I have addressed a polydisperse suspension composed of cubic hematite particles in thermodynamic equilibrium. From the viewpoint of developing a surface modification technique using cubic hematite ...particles, I have investigated the local internal structures of cubic particle aggregates in a quasi-two-dimensional (quasi-2D) system. The cubic particles have a full three-dimensional (3D) rotational ability in a quasi-2D system. I have conducted quasi-2D Monte Carlo simulations in the situation of no applied magnetic field to investigate the dependence of the local internal structures of particle aggregates on the magnetic particle-particle interaction strength and the standard deviation in the particle size distribution. The results obtained here are summarized as follows. In a polydisperse system with a small standard deviation, cubic particles tend to aggregate to form closely-packed structures with an aligned face-to-face configuration as the magnetic particle-particle interaction strength is increased. In a polydisperse system with a large standard deviation, they tend to aggregate to form loosely-packed structures with unstable face-to-face contact as the magnetic interaction strength is increased. That is, an increase in the value of standard deviation leads to a decrease in the orientation order of the constituent particles in the aggregates. I understood that the orientation order of the cubic particles decreases sharply within a narrow range of the standard deviation in the particle size distribution.
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.
In the present study, by means of quasi-two-dimensional Brownian dynamics simulations, we have addressed the physical phenomena of a suspension composed of cubic haematite particles in a rotating ...magnetic field in order to elucidate the relationship between aggregate structures and their response to a rotating magnetic field. In the case of a relatively weak magnetic particle-particle interaction, single particles remain without aggregating to form specific clusters, and the magnetic moment of single particles tends to follow a change in the direction of the rotating magnetic field. In the case of a strong magnetic particle-particle interaction, closely-packed clusters with a face-to-face configuration tend to form in the system, although the individual magnetic moments of the constituent particles do not follow the change in the magnetic field direction. As the magnetic field strength is increased, closely-packed structures are transformed into aggregate structures with an offset face-to-face configuration. In this situation, the magnetic moments of constituent particles are strongly restricted to the magnetic field direction, and the aggregates themselves may significantly rotate to follow the change in the orientation of the rotating magnetic field.
We have addressed the aggregation phenomena of a cubic haematite particle suspension in an alternating magnetic field in order to investigate the regime change in the aggregate structure. Brownian ...dynamics simulations have been performed for a quasi-two-dimensional system with an alternating magnetic field applied in the plane of the system. In a weak alternating field, the cubic particles aggregate to form closely-packed structures tending to an aligned face-to-face configuration with increasing magnetic particle-particle interaction strength. In a closely-packed cluster, the orientation of the magnetic moment of a constituent particle tends to be more strongly influenced by the magnetic interaction between neighbouring particles and less influenced by the direction of the alternating magnetic field. As the strength of the applied field is increased, the particle moments become more restricted to the direction of the alternating field and the closely-packed structures transform into elongated aggregates with an offset face-to-face configuration. As the direction of the alternating magnetic field switches from the positive to the negative x-direction, the elongated aggregates tend to collapse temporarily and when the orientation of the moments is again strongly restricted to the switched field direction, elongated aggregate structures with offset face-to-face contact are re-formed in the system.
Highlights of the present paper
We have investigated a regime change in the internal structure of cubic particle aggregates in an alternating magnetic field.
As the magnetic field strength is increased, closely-packed aggregates with an aligned face-to-face configuration transform into elongated aggregates with an offset face-to-face configuration.
We have clarified that the elongated aggregates collapse temporarily and then re-form when the direction of the alternating magnetic field switches.
We have suggested that the frequency of the magnetic field may be used as a means for controlling the local internal structure of particle aggregates.
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.
•Monte Carlo simulations have been employed for the aggregate structures.•Brownian dynamics simulations have been employed for the magneto-rheology.•Even a weak shear flow induces a significant ...regime change in the aggregates.•A strong external magnetic field drastically changes the aggregates.•The dependence of the viscosity on these factors is governed in a complex manner.
In the present study, we address a suspension composed ferromagnetic rod-like particles to elucidate a regime change in the aggregate structures and the magneto-rheological characteristics. Monte Carlo simulations have been employed for investigating the aggregate structures in thermodynamic equilibrium, and Brownian dynamics simulations for magneto-rheological features in a simple shear flow. The main results obtained here are summarized as follows. For the case of thermodynamic equilibrium, the rod-like particles aggregate to form thick chain-like clusters and the neighboring clusters incline in opposite directions. If the external magnetic field is increased, the thick chain-like clusters in the magnetic field direction grow thicker by adsorbing the neighboring clusters that incline in the opposite direction. Hence, a significant phase change in the particle aggregates is not induced by an increase in the magnetic field strength. For the case of a simple shear flow, even a weak shear flow induces a significant regime change from the thick chain-like clusters of thermodynamic equilibrium into wall-like aggregates composed of short raft-like clusters. A strong external magnetic field drastically changes these aggregates into wall-like aggregates composed of thick chain-like clusters rather than the short raft-like clusters. The internal structure of these aggregates is not strongly influenced by a shear flow, and the formation of the short raft-like clusters is maintained inside the aggregates. The main contribution to the net viscosity is the viscosity component due to magnetic particle-particle interaction forces in relation to the present volumetric fraction. Hence, a larger magnetic interaction strength and also a stronger external magnetic field give rise to a larger magneto-rheological effect. However, the dependence of the viscosity on these factors is governed in a complex manner by whether or not the wall-like aggregates are composed mainly of short raft-like clusters. An increase in the shear rate functions to simply decrease the effect of the magnetic particle-particle and the particle-field interactions.
By estimating the force and torque acting on the cube for the two cases of a uniform flow field and a rotational flow field, we have discussed whether or not there is a coupling between the ...translational and the rotational motion. From the characteristics of the friction coefficients, we may understand that there is no coupling between the translation motion and the rotational motion in the situation of the Reynolds number being sufficiently smaller than unity. In contrast, in the case of a non-slow flow field with the Reynolds number larger than unity, the coupling characteristics of the motion of a cube is certainly recognised and therefore the interaction with the ambient fluid is characterised by a variety of friction coefficients including friction coefficients that relate the forces acting on the cube to the angular velocities of the rotational motion. Hence, the employment of these translational and rotational diffusion coefficients for a cube enables the implementation of Brownian dynamics simulations for a suspension composed of cubic particles in order to analyse the dynamic characteristics of a cubic particle suspension.
Highlights
We have considered a flow problem around a cube in order to numerically clarify the characteristics of the translational and rotational friction or diffusion coefficients.
In a slow flow field the motion of the cube need only to be characterised by two friction coefficients, i.e. the translational and rotational friction coefficients.
In the case of a non-slow flow field, the coupling characteristics between the translational motion and the rotational motion are recognised.
Employment of these diffusion coefficients enables the implementation of Brownian dynamics simulations for a suspension composed of cubic particles.
In the previous study, from the viewpoint of surface modification technology, we considered a quasi-2D suspension in thermodynamic equilibrium in order to investigate the characteristics of magnetic ...cubic particles on a material surface. The present study has been expanded to include 3D Monte Carlo simulations of a suspension of magnetic cubic particles in order to discuss a regime change in the structures of cubic particle aggregates. We attempt to elucidate the dependence of a regime change in the aggregate structures on a variety of factors. The main results obtained here are summarised as follows. If the magnetic interaction strength is sufficiently large, closely packed clusters are formed by repeat and expansion of a cluster unit composed of eight particles, which may be the most preferred configuration as it gives rise to a minimum energy. A regime change in the internal structure of aggregates appears in a narrow range with increasing magnetic interaction strength. As the applied magnetic field strength is increased, closely packed clusters collapse and are transformed into wall-like clusters that are formed along the magnetic field direction. An increase in the volumetric fraction of particles induces a regime change from thick chain-like clusters to the formation of wall-like clusters.
It is widely known that Emily Berry (1981-), acclaimed London poet, describes some fixation of oral sensitivity in her work, especially in a particular poem “Our Love Could Spoil Dinner”. Similarly, ...another much younger poet Jenna Clake (1992-), while showing her deep concern with Berry in “HNY” (the poem actually begins ‘after Emily Berry’), writes “Pink Grapefruit” in which the oral sensitivity is foregrounded. Through a close reading of those poems, the present article will attempt to illustrate how Clake infuses the depths of oral sensitivity for her descriptions. Interestingly, Heather McAlpine’s re-reading of the imagery of “lips”, in part, through Mikhail Bakhtin can encourage us to investigate the meaning of Clake’s such infusion, by discussing the issue of the significant representation of the human mouth as a corporeal embodiment. Indeed, compared with other body functions, oral parts organize as the points at which the self and the world most peculiarly interpenetrate. Additionally, as my ultimate aim, I will demonstrate that physical manifestations of oral sensitivity can be significantly related with possible creative writings by which we can depict oral sensitivity in the world of fiction.
We have investigated the aggregate structure of a suspension composed of magnetic particles with a cubic geometry by means of Monte Carlo simulations. From the viewpoint of application to the ...technology of surface modification, we have considered a quasi-two-dimensional suspension in thermodynamic equilibrium. As the magnetic interaction strength is increased, the effects of the thermal energy are reduced and the particles tend to aggregate together. These aggregates of cubic particles are not chain-like, but are designated as closely packed clusters. An applied magnetic field tends to enhance the formation of clusters along the field direction but does not significantly regularise the internal structure of the cluster. This is mainly due to the preference of a face-to-face contact configuration for the alignment of particles with cubic geometry. The regime of the internal structure of aggregates has a significant effect on the characteristics of the alignment of the magnetic moments with regard to the external magnetic field direction. Our simulations indicate that larger closely packed clusters are formed with increasing volumetric fraction, whereas the internal structure of the closely packed clusters is not found to be significantly influenced by the change in the volumetric fraction.
