadway construction practices.

A facile method to prepare non-cationic mRNA lipid-nanoparticles based on frame guided assembly strategy

In recent years, lipid nanoparticle (LNP)-formulated messenger RNA (mRNA) has become a promising tool in vaccine development and protein replacement therapy. However, the cationic or ionizable lipid components in the current LNPs also bring the concerns on toxicity and immunogenicity. In this study, we have developed a novel cationic lipid-independent strategy to prepare mRNA-LNPs through frame-guided assembly (FGA). A general mRNA compacting method has been demonstrated to fold long mRNA strands into compact mRNA particles, which was subsequently served as the amphiphilic frames to guide the assembly of phospholipid through hydrophobic interaction. We have also demonstrated high mRNA encapsulation efficiency, good stability and intracellular delivery capability of our mRNA-LNPs, which is expected as a promising tool in mRNA therapeutics and vaccines.

Effect of compaction pressure on cold compaction of AA2024 swarf generated during milling operation

The solid-state recycling of aluminium swarf is a promising alternative to the conventional practice of remelting, which can lead to the loss of aluminium. The compaction process is an important step in the solid-state recycling of aluminium swarf. This study investigated the effect of cold compaction pressure on the material behaviour, density, and microstructure of compacted AA2024 machining swarf. The milling swarf was initially cleaned and chemical composition analysis was carried out. Morphology of swarf particle exhibited a wavy and straight regions attributable to milling conditions. The swarf then compacted at room temperature for 3 different pressure level viz. 1000, 1500, and 2000 kgf/cm2. The results showed that the density of the compacts increased with the increase in compaction pressure, reaching a value of 85% of the density of AA2024 at a pressure of 2000 kgf/cm2. Microstructure was analysed using scanning electron microscope to understand the bonding at the the swarf-swarf particle boundary. Vickers hardness results indicated that the hardness values of the compacted specimens also increased slightly with increasing compaction pressure. The overall combination of factors viz. plastic deformation, reorientation, rupturing of oxide layers, and mechanical interlocking contributes to the strength and compaction of swarf particles when subjected to higher compaction pressure used in this study. Further studies are in progress to improve the densification of the compacted specimens and to evaluate their suitability for extrusion applications.

Investigation and Improvement of the Pressure Control in Si Anode Based Solid-State Batteries

Solid state batteries (SSBs) are promising next generation propulsion for electric vehicles due to their improved safety, high gravimetric and volumetric energy densities, and increased reliability. Silicon is one of the limited choices for the anode material for the SSBs due to its high applicable capacity, low operating potential and natural abundance. However, significant challenges remain for the commercialization of Si anode based SSBs, including the insufficient operational and calendar life, requirement of high stack pressure for operation, and inadequate fast charge capability.Almost each of the technical challenges associated with Si anode is entangled with the volume change of Si during charging and discharging. Si possesses high lithium storage capacity because it can form various LixSiy compounds upon lithiation. For example, when 3.75 moles of Li+ is added to 1 mole of Si, the compound Li15Si4 is formed, which gives a capacity of 3578 mAh/gSi. What accompanies this is a considerable volume expansion (e.g., 280% increase for Li15Si4), resulting from the reorganization of the compound crystals. Assuming an anode that initially composes of perfectly compacted Si particles, this volume expansion translates to a 56% increase in the thickness of the Si anode. In a practical SSB, the real thickness variation in the Si anode is expected to be smaller because of the architecture design of the anode. Nonetheless, this volume change in Si creates many problems, including the Si particle pulverization, delamination of electrode from the current collector and electrolyte separator, loss of electronic and ion conductions in the electrode, among others. To maintain the electric contact in Si anode based SSBs, high stack pressures, from several MPa to several tens of MPa, are normally applied.In this work, we carefully measure the real-time stack pressure in a specially designed setup. The stress-strain characteristics of Si anode based SSBs during operation, including the stack pressure spike and the degradation of the average stack pressure, is studied and correlated with the Si anode structure changes. Furthermore, different measures, including external and internal ones, are explored to improve the cell pressure control. The external measures include selecting an appropriate spring and using a mechanical buffer layer, while the internal measure refers to an elastic current collector design. As a result, a better SSB pressure control is obtained. More importantly, a reduction of the stack pressure significantly below 10 MPa without compromising the cell performance is achieved.

An approach of geological mapping and geotechnical investigation: Case study from the Lalitpur Metropolitan City, Nepal

Urbanization is rapidly growing throughout the world, especially in the least developed and developing countries necessitating proper land use planning. However, the lack of sufficient study has created the possibility of unprecedented geohazards. In this study, a detailed geological and engineering geological mapping along with the geotechnical analysis of soils and sediments from the Bhainsepati–Pharsidol area of Lalitpur District has been carried out. Detailed geological maps and geological cross-sections were prepared on the scale of 1:25,000 following the most adopted stratigraphy of central Nepal for both hard rocks and Quaternary deposits. Two mappable geological units like the Tistung Formation and the Chandragiri Limestone of the Phulchauki Group are found within the hard rock succession at the study area’s hill sections. Similarly, the Quaternary succession is mapped into the Lukundol Formation and the Chapagaon Terrace deposits of Kathmandu Valley sediments from older to younger succession respectively. There is a distinct erosional unconformity between the rocks of the Phulchauki Group and the Quaternary Valley sediments. A kinematic analysis of discontinuities developed in the rocks was carried out in the rock slopes found in the area. Both field and laboratory analyses of soil samples were carried out for the representative samples. The laboratory tests include moisture content, specific gravity, particle size distribution, soil consistency, compaction, and consolidation properties. Finally, an engineering geological map was prepared on the same scale as geological mapping showing the details of the distribution of geo-materials. This study is expected to be valuable to make proper land-use decisions for town planning and developmental activities in the rapidly growing city of Nepal.

Measurement report: New insights into the mixing structures of black carbon on the eastern Tibetan Plateau – soot redistribution and fractal dimension enhancement by liquid–liquid phase separation

Abstract. Black carbon (BC; i.e. soot) absorbs radiation and contributes to glacier retreat over the Tibetan Plateau (TP). A lack of comprehensive understanding of the actual mixing state leads to large controversies in the climatic simulation of soot over the TP. In this study, ground-based sampling, electron microscopy analyses, and theoretical calculations were used to investigate the interactions among the liquid–liquid phase separation (LLPS), soot redistribution in secondary particles, and fractal dimension (Df) of soot particles on the eastern rim of the TP. We found that more than half of the total analysed particles were soot-containing particles. One-third of soot-containing particles showed a core shell structure that probably formed the LLPS phenomenon after long-range transport. Particle size and the ratio of organic coating thickness to soot size are two of the major possible factors that likely induce soot redistribution between organic matter and inorganic aerosols in individual particles. The Df sequence is ranked as externally mixed soot (1.79±0.09)< sulfate-coated soot (1.84±0.07)< organic-coated soot (1.95±0.06). We concluded that the soot redistribution process promoted the morphological compaction of soot particles. This study indicates that soot-containing particles experienced consistent ageing processes that induced a more compact morphology and soot redistribution in the LLPS particles on the remote eastern rim of the TP. Understanding the microscopic changes in aged soot particles could further improve the current climate models and evaluations of BC's radiative impacts on the eastern TP and similar remote air.

Geotechnical and Geochemical Properties of Residual and Termite Reworked Soils within the Premises of the Polytechnic Ibadan, Southwestern Nigeria

Three representative samples each from residual and termite reworked soils were collected within the premises of The Polytechnic Ibadan, southwestern Nigeria. Their suitability for construction purposes was determined by assessing their geotechnical and geochemical properties. Geotechnical tests carried out include moisture content, specific gravity, Atterberg limits, particle size distribution, compaction, UCS test and CBR. AAS was used to analyze the oxides composition of the soils. Both soil types were classified as low – intermediate plasticity clays with liquid limit between 25.5%-43.1%. The CBR values ranged from 80% – 85% and 20% – 50% for termite reworked soils and residual soils respectively. UCS ranged from 212.1KPa – 226.3 KPa and 191.7KPa – 200.0 KPa for the termite reworked and residual soils respectively. The OMC and MDD values for termite reworked soil ranged from 5.8% – 8.4% and 1968 kg/m3 – 2020kg/m3 respectively and between 12% – 15.2% and 1800 kg/m3-1940 kg/m3 for residual soils. Geochemistry result shows that the termite reworked soils contained a mean of 60.1% SiO2, 31.05% Al2O3, 1.7% CaO and 4.9% Fe2O3 while the residual soils contained a mean of 59.8% SiO2, 28% Al2O3, 1.6% CaO and 4.6% Fe2O3. This accounts for the better geotechnical properties exhibited by the termite reworked soils.

Porous Dust Particles in Protoplanetary Disks: Application to the HL Tau Disk

Dust particle sizes constrained from dust continuum and polarization observations by radio interferometry are inconsistent by at least an order of magnitude. Motivated by porous dust observed in small solar system bodies (e.g., from the Rosetta mission), we explore how the dust particle’s porosity affects the estimated particle sizes from these two methods. Porous particles have lower refractive indices, which affect both opacity and polarization fraction. With weaker Mie interference patterns, the porous particles have lower opacity at millimeter wavelengths than the compact particles if the particle size exceeds several hundred microns. Consequently, the inferred dust mass using porous particles can be up to a factor of six higher. The most significant difference between compact and porous particles is their scattering properties. The porous particles have a wider range of particle sizes with high linear polarization from dust self-scattering, allowing millimeter- to centimeter-sized particles to explain polarization observations. With a Bayesian approach, we use porous particles to fit HL Tau disk’s multiwavelength continuum and millimeter-polarization observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Very Large Array (VLA). The moderately porous particles with sizes from 1 mm–1 m can explain both continuum and polarization observations, especially in the region between 20 and 60 au. If the particles in HL Tau are porous, the porosity should be from 70%–97% from current polarization observations. We also predict that future observations of the self-scattering linear polarization at longer wavelengths (e.g., ALMA B1 and ngVLA) have the potential to further constrain the particle’s porosity and size.

Observed Polarized Scattered Light Phase Functions of Planet-forming Disks

Abstract Dust particles are the building blocks from which planetary bodies are made. A major goal of studies of planet-forming disks is to constrain the properties of dust particles and aggregates in order to trace their origin, structure, and the associated growth and mixing processes in the disk. Observations of the scattering and/or emission of dust in a location of the disk often lead to degenerate information about the kinds of particles involved, such as the size, porosity, or fractal dimensions of aggregates. Progress can be made by deriving the full (polarizing) scattering phase function of such particles at multiple wavelengths. This has now become possible by careful extraction from scattered light images. Such an extraction requires knowledge about the shape of the scattering surface in the disk, and we discuss how to obtain such knowledge as well as the associated uncertainties. We use a sample of disk images from observations with the Very Large Telescope/SPHERE to, for the first time, extract the phase functions of a whole sample of disks with broad phase-angle coverage. We find that polarized phase functions come in two categories. Comparing the extracted functions with theoretical predictions from rigorous T-Matrix computations of aggregates, we show that one category can be linked back to fractal, porous aggregates, while the other is consistent with more compact, less porous aggregates. We speculate that the more compact particles become visible in disks where embedded planets trigger enhanced vertical mixing.

Structural basis for high-order complex of SARNP and DDX39B to facilitate mRNP assembly

mRNA in eukaryotic cells is packaged into highly compacted ribonucleoprotein particles (mRNPs) in the nucleus and exported to the cytoplasm for translation. mRNP packaging and export require the evolutionarily conserved transcription-export (TREX) complex. TREX facilitates loading of various RNA-binding proteins on mRNA through the action of its DDX39B subunit. SARNP (Tho1 [transcriptional defect of Hpr1 by overexpression 1] in yeast) is shown to interact with DDX39B and affect mRNA export. The molecular mechanism of how SARNP recognizes DDX39B and functions in mRNP assembly is unclear. Here, we determine the crystal structure of a Tho1/DDX39B/RNA complex, revealing a multivalent interaction mediated by tandem DDX39B interacting motifs in SARNP/Tho1. The high-order complex of SARNP and DDX39B is evolutionarily conserved, and human SARNP can engage with five DDX39B molecules. RNA sequencing (RNA-seq) from SARNP knockdown cells shows the most affected RNAs in export are GC rich. Our work suggests the role of the high-order SARNP/DDX39B/RNA complex in mRNP assembly and export.

Laboratory study and constitutive modeling of time-dependent properties of a naturally filled discontinuity

Time-dependent properties of naturally filled discontinuities play a critical role in ensuring the long-term stability of tunnels. This study developed a novel sampling method to prepare samples of naturally filled discontinuities, which were then subjected to shear creep tests under varying normal stresses. The time-dependent properties, including creep deformation, instantaneous deformation, steady-state creep rate, and long-term strength, were carefully analyzed. The results showed an exponential increase in cumulative creep deformation and steady-state creep rate with the augmentation of shear stress. Notably, under lower normal stress (0.2 MPa), the local compaction and rotation of stone particles within the fillers of the discontinuity samples lead to a reduction in creep deformation. Drawing on the experimental results, a new rheological element based on the Kachanov–Rabotnov creep damage theory was proposed. By incorporating this nonlinear element in series with the classical Burgers model, a constitutive creep model was established to describe the three creep stages of naturally filled discontinuities. The presented experimental data, and the developed creep model, can serve as valuable references for ensuring the long-term stability and safety of tunnels traversing through discontinuities.

Densification of nanocrystalline hydroxyapatite powder via sintering: enhancing mechanical properties for biomedical applications

The effect of compaction load, sintering temperature and soaking time on the sinter-ability and densification of Nano crystalline hydroxyapatite (HA) was assessed. The compaction and sinter-ability of HA particles was done at three different compaction loads and temperatures ranging from 1 ton to 5 ton and 850 °C to 1250 °C, respectively. Compaction of the green pellets was best achieved at 5-ton compaction load and it’s percent green densification was up to 50% of the theoretical density of HA (3.16g cm−3). For sintered density, the best results were achieved at a temperature of 1250 °C and a compaction load of 1 ton which were 98% of the theoretical density. Soaking time at these sintering temperatures was varied between 1 and 3 h and was found that with the variation of soaking time from 3 h to 1 h, the sintered density decreased tremendously at 850 °C from 85% to 50% whereas at higher temperatures the decrease in density was only 4 to 6%. The maximum hardness of 625 (±28) HV1 was obtained for HA sintered at 1250 °C with a soaking time of 3 h. Phase analyses were carried out using an x-ray diffractometer. The HA phase was stable even at the highest sintering temperature of 1250 °C and did not decompose into α tri-calcium phosphate (TCP) and β TCP. The grain size was reduced by decreasing soaking time and lowering sintering temperature.

Drying of Compact and Porous NCM Cathode Electrodes in Different Multilayer Architectures: Influence of Layer Configuration and Drying Rate on Electrode Properties

Porous, nanostructured particles ensure the wetting of electrolyte up to the particle core and shortened diffusion paths, which is relevant not only for lithium‐ion batteries but also for postlithium systems like sodium‐ion batteries. The porous structure leads to a high C‐rate capability. However, compared to conventional compact NCM, porous NCM shows a reduced adhesion force but no or only slight negative influence on C‐rate capability by binder migration at higher drying rates. Herein, a multilayer concept is used to increase the adhesion force with equal or better electrochemical performance compared to single‐layer electrodes. Compact particles of high volumetric energy density and porous particles with high C‐rate capability are combined in a simultaneously coated multilayer electrode. Multilayers with compact NCM toward the current collector and porous NCM with reduced binder content toward the separator side show an about 16‐times higher adhesion force at lower drying rate and an about ten‐times higher adhesion force at increased drying rate compared to electrodes produced of porous NCM only. The specific discharge capacity of the multilayers is increased by 88% at the lower and 67% at the higher drying rate for a discharge rate of 3C compared to a single layer with compact NCM.

Nuclear mRNPs are compact particles packaged with a network of proteins promoting RNA-RNA interactions.

Messenger RNAs (mRNAs) are at the center of the central dogma of molecular biology. In eukaryotic cells, these long ribonucleic acid polymers do not exist as naked transcripts; rather, they associate with mRNA-binding proteins to form messenger ribonucleoprotein (mRNP) complexes. Recently, global proteomic and transcriptomic studies have provided comprehensive inventories of mRNP components. However, knowledge of the molecular features of distinct mRNP populations has remained elusive. We purified endogenous nuclear mRNPs from Saccharomyces cerevisiae by harnessing the mRNP biogenesis factors THO and Sub2 in biochemical procedures optimized to preserve the integrity of these transient ribonucleoprotein assemblies. We found that these mRNPs are compact particles that contain multiple copies of Yra1, an essential protein with RNA-annealing properties. To investigate their molecular and architectural organization, we used a combination of proteomics, RNA sequencing, cryo-electron microscopy, cross-linking mass spectrometry, structural models, and biochemical assays. Our findings indicate that yeast nuclear mRNPs are packaged around an intricate network of interconnected proteins capable of promoting RNA-RNA interactions via their positively charged intrinsically disordered regions. The evolutionary conservation of the major mRNA-packaging factor (yeast Yra1 and Aly/REF in metazoans) points toward a general paradigm governing nuclear mRNP packaging.

Mechanical Characterization of Coarse-Grained Waste Rocks Using Large-Scale Triaxial Tests and Neuroevolution of Augmenting Topologies

Mining operations produce large quantities of waste rocks, which are usually disposed of in waste rock piles, but can also be valorized in mine haul roads. The engineering performance of these haul roads significantly depends on the mechanical characteristics of the materials used for the construction. However, available experimental studies on coarse-grained waste rocks are relatively limited, mainly because of their large grain size and the scarcity of adapted testing equipment. In this study, a series of repeated load and monotonic triaxial tests (specimens 300 mm in diameter and 600 mm in height) were carried out to evaluate the resilient modulus, permanent deformation, and shear strength of coarse-grained waste rocks (up to 60 mm in diameter) with different gradations. Results showed that an increasing in maximum particle size and compaction effort resulted in a larger resilient modulus and shear strength and smaller permanent deformation. The optimal gravel-to-sand ratio to maximize resilient modulus and shear strength was around 5. Permanent strain was relatively constant when the gravel-to-sand ratio was between 1 and 5, but it decreased significantly when the ratio increased to 8. The impact of fines content and water content on the mechanical properties was relatively limited. Also, the MR-θ model and Rahman and Erlingsson model showed good fitting performance for resilient modulus and permanent strain, respectively. Finally, neuroevolution of augmenting topologies (NEAT) was used to develop a machine learning model for predicting the resilient modulus of waste rocks, based on 265 data sets. The model showed reliable accuracy, simple topology, and high generalizability capacity. The findings described in this article should be beneficial for the valorization of waste rocks in pavement engineering.

Analysis of Dispersivity in Marine Clays of Cartagena de Indias, Colombia

This study assessed the dispersivity of soils extracted from the northern region of Cartagena de Indias (Colombia) using the pinhole test, crumb test, and chemical–microstructural analyses. Dispersive soils are susceptible to erosive phenomena upon contact with water, yet they have not been adequately characterized in the city. To evaluate the dispersivity degree of different deformed and undisturbed soil samples, soil characterization tests included particle size analysis, chemical composition, Atterberg limits, specific gravity, and compaction. The results showed that the soils are highly plastic clays (i.e., CH) with a slight to moderate dispersivity level (i.e., ND3) according to the pinhole test and a moderate degree of dispersivity confirmed by the crumb test. The extracted soil sample sodium levels ranged from 0.72% to 1.94%, and the soil had an optimal moisture content of 26% and a maximum apparent dry unit weight of 13.87 kN/m3. According to standards and results, Cartagena de Indias’s studied marine clays are unsuitable for civil construction due to the degree of uncertainty in their behavior.

Facile and Robust Production of Ultrastable Micrometer-Sized Foams

Stable foams that can resist disproportionation for extended periods of time have important applications in a wide range of technological and consumer materials. Yet, legislative initiatives limit the range of surface active materials that can be used for environmental impact reasons. There is a need for technologies to efficiently produce multiphase materials using more eco-friendly components, such as particles, and for which traditional thermodynamics-based processing routes are not necessarily efficient enough. This work describes an innovative foaming technology that can produce ultrastable Pickering-Ramsden foams, with bubbles of micrometer-sized dimensions, through pressure-induced particle densification. Specifically, aqueous nanosilica-stabilized foams are produced by foaming a suspension at subatmospheric pressures, allowing for adsorption of the particles onto large bubbles. This is followed by an increase back to atmospheric pressure, which induces bubble shrinkage and compresses the adsorbed particle interface, forming a strong elastoplastic network that provides mechanical resistance against disproportionation. The foam’s interfacial mechanical properties are quantified to predict the range of processing conditions needed to produce permanently stable foams, and a general stability criterion is derived by considering the interfacial rheological properties under slow, unidirectional compression. Foams that are stable against disproportionation are characterized by interfaces whose mechanical resistance to compressive deformations can withstand their tendency to minimize the interfacial stress by reducing their surface area. Our ultrastable nanosilica foams are tested in real-life applications by introducing them into concrete. In comparison to other commercial air entrainers, our microfoam improves concrete’s freeze–thaw resistance while supplying higher material strength, providing an economically attractive, industrially scalable, and durable alternative for use in real-life applications involving cementitious materials. The applicability of our stability criterion to other rheologically complex interfaces and the versatile nature of our foaming technology enables usage for a broad class of materials, beyond the construction industry.