Colloidal Theory Research Articles

The Countoscope: Measuring Self and Collective Dynamics without Trajectories

Driven by physical questions pertaining to quantifying particle dynamics, microscopy can now resolve complex systems at the single-particle level, from cellular organisms to individual ions. Yet, available analysis techniques face challenges reconstructing trajectories in dense and heterogeneous systems where accurately labeling particles is difficult. Furthermore, the inescapable finite field of view of experiments hinders the measurement of collective effects. Inspired by Smoluchowski, we introduce a broadly applicable analysis technique that probes dynamics of interacting particle suspensions based on a remarkably simple principle: counting particles in finite observation boxes. Using colloidal experiments, advanced simulations, and theory, we first demonstrate that statistical properties of fluctuating counts can be used to determine self-diffusion coefficients, so alleviating the hurdles associated with trajectory reconstruction. We also provide a recipe for practically extracting the diffusion coefficient from experimental data at variable particle densities, which is sensitive to steric and hydrodynamic interactions. Remarkably, by increasing the observation box size, counting naturally enables the study of collective dynamics in dense suspensions. Using our novel analysis of particle counts, we uncover a surprising enhancement of collective behavior due to hydrodynamics as well as a new length scale which can be connected with hyperuniform structure. Our counting framework, the “countoscope,” thus enables efficient measurements of self and collective dynamics in dense suspensions and opens the way to quantifying dynamics and identifying novel physical mechanisms in diverse complex systems where single particles can be resolved. Published by the American Physical Society 2024

Density functional theory for responsive hard-sphere fluids

We investigate the equilibrium properties of responsive hard-sphere fluids, where the particle size is a coarse-grained property that fluctuates within an internal free-energy landscape, responding to changes in concentration or the application of external fields. For this purpose, we employ a generalised density functional theory for responsive colloids based on the fundamental measure theory for polydisperse hard-sphere mixtures. We find that increasing particle softness yields a substantial reduction in mean particle size, volume fraction and pressure. We also examine the density profiles and size segregation of responsive hard-sphere fluids subjected to three representative external potentials: a planar hard wall, gravitational and Archimedes buoyant fields. We observe that increasing stiffness or particle concentration enhances density oscillations, converging to the behaviour of a monodisperse fluid. In a gravitational field, size segregation occurs, with smaller particles accumulating at the bottom due to sedimentation. This effect is more pronounced when the Archimedes force is included, causing larger colloids to accumulate at the top, leading to density oscillations in this region that intensify with particle softness, an effect not observed in monodisperse systems. Finally, we demonstrate that responsiveness leads to distinct behaviour compared to conventional polydisperse non-responsive fluids, in which particle compression is not allowed.

Competition between cross-linking and force-induced local conformational changes determines the structure and mechanics of labile protein networks

Folded protein hydrogels are emerging as promising new materials for medicine and healthcare applications. Folded globular proteins can be modelled as colloids which exhibit site specific cross-linking for controlled network formation. However, folded proteins have inherent mechanical stability and unfolded in response to an applied force. It is not yet understood how colloidal network theory maps onto folded protein hydrogels and whether it models the impact of protein unfolding on network properties. To address this, we study a hybrid system which contains folded proteins (patchy colloids) and unfolded proteins (biopolymers). We use a model protein, bovine serum albumin (BSA), to explore network architecture and mechanics in folded protein hydrogels. We alter both the photo-chemical cross-linking reaction rate and the mechanical properties of the protein building block, via illumination intensity and redox removal of robust intra-protein covalent bonds, respectively. This dual approach, in conjunction with rheological and structural techniques, allows us to show that while reaction rate can ‘fine-tune’ the mechanical and structural properties of protein hydrogels, it is the force-lability of the protein which has the greatest impact on network architecture and rigidity. To understand these results, we consider a colloidal model which successfully describes the behaviour of the folded protein hydrogels but cannot account for the behaviour observed in force-labile hydrogels containing unfolded protein. Alternative models are needed which combine the properties of colloids (folded proteins) and biopolymers (unfolded proteins) in cross-linked networks. This work provides important insights into the accessible design space of folded protein hydrogels without the need for complex and costly protein engineering, aiding the development of protein-based biomaterials.

Mecanismos de formação dos urólitos em cães e gatos

Uroliths may have in its composition organic and minerals. There are multifactorial mechanisms involved in urolith formation however, the complete pathophysiology is yet not fully elucidated since involves epidemiological, genetic, dietary, infectious, racial factors, among others factors. Urolithiasis has been reported in humanity since 8,000 B.C until today and very common not only for humans but for dogs and cats. The classification is based on the chemical composition of the calculus, which can be formed by mineral compounds such as struvite (magnesian ammonium phosphate), calcium oxalate, calcium phosphate and silica or organic compounds such as ammonium urate, cystine and xanthine. Diagnosis involves carrying out laboratory and imaging tests and chemical and calculus physics. Some studies have been carried out to clarify the causes of urolith formation. There are seven theories that highlight the risk factors associated with its development: crystallization, inhibitor deficiency, matrix theory, colloidal theory, ionic, fixed growth theory and finally, renal cell injury theory. Knowing these theories aid in the correct understanding of the pathophysiology but mostly is necessary to understand animal and the environment factors together for a better treatment approach and prevention. Another important information is that urolith is a secondary manifestation to the existing problem and its removal depends on ruling out the primary cause. The main goal to be achieved is to reduce urolith occurrence and to minimize unnecessary invasive procedures by previous urolith identification, a better understanding of urolith formation mechanisms and, consequently, their risk factors to provide correct treatment for each type of urolith formed.

Effect of Solvent Composition on Non-DLVO Forces and Oriented Attachment of Zinc Oxide Nanoparticles.

Oriented attachment (OA) occurs when nanoparticles in solution align their crystallographic axes prior to colliding and subsequently fuse into single crystals. Traditional colloidal theories such as DLVO provide a framework for evaluating OA but fail to capture key particle interactions due to the atomistic details of both the crystal structure and the interfacial solution structure. Using zinc oxide as a model system, we investigated the effect of the solvent on short-ranged and long-ranged particle interactions and the resulting OA mechanism. In situ TEM imaging showed that ZnO nanocrystals in toluene undergo long-range attraction comparable to 1kT at separations of 10 nm and 3kT near particle contact. These observations were rationalized by considering non-DLVO interactions, namely, dipole-dipole forces and torques between the polar ZnO nanocrystals. Langevin dynamics simulations showed stronger interactions in toluene compared to methanol solvents, consistent with the experimental results. Concurrently, we performed atomic force microscopy measurements using ZnO-coated probes for the short-ranged interaction. Our data are relevant to another type of non-DLVO interaction, namely, the repulsive solvation force. Specifically, the solvation force was stronger in water compared to ethanol and methanol, due to the stronger hydrogen bonding and denser packing of water molecules at the interface. Our results highlight the importance of non-DLVO forces in a general framework for understanding and predicting particle aggregation and attachment.

Combining Scattering Experiments and Colloid Theory to Characterize Charge Effects in Concentrated Antibody Solutions.

Charges and their contribution to protein-protein interactions are essential for the key structural and dynamic properties of monoclonal antibody (mAb) solutions. In fact, they influence the apparent molecular weight, the static structure factor, the collective diffusion coefficient, or the relative viscosity, and their concentration dependence. Further, charges play an important role in the colloidal stability of mAbs. There exist standard experimental tools to characterize mAb net charges, such as the measurement of the electrophoretic mobility, the second virial coefficient, or the diffusion interaction parameter. However, the resulting values are difficult to directly relate to the actual overall net charge of the antibody and to theoretical predictions based on its known molecular structure. Here, we report the results of a systematic investigation of the solution properties of a charged IgG1 mAb as a function of concentration and ionic strength using a combination of electrophoretic measurements, static and dynamic light scattering, small-angle X-ray scattering, and tracer particle-based microrheology. We analyze and interpret the experimental results using established colloid theory and coarse-grained computer simulations. We discuss the potential and limits of colloidal models for the description of the interaction effects of charged mAbs, in particular pointing out the importance of incorporating shape and charge anisotropy when attempting to predict structural and dynamic solution properties at high concentrations.

Freezing-mediated formation of supraproteins using depletion forces

HypothesisLong-acting formulations such as microparticles, injectable depots and implantable devices can realize spatiotemporally controlled delivery of protein drugs to extend their therapeutic in vivo half-lives. To efficiently encapsulate the protein drugs into such drug delivery systems, (sub)micron-sized protein particles are needed. The formation of micronized supraproteins can be induced through the synergistic combination of attractive depletion forces and freezing. The size of the supraproteins can be fine-tuned from submicron to several microns by adjusting the ice crystallization rate through the freeze-quench depth, which is set by the target temperature.MethodsSupraprotein micron structures were prepared from protein solutions under various conditions in the presence and absence of nonadsorbing polyethylene glycol. Scanning electron microscopy and dynamic light scattering were employed to determine the sizes of the supraproteins and real-time total internal reflection fluorescent microscopy was used to follow the supraprotein formation during freezing. The protein secondary structure was measured before and after micronization by circular dichroism. A phase diagram of a protein–polyethylene glycol mixture was theoretically predicted to investigate whether the depletion interaction can elucidate the phase behavior.FindingsMicronized protein supraparticles could be prepared in a controlled manner by rapid freeze-drying of aqueous mixtures of bovine serum albumin, horseradish peroxidase and lysozyme mixed with polyethylene glycol. Upon freezing, the temperature quench initiates a phase separation process which is reminiscent of spinodal decomposition. This demixing is subsequently arrested during droplet phase separation to form protein-rich microstructures. The final size of the generated protein microparticles is determined by a competition between phase separation and cooling rate, which can be controlled by target temperature. The experimental phase diagram of the aqueous protein–polyethylene glycol dispersion aligns with predictions from depletion theory for charged colloids and nonadsorbing polymers.

Colloidal Engineering of Microplastic Capture with Biodegradable Soft Dendritic "Microcleaners".

The introduction of colloidal principles that enable efficient microplastic collection from aquatic environments is a goal of great environmental importance. Here, we present a novel method of microplastic (MP) collection using biodegradable hydrogel soft dendritic colloids (hSDCs). These dendritic colloids have abundant nanofibrils and a large surface area, which provide an abundance of interfacial interactions and excellent networking capabilities, allowing for the capture of plastic particles and other contaminants. Here, we show how the polymer composition and morphology of the hSDCs can impact the capture of microplastics modeled by latex microbeads. Additionally, we use colloidal DLVO theory to interpret the capture efficiencies of microbeads of different sizes and surface functional groups. The results demonstrate the microplastic remediation efficiency of hydrogel dendricolloids and highlight the primary factors involved in the microbead interactions and adsorption. On a practical level, the results show that the development of environmentally benign microcleaners based on naturally sourced materials could present a sustainable solution for microplastic cleanup.

Effective patchiness from critical points of a coarse-grained protein model with explicit shape and charge anisotropy.

Colloidal model systems are successful in rationalizing emergent phenomena like aggregation, rheology and phase behaviour of protein solutions. Colloidal theory in conjunction with isotropic interaction models is often employed to estimate the stability of such solutions. In particular, a universal criterion for the reduced second virial coefficient at the critical point is frequently invoked which is based on the behavior of short-range attractive fluids (Noro-Frenkel rule, ). However, if anisotropic models for the protein-protein interaction are considered, e.g. the Kern-Frenkel (KF) patchy particle model, the value of the criterion is shifted to lower values and explicitly depends on the number of patches. If an explicit shape anisotropy is considered, as e.g. in a coarse-grained protein model, the normalization of becomes ambiguous to some extent, as no unique exclusion volume can be defined anymore. Here, we investigate a low-resolution, coarse-grained model for the globular protein bovine serum albumin (BSA) and study effects of charge-anisotropy on the phase diagram (determined by simulations) at the isoelectric point. We present methods of assigning an "effective patchiness" to our protein model by comparing its critical properties to the KF model. We find that doubling the native charges increases the critical temperature Tc by ≈14% and that our BSA model can be compared to a 3 to 5 patch KF model. Finally, we argue that applying existing criteria from colloidal theory should be done with care, due to multiple, physically plausible ways of how to assign effective diameters to shape-anisotropic models.

Phase behavior of colloidal nanoparticles and their enhancement effect on the rheological properties of polymer solutions and gels.

The interaction between nanoparticles and polymers has been of great interest in colloidal theory and novel materials. For example, the properties of polyacrylamide solutions and gels, which are usually used for conformance control and water shut-off in oilfields, can be improved with the addition of nanoparticles. This underlying mechanism and its applicability are investigated in this paper. A strong relationship between the phase behaviors of nanoparticles in polymer solutions and their enhancement effect on the rheology of the nanocomposite polymer solutions and gels was observed. Experiment results showed that the stability of nanoparticles was dependent on several factors, including pH, salinity, and polymer type. At neutral pH conditions, the tendency of the aggregation of nanoparticles was strengthened upon increasing the salinity, polymer concentration, and electronegativity of the polymers. Rheological measurements showed that nanoparticles could improve the viscosity of polymer solutions or the fracture stress of gels only if nanoparticles were aggregated in the corresponding systems. In addition, these rheological parameters significantly increased with increasing salinity and nanoparticle concentration. As a result, the mobility ratio of polymer solutions may be increased several times by the addition of nanoparticles. Referring to the gels, their rupture pressure gradient in the ideal model was also found to increase with nanoparticle concentration. In particular, if the nanoparticle concentration was sufficiently high (reaching 2%), the formed gels would not be destroyed by the injected water, but rather functionally act as a porous medium for permeation.

STEAM PADA MODEL PjBL DAN HASIL BELAJAR KOLOID PESERTA DIDIK

Chemistry learning at SMA Negeri 7 Takalar is still dominated by ordinary cooperative learning. Students still have difficulty understanding colloid lessons where the material is conceptual and requires the application of concepts contextually. Therefore it is very important to do learning that involves students actively applying colloid theory and concepts through the STEAM approach to the Project Based Learning (PjBL) learning model. This research is a quasi-experimental research which aims to determine the learning outcomes of Colloid Students after learning with the STEAM approach in the PjBL Model Class XI MIPA SMA Negeri 7 Takalar. The research design was posttest only control group design. The population is all students of class XI MIPA SMA Negeri 7 Takalar which consists of three classes. The research samples for Class XI MIPA 2 and Class XI MIPA 3 as the experimental and control groups were randomly selected. The results of the descriptive analysis show that the average learning outcomes of the experimental class are higher than the control class. The results of the inferential statistical test showed that the learning outcomes of students using the t test at a value of α = 0.05 obtained tcount > ttable (2.83 > 1.99). The results of data analysis from hypothesis testing stated that the STEAM approach to the Project Based Learning Model had a significant influence on the colloidal learning outcomes of Class XI MIPA Students at SMA Negeri 7 Takalar

Fertilizer-Holding Performance of Graphene on Soil Colloids Based on Double Electric Layer Theory

Soil nutrient loss, which leads to low plant utilization, has become an urgent issue. Graphene can improve soil fertilizer-holding properties given its small size effect, strong adsorption properties, and large specific surface area. Herein, different amounts of graphene were added to soil samples to study its effect on soil nutrient retention and growth of pepper seedlings. The colloidal double electric layer theory forms the basis for an analysis of variations in soil nutrient concentration through measurements of the zeta potential, which is affected by variations in ion concentrations in soil colloids. We measured the zeta potential of graphene and soil mixed colloids and found that graphene could increase the concentration of nutrient ions in soil colloids. In addition, graphene reduced the loss of nutrients; increased the contents of ammonium nitrogen, effective phosphorus, and fast-acting potassium in the soil after leaching; and enhanced the stability of soil aggregates after leaching. In addition, pepper seedlings grown under graphene treatment for 60 days outperformed seedlings grown without graphene treatment, in terms of plant height and nutrient content. This study demonstrates that the addition of graphene to soil can reduce nutrient loss and promote fertility and plant growth.

Pulsed electrophoretic deposition of hybrid coatings from aqueous suspensions as surface functionalization and sealing technique of anodized AA2024. Part I: Morphological characterization, analysis of the interfacial interactions, and evaluation of pore impregnation of the anodic layer

In this two-part series, pulsed direct current for cathodic electrophoretic deposition (pulsed-CEPD) was studied as sealing technique of anodized AA2024 by depositing hybrid sol-gel films from aqueous suspensions. The coating was obtained using tetraethyl orthosilicate and hexadecyltrimethoxysilane as precursors and two pulse widths were used: 10 microseconds and 100 milliseconds. For comparison, continuous direct current for cathodic electrophoretic deposition was also performed. In this first article, it was developed a low-cost automated apparatus capable of creating pulsed fields using a commercial power supply. This was necessary since the automation system provided by the power supply manufacturer did not have a short enough response time able to create pulse widths in the order of microseconds. Field emission scanning electron microscopy (FESEM) and focused ion beam milling techniques were utilized to evaluate the surface morphology and interaction mechanisms in the interface anodic layer/film. Low voltage scanning transmission electron microscopy (STEM)-in-FESEM, and transmission electron microscopy (TEM) were used to evaluate the pore impregnation provided by pulsed-CEPD. Results demonstrated that the developed apparatus successfully created pulsed fields. FESEM micrographs of the anodic layer sealed by pulsed-CEPD showed that the shortest pulse provided the best films, likely due to the greater control of hydrogen bubbles generation and the promotion of a more regular deposition. Also, they revealed two interfacial interactions between the anodic layer and the film. STEM-in-FESEM images showed that the shortest pulse width provided greater pore impregnation by particles. This observation was confirmed by TEM, which demonstrated an incomplete pore impregnation for the longest pulse. Discussion regarding result interpretations is presented based on the generation and dissipation of H2(g) (considering the current interruption); on an alternative to the colloidal stability theory due to the presence of a pulsed field; and on the electrokinetic effects at the electrodes during pulsed-CEPD, that discusses how electroosmotic flow influences the deposition.

Mathematical Modeling of Double Filtration by Colloidal Theory with Study Water Containing Microcystis spp.

Mathematical Modeling of Double Filtration by Colloidal Theory with Study Water Containing Microcystis spp.

Using colloidal AFM probe technique and XDLVO theory to predict the transport of nanoplastics in porous media

The plastic concentration in terrestrial systems is orders of magnitude higher than that found in marine ecosystems, which has raised global concerns about their potential risk to agricultural sustainability. Previous research on the transport of nanoplastics in soil relied heavily on the qualitative prediction of the mean-field extended Derjaguin–Landau–Verwey–Overbeek theory (XDLVO), but direct and quantitative measurements of the interfacial forces between single nanoplastics and porous media are lacking. In this study, we conducted multiscale investigations ranging from column transport experiments to single particle measurements. The maximum effluent concentration (C/C0) of amino-modified nanoplastics (PS–NH2) was 0.94, whereas that of the carboxyl-modified nanoplastics (PS–COOH) was only 0.33, indicating PS-NH2 were more mobile than PS-COOH at different ionic strengths (1–50 mM) and pH values (5–9). This phenomenon was mainly attributed to the homogeneous aggregation of PS-COOH. In addition, the transport of PS-NH2 in the quartz sand column was inhibited with the increase of ionic strength and pH, and pH was the major factor governing their mobility. The transport of PS-COOH was inhibited with increasing ionic strength and decreasing pH. Hydrophilicity/hydrophobicity-mediated interactions and particle heterogeneity strongly interfered with interfacial forces, leading to the qualitative prediction of XDLVO, contrary to experimental observations. Through the combination of XDLVO and colloidal atomic force microscopy, accurate and quantitative interfacial forces can provide compelling insight into the fate of nanoparticles in the soil environment.

Study on the Properties of Waste Oil-Activated Crumb Rubber-Modified Asphalt Based on Molecular Dynamics Simulation and Rheology

To investigate the effect of activated crumb rubber content on the molecular interactions and the properties of crumb rubber-modified asphalt (CRMA) with waste oil, six models of asphalt with various rubber dosages were developed using Materials Studio software, and the molecular dynamics performance of the system was further examined. Then, the fatigue and high- and low-temperature performances of the CRMA binders were characterized by dynamic mechanical experiments in the laboratory. The mean square displacement and diffusion coefficient were used to quantify the migration of molecules. The aggregation state of the components was evaluated using a radial distribution function. The bulk modulus of the CRMA models was calculated to study the mechanical properties. Dynamic shear and bending beam rheometer tests were implemented to evaluate the road performances of the CRMA binders. The results show that increasing the amount of powder could improve the mechanical properties of the asphalt, that is, the modulus of 70% of the asphalt was improved by 57.5%. The rubber and waste oil were evenly dispersed in the system, and the distribution of asphalt components was in accordance with the colloid theory. The temperature-sensitive properties of the rubber led to the improvement of road properties of the CRMA binders with the increase of the admixture. Combined with the distribution of molecules in the asphalt model, the results of rheological indexes show that the waste oil could improve the rheology and stability of binders. This will provide theoretical support for upgrading the content of crumb rubber in CRMA binders.

Evaluation and molecular interaction of asphalt modified by rubber particles and used engine oil

This study investigates the molecular mechanism of used oil on improving the compatibility and viscosity reduction of rubberized asphalt (RA) using molecular simulations and lab tests. This validates the feasibility of producing waste oil modified RA while enhancing the sustainable use of resources and pavement performance. The model of RA with used oil was first built by Materials Studio software. Several molecular dynamics parameters were used to explore the molecular behavior, stability and viscosity of asphalt. Furthermore, the relevant experiments were employed to validate the results of molecular simulation. The results show that used oil molecules can promote the dispersion of macromolecules, including asphaltenes, resins and rubbers, making the system more in accord with the asphalt colloid theory. It supplements the light components in the system to provide a stable dispersion medium. FTIR spectra confirm the rubber activation with used oil and microwave radiation. The softening point difference of RA was reduced from 1.9 to 0.35 °C. Viscosity was even reduced by approximately 67.1%.

Front Cover: Colloidal Stability of TiO 2 Nanoparticles: The Roles of Phosphonate Ligand Length and Solution Temperature (Chem. Eur. J. 50/2022)

More than enough is too much! The cover shows a role of phosphonate ligand length in the colloidal stability of TiO2 nanoparticles. In contrast to classical colloid theory, the dodecylphosphonate ligand provided better colloidal stability than the longer or shorter n-alkylphosphonate ligands. The proposed method is applicable to a wide range of colloidal nanoparticle systems. More information can be found in the Research Article by Y. Okada and co-workers (DOI: 10.1002/chem.202201560).

Water as a Link between Membrane and Colloidal Theories for Cells.

This review is an attempt to incorporate water as a structural and thermodynamic component of biomembranes. With this purpose, the consideration of the membrane interphase as a bidimensional hydrated polar head group solution, coupled to the hydrocarbon region allows for the reconciliation of two theories on cells in dispute today: one considering the membrane as an essential part in terms of compartmentalization, and another in which lipid membranes are not necessary and cells can be treated as a colloidal system. The criterium followed is to describe the membrane state as an open, non-autonomous and responsive system using the approach of Thermodynamic of Irreversible Processes. The concept of an open/non-autonomous membrane system allows for the visualization of the interrelationship between metabolic events and membrane polymorphic changes. Therefore, the Association Induction Hypothesis (AIH) and lipid properties interplay should consider hydration in terms of free energy modulated by water activity and surface (lateral) pressure. Water in restricted regions at the lipid interphase has thermodynamic properties that explain the role of H-bonding networks in the propagation of events between membrane and cytoplasm that appears to be relevant in the context of crowded systems.

Density, zero shear viscosity and microstructure analysis of asphalt binder using molecular dynamics simulation

This study aims to develop molecular model of asphalt binder and investigate the reasonable simulation scale of molecular dynamics (MD) in researching the viscosity property and microstructure of asphalt binder. Eighteen MD models with atom numbers in the range of 10,000–750,000 for the three typical asphalt binder AAA-1, AAK-1, and AAM-1 in the Strategic Highway Research Program (SHRP) were constructed. Density, Zero Shear Viscosity (ZSV), and microstructure characters of the asphalt binders were analyzed by MD to compare with experiment data. The result shows that densities and the ZSV values of the MD models are all close to the experimental values. These models with atom numbers of 130,000–375,000 are well stabilized and have lower errors, which is recommended to research the density and viscosity properties. In the shearing process, the shear flow induces the conformational transitions of the asphalt binder, and most molecules tend to parallel the shear direction. Asphaltenes and saturates components are easier to reorient their conformation in shear flow. Through the density map obtained by MD simulation and the asphaltenes image from the High-resolution transmission electron microscopy in literature, we speculate that short and unordered planar accumulations structures dominate the asphalt binder microstructure, which is a further explanation of the colloidal theory.