Interparticle Interactions Research Articles

Local Energy Minima and Density of Energy Barriers in Dense Clusters of Magnetic Nanoparticles

In this paper, we focus on the properties of local energy minima and energy barriers in immobilized dense clusters of magnetic nanoparticles. Understanding of these features is highly interesting both for the fundamental physics of disordered systems with long-range interparticle interaction and for numerous applications of modern ferrofluids consisting of such clusters. In particular, it is needed to predict the ac-susceptibility of these systems and their magnetization relaxation after a sudden change in the external field, because both processes occur via magnetization jumps over energy barriers that separate the energy minima. Due to the exponential increase in the corresponding jump time with barrier height (tsw∼exp(ΔE/kT)), direct Langevin dynamics simulations of this process are not feasible. For this reason, we have developed efficient numerical methods both for finding as many energy minima as possible and for the reliable evaluation of energy barriers between them. Our results for the distribution of overlaps between the local energy minima imply that there is no spin-glass state in such clusters even when they consist of particles with a small anisotropy. Further, we show that the distributions of energy barrier heights are qualitatively different for clusters of particles with small, intermediate, and large anisotropies, which has important consequences for the magnetization dynamics of these systems.

Synthesis and characterization of magnetically-active nickel-yttrium oxide (Ni-Y2O3) nanocomposite particles prepared with modified ultrasound spray pyrolysis device

AbstractThe synthesis of magnetically-active nickel-yttrium oxide (Ni-Y2O3) nanocomposite particles is described in this work. The investigated material is produced with a modified ultrasound spray pyrolysis (USP) device which differs from a common USP setup in terms of use of three independently heating zones. They provide a direct feed of H2 to the second reaction zone and allow controlling the formation of the nanocomposite particles and facilitating their post-reaction stabilization with polyvinylpyrrolidone (PVP). According to the morphological and structural studies, the Ni-Y2O3 material takes a form of nanoparticles whose sizes are not homogeneously distributed as well as shapes are not smooth due to the successful formation of composite material with two interpenetrating phases. Moreover, the organic layer is detected on the surface of the nanoparticles which confirms the presence of PVP stabilizer. The magnetic investigations confirm that the Ni-Y2O3 nanocomposite reveals a spin glass-like behavior in which a collective freezing of magnetic moments might occur due to the interparticle interactions between Ni nanocrystallites presented in the sample.

Structural transitions in systems with a triple-well potential

Objectives. Recently studied phenomena in condensed matter physics have prompted new insights into the dynamic theory of crystals. The results of numerous experimental data demonstrate the impossibility of their explanation within the framework of linear models of the dynamics of many-particle systems, resulting in the necessity to account for nonlinear effects. Analyzing the dynamics of systems in condensed matter physics containing a sufficiently large number of particles shows that modes of motion can undergo changes depending on the potential of interparticle interaction. This is also reflected in the presence of domains with essentially chaotic phase space having a number of degrees of freedom N ≥ 1.5 and a certain set of interparticle interaction parameters. However, it is not only the dynamic model that appears to be strongly nonlinear. A similar nature of motion can be also observed in a static nonlinear many-particle system. The paper aims to study the influence of the external field specified by the interatomic triple-well potential on the equilibrium structure of a chain of interacting atoms.Methods. Methods of Hamiltonian mechanics are used.Results. Analytical expressions are obtained and analyzed for determining the phase portrait of the equilibrium structure of a chain of interacting atoms for various values of the parameter characterizing the local potential of the field in which each atom of the chain moves. Phase portraits of the equilibrium structure of the system are constructed in continuous and discrete representations of the equilibrium equations for various values of the parameter characterizing the local potential of the field in which each atom of the chain moves.Conclusions. It is shown that both periodic and random chaotic arrangements of atoms are implemented depending on the magnitude of the external field.

Colloidal Dispersions of Sterically and Electrostatically Stabilized PbS Quantum Dots: Structure Factors, Second Virial Coefficients, and Film-Forming Properties.

Electrostatically stabilized nanocrystals (NCs) and, in particular, quantum dots (QDs) hold promise for forming strongly coupled superlattices due to their compact and electronically conductive surface ligands. However, studies of the colloidal dispersion and interparticle interactions of electrostatically stabilized sub-10 nm NCs have been limited, hindering the optimization of their colloidal stability and self-assembly. In this study, we employed small-angle X-ray scattering (SAXS) experiments to investigate the interparticle interactions and arrangement of PbS QDs with thiostannate ligands (PbS-Sn2S64-) in polar solvents. The study reveals significant deviations from the ideal solution behavior in electrostatically stabilized QD dispersions. Our results demonstrate that PbS-Sn2S64- QDs exhibit long-range interactions within the solvent, in contrast to the short-range steric repulsion characteristic of PbS QDs with oleate ligands (PbS-OA). Introducing highly charged multivalent electrolytes screens electrostatic interactions between charged QDs, reducing the length scale of the repulsive interactions. Furthermore, we calculated the second virial (B2) coefficients from SAXS data, providing insights into how surface chemistry, solvent, and size influence pair potentials. Finally, we explore the influence of long-range interparticle interactions of PbS-Sn2S64- QDs on the morphology of films produced by drying or spin-coating colloidal solutions. The long-range repulsive term of PbS-Sn2S64- QDs promotes the formation of amorphous films, and screening the electrostatic repulsion by the addition of an electrolyte enables the formation of crystalline domains. These findings highlight the critical role of NC-NC interactions in tailoring the properties of functional materials made of colloidal NCs.

Estimation of mixing enthalpy of the liquid Sn-Ag-Cu system at 1423 K from data on the properties of binary subsystems using geometric models of solutions

The article considers the estimation of mixing enthalpy ΔНmix of the Sn-Ag-Cu ternary system melts at a temperature of 1423 K from the calorimetric data on the mixing enthalpy of binary subsystems Ag-Cu, Ag-Sn and Cu-Sn measured earlier. The geometric models by Toop, Kohler and Muggianu, where binary data is jointly processed in each case according to a specific mathematical procedure, were applied to the ΔНmix assessment. The results of calculations by these models are presented by the compositional dependences of ΔНmix of the ternary system in the form of 3D surfaces, projections of these surfaces onto the plane of the compositional triangle, as well as isotherms plotted for individual quasi-binary sections. It was found that modeling using the Kohler’s and Muggianu’s methods gives insignificantly different results, whereas the values of the mixing enthalpy of ternary compositions in the Toop’s model are noticeably more immersed into the negative (exothermic) region. As it is known from the scientific literature, the right choice of a geometric model depends on whether the ternary system under study belongs to a “symmetric” or “asymmetric” type. The shape of the available ΔНmix isotherms of binary subsystems indicates that the Sn-Ag-Cu system is “asymmetric”. The results calculated using the Toop’s model are recognized as the most correct ones, since that model is recommended in the literature for describing “asymmetric” systems. The common limitation of all geometric models, considering only binary interparticle interactions, and the advisability of extra experimental study of three-component melts formation to reveal the possible contribution of ternary interactions to the mixing enthalpy are noted.

To the theory of remagnetization kinetics of magnetic composites

Results of theoretical study of kinetics of the remagnetization of an ensemble of interacting ferromagnetic particles immobilized in a host non -magnetic medium are presented. The results show that the influence of interparticle interaction on the remagnetization is determined by the amplitude of the applied alternating field: it slows down this process in a weak field and accelerates it in a strong field. The interaction of particles increases both components of the complex magnetic susceptibility of the composite.

Exploring Anisotropy Contributions in Mn x Co1-x Fe2O4 Ferrite Nanoparticles for Biomedical Applications.

Designing well-defined magnetic nanomaterials is crucial for various applications, and it demands a comprehensive understanding of their magnetic properties at the microscopic level. In this study, we investigate the contributions to the total anisotropy of Mn/Co mixed spinel nanoparticles. By employing neutron measurements sensitive to the spatially resolved surface anisotropy with sub-Å space resolution, we reveal an additional contribution to the anisotropy constant arising from shape anisotropy and interparticle interactions. Our findings shed light on the intricate interplay among chemical composition, microstructure, morphology, and surface effects, providing valuable insights for the design of advanced magnetic nanomaterials for AC biomedical applications, such as cancer treatment by magnetic fluid hyperthermia.

Kinetically blocked self-assembly of colloidal strings with tunable interactions in magnetic fields.

Tunable self-assembly driven by external electric or magnetic fields is of significant interest in modern soft matter physics. While extensively studied in two-dimensional systems, it remains insufficiently explored in three-dimensional systems. In this study, we investigated the formation of vertical strings from an initial monolayer system of particles deposited on a horizontal substrate under the influence of an external magnetic field using experiments, computer simulations, and theoretical frameworks. We demonstrated that the main mechanism of string self-assembly is merging, driven by the interplay between gravity and induced tunable interparticle interactions. During this process, the system has to overcome a saddle point on the energy landscape, whose height increases with the string height. At a certain point, further self-assembly becomes kinetically blocked in a metastable state, far from equilibrium. This contrasts sharply with the typical scenario for tunable self-assembly in two dimensions, where the resulting structures usually correspond to the equilibrium state. Therefore, this finding opens up opportunities for more detailed control of three-dimensional tunable self-assembly by designing and tuning various potential barriers along the kinetic pathways.

Performance Evaluation of Polygonal and Cylindrical Ball Mills Using Discrete Element Method

ABSTRACTBall mills are frequently utilized in the chemical and mineral processing industries to reduce the size of particles. In mineral processing, cylindrical rotating mills with wear‐resistant materials are used at various operation scales. Polygon‐shaped rotating mills are used in artisanal and small‐scale mining due to technological and economic reasons. It is imperative to thoroughly evaluate polygon‐shaped mills to inform decisions regarding their improvement or replacement based on technological data. Even a minor enhancement in grinding efficiency and mill durability can yield substantial economic and environmental advantages. In this study, the performance of polygonal‐shaped mills was evaluated and compared with cylindrical profiles, taking into account power draw, collision energy dissipation, relative wear, and operational stability. The effect of installing lifters in the mills was also assessed. Simulations using the discrete element method (DEM) were carried out to describe the mechanical behavior of grinding media and its interaction with the mill walls. Notably, polygonal‐shaped mills without lifters facilitated interparticle interaction with limited centrifuging of particles compared to cylindrical mills without lifters. The installation of lifters in polygonal mills increased interparticle collisions and reduced power draw and wear rate. Cylindrical mills with lifters had high interparticle collisions similar to polygonal profiles but with much lower wear rate and high operational stability.

Micro‐ and nanorobots from magnetic particles: Fabrication, control, and applications

AbstractMagnetic microparticles (MPs) and nanoparticles (NPs) have long been used as ideal miniaturized delivery and detection platforms. Their use as micro‐ and nanorobots (MNRs) is also emerging in the recent years with the help of more dedicated external magnetic field manipulations. In this review, we summarize the research progress on magnetic micro‐ and nanoparticle (MNP)‐based MNRs. First, the fabrication of micro‐ and nanorobots from either template‐assisted NP doping methods or directly synthesized MPs is summarized. The external driving torque sources for both types of MNRs are analyzed, and their propulsion control under low Reynolds number flows is discussed by evaluating symmetry breaking mechanisms and interparticle interactions. Subsequently, the use of these MNRs as scientific models, bioimaging agents, active delivery, and treatment platforms (drug and cell delivery, and sterilization), and biomedical diagnostics has also been reviewed. Finally, the perspective of MNPs‐based MNRs was outlined, including challenges and future directions.

Iron oxide nanoparticles synthesized by coprecipitation method: Impacts of zinc doping and surface functionalization by polyvinylpyrrolidone on the magnetic properties and heating efficiency

Magnetic nanoparticles (NPs) are promising agents for magnetic hyperthermia (MH) due to their ability to convert electromagnetic energy into heat. Their high stability in solution, which is essential to prevent aggregation and ensure uniform distribution as well as their high specific absorption rate (SAR) and intrinsic loss power (ILP) values are especially important in magnetic hyperthermia. This study explores how doping iron oxide NPs with zinc and surface functionalizing them with polyvinylpyrrolidone (PVP) affects their magnetic and heating properties. The saturation magnetization (MS) of ZnxFe3-xO4 NPs at 50 K increases from 76 to 93.5 emu/g corresponding with increasing Zn content from x = 0 up to 0.20, and conversely their coercivity (HC) decreases from 135 down to 77 Oe. For PVP coated NPs, MS is reduced by the presence of nonmagnetic PVP, whereas their HC is increased due to reduced interparticle interactions. Furthermore, the high stability of PVP coated Zn0.20Fe2.80O4 NPs in solution is confirmed by the Zeta potential of 46 mV. Notable, high SAR of 460 W/g and ILP of 4.04 nH m2/kg values make them potential candidates for MH applications.

Room temperature ballistic transport of exciton-polaritons in a one-dimensional whispering gallery microcavity

In this work, we report the experimental observation of the ballistic transport of condensed exciton-polaritons at room temperature in a one-dimensional whispering-gallery microcavity. Such coherent transport, initiated by the pronounced inter-particle interactions of polaritons, leads to the generation of two symmetric emission beams in the momentum (angular) space. By means of spatially filtered angle-resolved photoluminescence imaging spectroscopy, we were able to identify their origin and successfully rationalize these observations using the potential energy-to-kinetic energy conversion picture. The energy-dependent emission linewidth, as well as TM to TE inter-mode scattering, have also been discussed.

Particulate fouling simulation in unit micropore using a hydrodynamically coupled Lagrangian framework

Predicting and mitigating pore clogging is challenging for the sustainable operation of water treatment systems. During transport and filtration through membrane micropores, buoyant contaminants in water gradually deposit on the surface, reducing the membrane's lifespan and performance, and sometimes completely blocking the pores. To alleviate the negative effects of fouling and to ensure sustainable operation, it is necessary to understand the fundamental mechanisms of fouling and to predict the probability of fouling formation under specific geometrical and material conditions. In this study, multiscale simulations are conducted to understand the fundamental mechanisms of particulate fouling at a microscopic level based on a Lagrangian framework incorporating inter-particle hydrodynamic interactions. We investigate both dead-end and cross-flow filtration, considering the direction of the feed stream relative to the unit micropore. The results elucidate the quantitative background of fouling history, which agrees with experimental findings. Depending on the level of hydrodynamic stress specific to the clog location and the nature of inter-particle interactions, deformation or resuspension of the clog is observed, competing with deposition, which leads to a two-way fouling history. Dominant deposition leads to micropore clogging, and to the best of the authors' knowledge, this is the first study to observe complete blockage and subsequent reopening. With this approach, the microscopic backgrounds between permanent and temporary pore blocking are distinguished. This study is expected to provide useful insights for controlling operational conditions to optimize anti-fouling performance in the transport and filtration through micropores.

Superparamagnetic Relaxation in Ensembles of Ultrasmall Ferrihydrite Nanoparticles

The paper examines the impact of interparticle interactions on the superparamagnetic relaxation of ultrasmall nanoparticle ensembles, using Fe2O3∙nH2O iron oxyhydroxide (ferrihydrite) nanoparticles as an example. Two samples were analyzed: ferrihydrite of biogenic origin (with an average particle size of d ≈ 2.7 nm) with a natural organic shell, and a sample (with d ≈ 3.5 nm) that underwent low-temperature annealing, during which the organic shell was partially removed. The DC and AC magnetic susceptibilities (χ′(T), χ′′(T)) in a small magnetic field in the superparamagnetic (SPM) blocking region of the nanoparticles were measured. The results show that an increase in interparticle interactions leads to an increase in the SPM blocking temperature from 28 to 52 K according to DC magnetization data. It is shown that below the SPM blocking temperature, magnetic interactions of nanoparticles lead to the formation of a collective state similar to spin glass in bulk materials. The scaling approach reveals that the dynamics of correlated magnetic moments on the particle surface slow down with increasing interparticle interactions. Simulation of χ′′(T) dependence has shown that the dissipation of magnetic energy occurs in two stages. The first stage is directly related to the blocking of the magnetic moment of nanoparticles, while the second stage reflects the spin-glass behavior of surface spins and strongly depends on the strength of interparticle interactions.

Interparticle interaction effect on superparamagnetic properties of ferrimagnetic particles

Uncoated and oleic acid coated ferrimagnetic particles are synthesized. Both samples contain similar magnetite particles. Structural characterization of these particles is performed using x-ray diffraction, Fourier transform infrared spectra, dynamic light scattering, transmission electron microscopy and thermogravimetric analysis. Average crystallite size of magnetite is 7 nm. Thickness of oleic acid layer on each magnetite particle is 1 nm. The oleic acid coated sample contains 23% oleic acid. Temperature dependence of the zero field cooled susceptibility curve of the uncoated magnetite particles peaks at 120 K. The zero field cooled and the field cooled susceptibility versus temperature curves bifurcate at 195 K. The peak temperature and the bifurcation temperature of the system decrease due to the oleic acid coating. The inverse susceptibility does not vary linearly with temperature in high temperature region. Magnetization versus applied magnetic field data at 250 K are analyzed in different ways to study the interparticle interaction effect on magnetization. We find that the interparticle interactions affect the magnetization process of ferrimagnetic nanoparticles.

Engineering impurity Bell states through coupling with a quantum bath

We theoretically demonstrate the feasibility of creating Bell states in multicomponent ultracold atomic gases by solely using the ability to control the interparticle interactions via Feshbach resonances. For this we consider two distinguishable impurities immersed in an atomic background cloud of a few bosons, with the entire system being confined in a one-dimensional harmonic trap. By analyzing the numerically obtained ground states we demonstrate that the two impurities can form spatially entangled bipolaron states due to mediated interactions from the bosonic bath. Our analysis is based on calculating the correlations between the two impurities in a two-mode basis, which is experimentally accessible by measuring the particle positions in the left or right sides of the trap. While interspecies interactions are crucial in order to create the strongly entangled impurity states, they can also inhibit correlations depending on the ordering of the impurities and three-body impurity-bath correlations. We show how these drawbacks can be mitigated by manipulating the properties of the bath, namely its size, mass, and intraspecies interactions, allowing one to create impurity Bell states over a wide range of impurity-impurity interactions. Published by the American Physical Society 2024

Shearmetry of Fluids with Tunable Rheology by Polarized Luminescence of Rare Earth-Doped Nanorods.

Shear stress plays a critical role in regulating physiological processes within microcirculatory systems. While particle imaging velocimetry is a standard technique for quantifying shear flow, uncertainty near boundaries and low resolution remain severe restrictions. Additionally, shear stress determination is particularly challenging in biofluids due to their significant non-Newtonian behaviors. The present study develops a shearmetry technique in physiological settings using a biomimetic fluid containing rare earth-doped luminescent nanorods acting in two roles. First, they are used as colloidal additives adjusting rheological properties in physiological media. Their anisotropic morphology and interparticle interaction synergistically induce a non-Newtonian shear-thinning effect emulating real biofluids. Second, they can probe shear stress due to the shear-induced alignment. The polarized luminescence of the nanorods allows for quantifying their orientational order parameter and thus correlated shear stress. Using scanning confocal microscopy, we demonstrate the tomographic mapping of the shear stress distribution in microfluidics. High shear stress is evident near the constriction and the cellular periphery, in which non-Newtonian effects can have a significant impact. This emerging shearmetry technique is promising for implementation in physiological and rheological environments of biofluids.

A cationic polyelectrolyte for enhancing dewatering of montmorillonite-containing coal slime: adsorption and modification mechanism

ABSTRACT In this study, a cationic polyelectrolyte (Poly dimethyl diallyl ammonium chloride, PDADMAC) was introduced as a filter aid to enhance the dewatering effect of montmorillonite (MT)-containing coal slime, and compared with cationic polyacrylamide (CPAM). The dewatering performance of PDADMAC and CPAM was evaluated based on vacuum filtration experiments. The modification mechanism of PDADMAC on Mt particle surface was revealed by filter cake pore distribution, zeta potential, contact angle and Atomic Force Microscopy (AFM). The adsorption difference between PDADMAC and CPAM on Mt surface was studied by Density Functional Theory (DFT). In addition, DLVO theory further explains the mechanism of PDADMAC enhancing dewatering from the perspective of interaction force. The optimal dosage of PDADMAC was 125 g/t, and the filter cake moisture content was reduced by 3%. Compared to CPAM, PDADMAC achieves efficient dewatering at a lower dosage. PDADMAC has a more prominent ability to neutralize charge, and its effect on interparticle interactions was a potential mechanism to promote dehydration.

The use of ensembles trees machine learning method in estimating damping of granular materials

Granular Materials (GM) employed within the mechanism of particle dampers attenuate the vibration energy due to their interparticle and particle-wall interactions. Estimating their damping effect using the analytical equivalent single mass approach overlooked the particles' individual losses that are built into the total damping. Alternatively, the numerical techniques (e.g., Discrete Element) are time-inefficient and computationally demanding. Therefore, this study explores the implementation of Machine learning (ML) algorithms to estimate the damping effect of GM. The ML model in this study will rely on a Data-Driven Modeling approach (DDM) incorporating the ensemble tress nonlinear regressor method. The models' training and testing data were obtained from an experimental setup of an acrylic beam internally integrated with Stainless Steel (SS) and glass spheres undergoing low excitation amplitude (RMS <1N). The main aim was to map between seven input features (e.g. filling ratio) and one targeted output: the beam's damped frequency response. Three ensemble trees' algorithms were used to create the DDM; Decision Tree, Random Forest, and XGBoost. The hyperparameter combination based on the Gridsearch CV function increases the prediction accuracy of each model. The developed ML models provided high accuracy (86-93%) in predicting the damping effect of the granular materials spheres.

Analysis of thixotropy of cement grout based on a virtual bond model

Thixotropy of cementitious materials is a crucial intrinsic property that determines the flowability and workability of cement-based grout. A novel virtual bond model of cement particles is developed in this paper to depict the thixotropy of cement grout. A particulate description of the reversible and erasable interparticle bonds is established based on experimental observations with a focus on the non-contact interactions mainly contributed in practice by calcium silicate hydrates (C–S–H). The structural breakdown of the cement network is realized through bonds breakage under applied motion, and the bonding network recovers with regeneration of interparticle connections that involve reversible hydrate reactions in the mixture. The balance between bond rupture and rebuilding can be tuned by assigning different strength limits for bond breakage. We have implemented this model in the open-source code Yade to carry out 3D discrete element method simulations of a rotational vane system filled with spherical particles, and the results show good agreement with experimental data. The modelling results reveal the transition from a solid-like structure to a fluid-like medium within cement suspensions caused by the evolution of broken interparticle bonds. The results also provide a distinct view of thixotropic variation upon disturbance. This model is extendable to other cohesive materials providing an explicit physical definition of the interparticle interactions. It also provides a theoretical explanation for the empirical estimations of thixotropy common in engineering industries and a potential means of measuring cementitious granular flow that may be useful in future studies.