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Self-Propelled Nanomotors
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Another important effect is caused by Brownian motion. The translational diffusion constant is inversely proportional to the size of the particle from the Stokes–Einstein relationD=kBT6πηR. Rotational Brownian motion dominates over ballistic motion as particles become smaller (the rotational diffusion constant scales as D ∝ R–3). This makes particles lose orientation at a very short time scale (e.g., a 1 μm swimmer loses orientation in 3 s, while a 5 nm particle randomizes its orientation in 1 μs.).
Rheological properties of suspensions
Published in V.M. Polunin, A.M. Storozhenko, P.A. Ryaplolv, Mechanics of Liquid Nano-and Microdispersed Magnetic Media, 2017
V.M. Polunin, A.M. Storozhenko, P.A. Ryaplolv
The viscosity and rheological behaviour of the magnetic fluids are influenced by the variation of temperature. Most of all, the temperature influences the viscosity of the carrier medium of the magnetic fluid, surfactants and, in addition to this, the variation of temperature influences the contribution of rotational diffusion to viscosity and the process of aggregation of the particles in the fluid. Therefore, the temperature dependences of the viscosity of the magnetic fluid and the carrier medium differ. This difference becomes larger with an increase of the temperature of the magnetic phase in the magnetic fluid and with increasing temperature. Viscometric experiments have confirmed that there is a large difference of the temperature dependence of the effective viscosity of the magnetic fluid from that for the carrier medium.
Geometry of Purple Membranes in Aqueous Medium
Published in Stoyl P. Stoylov, Maria V. Stoimenova, Molecular and Colloidal Electro-Optics, 2016
The rotational diffusion coefficient D = kT/f of particles with an arbitrary shape at temperature T is determined by the friction coefficient f when the particle is rotated around one of its axes. EOE from axis‐symmetrical particles is determined at rotation around the axis, which is orthogonal to the axis of symmetry. For particles with wettable surface, f is determined by their size, shape, and medium viscosity η at temperature T.
Optimization of image writer modes for optically rewritable electronic paper
Published in Liquid Crystals, 2022
Aleksey Kudreyko, Vladimir Chigrinov
Further, we introduce the values of the governing parameters. Let cm−1, cm−3, T = 300 K, s, I = 0.125 W/cm2 and . Thus, dimensionless parameter, which describes the absorbed optical energy can be taken as . Another important governing parameter is the rotational diffusion coefficient of azo dye. The value of this parameter also strongly affects the mean azo dye rotation time. The important point of the rotational diffusion coefficient is that it depends on the viscosity and characteristic size of the molecular cluster. The size of the cluster depends of the concentration of azo dye molecules (less than 1%) [8,10]. These facts enable us to analyse solutions of Equation (2) with different values of parameter D, but having fixed its order. We found that the acceptable azo dye rotation time will be achieved with s−1. The values of the defined parameters were chosen to satisfy our requirement regarding the reorientation time.
Generalised expressions for the association and dissociation rate constants of molecules with multiple binding sites
Published in Molecular Physics, 2018
Adithya Vijaykumar, Pieter Rein ten Wolde, Peter G. Bolhuis
We conducted multiple FFS simulations as described in the method sections for several values of the rotational diffusion constant . For simplicity we kept the same system as described in [28], which had identical patches A and B. We performed simulations for two systems, one where the patches are separated by an angle and one where this angle is . Using the generalised FFS expression introduced in [28], we extracted from these simulations the conditional probabilities , , α, and the flux through the first interface Φ. These values are reported in Table 1. Since and , we do not report these numbers explicitly.
Evaluation of the translational and rotational diffusion coefficients of a cubic particle (for the application to Brownian dynamics simulations)
Published in Molecular Physics, 2020
In order to elucidate the magnetorheological characteristics on a microscopic scale, there are several particle-based simulation techniques that may be employed such as molecular dynamics, Brownian dynamics, lattice Boltzmann, dissipative particle dynamics and multi-particle collision dynamics [15,16]. Among these simulation techniques, the Brownian dynamics method may the more straightforward for a particle suspension, where the particle Brownian motion may be accurately activated without introduction of the additional technique that is necessary in the lattice Boltzmann method, although the multi-body hydrodynamic interactions among particles are not taken into account in Brownian dynamics. For this reason, we here address the Brownian dynamics method as a simulation tool for a magnetic cubic particle suspension. In Brownian dynamics simulations it is required to treat the translational and rotational Brownian motion of magnetic particles [16]. In contrast to a suspension of spherical particles, particles with a non-spherical shape such as rod-like or cube-like require a more complex treatment in respect to the equations of motion as they require the inclusion of particle translational and rotational friction coefficients or diffusion coefficients. In the case of axisymmetric rod-like particles, the translational motion is decomposed into the motion in the major and the minor axis directions, and the rotational motion is treated in a similar manner. The translational and rotational diffusion coefficients that are required in simulations may be derived by modelling an axisymmetric particle such as a circular or a spheroid whose diffusion coefficients are given by well known mathematical expressions [16]. In the case of cubic particles which are not axisymmetric we are required to develop a simulation technique for a cubic particle suspension with appropriate diffusion coefficients. A success in the development of a Brownian simulation technique for a cubic particle suspension would be a useful contribution to the expansion of studies on their dynamic properties which may lead to the development of new applications for mechanical dampers and actuators.