Chain-like Clusters Research Articles

Effect of Inorganic Additive Strategy on the Stability of in Vanadium Redox Flow Battery Electrolyte by Molecular Dynamics.

Inorganic ions are considered to be effective additives to improve the temperature stability of all-vanadium redox flow batteries. In this study, molecular dynamics simulation has been performed to study the solvation structure and dynamic properties of VO2+ in the positive electrolyte by doping Na+, K+, and NH4+ in the presence of V2O5 precipitation. The results show that VO2+ ions aggregate into chainlike clusters in the electrolyte due to the induction of SO42-. The additives, which are stable in the solvation layers of VO2+, can work as protective shells to inhibit cluster growth. NH4+ is a superior dispersant compared with Na+ and K+ as it can stably exist in both the first solvation layer and the second solvation layer of VO2+. This work performed the molecular dynamics simulation of the electrolyte of vanadium redox flow batteries, and it gives some insights into the theoretical study of the modification of the cathode electrolyte.

Experimental study and mechanism analysis on the effect of pre-curing time on the microstructure and mechanical properties of magnetorheological elastomers under compression

The effects of the pre-curing time before exposing the carbonyl iron particles (CIPs) filled liquid polydimethylsiloxane (PDMS) mixture to a preparatory magnetic field on the magnetorheological (MR) effects of the magnetorheological elastomers (MREs) were experimentally and theoretically investigated. The anisotropic MRE samples with different pre-curing time were firstly fabricated and their compressive MR effects were tested. The results showed that the longer pre-curing time induces the shorter and more irregular particle chains formed in the MREs, and the sample pre-cured for 20 min showed the maximum MR effect. Then based on the rheological characterization, a rheological model was proposed to predict the rheological property evolution of CIPs/PDMS mixture with respect to the pre-curing time, and a modified three-dimensional (3D) particle dynamics (PD) model was developed to simulate the particle structure evolution in the MRE mixtures under a preparatory magnetic field. The simulation results showed that short chains were first formed owing to the magnetic attraction between the adjacent particles. Then these short chains approached each other to form long chains and even thick chain-like clusters. The later process can be restrained by increasing the pre-curing time, thus more short and incompact particle chains are formed in the MREs. Lastly, simplified microstructure models representing the wavy chains were used to explore the effect of particle arrangement on the MR effect of the MREs under compression. It is found that the wavy chains with incompactly packed particles are beneficial for improving the MR effect owing to the strong transverse magnetic attraction between the neighboring particles. This work demonstrates that PD simulation is an efficiency method to predict the particle arrangement evolution in the MRE mixture, and the possibility to tailoring the microstructures of the MREs by adjusting the viscosity of MRE mixtures to improve their MR effects, while keeping a high zero-field modulus simultaneously.

Multimodal Imaging-Guided Stem Cell Ocular Treatment.

Stem cell therapies are gaining traction as promising treatments for a variety of degenerative conditions. Both clinical and preclinical studies of regenerative medicine are hampered by the lack of technologies that can evaluate the migration and behavior of stem cells post-transplantation. This study proposes an innovative method to longitudinally image in vivo human-induced pluripotent stem cells differentiated to retinal pigment epithelium (hiPSC-RPE) cells by multimodal photoacoustic microscopy, optical coherence tomography, and fluorescence imaging powered by ultraminiature chain-like gold nanoparticle cluster (GNC) nanosensors. The GNC exhibits an optical absorption peak in the near-infrared regime, and the 7-8 nm size in diameter after disassembly enables renal excretion and improved safety as well as biocompatibility. In a clinically relevant rabbit model, GNC-labeled hiPSC-RPE cells migrated to RPE degeneration areas and regenerated damaged tissues. The hiPSC-RPE cells' distribution and migration were noninvasively, longitudinally monitored for 6 months with exceptional sensitivity and spatial resolution. This advanced platform for cellular imaging has the potential to enhance regenerative cell-based therapies.

Crystal structure and Hirshfeld surface analysis of 4,4'-di-meth-oxy-biphenyl-3,3',5,5'-tetra-carb-oxy-lic acid dihydrate.

In the crystal of the title compound, C18H14O10·2H2O, the arene rings of the biphenyl moiety are tilted at an angle of 24.3 (1)°, while the planes passing through the carboxyl groups are rotated at angles of 8.6 (1) and 7.7 (1)° out of the plane of the benzene ring to which they are attached. The crystal structure is essentially stabilized by O-H⋯O bonds. Here, the carboxyl groups of neighbouring host mol-ecules are connected by cyclic R 2 2(8) synthons, leading to the formation of a three-dimensional network. The water mol-ecules in turn form helical supra-molecular strands running in the direction of the crystallographic c-axis (chain-like water clusters). The second H atom of each water mol-ecule provides a link to a meth-oxy O atom of the host mol-ecule. A Hirshfeld surface analysis was performed to qu-antify the contributions of the different inter-molecular inter-actions, indicating that the most important contributions to the crystal packing are from H⋯O/O⋯H (37.0%), H⋯H (26.3%), H⋯C/C⋯H (18.5%) and C⋯O/O⋯C (9.5%) inter-actions.

Elucidation of the trapping characteristics of magnetic disk-like particles in a Hagen-Poiseuille flow via Brownian dynamics simulations (usage of multi-magnetic poles)

In the present study, we elucidate the behaviour of a suspension composed of magnetic disk-like particles that flow in a Hagen-Poiseuille flow in a gradient magnetic field and the trapping characteristics of the magnetic particles. To this end, we utilise multiple pairs of magnetic poles located outside the cylindrical system. Brownian dynamics simulations were performed in order to clarify the dependence of these characteristics on a variety of factors. It is seen that an increase in the magnetic field strength improves the trapping characteristics of disk-like particles if the influence of an applied magnetic field is sufficiently more dominant than that of a flow field and that of the magnetic particle-particle interaction. In the case of a strong magnetic particle-particle interaction, thin chain-like clusters are formed from an anchored particle trapped around a magnetic pole. If the two poles are sufficiently close to each other, an arch-type cluster is formed between them. We expect that this arch-type cluster may give rise to good trapping performance even in the presence of a strong flow field if the formation arises at a sufficiently large separation distance between the pair of magnetic poles. Highlights We have performed Brownian dynamics simulations for a magnetic disk-like particle suspension in a Hagen-Poiseuille flow. If the magnetic particle-particle interaction is sufficiently more dominant than the flow field, thin chain-like clusters are formed from an anchored particle. As the pole separation distance decreases, an arch-type configuration tends to be formed along the surface of the wall. This arch-type cluster that is formed between the pair of magnetic poles may be expected to improve the trapping characteristics depending on the pole separation distance.

Tailoring Se-rich glassy arsenoselenides employing the nanomilling platform

By XRPD analysis related to diffuse peak-halos in Se-rich glassy AsxSe100-x, the high-energy nanomilling driven reamorphization in these substances is recognized as molecular-to-network transformations of Se chains bridging cation polyhedrons (like AsSe3/2 pyramids) from preferential cis- to trans-configurated topology. At the medium-range structure, the process of reamorphization is revealed as enhancement in the intermediate-range ordering of these glasses due to high-angular shifted and broadened first sharp diffraction peak (FSDP) accompanied by suppression in extended-range ordering due to high-angular shifted but narrowed principal diffraction peak (PDP), so that peak-halos become more distinguishable after nanomilling. Principal trend in the XRPD patterns of glassy arsenoselenides with growing Se content is revealed as suppression in intermediate-range ordering accompanied by enhancement in extended-range ordering, resulting in more overlapped peak-halos. Irregular sequence of randomly distributed cis- and trans-configurated linkages in Se-rich g-AsxSe100-x is visualized by ab initio quantum-chemical modeling of molecular and chain-like network clusters.

Intriguing properties of graphite/polysiloxane composite-based pencil electrodes

Pencil leads can be considered well-defined and cheap graphite electrodes for a wide range of electrochemistry applications. These electrodes display many intriguing properties; however, the origin of these properties is not clear. Using various analytical approaches applied to two different commercially available Tombow (TO) and Staedtler (ST) pencils we reveal a causal relationship between the unique properties of pencils and their graphite/polysiloxane composite. We explore the impact of chloroform etching on chemical composition changes, thermal stability and electrochemical parameters of pencils. Using a combination of X-ray photoelectron spectroscopy (XPS) and gas chromatography-mass spectrometry (GC-MS/MS) various polydimethylsiloxanes in composites are revealed. The polysiloxane species leave into the chloroform solvent during the etching resulting in a significant decrease of their content within the electrodes. Differential scanning calorimetry (DSC) data, corroborated by gravimetric measurements, provide additional proof of the presence of composite structures in ST and TO pencils, showing glass transition temperatures at around 76 °C and 81 °C. The main difference between the TO and ST electrodes is the content and composition of the polysiloxanes within the graphite matrix. ST composites have significantly higher polymer content (∼ 30 %) with traces of Na and S impurities compared to TO ones (∼ 14 %) free of contaminations. Furthermore, mainly cyclic nanostructures appear in chloroform extracts of ST composites whereas rather chain-like clusters are liberated out of the TO counterparts. Complementary electrochemical experiments using cyclic voltammetry (CV), impedance spectroscopy (EIS) and the less known elimination voltammetry with linear scan (EVLS) reflect the performance superiority of TO electrodes with much lower polysiloxane content and free of impurities. High conductivity, low capacitive current along with favoured charge carrier transfer all promise a wide range of technological applications for the TO pencil material.

Anisotropy of field-controlled shear viscosity of dipolar fluids

We numerically study the anisotropic viscous response of dipolar hard spheres in the presence of an electric field. We find that the shear viscosity is sensitive to both the strength and orientation of the field relative to the shearing direction. The effect on the viscosity is strongest when the field is oriented in the shear gradient direction. We investigate the structure of the fluid in detail to explain the mechanism for the changes in viscosity, and show that the reorientation of chain-like clusters plays a crucial role. We show that the anisotropy arises from the polarization of the fluid induced by the field, leading to the orientation of chain-like clusters along the direction of the field.

High-pressure synthesis of metastable Bi–S crystalline compounds: Crystal structure and electron transport

A new metastable Bi3S4 single crystal has been obtained on the initial Bi: S = 2 : 3 mixture at a pressure of 8.0–8.5 GPa with slow cooling from 1300 to 800 °C at a rate of ∼3 °C/min followed by quenching. The crystal has a triclinic structure formed by Bi-centered S-polyhedrons and chain-like clusters of Bi atoms. The relationship between the triclinic model based on single-crystal X-ray diffraction data and the orthorhombic model previously proposed for high-pressure Bi–S and Bi–Se phases with a similar structural motif based on X-ray powder diffraction data is discussed. The new Bi3S4 phase is a narrow-gap (band gap of 0.234 eV) intrinsic n-type semiconductor with a shallow impurity level. Metastable Bi3S4 recovers the structure of bismuthinite Bi2S3 after annealing at 200 °C.

How particle interactions and clustering affect the dynamic magnetic susceptibility of ferrofluids

The effects of magnetic interparticle interactions on the frequency-dependent, dynamic magnetic susceptibility of ferrofluids are summarised with reference to recent theoretical and simulation studies. With weak to moderate interactions, the dynamic magnetic susceptibility qualitatively resembles the classic Debye prediction, but with features shifted to lower frequencies as the particle concentration and/or interaction strength are increased. This shows that the mutual spatial and orientational correlations arising from the interactions lead to slower collective motions. With strong interactions, and at low concentrations, the particles form chain-like and ring-like clusters, and this leads to distinct collective and intracluster motions being apparent in the dynamic magnetic susceptibility. The initial formation of chains increases the static susceptibility, while the subsequent formation of rings decreases it.

Regime change in the aggregate structures of spherical magnetic Janus particles (quasi-2D Monte Carlo simulations)

We have investigated a suspension composed of spherical magnetic Janus particles in thermodynamic equilibrium. The magnetic moment of Janus particles treated here is located at a position shifted from the particle centre, which is on the line perpendicular to the magnetic moment direction. We conducted quasi-2D Monte Carlo simulations to investigate the change in the regime of aggregate structures and the dependence of the regime on various factors, such as the strength of the magnetic particle-particle interaction, magnetic particle-field interaction, and the distance of the magnetic moment from the particle centre. In the absence of an applied magnetic field, the Janus particles aggregate to form stable clusters composed of a few particles with increased values of the magnetic particle-particle interaction strength. As the strength of the magnetic field is increased, these clusters collapse, and chain-like clusters are formed aligned in the direction of the magnetic field. The appearance of this regime change requires a stronger magnetic field as the position of the magnetic moment approaches the particle surface. This can be attributed to the fact that the magnetic interaction between neighbouring particles becomes more dominant as the magnetic moments of the constituent particles in the cluster units approach each other. Highlights We have addressed the aggregation phenomena in a suspension composed of spherical magnetic Janus particles. We have investigated the regime change in the aggregate structures of the Janus particles under various conditions. In a strong magnetic field, thick chain-like clusters are formed as the magnetic moment is shifted away from the particle centre. The present results are useful for elucidating the internal structure of complex aggregates in 3D systems.

Renally Clearable Ultraminiature Chain-Like Gold Nanoparticle Clusters for Multimodal Molecular Imaging of Choroidal Neovascularization.

Currently, available gold nanoparticles (GNPs) typically accumulate in the liver and spleen, leading to concerns for their long-term biosafety. To address this long-standing problem, ultraminiature chain-like gold nanoparticle clusters (GNCs) are developed. Via self-assembly of 7-8nm GNP monomers, GNCs provide redshifted optical absorption and scattering contrast in the near-infrared window. After disassembly, GNCs turn back to GNPs with a size smaller than the renal glomerular filtration size cutoff, allowing theirexcretion via urine. A one-month longitudinal study in a rabbit eye model demonstrates that GNCs facilitate multimodal molecular imaging of choroidal neovascularization (CNV)in vivo, non-invasively, with excellent sensitivity and spatial resolution. GNCs targeting αv β3 integrins enhance photoacoustic and optical coherence tomography (OCT) signals from CNV by 25.3-fold and 150%, respectively. With excellent biosafety and biocompatibility demonstrated,GNCs render a first-of-its-kind nanoplatform for biomedical imaging.

Impact dynamics of ferrofluid droplet on a PDMS substrate under the influence of magnetic field

We report the impact dynamics of a ferrofluid droplet on a PDMS substrate in the presence of a non-uniform magnetic field. Based on high-speed imaging, we unravel the various characteristic behaviors of the impinging ferrofluid droplet under the influence of a vertically applied magnetic field. We show that the magnetic, viscous, inertial, and interfacial energies non-trivially affect the equilibrium shape of the impacting ferrofluid droplet. Consequently, we reveal that the collective role of these forces ensures the ferrofluid droplet exhibits essentially three typical equilibrium shapes, i.e., no spike, single spike, and multiple spikes assemblies. Based on a phase diagram, we demonstrate the role of various dynamic forces in dictating the droplet’s equilibrium shape. We report the universality constant exhibited by the non-dimensionalized droplet diameter (ratio of the droplet’s equilibrium diameter to the semi-minor axis width of the ellipsoidal droplet just before impact), irrespective of the magnetic Bond number, on a PDMS substrate to be around 1.3. Consequently, we investigated the internal flow domain of the ferrofluid flow field in the presence of a magnetic field, essentially to understand its characteristic spreading behavior. Following bright-field visualization, we observed chain-like clustering of the magnetic nanoparticles inside the ferrofluid flow domain in a direction perpendicular to the magnet. Insights from bright field visualization enable us to qualitatively argue that the chaining phenomena of the nano-sized particles (present inside ferrofluid) in a direction perpendicular to the substrate ensure the formation of single/multiple assemblies of spikes. In addition, we also argue that the chain-formation of the magnetic nanoparticles increases the viscous force of the ferrofluid droplet in the presence of a magnetic field. This augmented viscous energy of the fluid in the presence of a magnetic field ensures the inverse relationship of the spreading diameter with magnetic field strength. The inference of the present study could be beneficial in the rational design of wide-ranging applications, such as ink-jet printing or 3D printing, requiring controlled droplet spreading phenomena.

Linked cluster expansion on trees.

The linked cluster expansion has been shown to be highly efficient in calculating equilibrium and nonequilibrium properties of a variety of 1D and 2D classical and quantum lattice models. In this article, we extend the linked cluster method to the Cayley tree and its boundaryless cousin the Bethe lattice. We aim to (a) develop the linked cluster expansion for these lattices, a novel application, and (b) to further understand the surprising convergence efficiency of the linked cluster method, as well as its limitations. We obtain several key results. First, we show that for nearest-neighbor Hamiltonians of a specific form, all finite treelike clusters can be mapped to one dimensional finite chains. We then show that the qualitative distinction between the Cayley tree and Bethe lattice appears due to differing lattice constants that is a result of the Bethe lattice being boundaryless. We use these results to obtain the explicit closed-form formula for the zero-field susceptibility for the entire disordered phase up to the critical point for Bethe lattices of arbitrary degree; remarkably, only 1D chainlike clusters contribute. We also obtain the exact zero field partition function for the Ising model on both trees with only the two smallest clusters, similar to the 1D chain. Finally, these results achieve a direct comparison between an infinite lattice with a nonnegligible boundary and one without any boundary, allowing us to show that the linked cluster expansion eliminates boundary terms at each order of the expansion, answering the question about its surprising convergence efficiency. We conclude with some ramifications of these results, and possible generalizations and applications.

球状磁性ヤヌス粒子からなる分散系を対象にした擬2次元モンテカルロ・シミュレーション（磁気モーメントが粒子中心から横方向にずれた粒子モデル）

I have addressed a magnetic Janus particle suspension in the thermodynamic equilibrium situation. The magnetic moment of Janus particles treated in the present study is shifted from the particle center, which is perpendicular to the magnetic moment direction. From the viewpoint of elucidating the internal structure of particle aggregates in a three-dimensional (3D) system, I have treated a dispersion composed of magnetic Janus particles with a full 3D rotational ability in a quasi-two-dimensional (2D) system. The quasi-2D Monte Carlo simulations have been performed in order to investigate the dependence of a regime change in the aggregate structures on various factors such as the magnetic particle-particle interaction strength, magnetic particle-field interaction strength and the distance of the magnetic moment from the particle center. In no applied magnetic field, the Janus particles aggregate to form a stable cluster unit composed of 2-4 particles if the magnetic particle-particle interaction strength is increased. As the magnetic field is increased, the cluster units collapse and chain-like clusters are formed aligned in the magnetic field direction. In the situation of a strong magnetic field, the chain-like clusters composed of Janus particles tend to be thicker as the magnetic moment is shifted away from the particle center. This is because the magnetic interaction between neighboring particles increases due to the magnetic moments of constituent particles in chain-like clusters being closer to each other. The present results are useful for elucidating the internal structure of complex aggregates in a 3D system.

Molecular Structure and Dynamics in Wet Gecko β-Keratin.

Molecular dynamics simulations are performed to investigate the molecular picture of water sorption in gecko keratin and the influence of relative humidity (RH) on the local structure and dynamics in water-swollen keratin. At low RHs, water sorption occurs through hydrogen bonding of water with the hydrophilic groups of keratin. At high RHs (>80%), additional water molecules connect to the first "layer" of amide-connected water molecules (multimolecular sorption) through hydrogen bonds, giving rise to a sigmoidal shape of the sorption isotherm. This causes the formation of large chain-like clusters surrounding the hydrophilic groups of keratin, which upon a further increase of the RH form a percolating water network. An examination of the dynamics of water molecules sorbed in keratin demonstrates that there are two states, bound and free, for water. The dynamics of water in these states depends on the RH. At low RHs, large-scale translational motions of tightly bound water molecules to keratin are needed to remake the entire hydration shell of the keratin. At high RHs (>80%), the water molecules more quickly exchange between the two states. The center-of-mass mean-square displacement of water molecules indicates a hopping motion of water molecules in the keratin solvation shell. The hopping mechanism is more pronounced at RHs < 80%. At higher RHs, water translation through water clusters (water network) dominates. We have observed two regimes for the dependence of dynamical properties on the RH: a regime of gradual increase of the dynamics over 10% < RH < 80% and a regime of drastic dynamic acceleration at RH > 80%. The latter regime begins exactly where the water uptake and the volume swelling also increase much more and where a drastic change in the elastic properties of gecko keratin has been observed. A nearly linear relation between the relaxation times for all dynamical processes and the water content of gecko keratin is observed.

The behavior and heat generation effect of a magnetic rod-like particle suspension in an alternating and a rotating magnetic field

We have investigated the behavior of magnetic rod-like particles and their relationship with the heat generation effect for both alternating and rotating magnetic fields, by means of Brownian dynamics simulations. As a common feature for both type of magnetic field variations, in the case of significantly strong particle-particle interaction strengths, densely-packed clusters are formed, which do not contribute to the heat generation. For the case of the alternating magnetic field, in the intermediate frequency range, linear thick chain-like clusters are formed and the constituent rod-like particles themselves tend to rotate to follow the change in the field. In contrast, for the case of the rotating field, linear clusters rotate as a whole body to respond to the magnetic field rotation. In both type of magnetic field variations, the magnetic interactions between the constituent particles in a cluster tend to function to suppress the relaxational motion of the rod-like particles, which, as a result, leads to increase in the heat generation effect in certain situations. In a relatively large frequency region, the rotating applied magnetic field gives rise to a larger heat generation effect, whereas in contrast, in the lower frequency region the alternating magnetic field yields the larger heating effect. Highlights The behavior of magnetic rod-like magnetic particles has been elucidated in the case of an alternating and a rotating magnetic field. The magnetic interactions between the constituent particles in a cluster tend to suppress the relaxation motion of the rod-like particles. The frequency and strength of a time-dependent magnetic field have complex influences on the heating effect. In a relatively large frequency region, the rotating applied magnetic field gives rise to a larger heat generation effect. In a relatively lower frequency region, the alternating magnetic field is superior to the rotating field.

Age differential response to bevacizumab therapy in choroidal neovascularization in rabbits

Choroidal neovascularization (CNV) in young rabbits has been shown to have a rapid, robust response after treatment with bevacizumab, an anti-vascular endothelial growth factor (VEGF) medication. This investigation evaluates an age differential response to bevacizumab in older populations of rabbits using multimodal high resolution molecular imaging. Young (4 months old) and life span (14 months old) rabbits were given subretinal injections of Matrigel and VEGF to produce CNV. All CNV rabbit models were then treated with a bevacizumab intravitreal injection. Rabbits were then monitored longitudinally using photoacoustic microscopy (PAM), optical coherence tomography (OCT), color photography, and fluorescence imaging. Chain-like gold nanoparticle clusters (CGNP) conjugated with tripeptide arginylglycylaspartic acid (RGD) was injected intravenously for molecular imaging. Robust CNV developed in both young and old rabbits. After intravitreal bevacizumab injection, fluorescence signals were markedly decreased 90.13% in the young group. In contrast, old rabbit CNV area decreased by only 10.56% post-bevacizumab treatment. OCT images confirmed a rapid decrease of CNV in the young group. CGNPs demonstrated high PAM signal in old rabbits and minimal PAM signal in young rabbits after bevacizumab, indicating CNV regression. There is a significant difference in response to intravitreal bevacizumab treatment between young and old rabbits with CNV which can be monitored with multimodal molecular imaging. Old rabbits demonstrate significant persistent disease activity. This represents the first large eye model of persistent disease activity of CNV and could serve as the foundation for future investigations into the mechanism of persistent disease activity and the development of novel therapies.

Short to medium range order and atomic dynamic property within the surface of nanoscale metallic glasses revealed by molecular dynamics simulations

The surface microstructure and its atomic dynamic property of a metallic glass nano pillar were investigated by using molecular dynamics simulations. The short-range order motifs in the surface contain a large number of unstable bonded pairs and clusters, leading surface to approach the structural property of liquid phase. A proportion of <0, 0, 12, 0> clusters in the surface constitute chain-like super clusters, but its overall degree of medium-range order is lower than that in the core region. The atomic mobility in the surface at different scales are enhanced significantly. Generally, the lower the degree of order for the cluster, the stronger its migration ability. The surface region could be divided into three consecutive sublayers, which are solid-like layer, semi-solid layer and liquid-like layer. The content of liquid-like clusters increases sequentially in these three sublayers. A schematic illustration of the relationship between the hierarchical structure and the possible relaxation modes was proposed.

Elucidation of the relationship between aggregate structures and magnetorheological properties of a magnetic cubic particle suspension by means of Brownian dynamics simulations

We have developed a Brownian dynamics simulation technique for a cubic magnetic particle suspension in a simple shear flow in order to elucidate the relationship between the particle aggregates and the magnetorheological characteristics. A magnetic field is applied in the direction normal to the shearing plane. In a weak applied magnetic field, if the magnetic particle–particle interaction strength is sufficiently large, the particles aggregate to form closely-packed clusters even when subject to the influence of the shear flow. As the magnetic field strength is increased, the closely-packed aggregate structures are transformed into chain-like structures. The net viscosity is increased because the chain-like clusters give rise to a larger resistance to the flow field. As the magnetic field strength is further increased, the chain-like clusters grow into wall-like clusters aligned in the direction of the magnetic field. If the wall-like clusters are the predominant clusters, a magnetic force arises due to a characteristic of the particle arrangement in the wall-like clusters that tends to accelerate the flow field and, as a consequence, decrease the net viscosity. From these results, it may be suggested that under certain conditions a magnetic cubic particle suspension may exhibit a negative contribution to the magnetorheological characteristic. Highlights of the present study We have developed a Brownian dynamics (BD) simulation technique for a magnetic cubic particle suspension. BD simulations have been performed in order to investigate the relationship between particle aggregates and magnetorheological properties. The net viscosity exhibits a complex dependence on the regime of particle aggregates. It is suggested that under certain conditions a magnetic cubic particle suspension may exhibit a negative contribution to the magnetorheological characteristics. An increase in the shear rate causes instability in the face-to-face configuration and leads to the collapse of closely-packed clusters.