Effect of agglomeration of magnetic nanoparticles on the Casimir pressure through a ferrofluid

Abstract

The impact of agglomeration of magnetic nanoparticles on the Casimir pressure is investigated in the configuration of two material plates and a layer of ferrofluid confined between them. Both cases of similar and dissimilar plates are considered in the framework of the Lifshitz theory of dispersion forces. It is shown that for two dielectric (SiO 2 ) plates, as well as for one dielectric (SiO 2 ) and another one metallic (Au) plates, an agglomeration of magnetite nanoparticles results in only quantitative differences in the values of the Casimir pressure if the optical data for Au are extrapolated to low frequencies by means of the Drude model. If, however, an extrapolation by means of the plasma model is used in computations, which is confirmed in experiments on measuring the Casimir force, one finds that the pressure changes its sign when some share of magnetic nanoparticles of sufficiently large diameter is merged into clusters by two or three items.The revealed effect of sign change is investigated in detail at different separations between the plates, diameters of magnetic nanoparticles and shares of particles merged into clusters of different sizes. The obtained results may be useful when developing ferrofluid-based microdevices and for resolution of outstanding problems in the theory of Casimir forces.

Dynamical Sensitivity of Three-Layer Micro Electromechanical Systems to the Optical Properties of the Intervening Liquid Layer

“…Previous studies have shown that ethanol could produce repulsive Casimir forces in a system consisting of different interacting bodies (with dielectric functions ε Liquid , ε 1 , ε 2 , respectively) if the condition ε 1 < ε Liquid < ε 2 is satisfied [26][27][28], and kerosene is also used in ferrofluid-based microdevices. In any case, both materials, as an intervening medium, have attracted attention in investigations related to Casimir forces [29][30][31][32]. The dielectric response of ethanol at imaginary frequencies can be described by a three-oscillator Ninham-Parsegian model [29]:…”

“…Actually, a three-layer system consisting of two actuating components immersed inside a liquid has attracted extensive attention because it provides unique advantages. In this system, under certain conditions, it is possible to generate repulsive Casimir forces leading to stable operation without employing a restoring mechanical spring [26][27][28][29][30][31][32][33][34][35][36]. Moreover, with a ferrofluid between the actuating components one can open new opportunities in nanotechnology [29], for instance, in micromechanical sensors [30], microfluidics [31,36], and micro robotics [37].…”

“…In this system, under certain conditions, it is possible to generate repulsive Casimir forces leading to stable operation without employing a restoring mechanical spring [26][27][28][29][30][31][32][33][34][35][36]. Moreover, with a ferrofluid between the actuating components one can open new opportunities in nanotechnology [29], for instance, in micromechanical sensors [30], microfluidics [31,36], and micro robotics [37]. Therefore, we consider here a MEMS operating inside a fluid, and the main aim is to investigate how stable operation is sensitive to optical properties of the intervening layer by taking also into account the dynamic viscosity of the intervening fluids as well as the fluid slip length on the walls of the actuating plate.…”

Interparticle Correlations in the Simple Cubic Lattice of Ferroparticles: Theory and Computer Simulations

“…where ρ is the magnetic particle number concentration and α = mH/k B T is the Langevin parameter (the relation of the Zeeman interaction energy of the particle magnetic moment m with the external magnetic field H to the thermal energy k B T = β −1 ). Since then ferrofluids have been the subject of intense scrutiny, with regard to their structure, phase behavior, and dynamics [6][7][8][9][10][11][12]. It became clear that a theory based on a single-particle approximation, like expressions (1), is only valid for an infinitely diluted suspension, when the interparticle magnetic interactions can be neglected.…”

Магнитные Характеристики Наночастиц Магнетита, Внедренных Из Феррожидкости В Пористый Кремний

“…Сходные феррожидкости применялись ранее для различных целей, например для внедрения в поры микроструктурированных оптических волокон [9]. Отметим также, что в последние годы они использовались как модельный объект в ряде фундаментальных физических работ [10][11][12]. Согласно [13], в синтезированных таким способом материалах диаметр наночастиц магнетита распределен по логнормальному закону с медианным значением 8.2 nm и параметром скейлинга 0.17 (это означает, что практически все частицы имеют размер менее 15 nm).…”