Colloidal Particles Research Articles

Structural evolution of particle configurations: Zero-temperature phases under increasing confinement.

In this study, we investigate the phase behavior and structural organization of colloidal particles in a two-dimensional (2D) system under isotropic harmonic confinement using overdamped Langevin dynamics simulations. We employ a modified mermaid potential, which introduces an additional short-distance term resulting in a null-force region, distinct from the conventional mermaid potential. This modification facilitates a richer exploration of self-assembled structures, revealing a variety of phases influenced by the interplay between confinement strength V0 and the interaction potential. Our analysis spans a wide range of parameters, resulting in a detailed phase diagram that captures transitions from dispersed clusters to well-ordered patterns, including square, triangular, rhomboidal, and mixed configurations, as the confinement strength increases. The findings underscore the intricate balance of forces governing the self-assembly of colloidal systems and offer valuable insights for future experimental realizations.

Effect of colloidal particle size on physicochemical properties and aggregation behaviors of two alkaline soils

Abstract. Colloidal particles are the most active soil components, and they vary in elemental composition and environmental behaviors with the particle size due to the heterogeneous nature of natural soils. The purposes of the present study are to clarify how particle size affects the physicochemical properties and aggregation kinetics of soil colloids and to further reveal the underlying mechanisms. Soil colloidal fractions, from two alkaline soils – Anthrosol and Calcisol – were subdivided into three ranges: d<2 µm, d<1 µm and d<100 nm. The organic and inorganic carbon contents, clay mineralogy and surface electrochemical properties, including surface functional groups and zeta potentials, were characterized. Through a time-resolved light scattering technique, the aggregation kinetics of soil colloidal fractions were investigated, and their critical coagulation concentrations (CCCs) were determined. With decreasing colloidal particle diameter, the total carbon content, organic carbon, organic functional groups' content and illite content all increased. The zeta potential became less negative, and the charge variability decreased with decreasing particle diameter. The CCC values of Anthrosol and Calcisol colloids followed the descending order of d<100 nm, d<1 µm and d<2 µm. Compared with the course factions (d<1 and d<2 µm), soil nanoparticles were more abundant in organic carbon and more stable clay minerals (d<100 nm); thus they exhibited strongest colloidal suspension stability. The differences in organic matter contents and clay mineralogy are the fundamental reasons for the differences in colloidal suspension stability behind the size effects of Anthrosol and Calcisol colloids. The present study revealed the size effects of two alkaline soil colloids on carbon content, clay minerals, surface properties and suspension stability, emphasizing that soil nanoparticles are prone to be more stably dispersed instead of being aggregated. These findings can provide references for in-depth understanding of the environmental behaviors of the heterogeneous soil organic–mineral complexes.

Nanosponges : Formulation And Evaluation Of Nanosponges

This review aims that the study of to formulate and evaluate nonosponges as a Novel drug delivery systems, exploiting their potential to improve the biological availability of drug with long half lives. Nanosponges, tiny mesh structure with enhanced ability to encapsulate water and lipid soluble drug, have gained significant attention in the field of pharmaceuticals. These spherical colloidal particles possess a hydrophobic core, allowing for the transport of therapeutic molecules with both hydrophilic and hydrophobic properties composed of 3D network with long -chain polyester backbones and cross -linkers, nonosponges can be synthesized through the treatment of cyclodextrins with appropriate cross-linkers. The study will investigate the physicochemical properties, in-vitro release profile and biological efficiency of nonosponges, providing insights into their potential applications in pharmaceutical technology.

In silico optimization of a challenging bispecific antibody chromatography step.

Mechanistic modeling of chromatographic steps is an effective tool in biopharma process development that enhances process understanding and accelerates optimization efforts and subsequent risk assessment. A relatively new model for ion exchange chromatography is the colloidal particle adsorption (CPA) formalism, which promises improved separation of material and molecule-specific parameters. This case study demonstrates a straightforward CPA modeling workflow to describe an ion exchange chromatography polishing step of a knobs-into-holes construct bispecific antibody molecule. An adapted Yamamoto method was used to calculate charge and equilibrium parameters at three pH values. The remaining model parameters, binding kinetics, and effective mass transfer coefficients were determined via inverse fitting. The model was created from six experiments in total, tested on model parameter uncertainty, and evaluated on its power to predict changes in the biomolecule's retention behavior when variations in elution salt concentration occur. Finally, a three-step-gradient experiment was optimized, separating the desired bispecific antibody from its low and high molecular weight impurities, achieving a monomer yield of 68% and purity of 96%. Testing the model against a different load composition demonstrated its ability to extrapolate. An in silico one-factor-at-time and two-parameter screening of the optimized method identified the salt concentration to elute weaker binding impurities as a critical process attribute, while deviations in the buffer pH had a minor influence.

AF4/ICP-ToF-MS for the investigation of species-specific adsorption of organometallic contaminants on natural colloidal particles.

Organotin (OT) compounds, while crucial in many industrial applications, pose substantial risks to the environment and human health. The toxicity and environmental behaviour of OTs depend on their chemical form, i.e., the type and number of organic substituents. Each species thus exhibits distinct toxicity profiles and varying binding affinities to environmental colloids, which influence their mobility, bioavailability, and environmental impacts. To date, however, most studies addressed speciation and colloidal characterization separately, leaving the combined determinations of organometallics along with their carrier colloids largely elusive. Here, we develop and validate an on-line measurement system to quantify the adsorption dynamics of 10 OT species on natural colloidal particles (<500 nm). The approach integrates a versatile fractionation technique (AF4), with a state-of-the-art multi-element analyzer (ICP-ToF-MS), achieving Sn detection limits as low as 6.0 ng/L. The method separates colloid-free OT species from those bound to colloids and enables the determination of OT interactions with distinct colloidal fractions. Validated in both fractionation and detection, the method provides reliable data that could elucidate the species-specific and temporal aspects of species-colloids adsorption processes. The results feature comparative studies of 10 OT species, offering critical insights into OT mobility and distribution in environmental systems.

Complex Core-Shell Architectures through Spatially Organized Nano-Assemblies.

Core-shell structures demonstrate superior capability in customizing properties across multiple scales, offering valuable potential in catalysis, medicine, and performance materials. Integrating functional nanoparticles in a spatially controlled manner is particularly appealing for developing sophisticated architectures that support heterogeneous characteristics and tandem reactions. However, creating such complex structures with site-specific features remains challenging due to the dynamic microenvironment during the shell-forming process, which considerably impacts colloidal particle assembly. Here, we describe a method to spatially deploy nanoscale assemblies within microscale structures comprising a dense shell and a liquid core through colloidal surface decoration coupled with emulsion-based synthesis. Exploiting a spectrum of nanoparticles grafted with incrementally varying densities of organic ligands, we reveal that nanofeatures can be selectively sculpted onto the shell exterior, within the shell wall, and on the interior surface. The versatility of this mechanism is validated by systematically arranging nanoparticles with various compositions, shapes, and dimensions. Spatially integrated nanotitania endows the core-shell structures with localized photocatalytic abilities. Additionally, distinctive surface modifications enable the simultaneous yet independent implantation of diverse nanoparticles, yielding intricate architectures with programmable functions. This generalizable approach showcases a synthetic strategy to attain structural complexity and functional sophistication reminiscent of those of biological systems in nature.

Dynamic Reconstruction of Fluid Interface Manipulated by Fluid Balancing Agent for Scalable Efficient Perovskite Solar Cells.

Laboratory-scale spin-coating techniques are widely employed for fabricating small-size, high-efficiency perovskite solar cells. However, achieving large-area, high-uniformity perovskite films and thus high-efficiency solar cell devices remain challenging due to the complex fluid dynamics and drying behaviors of perovskite precursor solutions during large-area fabrication processes. In this work, a high-quality, pinhole-free, large-area FAPbI3 perovskite film is successfully obtained via scalable blade-coating technology, assisted by a novel bidirectional Marangoni convection strategy. By incorporating methanol (MeOH) as a fluid balance agent, the direction of Marangoni convection is effectively regulated, mitigating the disordered motion of colloidal precursor particles during the printing process. As a result, champion power conversion efficiencies (PCEs) of 24.45% and 20.32% are achieved for small-area FAPbI3 devices (0.07cm2) and large-area modules (21cm2), respectively. Notably, under steady illumination, the device reached a stabilized PCE of 24.28%. Furthermore, the unencapsulated device exhibited remarkable operational stability, retaining 92.03% of its initial PCE after 1800h under ambient conditions (35±5% relative humidity, 30°C). To demonstrate the universality of this strategy, a blue perovskite light-emitting diode is fabricated, showing an external quantum efficiency (EQE) of 14.78% and an electroluminescence wavelength (EL) of 494nm. This work provides a significant technique for advancing solution-processed, industrial-scale production of high-quality and stable perovskite films and solar cells.

Dynamically reconfigurable acoustofluidic metasurface for subwavelength particle manipulation and assembly

Particle manipulation plays a pivotal role in scientific and technological domains such as materials science, physics, and the life sciences. Here, we present a dynamically reconfigurable acoustofluidic metasurface that enables precise trapping and positioning of microscale particles in fluidic environments. By harnessing acoustic-structure interaction in a passive membrane resonator array, we generate localized standing acoustic waves that can be reconfigured in real-time. The resulting radiation force allows for subwavelength manipulation and patterning of particles on the metasurface at individual and collective scales, with actuation frequencies below 2 MHz. We further demonstrate the capabilities of the reconfigurable metasurface in trapping and enriching beads and biological cells flowing in microfluidic channels, showcasing its potential in high-throughput bioanalytical applications. Our versatile and biocompatible particle manipulation platform is suitable for applications ranging from the assembly of colloidal particles to enrichment of rare cells.

Two-Dimensional Square Lattice of Colloidal Particles Formed by Electrostatic Adsorption in Confined Space.

In this study, we demonstrate a novel and efficient fabrication methodology for nonclose-packed, two-dimensional (2D) colloidal crystals exhibiting square lattice structures. In our recent work, we detailed the formation of 2D colloidal crystals via the electrostatic adsorption of three-dimensional (3D) charged colloidal crystals onto oppositely charged substrates. These 3D colloidal crystals possessed a face-centered cubic (FCC) lattice structure with their (111) planes aligned parallel to the substrate, facilitating the formation of 2D crystals with triangular lattice arrangements upon adsorption. This work presents the synthesis of 2D crystals with square lattices─a configuration widely used in photonics. We prepared 3D colloidal crystals of silica particles with four-fold symmetry in a micrometer-scale gap between two coverslips. The bottom glass surface is modified with a cationic silane coupling reagent, aminopropyltriethoxysilane, generating pH-responsive charge characteristics with an isoelectric point (iep) near pH 8. When the pH is greater than iep, the surface is charged negatively. As pH decreases below iep, the sign of the surface charge reverses to positive. Controlled pH lowering below the iep induces adsorption of the lowermost lattice plane of 3D crystals onto the substrate, yielding 2D crystals with a distinct square lattice. We further synthesized three-layer body-centered cubic (BCC) structures by stacking alternating layers of the 2D square lattices of silica and polystyrene particles. By aligning the refractive index of the surrounding medium (aqueous solution of ethylene glycol) with that of silica particles, we successfully fabricated a structure that is optically identical to a simple cubic lattice. These findings advance the development of 2D crystalline materials for photonic and plasmonic applications.

A Wenzel Interfaces Design for Homogeneous Solute Distribution Obtains Efficient and Stable Perovskite Solar Cells.

The coffee-ring effect, caused by uneven deposition of colloidal particles in perovskite precursor solutions, leads to poor uniformity in perovskite films prepared through large-area printing. In this work, the surface of SnO2 is roughened to construct a Wenzel model, successfully achieving a super-hydrophilic interface. This modification significantly accelerates the spreading of the perovskite precursor solution, reducing the response delay time of perovskite colloidal particles during the printing process. Additionally, the micro-spherical depression structure on the SnO2 surface effectively inhibits the migration of colloidal particles toward the edges of liquid film, trapping perovskite colloidal particles at the buried interfaces and improving film uniformity. Due to the synergistic effect of super-hydrophilicity and micro-rough structure on the surface of SnO2, leading to a substantial improvement in the quality of perovskite crystals. Therefore, the efficiency of printing prepared flexible devices (0.101 cm2) reached 25.42% (certified 25.12%). Moreover, the efficiency of rigid and flexible large-scale perovskite solar modules (PSMs) based on meniscus-coating manufacture reached 21.34% and 16.99% (100 cm2), respectively, and demonstrated superior environmental stability by maintaining an initial efficiency of 91% after being stored in atmospheric conditions for 2000 h, offering practical guidance for fabricating high-performance and stable large-scale perovskite solar cells (PSCs).

Full-Spectrum Mechanochromic Photonic Films with Large Interparticle Distance.

Non-close-packed crystalline arrays of colloidal particles in an elastic matrix exhibit mechanochromism. However, small interparticle distances often limit the range of reversible color shifts and reduce reflectivity during a blueshift. A straightforward, reproducible strategy using matrix swelling to increase interparticle distance and improve mechanochromic performance is presented. Photonic composites are initially prepared with silica particle arrays embedded in an elastomer matrix at volume fractions of 0.35-0.5. To increase interparticle distance, the composites are immersed in an elastomer-forming monomer, causing the matrix to swell, followed by photopolymerization, thereby producing liquid-free composites. The degree of swelling is controllable up to 3.16, depending on monomer choice, matrix volume fraction, and crosslinking density. The process can be repeated to further increase swelling up to 10.36. This method can reduce the volume fraction of silica particles from 40% to 3.8%, while interparticle distance increases from 53 to 257nm. The swollen photonic composites exhibit a full visible spectrum under compression, while minimizing reflectivity loss. This allows red-colored photonic composites to be transformed into vivid multicolor patterns when compressed with stamps featuring spatial height variations.

Spatially Isomeric Fulleropyrrolidines Enable Controlled Stacking of Perovskite Colloids for High-Performance Tin-Based Perovskite Solar Cells.

The advancement of tin-based perovskite solar cells (TPSCs) has been severely hindered by the poor controllability of perovskite crystal growth and the energy level mismatch between the perovskite and fullerene-based electron transport layer (ETL). Here, we synthesized three cis-configured pyridyl-substituted fulleropyrrolidines (PPF), specifically 2-pyridyl (PPF2), 3-pyridyl (PPF3), and 4-pyridyl (PPF4), and utilized them as precursor additives to regulate the crystallization kinetics during film formation. The spatial distance between the two pyridine groups in PPF2, PPF3, and PPF4 increases sequentially, enabling PPF4 to interact with more perovskite colloidal particles. These interactions effectively enlarge the precursor colloid size and decelerate the crystallization rate of the perovskite, resulting in high-quality PPF4-based perovskite films with reduced defect density and lower exciton binding energy. Additionally, we incorporated a well-defined fullerene bis-adduct, C60BB, as an interlayer between the perovskite and PCBM layers to optimize energy level alignment. Through the synergistic effects of PPF4 and C60BB, our champion device achieved an efficiency of 16.05 % (certified: 15.86 %), surpassing the 16 % efficiency bottleneck and setting a new benchmark for TPSCs. Moreover, the devices exhibited outstanding stability, retaining 99 % of their initial efficiency after 600 hours of maximum power point tracking under 1 sun condition.

One- and two-particle microrheology of soft materials based on optical-flow image analysis.

Particle-tracking microrheology probes the rheology of soft materials by accurately tracking an ensemble of embedded colloidal tracer particles. One-particle analysis, which focuses on the trajectory of individual tracers is ideal for homogeneous materials that do not interact with the particles. By contrast, the characterization of heterogeneous, micro-structured materials or those where particles interact directly with the medium requires a two-particle analysis that characterizes correlations between the trajectories of distinct particle pairs. Here, we propose an optical-flow image analysis as an alternative to the tracking-based algorithms to extract one and two-particle microrheology information from video microscopy images acquired using diverse imaging contrast modalities. This technique, termed optical-flow microrheology (OFM), represents a high-throughput, operator-free approach for the characterization of a broad range of soft materials, making microrheology accessible to a wider scientific community.

Spatiotemporal evolution of heterogeneous structures in agarose gels revealed by particle tracking.

Upon decreasing the temperature, agarose solution exhibited gelation and phase separation, forming a cloudy gel consisting of agarose-rich and agarose-poor phases. Both phenomena contribute to the formation of a heterogeneous gel structure, but the primary influence of both processes on this heterogeneity remains unclear. In this study, we defined the specific gelation and phase separation temperatures of an agarose solution and examined the resulting gel structures with and without phase separation. Microscopic observation and colloid diffusion analysis revealed that phase separation leads to inhomogeneities several micrometers in size. Furthermore, we found that the distributions of colloidal diffusion coefficients and particle displacements strongly reflected the heterogeneity primarily induced by phase separation and gelation. Our findings contribute to the physicochemical understanding of the heterogeneous structures of various (bio) polymer gels associated with the phase separation of polymers.

Fabrication and characterization of a novel non-dairy whipping cream formed by only gliadin colloidal particles and shea butter

Fabrication and characterization of a novel non-dairy whipping cream formed by only gliadin colloidal particles and shea butter

Direct quantification of the plasmon dephasing time in ensembles of gold nanorods through two-dimensional electronic spectroscopy.

In this study, we used two-dimensional electronic spectroscopy to examine the early femtosecond dynamics of suspensions of colloidal gold nanorods with different aspect ratios. In all samples, the signal distribution in the 2D maps at this timescale shows a distinctive dispersive behavior, which can be explained by the interference between the exciting field and the field produced on the nanoparticle's surface by the collective motion of electrons when the plasmon is excited. Studying this interference effect, which is active only until the plasmon has been dephased, allows for a direct estimation of the dephasing time of the plasmon of an ensemble of colloidal particles. Our findings provide insight into the fundamental behavior of plasmonic states and highlight the potential of two-dimensional electronic spectroscopy in uncovering ultrafast and coherent optical phenomena at the nanoscale.

Advances in the photon avalanche luminescence of inorganic lanthanide-doped nanomaterials.

Photon avalanche (PA)-where the absorption of a single photon initiates a 'chain reaction' of additional absorption and energy transfer events within a material-is a highly nonlinear optical process that results in upconverted light emission with an exceptionally steep dependence on the illumination intensity. Over 40 years following the first demonstration of photon avalanche emission in lanthanide-doped bulk crystals, PA emission has been achieved in nanometer-scale colloidal particles. The scaling of PA to nanomaterials has resulted in significant and rapid advances, such as luminescence imaging beyond the diffraction limit of light, optical thermometry and force sensing with (sub)micron spatial resolution, and all-optical data storage and processing. In this review, we discuss the fundamental principles underpinning PA and survey the studies leading to the development of nanoscale PA. Finally, we offer a perspective on how this knowledge can be used for the development of next-generation PA nanomaterials optimized for a broad range of applications, including mid-IR imaging, luminescence thermometry, (bio)sensing, optical data processing and nanophotonics.

Stabilizing bicontinuous particle-stabilized emulsions formed via solvent transfer-induced phase separation.

Bicontinuous particle-stabilized emulsions (bijels) are unique soft materials that combine the bulk properties of two immiscible fluids into a single interconnected structure. This structure is achieved through the formation of two interwoven fluid networks, stabilized by an interfacial layer of colloidal particles. Bijels with submicron-scale domain networks can be synthesized via solvent transfer-induced phase separation (STrIPS). However, the fluid network structure in STrIPS-bijels tends to degrade over time, limiting their practical applications. In this study, we identify that the destabilization of STrIPS-bijels is driven by the exchange of matter between the bijel and the surrounding oil phase. Confocal laser scanning microscopy reveals that over time, aqueous components from the bijel dissolve into the surrounding oil, leading to an inward flow of oil into the bijel. This process disrupts the fluid bicontinuous structure within hours. To extend the stability of the bijel to several weeks, we explore strategies to reduce the dissolution of the aqueous phase and the inflow of oil. Specifically, we investigate the effects of the oil's chemical composition and properties, as well as modifications to the surface chemistry of the supporting glass substrates. Our results show that while the particle scaffold of STrIPS-bijels exhibits long-term stability, the maintenance of the fluid bicontinuous network depends on minimizing the loss of aqueous components. The enhanced control over the stability of the fluid bicontinuous structure developed in this work is critical for advancing STrIPS-bijels as functional materials for applications in catalysis, separations, and energy storage.

Stability of electrostatically stabilized Pickering emulsion of silica particles and soy hull polysaccharides: Mechanism of pH and ionic strength.

To enhance the surface hydrophobicity and emulsification capacity of silica colloidal particles, a natural surface modification of soy hull polysaccharides (SHP) was conducted. Here, the effects of pH and ionic strength on the stability, microstructure and rheological properties of concentrated Pickering emulsions were investigated. Experimental results show emulsions gelled at pH2, with increasing pH (2-10), SiO2-SHP absolute zeta potential (from -19.6 to -44.7mV) and interfacial tension (from 15.2 to 25.09 mN/m) increased, and viscosity, viscoelasticity and storage stability decreased. Additionally, at low NaCl concentrations (<150mM), SiO2-SHP interfacial tension remained low (21.3 mN/m), promoting stable emulsions (TSI<1.5). In this case, the electrostatic interaction was slightly affected by ions, facilitating the occurrence of composite coagulation. However, as ionic concentration increased (150-300mM), interfacial tension increased (from 20.5 to 27.6 mN/m). Thus, our study presents important insights into the pH and salt ions dependent mechanism of emulsion stabilization by SiO2-SHP.

Collective Dynamics of Intelligent Active Brownian Particles with Visual Perception and Velocity Alignment in 3D: Spheres, Rods, and Worms

Many living systems, such as birds and fish, exhibit collective behaviors like flocking and swarming. Recently, an experimental system of active colloidal particles has been developed, where the motility of...