Colloidal Particles Research Articles

The colloidal nature and osmotic potential of alkali-silica reaction products and their role for the ASR expansion mechanism

The chemical basics of the ASR are largely revealed and widely accepted, but the nature of the expansion mechanism is still not yet sufficiently well understood. Recent observations showed that ASR products could be considered as colloidal systems. In order to clarify if and to what extent this is the case and whether it could help to better understand the nature of the ASR products and the mechanism of ASR expansion in concrete, 10 ASR products of different composition, water content and synthesised at two temperatures (40 and 60 °C) were investigated over a period of 1.5 years. The ASR products were studied by means of NTA, SEM, 29Si NMR, XRD and an osmotic cell test. The results show that ASR products contain particles of colloidal size, mainly between 50–600 nm and of different shape. The particles are unable to pass pores with a size smaller than themselves what represents a mechanism of semi-permeability in all concrete constituents with respective pore sizes, resulting in the Donnan effect and osmosis. The particles are irreversibly linked by the addition of Ca, which leads to a decrease in the particle concentration, the formation of crystalline phases and thus to a decrease in the osmotic potential of the ASR products. Based on the colloidal nature of the ASR products, expansion caused by ASR in concrete can be explained osmotically.

Critical Casimir levitation of colloids above a bull's-eye pattern.

Critical Casimir forces emerge among particles or surfaces immersed in a near-critical fluid, with the signof the force determined by surface properties and with its strength tunable by minute temperature changes. Here, we show how such forces can be used to trap a colloidal particle and levitate it above a substrate with a bull's-eye pattern consisting of a ring with surface properties opposite to the rest of the substrate. Using the Derjaguin approximation and mean-field calculations, we find a rich behavior of spherical colloids at such a patterned surface, including sedimentation toward the ring and levitation above the ring (ring levitation) or above the bull's-eye's center (point levitation). Within the Derjaguin approximation, we calculate a levitation diagram for point levitation showing the depth of the trapping potential and the height at which the colloid levitates, both depending on the pattern properties, the colloid size, and the solution temperature. Our calculations reveal that the parameter space associated with point levitation shrinks if the system is driven away from a critical point, while, surprisingly, the trapping force becomes stronger. We discuss the application of critical Casimir levitation for sorting colloids by size and for determining the thermodynamic distance to criticality. Our results show that critical Casimir forces provide rich opportunities for controlling the behavior of colloidal particles at patterned surfaces.

Is it Possible to Detect a Rotating Spherical Colloidal Particle?

A single micrometer‐size spherical colloid has been set in rotation by transfer of light orbital angular momentum. This particle is floating at an air–water interface. Steady‐state rotational frequencies of the order of one hertz have been observed, depending on the topological charge of the beam and on its power, in agreement with expected values. The detection is performed using the rotational Doppler shift of the diffused light. Two time constants have been evidenced in the rotational velocity dynamics. The first one is related to the friction of the colloid with the fluid (air and water), whereas the other one is principally associated with the wall friction of the air–liquid interface with the container. This measurement technique makes it possible to identify dynamic parameters of the rotational movement of any spherical object, which is usually impossible to detect.

Adjusting Interface Action and Spacing for Control of Particle Potential.

As the core issue of physical chemistry, how to acquire, control, even adjust surface charging of colloidal particle is far from being completely understood. So poly(lauryl methacrylate) (PLMA) is first introduced with different chain lengths onto crude anatase titanium dioxide (TiO2) nanoparticles (150-200 nm) through two-step surface modification. Along with rising basic nonionic polyisobutylene succinimide (PIBS) concentration, those modified TiO2 nanoparticles (TiO2-NH-PLMA) with the low grafting amount (0.33-4.86 wt.%) and the short chain of the grafted PLMA fragments (layer thickness: 3.0-6.9 nm) underwent charge reversal from being positively to negatively charged in nonpolar isododecane solution. And the more modified ones (PLMA grafting amount: 11.10%; layer thickness: 9.5 nm) remained original electropositivity under same conditions. Based on molecular dynamics simulation, once the repeating unit number exceeds 12, these long grafted PLMA chains will bring about strong steric hindrance to increase interface spacing and weaken interface action against PIBS absorption. This may propose a unique strategy for adjusting or stabilizing surface potential of colloid particles by grafted polymer chains. It is anticipated to provide a facile, precise, and promising control to electronic ink for electrophoretic display.

Transition path time over a barrier of a colloidal particle in a viscoelastic bath

We experimentally study the statistics of the transition path time taken by a submicron bead to successfully traverse an energy barrier created by two optical tweezers in two prototypical viscoelastic fluids, namely, aqueous polymer and micellar solutions. We find a very good agreement between our experimental distributions and a theoretical expression derived from the generalized Langevin equation for the particle motion. Our results reveal that the mean transition path times measured in such viscoelastic fluids have a nontrivial dependence on the barrier curvature and they can be significantly reduced when compared with those determined in Newtonian fluids of the same zero-shear viscosity. We verify that the decrease of the mean transition path time can be described in terms of an effective viscosity that quantitatively coincides with that measured by linear microrheology at a frequency determined by the reactive mode that gives rise to the unstable motion over the barrier. Therefore our results uncover the linear response of the particle during its thermally activated escape from a metastable state even when taking place in a non-Markovian bath. Published by the American Physical Society 2024

Investigation on the interfacial and emulsion stabilized behavior of dextran/ferritin/resveratrol composite nanoparticles

Glycation of ferritin provides a viable approach to enhance its physicochemical and functional properties. However, there is limited research on the interfacial adsorption properties of glycated ferritin-based colloidal particles. Therefore, this study selected recombinant human H-chain ferritin (rHuHF), rHuHF encapsulated with resveratrol (rHuHF–Res), and rHuHF–dextran glycoconjugates loaded with resveratrol (Dex–rHuHF–Res) as emulsifiers to investigate their interfacial adsorption properties. The results revealed that Dex–rHuHF–Res exhibited superior emulsifying properties and rheological behavior. It also increased the hydrophobicity of the microenvironment around Tyr and Trp residues, while hydrogen bonds, hydrophobic force, and salt bridge were identified as the most important intermolecular interactions. Dex–rHuHF–Res exhibited the biggest contact angle and lowest interface tension, which further reduced the diffusion (Kdiff) from the aqueous phase to the interface but promoted the penetration (Kp) and rearrangement (Kr) rates at the interface. Meanwhile, the emulsion stabilized by Dex–rHuHF–Res displayed excellent freeze-thaw stability, and Dex–rHuHF–Res can be more densely accumulated at the O/W interface to form an interface layer. These findings highlight the promising application of glycated ferritin in stabilizing Pickering emulsions, and deepen our understanding of the interplay among particle interaction, interface adsorption properties, and emulsion stability.

Electrophoretic velocity of ion-releasing colloidal particles

By means of a matched asymptotic expansions approach the electrophoretic velocity and zeta potential of a catalytic particle that uniformly releases ions have been investigated. Attention is focused on large, compared to diffuse layer, particles characterized by the surface potential Φs and Damköhler number Da. The latter represents the ratio of the surface reaction rate to the diffusive transfer one. For vanishing Da, we recover the classical Smoluchowski formula for the electrophoretic velocity, which states that the zeta potential of the particle is equal to Φs and that the migration direction is determined by its sign. For small values of Da we show that the migration velocity is controlled mostly by Φs and affected by an ion release only slightly. However, even small Da can induce the electrophoresis of electro-neutral particles that would be immobile if inert. For larger Da the direction of migration and the sign of zeta potential become independent of Φs and are solely determined by the difference in diffusivity of released cations and anions. Still, the surface potential affects the magnitude of the particle velocity.

Surface potentials of conductors in electrolyte solutions.

When we place conducting bodies in electrolyte solutions, their surface potential Φs appears to be much smaller in magnitude than the applied one Φ0 and normally does not obey the classical electrostatic boundary condition of a constant potential expected for conductors. In this paper, we demonstrate that an explanation of these observations can be obtained by postulating that diffuse ions condense at the "wall" due to the reduced permittivity of a solvent. For small values of Φ0, the surface potential responds linearly. On increasing Φ0 further, Φs augments nonlinearly and then saturates to a constant value. Analytical approximations for Φs derived for these three distinct modes show that it always adjusts to salt concentration, which is equivalent to a violation of the constant potential condition. The latter would be appropriate for highly dilute solutions but only if Φ0 is small. Surprisingly, when the plateau with high Φs is reached, the conductor surface switches to a constant charge density condition normally expected for insulators. Our results are directly relevant for conducting electrodes, mercury drops, colloidal metallic particles, and more.

Multilevel immobilized CNT/SCN purification beads and the removal efficiency over TC[sbnd]HCl/clay composite pollutant in the underwater environment

Natural water bodies often contain a significant amount of suspended colloidal particles, which not only reduce water transparency but also have a high adsorption capacity for soluble pollutants. These composite pollutants can migrate rapidly with water flow, which are usually difficult to degrade and remove by traditional methods. Aiming at suspended contaminated waterbodies, this study introduced a multilevel loading method to prepare carbon nanotube/sulfur doped carbon nitride (CNT/SCN) composite photocatalytic purification beads. The surface of the obtained core-shell structured purification beads is loaded with CNT/SCN photocatalysts which exhibit three-dimensional conductive and porous characteristics. TCHCl was introduced as the target pollutant, and the removal efficiency of the composite purification beads under different water turbidity and hydrodynamic conditions were investigated. The results showed that during 15 h of degradation process, at the depth of 20 cm, with the flow rate of 0.015 m3/h and water turbidity of 10.3 NTU, the purification beads achieved a removal efficiency of 54.9% for tetracycline hydrochloride (TCHCl), which was 2.03 times higher than that of SCN purification beads. The three-dimensional porous structure of the surface exhibited excellent adsorption and trapping capabilities for suspended colloidal particles. The introduction of carbon nanotubes enhanced charge transfer ability of the surface layer and reduces the local charge accumulation effect caused by surface adsorption, which effectively enhances the adsorption of suspended colloid, and also significantly improved the degradation efficiency of TCHCl. This study provides a valuable insight for the engineering application of photocatalytic technology.

Electrohydrodynamic flow about a colloidal particle suspended in a non-polar fluid

Nonlinear electrokinetic phenomena, where electrically driven fluid flows depend nonlinearly on the applied voltage, are commonly encountered in aqueous suspensions of colloidal particles. A prime example is the induced-charge electro-osmosis, driven by an electric field acting on diffuse charge induced near a polarizable surface. Nonlinear electrohydrodynamic flows also occur in non-polar fluids, driven by the electric field acting on space charge induced by conductivity gradients. Here, we analyse the flows about a charge-neutral spherical solid particle in an applied uniform electric field that arise from conductivity dependence on local field intensity. The flow pattern varies with particle conductivity: while the flow about a conducting particle has a quadrupolar pattern similar to induced-charge electro-osmosis, albeit with opposite direction, the flow about an insulating particle has a more complex structure. We find that this flow induces a force on a particle near an electrode that varies non-trivially with particle conductivity: while it is repulsive for perfectly insulating particles and particles more conductive than the suspending medium, there exists a range of particle conductivities where the force is attractive. The force decays as the inverse square of the distance to the electrode and thus can dominate the dielectrophoretic attraction due to the image dipole, which falls off with the fourth power with the distance. This electrohydrodynamic lift opens new possibilities for colloidal manipulation and driven assembly by electric fields.

Mechanisms behind the changes in zein colloidal composite nanoparticles under different mass ratios and pH conditions

The hydrophobicity of zein (Z) makes it a candidate for encapsulating hydrophobic compounds and stabilizing Pickering emulsions. However, the high aggregation tendency of Z colloidal particles has limited its applications. Using an available and low-cost hydrophilic biopolymer to coat Z colloidal particles is an efficient way to increase their applications. In this work, the aggregation of Z particles was modulated by incorporating Farsi gum (FG), an emerging hydrocolloid with attractive characteristics, into the colloidal particles. Z/water-soluble portion of FG (WFG) particles were fabricated at pH range of 3–7 and 10:1–1:2 mass ratios using an anti-solvent procedure and then characterized. Zeta potential values indicated that in the presence of WFG, the colloidal stability of the particles increased. At higher pH values (pH 7), the Z:WFG (1:1) colloidal particles were smaller than the Z particles. Although WFG incorporation decreased the interfacial adsorption rate of particles due to the higher molecular weight and viscosity of the system, both Z and Z:WFG particles could efficiently reduce interfacial tension. The interfacial layer films developed by Z (pH 4) and Z: WFG (pH 4) particles revealed non-Newtonian and dominant viscouse (G″>G′) characters. This work can help to design Pickering emulsions using alcohol-soluble-based particles.

Neutral Interface Directed 3D Confined Self-Assembly of Block Copolymer: Anisotropic Patterned Particles with Ordered Structures.

Three-dimensional confined self-assembly (3D-CSA) of block copolymers (BCPs) is a distinctive and robust strategy that can yield colloidal polymer particles boasting ordered internal structures and diverse morphologies. The unique advantage of neutral interface lies in its ability to create anisotropic particles with surface patterns. The resulting unique polymer particles exhibit deformability under swelling, coupled with excellent spreadability and optical properties. These particles can also be used for fabrication of anisotropic nanoobjects or mesoporous particles via disassembly or serving as templates. This review comprehensively outlines the research advancements in neutral interface-guided 3D-CSA systems, including surfactant engineering, internal structure control, properties and future possibilities of anisotropic patterned particles.

Analysis of a Navier–Stokes phase-field crystal system

We consider an evolution system modeling a flow of colloidal particles which are suspended in an incompressible fluid and accounts for colloidal crystallization. The system consists of the Navier–Stokes equations for the volume averaged velocity coupled with the so-called Phase-Field Crystal equation for the density deviation. Considering this system in a periodic domain and assuming that the viscosity as well as the mobility depend on the density deviation, we first prove the existence of a weak solution in dimension three. Then, in dimension two, we establish the existence of a (unique) strong solution.

Reconfiguring Alginate-Based Supra-amphiphiles via Redox-Responsive Pickering Emulsions for Enhancing Pesticide Droplet Retention.

In view of the micro/nanostructure tunability of colloid particles, they acted as agrichemical delivery systems. Herein, supra-amphiphilic colloids were fabricated using a host-guest interfacial recognition-architected emulsion template strategy and controlled their agricultural interfacial interactions with the superhydrophobic target surface. Interestingly, the supramolecular interfacial system possessed redox-stimulated molecular reconfigurability by regulating aggregation/disaggregation behaviors. Therefore, the surface roughness of silver willow-like supramolecular colloids was readily modulated by tuning the micro/nanointerfaces of the emulsion template, which exhibited a topology and pliability that allowed them to adapt to the micro/nanostructures of leaf surfaces. It simultaneously solved comprehensive problems of adhesion, bounding, and rainwashing of pesticide droplets by the multiscale coupling effect. Intriguingly, the pesticide retention dominantly depended on the degree of surface roughness of silver willow-like supramolecular colloids, and the most roughened one showed greatest in vitro antifungal efficiency against Botrytis cinerea, reaching 91.8% even through multiple rainwashing. Results disclosed that the supra-amphiphilic colloids addressed the entire application processes for promoting the development of sustainable agricultural science.

Redox--animated supra-amphiphilic host-guest interfacial recognition for reconfiguring alginate--derived hierarchical colloidal particles to enhance foliar pesticide deposition

Insufficient deposition of pesticide droplets is a major factor contributing to ineffective control of agriculture. Improving the deposition of colloidal particle as agricultural delivery system is very important. Herein, supra-amphiphilic soft template was programmed by recognizing host–guest molecules on emulsion droplet surface. The supra-amphiphilic interfacial system possessed self-regulated amphiphilicity by modulating aggregation/disaggregation of supra-amphiphiles responding to redox-stimulus to control interface flexibility/functionalization characteristics of supramolecular colloids. This interface adjustability of hierarchical colloids greatly facilitated their prediction, control of corresponding targeting interfacial interaction responses of leaves. Then hierarchical particles exhibited a topology, pliability that allowed them to adapt to the micro/nanostructures of leaf surfaces, thus facilitating easier passage into the targeted pathogens. In vitro plot experiments, the supra-amphiphilic colloid with flexibility performed greatest antifungal capabilities against Botrytis Cinerea, reaching up to 88.65%, even after multiple rain erosions. Modulating the interfacial interactions towards hierarchical targets technically inspired a new green, sustainable agricultural application.

Ordered assemblies of peptide nanoparticles with only positive charge

Surface charge patchiness of different charge types can influence the solution behaviours of colloidal particles and globular proteins. Herein, coiled-coil ‘bundlemer’ nanoparticles that display only a single type of surface charge (SC) are computationally designed to compare their solution behaviours to mixed charge-type (MC) counterparts with both positively and negatively charged side chains. Nematic and columnar liquid crystal phases are discovered in low concentrations of SC particles, indicative of particle end-to-end stacking into columns combined with lateral electrostatic repulsion between columns, while MC particles with the same net charge and particle shape produced only amorphous, soluble aggregates. Similarly, porous lattices are formed in mixtures of SC/MC particles of opposite charges while MC/MC mixtures of opposite charges produce only amorphous aggregates. The lattice structure is inferred with a machine learning optimization approach. The differences between SC and MC particle behaviours directly show the importance of surface electrostatic patchiness.

Technical, environmental, and safety aspects in LignoSphere pilot plant design

The development of pilot plants is important in establishing new technology to close the gap between lab-scale and full-scale operations by minimizing technical uncertainties. Currently, limited research is available to evaluate different aspects of pilot plants for producing lignin-based materials before commercialization. This paper focuses on designing a safe and eco-friendly pilot plant for optimizing production of dried colloidal lignin particles (CLPs). The process starts with dissolving lignin in a ternary solvent mixture, introducing it into water to generate CLPs via self-assembly, recovering the solvents, and spray-drying CLPs. Based on reported lab-scale results, a detailed study was conducted to design the pilot plant, considering the technical, safety, and environmental factors according to standards and European Union legislation. The planned daily capacity of the pilot plant was 20 kg with 2.2 M€ fixed capital costs. This process design research can be applied in similar processes that involve lignin dissolution before scale-up.

Fourier-space Monte Carlo simulations of two-dimensional nematic liquid crystals

Thermal fluctuations are ubiquitous in mesoscopic and microscopic systems. Take nematic liquid crystals (LCs) as an example; their director fluctuations can strongly scatter light and give rise to random motions and rotations of topological defects and solid inclusions. These stochastic processes contain important information about the material properties of the LC and dictate the transport of the immersed colloidal particles. However, modeling thermal fluctuations of the nematic field remains challenging. Here, we introduce a new Monte Carlo simulation method, namely the Fourier-space Monte Carlo (FSMC) method, which is based on the Oseen–Frank elastic distortion energy model. This method accurately models the thermal fluctuations of a nematic LC’s director field. In contrast to the traditional real-space MC method, which perturbs the director locally, the FSMC method samples different eigenmodes of the director distortions in the Fourier space, aligning with the equipartition theorem. We apply FSMC to study defect fluctuations and trajectories in a two-dimensional nematic LC confined to various geometries. Our results show that FSMC can effectively sample degenerate defect configurations and reproduce long-range elastic interactions between defects. In addition, we conduct three-dimensional molecular dynamics simulations using a coarse-grained Gay–Berne potential, which corroborates the findings from FSMC. Taken together, we have developed a new Monte Carlo method to accurately model thermal fluctuations in nematic LCs, which can be useful for searching global free-energy minimum states in nematic, smectic, and other LC mesophases and can also be helpful in modeling the thermal motions of defects and inclusions in LCs.

Adaptive Opto-Thermal-Hydrodynamic Manipulation and Polymerization (AOTHMAP) for 4D Colloidal Patterning.

Precision colloidal patterning holds great promise in constructing customizable micro/nanostructures and functional frameworks, which showcases significant application values across various fields, from intelligent manufacturing to optoelectronic integration and biofabrication. Here, a direct 4D patterning method via adaptive opto-thermal-hydrodynamic manipulation and polymerization (AOTHMAP) with single-particle resolution is reported. This approach utilizes a single laser beam to automatically transport, position, and immobilize colloidal particles through the adaptive utilization of light-induced hydrodynamic force, optical force, and photothermal polymerization. The AOTHMAP enables precise 1D, 2D, and 3D patterning of colloidal particles of varying sizes and materials, facilitating the construction of customizable microstructures with complex shapes. Furthermore, by harnessing the pH-responsive properties of hydrogel adhesives, the AOTHMAP further enables 4D patterning by dynamic alteration of patterned structures through shrinkage, restructuring, and cloaking. Notably, the AOTHMAP also enables biological patterning of functional bio-structures such as bio-micromotors. The AOTHMAP offers a simple and efficient strategy for colloidal patterning with high versatility and flexibility, which holds great promises for the construction of functional colloidal microstructures in intelligent manufacturing, as well as optoelectronic integration and biofabrication.

Simple Models of Directly Measured Energy Landscapes for Different Shaped Particles in Nonuniform AC Electric Fields.

We report direct measurements of potential energy landscapes for different shaped colloidal particles interacting with nonuniform AC electric fields. Epoxy particle shapes investigated include disks, ellipses, squares, rectangles, and rhombuses, which are all part of the superelliptical prism shape class and are chosen to systematically vary particle anisotropy and corner features. The measurement configuration consists of noninteracting single particles sedimented onto microscope slides within electric fields between parallel coplanar electrodes. Thermally sampled positions and orientations of single particles in nonuniform fields are tracked in an optical microscope, and measured potential energy landscapes are obtained via Boltzmann inversions. We develop a new analytically simple model that captures all measured energy landscapes for superelliptical prism shaped colloidal particles with electrostatic double layers. The model recovers known validated potentials for spherical and ellipsoidal particles, and therefore captures energy landscapes for a variety of different colloidal particle sizes, shapes, and materials reported in prior studies.