Colloidal Behavior Research Articles

Effects of the same valence metal cations on the aggregation behavior of PFR

In recent years, phenol-formaldehyde resin (PFR) as a colloid plugging agent was extensively used in enhanced oil recovery. It has been popularly concerned that the influence of environment on the structure, migration and aggregation behavior of PFR. The classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory can explain the interaction potential between particles. However, the classical DLVO cannot explain differences when colloids aggregate in the same valence metal cation solution. In this work, the effects of ion specificity of divalent metal cations (i. e., Mg2 + and Ca2 +) on the aggregation rate, fractal dimension, zeta potential and the critical coagulation concentration (CCC) of PFR were systematically studied by dynamic light scattering experiment, electrophoretic light scattering and spectral turbidimetry. The experimental results showed that metal cations with poor hydration (i. e., Mg2 +) can promote aggregation more than metal cations with good hydration (i. e., Ca2 +). The hydrated differences of ions can be explained quantitatively by the improved DLVO theory introducing Lewis acid-base interaction. This result revealed the important significance of ion specificity in the aggregation behavior of PFR colloids, and made it possible to understand the co-transport process of PFR aggregates and metal cations in reservoirs. Thus, it is possible to precisely control the aggregation rate and the fractal dimension of PFR aggregates.

Palm Lipid Emulsion Droplet Crystallinity and Gastric Acid Stability in Relation to in vitro Bioaccessibility and in vivo Gastric Emptying.

It is poorly understood how the physical state of emulsified triacylglycerol (TAG) alters colloidal behavior in the gastrointestinal tract to modulate lipid digestion and absorption. We, therefore, aimed to investigate the individual and combined effects on fatty acid (FA) bioaccessibility using the dynamic TIM-1 in vitro digestion model and integrate the results with those from a human clinical study. Four 20% oil-in-water emulsions with overlapping particle size distributions contained either partially crystalline solid (palm stearin) or liquid (palm olein) lipid droplets at 37°C and either the colloidally acid-stable Tween 80 (2.2%) or acid-unstable Span 60 (2.5%) emulsifier. Experimental meals were fed to the TIM-1, and jejunal and ileal dialysates were analyzed over 6 h to measure free FA concentration. Cumulative FA bioaccessibility was significantly higher for the liquid stable emulsion compared to all others (p < 0.05), which did not differ (p > 0.05). Emulsified TAG physical state was associated with differences in overall bioaccessibility (higher for liquid state TAG) in the colloidally stable emulsions, but this difference was blunted in droplets susceptible to acidic flocculation. In contrast, human postprandial TAG concentrations did not differ significantly between the emulsions. The discrepancy may relate to differences in in vivo gastric emptying (GE) as evidenced by ultrasonography. When the in vivo differences in GE were accounted for in follow-up TIM-1 experiments, the findings aligned more closely. Cumulative FA bioaccessibility for the liquid stable emulsion no longer differed significantly from the other emulsions, and SU’s bioaccessibility was the lowest, consistent with the in vivo observations. This work highlights the potential for TAG physical state and colloidal stability to interactively alter behavior in the gastrointestinal tract with implications for FA absorption, and the importance of establishing and improving in vitro–in vivo correlations in food-nutrition research.

Molecular and Nano-Structural Optimization of Nanoparticulate Mn2+-Hexarhenium Cluster Complexes for Optimal Balance of High T1- and T2-Weighted Contrast Ability with Low Hemoagglutination and Cytotoxicity.

The present work introduces rational design of nanoparticulate Mn(II)-based contrast agents through both variation of the μ3 (inner) ligands within a series of hexarhenium cluster complexes [{Re6(μ3-Q)8}(CN)6]4− (Re6Q8, Q = S2−, Se2− or Te2−) and interfacial decoration of the nanoparticles (NPs) K4−2xMnxRe6Q8 (x = 1.3 − 1.8) by a series of pluronics (F-68, P-123, F-127). The results highlight an impact of the ligand and pluronic for the optimal colloid behavior of the NPs allowing high colloid stability in ambient conditions and efficient phase separation under the centrifugation. It has been revealed that the K4−2xMnxRe6Se8 NPs and those decorated by F-127 are optimal from the viewpoint of magnetic relaxivities r1 and r2 (8.9 and 10.9 mM−1s−1, respectively, at 0.47 T) and low hemoagglutination activity. The insignificant leaching of Mn2+ ions from the NPs correlates with their insignificant effect on the cell viability of both M-HeLa and Chang Liver cell lines. The T1- and T2-weighted contrast ability of F-127–K4−2xMnxRe6Q8 NPs was demonstrated through the measurements of phantoms at whole body 1.5 T scanner.

Aqueous aggregation and deposition kinetics of fresh and carboxyl-modified nanoplastics in the presence of divalent heavy metals

The presence of heavy metals alters the colloidal stability and deposition of nanoplastics (NPs) in urban waters. Such processes are important to assess the mobility and fate of NPs and their associated heavy metals. Up to date, few studies have reported the impact of heavy metals on the colloidal behaviors of NPs and the involved mechanisms. In the study, time-resolved dynamic light scattering (DLS) and quartz crystal microbalance with dissipation (QCM-D) methods were used to assess the aggregation and deposition kinetics of polystyrene nanospheres with divalent heavy metals. For comparison, carboxyl-modified polystyrene nanospheres were used. Results reveal that heavy metals destabilized NPs more significantly than calcium ions. Spectroscopy and transmission electron microscopy analysis propose that heavy metals destabilized NPs via inner-sphere coordination with carboxyl groups and cation-π interactions, further leading to the formation of different dimensional aggregates. QCM-D results suggest that the deposition rate, irreversibility, and film compactness of NPs on silica surfaces first increased but further decreased as heavy metal concentration increased. Such deposition behaviors depended on the bridging effects between NPs and silica and aggregation-induced diffusion limitation. In that case, the destabilization and retention ability of heavy metals for NPs were related to their electronegativity and hydration shell thickness. In urban waters, the presence of natural organic matter (NOM) decreased the destabilization and retention ability of heavy metals, whereas heavy metals with environmentally relevant concentrations still enhanced the aggregation and deposition of NPs compared with other environmental cations. This study highlights the impact of heavy metal property on the colloidal behaviors of NPs, thus deepening our understanding of the mobility and fate of NPs associated with heavy metals in urban waters.

Effect of concentration of silica encapsulated ds-DNA colloidal microparticles on their transport through saturated porous media

We investigated the transport and retention kinetics of silica encapsulated – silica core double stranded DNA particles (SiDNASi) through 15 cm saturated quartz sand columns as a function of a wide range of colloid injection concentrations (C0 = 8.7 ×102 - 6.6 ×108 particles ml−1). The breakthrough curves (BTCs) exhibited an overall 2-log increase of maximum relative effluent concentration with increasing C0. Inverse curve fitting, using HYDRUS1D, demonstrated that a 1-site first order kinetic attachment (katt) and detachment (kdet) model sufficed to explain the C0-dependent SiDNASi retention behaviour. With increasing C0, katt log-linearly decreased, which could be expressed as an overall decrease in the single-collector removal efficiency (ƞ). The decrease in ƞ was likely due to increased electrostatic repulsion between aqueous phase- solid phase colloids, formation of shadow zones downstream of deposited colloids and removal of weakly attached colloids from the solid phase (quartz sand) attributing to increased aqueous phase-solid phase intercolloidal collisions as a function of increasing SiDNASi concentration. Our results implied, firstly, that the aqueous phase colloid concentration should be carefully considered in determining colloidal retention behaviour in saturated porous media. Secondly, colloidal transport and retention dynamics in column studies should not be compared without considering colloid influent concentration. Thirdly, our results implied that the applicability of SiDNASi as a conservative subsurface tracer was restricted, since transport distance and retention was colloid concentration dependent. However, the uniqueness of the DNA sequences in SiDNASi imparts the advantage of concurrent use of multiple SiDNASi for flow tracking or porous media characterization.

Migration modelling of As(V) loaded by humic acid and nano iron oxide composite colloids affected by various environmental factors

• Adsorption of nano-iron oxide on arsenic diminishes with increasing humic acid, pH, and iron oxide. • Increasing ionic strength has an inhibitory effect on the arsenic migration. • The fractal model can accurately capture the arsenic migration in porous media. Nanoparticles have been applied to remediate heavy metal pollutants (e.g., arsenic) in groundwater and soil, where the migration mechanism of pollutants in this multi-component system has not been fully understood. To better understand how nano-iron oxide affects arsenic migration under multivariate influence, this study prepared arsenic loaded composite colloids using arsenic (As(V)), humic acid, and nano iron oxide (n-α-Fe 2 O 3 ). Then we explored the migration behavior of the composite colloids (HA-n-α-Fe 2 O 3 ) loaded As(V) in a quartz sand column affected by n-α-Fe 2 O 3 under various humic acid concentrations, pH values, ionic strengths, and ferric oxide contents. Two migration models, including a classical advection-dispersion equation (ADE) and a Hausdorff fractal advection-dispersion equation (HADE), were used to quantify the observed co-migration of arsenic conveyed by HA-n-α-Fe 2 O 3 colloids loaded As(V) in the column. Our analysis indicates that the adsorption capability of nano-iron oxide on arsenic decreases with pH, humic acid and iron oxide concentrations, thus accelerating arsenic movement. While, the increasement of ionic strength enhances the adsorption force of nano-iron oxide on arsenic and suppresses arsenic migration. Furthermore, simulation results suggest that the HADE model outperforms the traditional ADE model in characterizing arsenic migration, where the time derivative index is an indicator of anomalous diffusion.

Application of temporal moment analysis to interpret colloid and colloid-facilitated solute transport under varying size exclusion and attachment coefficient.

Colloidal particles can attach the contaminants like heavy metals and radionuclides and act as contaminant carriers to provide a faster movement of pollutants through the interconnecting pores of the porous medium. The electrostatic repulsive force between the negatively charged colloids and the solid surface restricts the transport of the mobile colloids to the larger pores of the porous medium and initiates the size exclusion mechanism. The temporal moment analysis is treated as an effective tool to interpret the solute breakthrough curves for analyzing the statistical behavior of the contaminants. In past literature, the temporal moments have not been incorporated with the breakthrough curves of colloids and colloid-facilitated contaminants for statistical interpretation. In this research study, the temporal variations of concentrations of mobile colloids, solute attached to the mobile colloids, and the dissolved solute are obtained numerically in a fully saturated one-dimensional column considering a continuous source for varying size exclusion and colloid attachment coefficient. Utilizing the simulated spatially varying breakthrough curves, the temporal moments are estimated to calculate the mass recovery, average residence time, and the spreading of mobile colloids and dissolved solutes. The temporal moment analysis suggests that the velocity enhancement for higher size exclusion reduces the average residence time of the mobile colloids and the solute adsorbed to the mobile colloids significantly. The mass recovery of mobile colloids and the solute attached to the mobile colloids increases at a specific depth for higher size exclusion. The estimated second central moment attributes that the solute spreading follows the nonlinear trend for low size exclusion. The peaks of the relative concentration of mobile colloids and solute attached to mobile colloids drastically decrease with an increase in attachment coefficient. The peak of the relative concentration of dissolved contaminant enhances with attachment coefficient. The high second temporal moment of the dissolved contaminant at a higher attachment coefficient indicates the slow interaction of dissolved solute and porous medium and that enables a greater spreading of solute through the interconnecting porous medium. The study suggests that the faster movement of mobile colloids and the solute attached to the mobile colloids at higher exclusion imparts a potential risk of groundwater contamination and thorough statistical interpretation is needful to analyze the behavior of colloids and colloid-facilitated contaminants. The research work does not consider the transient flow field and the effect of the presence of air phase in the partially saturated soil column in the groundwater system.

Relationship between Some Colloidal Properties of Non-Ionic-Anionic Surfactant Mixtures

Non-ionic surfactants are compatible with different types of materials, therefore they can be applied in various packages. Fatty-acid derivates as non-ionic surfactants and their mixtures were investigated to study their colloidal behavior. The HLB value, the particle size, the emulsification capacity and the interfacial tension of various commercial, non-ionic surfactants, and their mixtures with sodium lauryl-ether-sulfate (SLES), were determined. The surfactant mixtures were prepared in different non-ionic: anionic surfactant ratios to examine their effect on several surfactant characteristics. The interfacial tension between the oil phase and aqueous phase was measured using the spinning drop method and the average hydrodynamic diameter of surfactants in the aqueous solution was determined using the dynamic light scattering method. The relationship between various colloidal properties of surfactants was investigated. It was found that there is a significant relationship between the colloidal characteristics and the structure of surfactants that can contribute to their efficient selection method.

Reduction and Elimination of Humic Acid Fouling in Air Sparged Membrane Distillation Using Nanocarbon Immobilized Membrane.

In this paper, we present the treatment of humic acid solution via carbon nanotube immobilized membrane (CNIM) distillation assisted by air sparging (AS). Carbon nanotubes offer excellent hydrophobicity to the modified membrane surface and actively transport water vapor molecules through the membrane to generate higher vapor flux and better rejection of humic acid. The introduction of air sparging in the membrane distillation (MD) system has changed the humic substance fouling by changing the colloidal behavior of the deposits. This modified MD system can sustain a higher run time of separation and has enhanced the evaporation efficiency by 20% more than the regular membrane distillation. The air sparging has reduced the deposition by 30% in weight and offered lesser fouling of membrane surface even after a longer operating cycle. The water vapor flux increased with temperature and decreased as the volumetric concentrating factor (VCF) increased. The mass transfer coefficient was found to be the highest for the air sparged—carbon nanotube immobilized membrane (AS-CNIM) integrated membrane distillation. While the highest change in mass transfer coefficient (MTC) was found for polytetrafluoroethylene (PTFE) membrane with air sparging at 70 °C.

Visualization of Concentration Gradients and Colloidal Dynamics under Electrodiffusiophoresis.

In this work, we present an experimental study of the dynamics of charged colloids under direct currents and gradients of chemical species (electrodiffusiophoresis). In our approach, we simultaneously visualize the development of concentration polarization and the ensuing dynamics of charged colloids near electrodes. With the aid of confocal microscopy and fluorescent probes, we show that the passage of current through water confined between electrodes, separated about a hundred microns, results in significant pH gradients. Depending on the current density and initial conditions, steep pH gradients develop, thus becoming a significant factor in the behavior of charged colloids. Furthermore, we show that steep pH gradients induce the focusing of charged colloids away from both electrodes. Our results provide the experimental basis for further development of models of electrodiffusiophoresis and the design of non-equilibrium strategies for the fabrication of advanced materials.

Empty liquid state and re-entrant phase behavior of the patchy colloids confined in porous media.

Patchy colloids with three and four equivalent patches, confined in an attractive random porous medium, undergo re-entrant gas-liquid phase separation with the liquid phase density approaching zero at low temperatures. The (bonding) colloid-colloid interaction causes the liquid-gas phase separation, which is modulated by the presence of the randomly distributed hard-sphere obstacles, attracting the colloids via Yukawa potential. Due to this interaction, a layer of mutually bonded colloids around the obstacles is formed. The network becomes nonuniform, with colloid particles locally centered on the obstacles. Features described in this article may open possibilities to produce equilibrium gels with predefined nonuniform distribution of particles and indicate how complicated the phase behavior of biological macromolecules in a crowded environment may be.

Nanodiamonds as traps for fibroblast growth factors: Parameters influencing the interaction

Fibroblast growth factors (FGFs) deliver external cell communication signals, to regulate mammalian development, metabolism and homeostasis. Blocking the FGF interactions with their receptors at the cell membrane is one of the promising strategies for treatment of diseases related to dysregulated FGF signaling, such as cancer, metabolic syndromes, and developmental disorders. Recently, detonation nanodiamonds (NDs) with positive ζ-potential were identified as highly effective and selective FGF binders, sequestering FGF molecules and preventing their interaction with receptors under physiological conditions, thus potentially eliminating the effect of FGF overexpression. Here, we investigated the influence of ND origin (detonation vs. high-pressure high-temperature), surface modification, size and separation/purification steps on the sequestration ability and binding affinity of FGF2, a representative member of the FGF family. We measured FTIR and Raman spectra of the NDs, assessed their colloidal behavior and ζ-potential, and correlated their properties with FGF2 interaction levels. Using Western blot and ELISA, we quantified the strength of the interaction between detonation NDs and FGF2. All NDs with positive ζ-potential sequestered FGF2 at its physiologically relevant concentrations. Hydrogenated detonation NDs showed the highest binding capacity. Using Langmuir model, we estimated the apparent dissociation constant between FGF2 and detonation ND with positive ζ-potential to be in the nanomolar range in full fetal bovine serum. Because such tight interaction between a protein and a solid nanoparticle occurred in ∼105-fold molar excess of serum proteins, we believe that NDs can potentially be used in vivo as selective FGF traps to regulate disorders caused by aberrant FGF signaling.

Effects of low molecular weight organic acids on aggregation behavior of biochar colloids at acid and neutral conditions

Low molecular weight organic acids (LMWOAs), as active components in the rhizosphere carbon cycling, may influence the environmental behaviors of biochar colloids. This study selected the pine-wood and wheat-straw biochars (PB and WB) as two typical biochars. The effects of typical LMWOAs (oxalic acid, citric acid, and malic acid) on aggregation kinetics of PB and WB colloids were investigated under pH 4 and 6 conditions. Critical coagulation concentrations (CCCs) of both PB and WB colloids were decreased with the LMWOAs regardless of the types of biochar and the solution pH, and the most significant effect occurred in pH 4 due to more LMWOAs sorption on the biochar colloids. The different types of LMWOAs caused various CCCs changes. For example, the CCC values of PB colloids decreased from 75 mM to 56, 52, and 47 mM in the pH 4 NaCl solutions when 1 mM oxalic acid, citric acid, and malic acid were present in the suspensions, respectively. The chemical structure (functional groups) and molecular weight of LMWOAs, solution pH, and the electrophoretic mobility (EPM) of biochar co-influence the interactions between biochar colloids and LMWOAs, thus affecting the stability of biochar colloids in the presence of LMWOAs. The presence of LMWOAs accelerated the aggregation of colloidal biochar by increasing the interaction of surface bridging bonds (hydrogen bonding) and decreasing the repulsive force between colloidal biochar particles. This study showed that LMWOAs could accelerate the aggregation of biochar colloids in acidic or neutral environments and reduce the mobility of biochar colloids in soil rhizosphere.

Colloidal stability classification of TiO2 nanoparticles in artificial and in natural waters by cluster analysis and a global stability index: Influence of standard and natural colloidal particles

In the field of exposure-driven risk assessment of engineered nanoparticles (NPs), the highly complex interactions of NPs with natural components in surface waters are considered key factors to understand their fate and behavior in the environment.However, since experimental approaches aiming at imitating environmentally relevant conditions include many parameters and lead to a high number of outcomes, statistical tools can be extremely useful to support the results' interpretation.In this context, a multimethod approach was applied to investigate the colloidal behavior of TiO2 NPs in both artificial waters and natural brackish water (from the Venice lagoon, Italy), in the presence of standard kaolinite and natural organic matter (NOM), or of the fine fraction of natural colloidal particles (NCPs) from the lagoon sediment. In detail, the experimental data obtained, i.e. hydrodynamic size, surface charge and sedimentation velocity values, were i) statistically treated by hierarchical clustering and ii) merged into a global stability index (IG). The hierarchical clustering allowed to group the dispersions into three colloidal stability classes, where the main discriminant was the medium composition (i.e. ionic strength and presence of NOM), while the IG allowed to establish a colloidal stability ranking of the dispersions within each class. Moreover, the comparison among the different dispersions suggested that kaolinite could be considered as a suitable surrogate for NCPs, to estimate the colloidal behavior and environmental fate of TiO2 NPs in natural aqueous media.

A thermodynamic investigation of the effect of cationic structure on the self-aggregation behavior of Surface-Active ionic liquids in the presence of an amino acid

A series of imidazolium-based ionic liquids (ILs) with varying side alkyl chain length at N3 position which includes [C12mim][Br], [C12eim][Br], and [C12bim][Br] have been synthesized and characterized by 1H NMR. Then, their aggregation behavior in the presence of different concentrations of the amino acid L-Tryptophan (L-Trp) at different temperatures has been examined using conductometric, tensiometric, and UV–vis (absorption spectra) techniques. The critical micelle concentration (CMC) of ILs has been investigated in the absence and presence of amino acid to acquire a better understanding of the colloidal behavior of ILs in presence of amino acid as an external additive. The addition of amino acid is observed to reduce the CMC values of the ILs examined in an aqueous media. Likewise, applying a charged pseudo-phase model of micellization, the thermodynamic parameters of micellization, such as a change in standard free energy (ΔGmo), change in standard enthalpy (ΔHmo), and change in standard entropy (ΔSmo), have been scrutinized from the dependence of CMC on temperature. The surface tension approach was also used to evaluate interfacial characteristics. It was discovered that increasing the length of the side chain increases surface activity. All of the estimated parameters were utilized to determine the electrostatic and hydrophobic contributions of IL to the formation of micellar aggregates.

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid

Factors affecting the rheological behaviour of carbomer dispersions in hydroalcoholic medium: Towards the optimization of hand sanitiser gel formulations

Hand sanitizers represent a primary measure for the prevention of transmissible infections, whose use has been greatly increased during CoViD-19 pandemic. Most of the commercially available products are hydrogels, employing carbomers as thickening agents. However, few information is still available regarding performances of carbomers in hydroalcoholic media containing a percentage of alcohols ≥ 60% v/v as recommended for disinfection. The aim of this study was to investigate the colloidal behaviour of carbomer 974 and carbomer 980 in hydroalcoholic media containing from 50 to 80% w/w of alcohol (ethanol or isopropanol) and neutralised with triethanolamine or aminomethyl propanol. Both carbomers provide transparent hydrogels in water, but carbomer 980 should be preferred for the formulation of hydrogel with a percentage of alcohol ≥ 50% w/w for its better solvation. The critical alcohol concentration (CAlC), above which polymer precipitation occurs, depends on the type of alcohol and base used. Carbomer dispersions with a higher content of alcohol can be prepared using aminomethyl propanol rather than triethanolamine. The choice of the more suitable components is fundamental for the isopropanol-based dispersions since the CAlC is closer to the recommended concentrations for disinfection. Overall, these results provide helpful insights for the correct preparation of alcohol-based hand sanitizers using carbomers.

Recent progress in environmental remediation, colloidal behavior and biological effects of MXene: a review

Recent progress in environmental remediation, colloidal behavior and biological effects of MXene was summarized.

Colloidal stabilities and deposition behaviors of chromium (hydr)oxides in the presence of dissolved organic matters: role of coprecipitation and adsorption

The coprecipitation or surface adsorption of dissolved organic matters determined the colloidal stabilities and deposition behaviors of Cr (hydr)oxides.

Stabilizer-free Vitamin E Nanovehicle for Biological Research.

In molecular biology research, a vitamin E (VE) vehicle (VE dissolved in organic solvent) is often added to water media without a stabilizer. However, the detailed behavior of VE colloids in water media is unclear. In this study, we reveal that VE nanoemulsion readily forms in water-based media through the existing protocol. The colloid size was changed from 39 nm to the submicron scale by adjusting the initial concentration of the VE solution and adding a buffer. The radical scavenging effect of the dispersed nanosized VEs is comparable to that of the water-soluble antioxidant Trolox, providing excellent antioxidant performance in colloid form. The cytoprotection effect of the VE colloids under a lipid oxidation condition largely depends on the size of the nanodispersion. Smaller dispersed particles are more efficient radical scavengers than larger particles for a constant VE amount owing to sophisticated uptake behavior of cell. This unveiled fundamental knowledge pave the way for a preparative protocol of stabilizer-free VE vehicles, which are expected to become widely used in molecular biology research.