Brownian dynamics simulations of colloidal hard spheres. Effects of sample dimensionality on self-diffusion

AbstractThe effect of time-dependent external fields on the structures formed by particles with induced dipoles dispersed in a viscous fluid is investigated by means of Brownian Dynamics simulations. The physical effects accounted for are thermal fluctuations, dipole-dipole and excluded volume interactions. The emerging structures are characterised in terms of particle clusters (orientation, size, anisotropy and percolation) and network structure. The strength of the external field is increased in one direction and then kept constant for a certain amount of time, with the structure formation being influenced by the slope of the field-strength increase. This effect can be partially rationalized by inhomogeneous time re-scaling with respect to the field strength, however, the presence of thermal fluctuations makes the scaling at low field strength inappropriate. After the re-scaling, one can observe that the lower the slope of the field increase, the more network-like and the thicker the structure is. In the second part of the study the field is also rotated instantaneously by a certain angle, and the effect of this transition on the structure is studied. For small rotation angles ($$\theta \le 20^{{\circ }}$$ θ ≤ 20 ∘ ) the clusters rotate but stay largely intact, while for large rotation angles ($$\theta \ge 80^{{\circ }}$$ θ ≥ 80 ∘ ) the structure disintegrates and then reforms, due to the nature of the interactions (parallel dipoles with perpendicular inter-particle vector repel each other). For intermediate angles ($$20<\theta <80^{{\circ }}$$ 20 < θ < 80 ∘ ), it seems that, during rotation, the structure is altered towards a more network-like state, as a result of cluster fusion (larger clusters). The details provided in this paper concern an electric field, however, all results can be projected into the case of a magnetic field and paramagnetic particles.

Download Full-text

Influence of size polydispersity on magnetic field tunable structures in magnetic nanofluids containing superparamagnetic nanoparticles.

Nanoscale Advances ◽

10.1039/d1na00131k ◽

2021 ◽

Author(s):

Dillip Kumar Mohapatra ◽

Philip James Camp ◽

John Philip

Keyword(s):

Magnetic Field ◽

Particle Size ◽

Light Scattering ◽

Optical Microscopy ◽

Brownian Dynamics ◽

Phase Contrast ◽

Superparamagnetic Nanoparticles ◽

Magnetic Nanofluids ◽

Dynamics Simulations ◽

Brownian Dynamics Simulations

We probe the influence of particle size polydispersity on field-induced structures and structural transitions in magnetic fluids (ferrofluids) using phase contrast optical microscopy, light scattering and Brownian dynamics simulations. Three...

Download Full-text

The behaviour of magnetic spherical particles and the heating effect in a rotating magnetic field via Brownian dynamics simulations

Molecular Physics ◽

10.1080/00268976.2021.1892225 ◽

2021 ◽

pp. e1892225

Author(s):

Seiya Suzuki ◽

Akira Satoh ◽

Muneo Futamura

Keyword(s):

Magnetic Field ◽

Brownian Dynamics ◽

Rotating Magnetic Field ◽

Spherical Particles ◽

Heating Effect ◽

Dynamics Simulations ◽

Brownian Dynamics Simulations

Download Full-text

Hard discs under steady shear: comparison of Brownian dynamics simulations and mode coupling theory

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2009.0191 ◽

2009 ◽

Vol 367 (1909) ◽

pp. 5033-5050 ◽

Cited By ~ 37

Author(s):

Oliver Henrich ◽

Fabian Weysser ◽

Michael E. Cates ◽

Matthias Fuchs

Keyword(s):

Brownian Dynamics ◽

Mode Coupling ◽

Transition Density ◽

Two Dimensions ◽

Coupling Theory ◽

Mode Coupling Theory ◽

Stationary Structure ◽

Homogeneous Shear Flow ◽

Dynamics Simulations ◽

Brownian Dynamics Simulations

Brownian dynamics simulations of bidisperse hard discs moving in two dimensions in a given steady and homogeneous shear flow are presented close to and above the glass transition density. The stationary structure functions and stresses of shear-melted glass are compared quantitatively to parameter-free numerical calculations of monodisperse hard discs using mode coupling theory within the integration through transients framework. Theory qualitatively explains the properties of the yielding glass but quantitatively overestimates the shear-driven stresses and structural anisotropies.

Download Full-text