Colloidal Behavior Research Articles

Molecular Dynamics Simulation Studies of Bile, Bile Salts, Lipid-Based Drug Formulations, and mRNA–Lipid Nanoparticles: A Review

Lipid-based formulation (LBF) is an effective approach for delivering hydrophobic drugs into the systemic circulation by oral administration. However, much of the physical detail regarding the colloidal behavior of LBFs and their interactions with the contents of the gastrointestinal (GI) environment is not well characterized. Recently, researchers have started to use molecular dynamics (MD) simulations to investigate the colloidal behavior of LBF systems and their interactions with bile and other materials present in the GI tract. MD is a computational method, based on classical mechanics, that simulates the physical movements of atoms and provides atomic-scale information that cannot easily be retrieved using experimental investigations. MD can provide insight into assist the development of drug formulations in a cost and time-effective manner. This review summarizes the application of MD simulation to the study of bile, bile salts, and LBFs and their behavior within the GI environment and also discusses MD simulations of lipid-based mRNA vaccine formulations.

Modulation of Colloidal Assembly Behavior Enables Printable Low‐Dimensional Perovskite Photovoltaics

AbstractThe multiple quantum wells (QWs) distribution in low‐dimensional perovskite films hinders charge transport due to the fundamental difficulty of controlling crystal growth from precursor solutions, yielding poorly homogeneous low‐dimensional perovskite solar cells (PSCs), especially in upscaling fabrication. Here, efficient low‐dimensional PSCs are realized by modulating the colloidal assembly behavior in the precursor solution to induce intermediate structures. In combination with in situ liquid time‐of‐flight secondary ion mass spectrometry, the assembly behavior of organic cations involved lead iodide‐dominated colloidal soft framework is visualized by investigating the precursor species differences under hydrogen bonding interactions. Subsequently, solid‐state reactions emerge and the formamidine (FA)‐based perovskite films exhibit significantly suppressed multiple QWs distribution. Encouragingly, the FA device (n=9, by meniscus‐assisted coating) achieves a power conversion efficiency (PCE) of 20.28 % for a size of 0.04 cm2 and a PCE of 15.35 % for a mini‐module of 16.94 cm2 with superior stability.

Modulation of Colloidal Assembly Behavior Enables Printable Low-Dimensional Perovskite Photovoltaics.

The multiple quantum wells (QWs) distribution in low-dimensional perovskite films hinders charge transport due to the fundamental difficulty of controlling crystal growth from precursor solutions, yielding poorly homogeneous low-dimensional perovskite solar cells (PSCs), especially in upscaling fabrication. Here, efficient low-dimensional PSCs are realized by modulating the colloidal assembly behavior in the precursor solution to induce intermediate structures. In combination with in situ liquid time-of-flight secondary ion mass spectrometry, the assembly behavior of organic cations involved lead iodide-dominated colloidal soft framework is visualized by investigating the precursor species differences under hydrogen bonding interactions. Subsequently, solid-state reactions emerge and the formamidine (FA)-based perovskite films exhibit significantly suppressed multiple QWs distribution. Encouragingly, the FA device (n = 9, by meniscus-assisted coating) achieves a power conversion efficiency (PCE) of 20.28% for a size of 0.04 cm2 and a PCE of 15.35% for a mini-module of 16.94 cm2 with superior stability.

Photoactive and Intrinsically Fuel Sensing Metal-Organic Framework Motors for Tailoring Collective Behaviors of Active-Passive Colloids.

Microorganisms display nonequilibrium predator-prey behaviors, such as chasing-escaping and schooling via chemotactic interactions. Even though artificial systems have revealed such biomimetic behaviors, switching between them by control over chemotactic interactions is rare. Here, a spindle-like iron-based metal-organic framework (MOF) colloidal motor which self-propels in glucose and H2 O2 , triggered by UV light is reported. These motors display intrinsic UV light-triggered fuel-dependent chemotactic interactions, which are used to tailor the collective dynamics of active-passive colloidal mixtures. In particular, the mixtures of active MOF motors with passive colloids exhibit distinctive "chasing-escaping" or "schooling" behaviors, depending on glucose or hydrogen peroxide being used as the fuel. The transition in the collective behaviors is attributed to an alteration in the sign of ionic diffusiophoretic interactions, resulting from a change in the ionic clouds produced. This study offers a new strategy on tuning the communication between active and passive colloids, which holds substantial potentials for fundamental research in active matter and practical applications in cargo delivery, chemical sensing, and particle segregation.

The Relationship between Gelation Behavior and the Amount of Polymer Dose per Silica Surface Area of "Shake-Gels" Consisting of Silica Nanoparticles and Poly(Ethylene Oxide).

The understanding and control of the rheological behaviors of colloids and polymer mixtures is an important issue for scientific interests and industrial applications. Aqueous mixed suspensions of silica nanoparticles and poly(ethylene oxide) (PEO) under certain conditions are interesting systems called "shake-gels", whose states vary reversibly between sol-like and gel-like under repeated shaking and being left to stand. Previous studies have indicated that the amount of PEO dose per silica surface area (Cp) is a crucial parameter for the formation of shake-gels and the relaxation time from gel-like to sol-like states. However, the relationship between the gelation dynamics and the Cp values has not been fully investigated. To determine how the gelation dynamics are affected by the Cp, we measured the time taken for silica and PEO mixtures to gelate from the sol-like to gel-like states as a function of the Cp under different shear rates and flow types. Our results show that the gelation time decreased with increasing shear rates and depended on the Cp values. Moreover, the minimum gelation time was found around a certain Cp (=0.03 mg/m2) for the first time. The finding suggests that there is an optimum Cp value at which the bridging of silica nanoparticles using PEO is significant, and thus, the shake-gels and stable gel-like states are most likely to form.

Capillary Assembly of Anisotropic Particles at Cylindrical Fluid-Fluid Interfaces.

The unique behavior of colloids at liquid interfaces provides exciting opportunities for engineering the assembly of colloidal particles into functional materials. The deformable nature of fluid-fluid interfaces means that we can use the interfacial curvature, in addition to particle properties, to direct self-assembly. To this end, we use a finite element method (Surface Evolver) to study the self-assembly of rod-shaped particles adsorbed at a simple curved fluid-fluid interface formed by a sessile liquid drop with cylindrical geometry. Specifically, we study the self-assembly of single and multiple rods as a function of drop curvature and particle properties such as shape (ellipsoid, cylinder, and spherocylinder), contact angle, aspect ratio, and chemical heterogeneity (homogeneous and triblock patchy). We find that the curved interface allows us to effectively control the orientation of the rods, allowing us to achieve parallel, perpendicular, or novel obliquely orientations with respect to the cylindrical drop. In addition, by tuning particle properties to achieve parallel alignment of the rods, we show that the cylindrical drop geometry favors tip-to-tip assembly of the rods, not just for cylinders, but also for ellipsoids and triblock patchy rods. Finally, for triblock patchy rods with larger contact line undulations, we can achieve strong spatial confinement of the rods transverse to the cylindrical drop due to the capillary repulsion between the contact line undulations of the particle and the pinned contact lines of the sessile drop. Our capillary assembly method allows us to manipulate the configuration of single and multiple rod-like particles and therefore offers a facile strategy for organizing such particles into useful functional materials.

Silica-Functionalized Nanolimes for the Conservation of Stone Heritage.

The relatively recent development of nanolimes (i.e., alcoholic dispersions of Ca(OH)2 nanoparticles) has paved the way for new approaches to the conservation of important art works. Despite their many benefits, nanolimes have shown limited reactivity, back-migration, poor penetration, and lack of proper bonding to silicate substrates. In this work a novel solvothermal synthesis process is presented by which extremely reactive nanostructured Ca(OH)2 particles are obtained using calcium ethoxide as the main precursor species. Moreover, it is demonstrated that this material can be easily functionalized with silica-gel derivatives under mild synthesis conditions, thereby preventing particle growth, increasing total specific surface area, enhancing reactivity, modifying colloidal behavior, and functioning as self-integrated coupling agents. Additionally, the formation of calcium silicate hydrate (CSH) nanocement is promoted by the presence of water, resulting in optimal bonding when applied to silicate substrates, as evidenced by the higher reinforcement effect produced on treated Prague sandstone specimens as compared to those consolidated with nonfunctionalized commercial nanolime. The functionalization of nanolimes is not only a promising strategy for the design of optimized consolidation treatments for the cultural heritage, but may also have important implications for the development of advanced nanomaterials for building, environmental, or biomedical applications.

Experimental study of montmorillonite erosion in low ionic strength water under stagnant and flow conditions in artificial fractures

Compacted bentonite has been proposed as a buffer material in several geological repository concepts for high-level radioactive waste. However, in dilute groundwater, bentonite, especially when dominated by Na-montmorillonite, has been found to be susceptible to erosion and excessive mass loss may compromise the safety of the repository. Herein, results from twelve erosion tests with either flowing or stagnant aqueous solutions, performed with custom-designed artificial fractures made of Poly(methyl methacrylate) are reported. The fracture aperture was 0.1 mm in all tests. Na-montmorillonite or an equal mix by weight of Na- and Ca-montmorillonite were employed. Eleven of the tests were performed with the fracture being vertical, and in one test the fracture was horizontal. The transparent artificial fracture setup allowed monitoring of the expansion of the montmorillonite into the fracture. In all but one test, the diameter reached a limit value, normally within one month of the start of the test. The final diameters varied between 5.9 and 8.7 cm and no clear correlation to flow rate, type of montmorillonite or ionic strength could be discerned. The initial diameter of the emplaced clay was 3.5 cm. The erosion was monitored regularly by turbidity measurements. In general, erosion rates decreased with time and were ultimately low enough that an extrapolation or upscaling of the results to repository scale and operating time would imply a total erosion below the critical value for repository safety. This was the case for all vertical fractures, regardless of montmorillonite type and ionic strength of the aqueous solution. The observed decrease in erosion rates was not due to depletion of montmorillonite at the source because at the end of each test 90% or more of the montmorillonite remained. Further, the ionic strengths were below the critical coagulation concentration, hence gelation cannot provide an explanation to the reduction in erosion rates. Finally, the diameters of the extruded montmorillonite reached the limit while the erosion rates continued to decrease. Consequently, the observed limited expansion was not due to a steady state between erosion and swelling. Rather, the expansion behaviour suggests the presence of frictional forces between the montmorillonite and the fracture walls. The results from this study are beyond the current understanding of montmorillonite colloid behaviour and cannot be explained by existing models.

Complex Dispersion of Detonation Nanodiamond Revealed by Machine Learning Assisted Cryo-TEM and Coarse-Grained Molecular Dynamics Simulations.

Understanding the polydispersity of nanoparticles is crucial for establishing the efficacy and safety of their role as drug delivery carriers in biomedical applications. Detonation nanodiamonds (DNDs), 3-5 nm diamond nanoparticles synthesized through detonation process, have attracted great interest for drug delivery due to their colloidal stability in water and their biocompatibility. More recent studies have challenged the consensus that DNDs are monodispersed after their fabrication, with their aggregate formation poorly understood. Here, we present a novel characterization method of combining machine learning with direct cryo-transmission electron microscopy imaging to characterize the unique colloidal behavior of DNDs. Together with small-angle X-ray scattering and mesoscale simulations we show and explain the clear differences in the aggregation behavior between positively and negatively charged DNDs. Our new method can be applied to other complex particle systems, which builds essential knowledge for the safe implementation of nanoparticles in drug delivery.

Solid-amorphous transition is related to the waterlike anomalies in a fluid without liquid-liquid phase transition.

The most accepted origin for the water anomalous behavior is the phase transition between two liquids (LLPT) in the supercooled regime connected to the glassy first order phase transition at lower temperatures. Two length scale potentials are an effective approach that has long been employed to understand the properties of fluids with waterlike anomalies and, more recently, the behavior of colloids and nanoparticles. These potentials can be parameterized to have distinct shapes, as a pure repulsive ramp, such as the model proposed by de Oliveira et al. [J. Chem. Phys. 124, 64901 (2006)]. This model has waterlike anomalies despite the absence of LLPT. To unravel how the waterlike anomalies are connected to the solid phases, we employ molecular dynamics simulations. We have analyzed the fluid-solid transition under cooling, with two solid crystalline phases, BCC and HCP, and two amorphous regions being observed. We show how the competition between the scales creates an amorphous cluster in the BCC crystal that leads to amorphization at low temperatures. A similar mechanism is found in the fluid phase, with the system changing from a BCC-like to an amorphous-like structure in the point where a maxima in kT is observed. With this, we can relate the competition between two fluid structures with the amorphous clusterization in the BCC phase. These findings help to understand the origins of waterlike behavior in systems without the liquid-liquid critical point.

Role of the Protein Corona in the Colloidal Behavior of Microplastics.

Microparticles of polyethylene and polypropylene are largely found in aquatic environments because they are the most produced and persistent plastic materials. Once in biological media, they are covered by a layer of molecules, the so-called corona, mostly composed of proteins. A yeast protein extract from Saccharomyces cerevisiae was used as a protein system to observe interactions in complex biological media. Proteins, acting as surfactants and providing hydrophilic surfaces, allow the dispersion of highly hydrophobic particles in water and stabilize them. After 24 h, the microplastic quantity was up to 1 × 1011 particles per liter, whereas without protein, no particles remained in solution. Label-free imaging of the protein corona by synchrotron radiation deep UV fluorescence microscopy (SR-DUV) was performed. In situ images of the protein corona were obtained, and the adsorbed protein quantity, the coverage rate, and the corona heterogeneity were determined. The stability kinetics of the microplastic suspensions were measured by light transmission using a Turbiscan analyzer. Together, the microscopic and kinetics results demonstrate that the protein corona can very efficiently stabilize microplastics in solution provided that the protein corona quality is sufficient. Microplastic stability depends on different parameters such as the particle's intrinsic properties (size, density, hydrophobicity) and the protein corona formation that changes the particle wettability, electrostatic charge, and steric hindrance. By controlling these parameters with proteins, it becomes possible to keep microplastics in and out of solution, paving the way for applications in the field of microplastic pollution control and remediation.

Relating mechanistic fate with spatial positioning for colloid transport in surface heterogeneous porous media

Hypotheses: The transport behavior of colloids in subsurface porous media is altered by surface chemical and physical heterogeneities. Understanding the mechanisms involved and distribution outcomes is crucial to assess and control groundwater contamination. The multi-scale processes that broaden residence time distribution for particles in the medium are here succinctly described with an upscaling model. Experiments/model: The spatial distribution of silver particles along glass bead-packed columns obtained from X-ray micro-computed tomography and a mechanistic upscaling model were used to study colloid retention across interface-, collector-, pore-, and Darcy-scales. Simulated energy profiles considering variable colloid-grain interactions were used to determine collector efficiencies from particle trajectories via full force-torque balance. Rate coefficients were determined from collector efficiencies to parameterize the advective–dispersive-reactive model that reports breakthrough curves and depth profiles. Findings: Our results indicate that: (i) with surface heterogeneity, individual colloid-grain interactions are non-unique and span from repulsive to attractive extremes; (ii) experimentally observed spatial positioning of retention at grain-water interfaces and grain-to-grain contacts is governed respectively by mechanistic attachment to the grain surface and retention without contact at rear-flow stagnation zones, and (iii) experimentally observed non-monotonic retention profiles and heavy-tailed breakthrough curves can be modeled with explicit implementation of heterogeneity at smaller scales.

The Colloidal Properties of Nanocellulose.

Nanocelluloses are anisotropic nanoparticles of semicrystalline assemblies of glucan polymers. They have great potential as renewable building blocks in the materials platform of a more sustainable society. As a result, the research on nanocellulose has grown exponentially over the last decades. To fully utilize the properties of nanocelluloses, a fundamental understanding of their colloidal behavior is necessary. As elongated particles with dimensions in a critical nanosize range, their colloidal properties are complex, with several behaviors not covered by classical theories. In this comprehensive Review, we describe the most prominent colloidal behaviors of nanocellulose by combining experimental data and theoretical descriptions. We discuss the preparation and characterization of nanocellulose dispersions, how they form networks at low concentrations, how classical theories cannot describe their behavior, and how they interact with other colloids. We then show examples of how scientists can use this fundamental knowledge to control the assembly of nanocellulose into new materials with exceptional properties. We hope aspiring and established researchers will use this Review as a guide.

Effect of different aging treatments on the transport of nano-biochar in saturated porous media

Widely used for soil amendment, carbon sequestration, and remediation of contaminated soils, biochars (BCs) inevitably produce a large number of nanoparticles with relatively high mobility. Geochemical aging alters chemical structure of these nanoparticles and thus affect their colloidal aggregation and transport behavior. In this study, the transport of ramie derived nano-BCs (after ball-milling) was investigated by different aging treatments (i.e., photo (PBC) and chemical aging (NBC)) as well as the managing BC under different physicochemical factors (i.e., flow rates, ionic strengths (IS), pH, and coexisting cations). Consequences of the column experiments indicated aging promoted the mobility of the nano-BCs. Compared to the nonaging BC, consequences of spectroscopic analysis demonstrated the aging BCs exhibited a number of tiny corrosion pores. Both of these aging treatments contribute to a more negative zeta potential and a higher dispersion stability of the nano-BCs, which is caused by the abundance of O-functional groups. Also the specific surface area and mesoporous volume of both aging BCs increased significantly, with the increase being more pronounced for NBC. The breakthrough curves (BTCs) obtained for the three nano-BCs were modelled by the advection-dispersion equation (ADE), which included first-order deposition and release terms. The ADE revealed high mobility of aging BCs, which meant their retention in saturated porous media was reduced. This work contributes to a comprehensive understanding of the transport of aging nano-BCs in the environment.

Unusual yield stress behaviour of silica suspensions in the presence of maleic and fumaric acids: Composite precipitate bridging

There are many instances of unusual colloidal suspension behaviour being reported. This study provided a new approach to finding the cause of one such behaviour helping to alleviate biofouling and scaling problems. The yield stress-pH behaviour of silica suspensions in the presence of maleate and fumarate is different depending upon the direction of the step change in the pH employed. In the direction from high to low pH, i.e. 11–2, the suspension displayed a continuous yield stress behaviour down to pH 6. In the opposite direction, the yield stress was small at pH 4–5, absent at pH 8.5 and increased sharply from pH ∼ 9.5. Precipitate bridging is responsible for the yield stress behaviour. At high pH, the precipitates were already well-formed to bridge particles. This was not the case in the low to high pH direction. The precipitates were composite formed by soluble silica, organic acid anion and positively charged metal ions hydrolysis products. Yield stress was observed under the conditions of i) high silica solubility, i.e. at pH > 9 and ii) fumaric or maleic acids being present in significant concentration. The Al(III), Fe(III) and Fe(II) impurities already present in relatively important quantity formed the hydrolysis products upon leaching or solubilisation of the silica. The composite precipitates bridged the silica particles via heterogeneous charge and van der Waals attraction. Their formation is limited by the amount of Al(III), Fe(III) and Fe(II) present and they must be small enough to be in sufficient number to have all the particles in the network bridged. Fumarate played a role in forming and stabilising the small precipitate particles, and enhancing the yield stress. Biofouling and scaling in processes involving this type of composite materials can be mitigated by making sure that a high pH operating environment is avoided.

Advantages of a Millifluidic Approach to the Characterization of Long-Time Solvency Effects on Bulk Asphaltene Precipitation

The colloidal and aggregation behavior of asphaltenes in bulk dispersions is largely dependent on the solvent environment. Increasing the aliphatic fraction in these systems drives the aggregation of asphaltene clusters, leading to precipitation out of the bulk that can result in complications in the oil recovery and refining process. In this work, a millifluidic device is used to characterize the precipitation behavior of two asphaltene subfractions in good and poor solvent conditions to characterize the long-time solvency effects. Advantages to this approach are high discretization of the concentration gradient as well as shorter path lengths, which allow for better resolution of optical measurements in these extremely opaque systems. To measure precipitation, the critical aliphatic volume fraction (CAVF), defined in this work as the highest fraction of aliphatic solvent at which there is no visible precipitation in the sample, functions as a compositional breakpoint between stable and unstable dispersions. Results from this work show that asphaltene dispersions will reach a steady state after long times, on the order of months, of sample aging. Further, precipitation is visible at lower aliphatic fractions than what was determined in experiments using shorter aging times. This demonstrates how long-term effects should be considered when determining the stability of asphaltene dispersions.

Colloidal stability and aggregation behavior of CdS colloids in aquatic systems: Effects of macromolecules, cations, and pH

Redox-dynamic environments such as river floodplains and paddy fields have been demonstrated to be important sources of CdS colloids. To date, the aggregation kinetics of CdS colloids had not yet been studied, and the structure and properties of macromolecules on the interaction between different macromolecules and CdS colloids, as well as the aggregation behavior of CdS colloids are unclear. This study investigated the colloidal stability of CdS colloids in model aqueous systems with various solution chemistry and representative of macromolecules. The results showed that increased electrolyte concentration destabilized CdS colloids by charge screening, with the cationic effect following Ca2+ > Mg2+ > K+ > Na+; Higher solution pH stabilized CdS colloids by raising the critical coagulation concentration from 33 to 56 mM NaCl. Electron microscopy and spectroscopy verified the strong interaction between macromolecules and CdS colloids, and macromolecule adsorbed on the surface of CdS to form a protective layer called “NOM corona”. The interaction between macromolecules and CdS induced distinct aggregation behaviors in NaCl and CaCl2 solutions. The steric repulsion generated by “NOM corona” significantly stabilized CdS colloids in NaCl solution, and the stabilizing order was consistent with the adsorbing capacity of macromolecules on CdS colloids, namely Bovine serum albumin (BSA) > sodium alginate (SA) > calf thymus DNA (DNA) > Suwannee River humic acid (HA). BSA and DNA also inhibited CdS colloids aggregation in the CaCl2 solution due to the balance of steric hindrance, cation bridging, and electrostatic repulsion. For HA and SA, Ca2+ bridging and EDL compression contributed to their destabilization of CdS colloids in CaCl2 solution. Macromolecules concentration affect corona formation that alter stability of CdS colloids. There results showed that the complex influences of solution chemistry and macromolecules on fate and transport of CdS colloids in environment. The findings will help to understand the potential risks of CdS colloids in environment.

Aluminum-induced colloidal destabilization of iron-organic matter nanoaggregates

The structural organization of heterogeneous and multiphase natural aggregates depends on the biophysicochemical conditions prevailing in the environment, with major ions playing a crucial role. In this study, the impact of aluminum (Al) on iron-organic matter (Fe-OM) aggregates was investigated since Al can interact with OM and can be incorporated in Fe-oxyhydroxides or adsorbed on their surface. Mimetic environmental Fe-OM-Al aggregates were synthesized at various [Fe] and [Al] with a constant [OM]. At low [Al + Fe], Fe-OM-Al aggregates exhibit a colloidal behavior. Within the aggregates, Fe is present as Fe(III)-oligomers and ferrihydrite-like nanoparticles whereas Al forms monomers, oligomers and small polymers, all bound to OM. The Al and Fe phases interacted with each other. At high [Fe + Al], the Fe(III)-oligomers and Al monomers/oligomers polymerized which increases the size and quantity of the ferrihydrite-like nanoparticles and Al polymers and then branched out the OM, resulting in a large settling network. The effect of Al on the Fe-OM aggregates structure could also have an impact on the fate of pollutants. The occurrence of Al amorphous hydroxides and the increase in ferrihydrite-like nanoparticles lead to a higher availability of surface reactive sites and subsequently to an increase in the sorption capacity of the Fe-OM aggregates for pollutants that exhibit a greater affinity for minerals than for organics.

The formation of schwertmannite colloids and natural remediation of toxic elements from Shojin River, Hokkaido, Japan

AbstractPassive treatment systems are a sustainable solution to mine drainage remediation, however, clarity lacks in the detailed understanding of the geochemical processes that govern the remediation processes. A study was carried out at Shojin River in Southwest Hokkaido, Japan, which has an acidic pH and is high in Fe, to represent the principal processes that occur in mine drainages of similar characteristics. At Shojin, Fe and S were mined from the Shojingawa mine, after which, wastewater contaminated by toxic elements such as Fe, As and Pb continue to flow from the underground. This wastewater flows through industrial and fishing areas, hence ensuring that the water meets environmental standards is important. In particular, the role of colloidal materials in transporting the toxic elements was investigated by analyzing the distribution of the elements (Fe, As and Pb) in the drainage as the dissolved and colloidal fractions, obtained from micro‐, and ultrafiltration respectively. Iron, particularly schwertmannite colloid formation was observed in the Shojin River system. Itwas present in the dissolved fraction in the wastewater like As, but after mixing with the uncontaminated river water, Fe in the colloid fraction gradually increased toward the downstream. Arsenic trends are similar to those of iron, indicating efficient sequestration by the schwertmannite colloids. Lead is dominantly in the dissolved fraction throughout the drainage and is comparatively less sequestered due to competitive adsorption with As and its pH dependence to be efficiently adsorbed. A detailed observation of the concentration trends suggests that pH 3.1 may efficiently allow colloid formation and subsequently, toxic element sequestration. The behavior of Fe colloids in Shojin River was compared to those of a circum‐neutral drainage system (Ainai mine drainage). The formation of the colloids in the acidic system was limited by the pH range, while colloids formed faster and more abundantly in the circumneutral system. The acidic and circum‐neutral systems are abundant in schwertmannite and ferrihydrite colloids respectively. The colloids in both systems were transported after their formation, however, the colloids in the Shojin (acidic) system were transported further than those of the circumneutral system. Aggregation is observed in both systems which results in a deposition of the colloid aggregates and hence an efficient removal of Fe and As, and minimally, Pb from the mine drainages.

Gold nanoparticle shape dependence of colloidal stability domains.

Controlling the spatial arrangement of plasmonic nanoparticles is of particular interest to utilize inter-particle plasmonic coupling, which allows changing their optical properties. For bottom-up approaches, colloidal nanoparticles are interesting building blocks to generate more complex structures via controlled self-assembly using the destabilization of colloidal particles. For plasmonic noble metal nanoparticles, cationic surfactants, such as CTAB, are widely used in synthesis, both as shaping and stabilizing agents. In such a context, understanding and predicting the colloidal stability of a system solely composed of AuNPs and CTAB is fundamentally crucial. Here, we tried to rationalize the particle behavior by reporting the stability diagrams of colloidal gold nanostructures taking into account parameters such as the size, shape, and CTAB/AuNP concentration. We found that the overall stability was dependent on the shape of the nanoparticles, with the presence of sharp tips being the source of instability. For all morphologies evaluated here, a metastable area was systematically observed, in which the system aggregated in a controlled way while maintaining the colloidal stability. Combining different strategies with the help of transmission electron microscopy, the behavior of the system in the different zones of the diagrams was addressed. Finally, by controlling the experimental conditions with the previously obtained diagrams, we were able to obtain linear structures with a rather good control over the number of particles participating in the assembly while maintaining good colloidal stability.