Colloidal Particles Research Articles

Diffusionless rotator-crystal transitions in colloidal truncated cubes.

Upon osmotic compression, rotationally symmetric faceted colloidal particles can form translationally ordered, orientationally disordered rotator mesophases. This study explores the mechanism of rotator-to-crystal phase transitions where orientational order is gained in a translationally ordered phase, using rotator-phase forming truncated cubes as a testbed. Monte Carlo simulations were conducted for two selected truncations (s), one for s = 0.527 where the rotator and crystal lattices are dissimilar and one for s = 0.572 where the two phases have identical lattices. These differences set the stage for a qualitative difference in their rotator-crystal transitions, highlighting the effect of lattice distortion on phase transition kinetics. Our simulations reveal that significant lattice deviatoric effects could hinder the rotator-to-crystal transition and favor arrangements of lower packing fraction instead. Indeed, upon compression, it is found that for s = 0.527, the rotator phase does not spontaneously transition into the stable, densely packed crystal due to the high lattice strains involved but instead transitions into a metastable solid phase to be colloquially referred to as "orientational salt" for short, which has a similar lattice as the rotator phase and exhibits two distinct particle orientations having substitutional order, alternating regularly throughout the system. This study paves the way for further analysis of diffusionless transformations in nanoparticle systems and how lattice-distortion could influence crystallization kinetics.

Spatially Confined Assembly and Immobilization of Hierarchical Nanoparticle Architectures inside Microdroplets in Magnetic Fields.

Magnetic field-directed colloidal interactions offer facile tools for assembly of structures that range from linear chains to multidimensional hierarchical architectures. While the field-driven assembly of colloidal particles has commonly been investigated in unbounded media, a knowledge gap remains concerning such assembly in confined microenvironments. Here, we investigate how confinement of ferromagnetic nanoparticles in microspheres directs their magnetic assembly into hierarchical architectures. Microdroplets from polydimethylsiloxane (PDMS) liquid precursor containing dispersed iron oxide magnetic nanoparticles (MNPs) were placed in a static magnetic field leading to the formation of organized assemblies inside the host droplets. By changing the MNP concentrations, we revealed a sequence of microstructures inside the droplets, ranging from linear chains at a low MNP loading, transitioning to a combination of chains and networked bundles, to solely 3D bundles at high MNP loading. These experimental results were analyzed with the aid of COMSOL simulations where we calculated the potential energy to identify the preferred assembly conformations. The chains at high MNP loading minimized their energy by aggregating laterally to form bundles with their MNP dipoles being out-of-registry. We cured these PDMS droplets to immobilize the assemblies by forming soft microbeads. These microbeads constitute an "interaction toolbox" with different magnetic macroscale responses, which are governed by the structuring of the MNPs and their magnetic polarizability. We show that thanks to their ability to rotate by field-induced torque under a rotating field, these microbeads can be employed in applications such as optical modulators and microrollers.

Transient electrophoresis of colloidal particles in a salt-free medium

A general theory is developed for the time dependent transient electrophoretic mobility of spherical colloidal particles in a salt-free liquid medium containing only counterions when a step external electric field is suddenly applied to the colloidal suspension. It is found that as in the case of the steady electrophoretic mobility in a salt-free medium, there is a certain critical value of the particle surface charge separating two cases, that is, the low-surface-charge case and the high-surface-charge case. In the latter case the counterion condensation takes place near the particle surface. For the low-surface charge case, the transient electrophoretic mobility agrees with that of a sphere in an electrolyte solution in the limit of very low electrolyte concentrations. For the high-surface-charge case, however, the transient mobility becomes independent of the particle surface charge because of the counterion condensation effects. A simple expression is derived for the ratio of the transient electrophoretic mobility to the steady electrophoretic mobility, which is found to take the same form irrespective of the magnitude of the particle surface charge. Using this equation, it is now possible to predict how the system will approach its final steady state.

Topologically controlled synthesis of active colloidal bipeds

Topological growth control allows to produce a narrow distribution of outgrown colloidal rods with defined and adjustable length. We use an external magnetic field to assemble paramagnetic colloidal spheres into colloidal rods of a chosen length. The rods reside above a metamorphic hexagonal magnetic pattern. The periodic repetition of specific loops of the orientation of an applied external field renders paramagnetic colloidal particles and their assemblies into active bipeds that walk on the pattern. The metamorphic patterns allow the robust and controlled polymerization of single colloids to bipeds of a desired length. The colloids are exposed to this fixed external control loop that causes multiple simultaneous responses: Small bipeds and single colloidal particles interpret the external magnetic loop as an order to walk toward the active zone, where they assemble and polymerize. Outgrown bipeds interpret the same loop as an order to walk away from the active zone. The topological transition occurs solely for the growing biped and nothing is changed in the environment nor in the magnetic control loop. As in many biological systems the decision of a biped that reached its outgrown length to walk away from the reaction site is made internally, not externally.

A versatile method for facile and reliable synthesis of colloidal particles with a size and composition gradient

Abstract Colloidal particles play a pivotal role in numerous applications across various disciplines, many of which necessitate precise control over particle size and size distribution. Seeded growth reactions have been established as effective methods for reproducibly accessing tailor-made particles. However, conventional batch-wise syntheses only yield discrete particle sizes. With the increasing focus on complex structures in current research, there is a demand for innovative and adaptable techniques to produce colloidal particles with precise sizes and size distributions. The Controlled Emulsion Extraction Process (CrEEP) is capable of addressing this challenge. Here, we present in detail how this synthesis works and demonstrate its reliability and versatility. Our approach exploits the time-dependent particle growth and enables accessing dispersions of controlled particle size distributions. We highlight these possibilities through a variation of the monomer feed and feed composition, resulting in gradual changes in both size and glass transition temperature, respectively. Beyond its application to polymer particles, CrEEP can be seamlessly extended to other seeded-growth mechanisms, such as the silica Stöber synthesis. Consequently, the Controlled Extraction Stöber Process (CrESP) similarly yields a size gradient, showcasing the generality of this synthetic advancement. Graphical abstract

Performance repair of building materials using alumina and silica composite nanomaterials with electrodynamic properties

Abstract In recent years, the service life of building materials has become the focus of attention. Among them, the service life of concrete and steel bars is particularly affected by the corrosion of external ions (such as Cl−) in the environment. To solve this problem, a new type of composite nanocolloid was prepared through a controllable preparation method. The composite nanocolloid is prepared from aluminum chloride sol and silica sol as raw materials. The prepared colloidal particles have a particle size distribution between 10.5 and 17.5 nm, exhibiting excellent stability and dispersibility. In order to verify the improvement effect of the composite nanocolloid on the properties of building materials, the influence of it on the porosity of concrete and the anti-corrosion performance of steel bars was experimentally studied. The results indicate that the moisture absorption and dehumidification speed of concrete treated with composite nano colloids is slower, and the pore size distribution is mainly concentrated in 100–1,000 nm, indicating that the colloids can effectively optimize the pore structure of concrete. In addition, the processed steel plate samples showed high AC impedance values and low corrosion current logarithmic values in electrochemical testing, indicating that composite nanocolloids have a significant protective effect on the corrosion of steel bars, which can effectively improve the performance of building materials and extend their service life.

Performance repair of building materials using alumina and silica composite nanomaterials with electrodynamic properties

Abstract In recent years, the service life of building materials has become the focus of attention. Among them, the service life of concrete and steel bars is particularly affected by the corrosion of external ions (such as Cl−) in the environment. To solve this problem, a new type of composite nanocolloid was prepared through a controllable preparation method. The composite nanocolloid is prepared from aluminum chloride sol and silica sol as raw materials. The prepared colloidal particles have a particle size distribution between 10.5 and 17.5 nm, exhibiting excellent stability and dispersibility. In order to verify the improvement effect of the composite nanocolloid on the properties of building materials, the influence of it on the porosity of concrete and the anti-corrosion performance of steel bars was experimentally studied. The results indicate that the moisture absorption and dehumidification speed of concrete treated with composite nano colloids is slower, and the pore size distribution is mainly concentrated in 100–1,000 nm, indicating that the colloids can effectively optimize the pore structure of concrete. In addition, the processed steel plate samples showed high AC impedance values and low corrosion current logarithmic values in electrochemical testing, indicating that composite nanocolloids have a significant protective effect on the corrosion of steel bars, which can effectively improve the performance of building materials and extend their service life.

Combined extraction of manganese during water purification of technogenic solutions

A method for demanganization of technogenic aqueous solutions is presented. This method involves electrocoagulation purification of aqueous systems from high metal contents and extraction of manganese (II) ions by carbon sorbent adsorption. A coagulation technology based on electrogenerated aluminum hydroxide was used. According to diffraction analysis, such a hydroxide exhibits an amorphous porous hydrogel structure with a developed sorbing surface. The micellar structure of the as-generated aluminum hydroxide, which was attributed to a modification of gibbsite, is represented by the following colloidal particle: {[m Al(OH)3] nAl(OH)2+ (n-x) OH-}x+ xOH-. The associative process of sorption on gibbsite occurs by dispersion interaction, which is governed by the force of electrostatic attraction of instantaneous and induced dipoles of electrically neutral sorbent molecules and the [Mn (OH2)2(OH)2]0 manganese hydroxo-aquo complex. The adsorption limiting value of manganese ions amounted to 4.9 mmol/g at 298 K and pH 5.8, with the adsorption equilibrium constant reaching 1.36 . 104. The electricity consumption corresponded to 12.0 А.h at an optimal electrocoagulation duration of 15 min and a current density of 1.6 мА/сm2. The final purification of aqueous solutions using carbon sorbents was conducted in a slightly alkaline medium at pH 7.5. The manganese sorption value reached 1.68 mmol/g. Therefore, the resource-saving effect of processing of technogenic hydro-mineral solution is manifested in a significant reduction of heavy metal salts and in obtaining of demanded mixed coagulants of aluminum and iron sulfates from water purification wastes. Another positive effect of electrochemical water purification consist in water disinfection and its improved ogranoleptic parameters.

Combined extraction of manganese during water purification of technogenic solutions

A method for demanganization of technogenic aqueous solutions is presented. This method involves electrocoagulation purification of aqueous systems from high metal contents and extraction of manganese (II) ions by carbon sorbent adsorption. A coagulation technology based on electrogenerated aluminum hydroxide was used. According to diffraction analysis, such a hydroxide exhibits an amorphous porous hydrogel structure with a developed sorbing surface. The micellar structure of the as-generated aluminum hydroxide, which was attributed to a modification of gibbsite, is represented by the following colloidal particle: {[m Al(OH)3] nAl(OH)2+ (n-x) OH-}x+ xOH-. The associative process of sorption on gibbsite occurs by dispersion interaction, which is governed by the force of electrostatic attraction of instantaneous and induced dipoles of electrically neutral sorbent molecules and the [Mn (OH2)2(OH)2]0 manganese hydroxo-aquo complex. The adsorption limiting value of manganese ions amounted to 4.9 mmol/g at 298 K and pH 5.8, with the adsorption equilibrium constant reaching 1.36 . 104. The electricity consumption corresponded to 12.0 А.h at an optimal electrocoagulation duration of 15 min and a current density of 1.6 мА/сm2. The final purification of aqueous solutions using carbon sorbents was conducted in a slightly alkaline medium at pH 7.5. The manganese sorption value reached 1.68 mmol/g. Therefore, the resource-saving effect of processing of technogenic hydro-mineral solution is manifested in a significant reduction of heavy metal salts and in obtaining of demanded mixed coagulants of aluminum and iron sulfates from water purification wastes. Another positive effect of electrochemical water purification consist in water disinfection and its improved ogranoleptic parameters.

The impact of viscosity asymmetry on phase separating binary mixtures with suspended colloids.

The introduction of neutrally wetting colloidal particles into coarsening binary fluids is known to arrest the dynamics of the phase separation, as the colloids tend to be captured by the growing interfaces to reduce the free energy of the system. This phenomenon has often been studied in systems with symmetric fluid viscosities. In this study, we investigate the behavior of colloidal particles introduced into asymmetric binary fluids with a viscosity contrast. Our results show that due to the broken symmetry the colloidal particles more easily escape from the interface towards the more viscous fluid, which reduces the lifetime of the jammed phase. Moreover, the presence of colloidal particles near the interfaces promotes the formation of micro-droplets with typical sizes comparable to the colloids.

A curcumin-loaded biopolymeric nanocomposite alleviates dextran sulfate sodium induced ulcerative colitis via suppression of inflammation and oxidative stress

Functional drugs nano delivery systems manufactured from natural active products are promising for the field of biomedicines. In this study, an anti-ulcerative colitis (UC) curcumin loaded biopolymeric nanocomposite (CZNH) was fabricated and investigated. CZNH nanocomposite was obtained using the anti-solvent precipitation method, wherein curcumin-loaded zein colloidal particles served as the core, while sodium casein (NaCas) and hyaluronic acid (HA) formed the outermost layer of CZNH nanocomposite. Fourier transform infrared (FT-IR) spectrum and transmission electron microscopy (TEM) findings demonstrated that CZNH nanocomposite was a double-layer spherical micelle (250 nm) resulting from the hydrogen bond interactions and electrostatic adsorptions between zein, NaCas, and HA. Furthermore, CZNH nanocomposite exhibited prominent resuspension and storage stability in aqueous solution, which can be stored at 4 °C for approximately 30 days. In vivo anti-UC studies showed that CZNH nanocomposite could effectively alleviate UC symptoms via mediating inflammatory factors [tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6], myeloperoxidase (MPO), and oxidative stress factor [malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px)]. This study suggested that the CZNH nanocomposite showed great promise as an efficient curcumin nanocarrier for UC therapy.

Adsorption on a Spherical Colloidal Particle from a Mixture of Nanoparticles with Competing Interactions.

Adsorption of nanoparticles on a spherical colloidal particle is studied by molecular dynamics simulations. We consider a generic model for a mixture of nanoparticles with energetically favored self-assembly into alternating layers of the two components. When both components are attracted to the colloidal particle, the adsorbed nanoparticles self-assemble either into alternating parallel tori and clusters at the two poles of the colloidal particle, or into alternating spirals wrapped around the spherical surface. The long-lived metastable states obtained in simulations follow from the spherical shape of the adsorbing surface and the requirement that the neighboring chains of the nanoparticles are composed of different components. A geometrical construction leading to all such patterns is presented. When the second component particles are repelled from the colloidal particle and the attraction of the first component is strong, the attracted particles form a monolayer at the surface of the colloidal particle that screens the repulsion of the second component. The subsequent adsorbed alternating spherical layers of the two components form together a thick shell. This structure leads to the adsorption that is larger than in the case of the same attraction of the two components to the colloidal particle.

Decoupling of rotation and translation at the colloidal glass transition.

In dense particle systems, the coupling of rotation and translation motion becomes intricate. Here, we report the results of confocal fluorescence microscopy where simultaneous recording of translational and rotational particle trajectories from a bidisperse colloidal dispersion is achieved by spiking the samples with rotational probe particles. The latter consist of colloidal particles containing two fluorescently labeled cores suited for tracking the particle's orientation. A comparison of the experimental data with event driven Brownian simulations gives insights into the system's structure and dynamics close to the glass transition and sheds new light onto the translation-rotation coupling. The data show that with increasing volume fractions, translational dynamics slows down drastically, whereas rotational dynamics changes very little. We find convincing agreement between simulation and experiments, even though the simulations neglect far-field hydrodynamic interactions. An additional analysis of the glass transition following mode coupling theory works well for the structural dynamics but indicates a decoupling of the diffusion of the smaller particle species. Shear stress correlations do not decorrelate in the simulated glass states and are not affected by rotational motion.

Thermal design of a non-isothermal microfluidic channel for measuring thermophoresis

Thermophoresis describes mass transport in a non-isothermal temperature field and thus provides a fundamental understanding of the behavior of colloidal particles. Various methods have been proposed for measuring the Soret coefficient, a representative value of thermophoresis. In particular, microscopic channels are an emerging method as they shorten the equilibrium time and allow direct observation of the particles. However, little emphasis has been placed on the simultaneous consideration of fluid dynamics, heat transfer, and mass transfer characteristics within the microfluidic channel, despite the simultaneous presence of natural convection and thermodiffusion phenomena. In this study, we present a novel approach to address this gap by introducing a figure of merit, which incorporates essential parameters to accurately characterize a specific cell configuration. This figure of merit allows for the identification of a reliable measurement range in a microfluidic channel with a temperature gradient, while accounting for fluid dynamics, heat transfer, and mass transfer characteristics. The proposed approach is validated through rigorous simulations and experiments, enabling an evaluation of the impact of figure of merit-derived parameters on the measurement channel. The findings from our study demonstrate that the figure of merit serves as a representative measure for stable thermophoretic measurements in a microfluidic channel. Moreover, we propose a threshold value that signifies the transition from a diffusion-dominant to a convection-dominant field.

Self-organization of C60 fullerene molecules in xylene/ethanol mixtures

Fullerene molecules have been intensively studied over the past few decades due to their unique chemical and physical properties, which have great potential in a wide range of applications. In this article, the formation and aging of C60 colloids in the xylene/ethanol system is considered. The peculiarities of these processes are studied by the methods of refractometry, optical absorption, Raman spectroscopy and dynamic light scattering (DLS). It has been experimentally established that the formation of colloidal particles in a C60/xylene/ethanol mixture depends on the volume content of the components and the storage time of the solution. The time required to achieve stability of self-organization of solute molecules in a C60/xylene/ethanol mixture is discussed.

Self-organization of C60 fullerene molecules in xylene/ethanol mixtures

Fullerene molecules have been intensively studied over the past few decades due to their unique chemical and physical properties, which have great potential in a wide range of applications. In this article, the formation and aging of C60 colloids in the xylene/ethanol system is considered. The peculiarities of these processes are studied by the methods of refractometry, optical absorption, Raman spectroscopy and dynamic light scattering (DLS). It has been experimentally established that the formation of colloidal particles in a C60/xylene/ethanol mixture depends on the volume content of the components and the storage time of the solution. The time required to achieve stability of self-organization of solute molecules in a C60/xylene/ethanol mixture is discussed.

Depletion potential, correlation functions and demixing transition in model colloid-polymer mixtures

We describe a theoretical framework to calculate depletion potential between colloid particles induced by non-adsorbing ideal polymer chains (s-species) and correlation functions in a coarse-grained one-component system of colloids (c-species). A Padé approximant is used to express the depletion potential as a pair potential with many-body contributions subsumed in it. The depletion potential and correlation functions of c-species are calculated using a self-consistent procedure. Results for several values of size ratio q=σsσc (σs and σc are, respectively diameters of the polymer chain and a colloid particle) and packing fractions of s- and c-species are reported. The spinodal curve and critical point of demixing transition are determined for several values of q. Calculated values are compared with values found from other theories and simulations.

Emergent patterns in shape-asymmetric Quincke rollers

This study investigates the Quincke rolling phenomenon of snowman-shaped colloidal particles. These chiral rollers exhibit individual and collective dynamic states that depend upon the population and driving field strength. In addition to the previously identified dynamic states, such as spinning and vortex states, we identify the standing and bounded motion of the particles. The bounded motion involves the confined orbiting of particles around the center of mass due to hydrodynamic interactions at low particle area fractions. Our findings provide valuable insights into the behavior of active systems and the fabrication of active materials, emphasizing emergent order and adaptability as key guiding principles.

The creeping movement of a soft colloidal particle normal to a planar interface

A methodological blend of analytical and numerical strategies employing collocation techniques is presented to investigate the task of describing the Stokes flow generated by a soft particle (composite sphere) moving perpendicularly to a planar interface of infinite extent, separating two semi-infinite, immiscible viscous fluid domains. The particle consists of a solid core enclosed by a porous membrane allowing fluid passage. The movement of the soft nanoparticle has been examined through a continuum mathematical model. This model incorporates the Stokes and Brinkman equations, accounting for the hydrodynamic fields both outside and within the porous membrane layer, respectively. The motion is investigated under conditions characterized by low Reynolds and capillary numbers, where the interface experiences negligible deformation. The solution combines cylindrical and spherical fundamental solutions via superposition. Initially, the boundary conditions at the fluid–fluid interface are satisfied utilizing Fourier–Bessel transforms, subsequently addressing the conditions at the soft particle's surface through a collocation method. The normalized drag force exerted on the particle is accurately calculated, exhibiting robust convergence across various geometric and physical parameters. These findings are effectively visualized via graphs and tables. We juxtapose our drag force coefficient results with established literature data, particularly focusing on the extreme cases. The findings highlight the substantial impact of the interface on the drag force coefficient. Across the full range of viscosity ratios, the normalized drag force decreases as the relative thickness of the porous layer increases. These results enhance the understanding of practical systems and industrial processes such as sedimentation, flotation, electrophoresis, and agglomeration.

Water-induced reversible deformation materials: Synthesis and UV polymerization of sulfonic based polyacrylates

Reversible deformable materials driven by water or humidity have crucial applications in many areas. A novel sulfonic based cross-linked polyacrylates were prepared by simple UV emulsion copolymerization of functional sulfonic based acrylates with conventional acrylates and epoxy acrylate resins. The structure of sulfonic based acrylates was characterized by FT-ATR,1H-NMR, high-resolution mass spectrometry. The thermal properties, surface morphology and structure of the cured polymers were analyzed. The reversible deformation induced by water and humidity were explored. Based on analysis of surface morphology, XPS and etching experiments, a reasonable deformation mechanism is proposed that the hydrophilic groups migrate to the surface of the oil-in-water colloidal particle film due to the difference in polarity and show a gradient distribution, and hydration of hydrophilic groups results in water absorption and film expansion. Reversible deformation materials driven by water or humidity are of great significance in the field of research on smart material systems.