Sedimentation equilibria of ferrofluids: II. Experimental osmotic equations of state of magnetite colloids

Luigjes, Bob; Thies‐Weesie, Dominique M. E.; Erné, Ben H.; Philipse, Albert P.

doi:10.1088/0953-8984/24/24/245104

Cited by 27 publications

(42 citation statements)

References 43 publications

(120 reference statements)

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“…These values are actually quite high for typical ferrofluids, although recent experimental measurements of osmotic equations of state show that values of λ 2 are achievable [25,26]. field leads to an enhancement of attractive interactions.…”

Section: Resultsmentioning

confidence: 99%

“…The theory is based on a logarithmic representation of the Helmholtz free energy, and hence it will be referred to as the logarithmic free energy (LFE) theory; it will be summarized briefly in Sec. II C. A critical comparison of these theories with the equations of state from simulations of DHSs and experimental sedimentation profiles of real ferrofluids [25,26] shows that the LFE theory is superior over all realistic ranges of volume fraction and dipolar coupling constant. To understand processes such as magnetophoresis in an applied magnetic field, however, requires knowledge of how the virial coefficients vary with field strength.…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamics of ferrofluids in applied magnetic fields

2013

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The thermodynamic properties of ferrofluids in applied magnetic fields are examined using theory and computer simulation. The dipolar hard sphere model is used. The second and third virial coefficients (B 2 and B 3 ) are evaluated as functions of the dipolar coupling constant λ, and the Langevin parameter α. The formula for B 3 for a system in an applied field is different from that in the zero-field case, and a derivation is presented. The formulas are compared to results from Mayer-sampling calculations, and the trends with increasing λ and α are examined. Very good agreement between theory and computation is demonstrated for the realistic values λ 2. The analytical formulas for the virial coefficients are incorporated in to various forms of virial expansion, designed to minimize the effects of truncation. The theoretical results for the equation of state are compared against results from Monte Carlo simulations. In all cases, the so-called logarithmic free energy theory is seen to be superior. In this theory, the virial expansion of the Helmholtz free energy is re-summed in to a logarithmic function. Its success is due to the approximate representation of high-order terms in the virial expansion, while retaining the exact low-concentration behavior. The theory also yields the magnetization, and a comparison with simulation results and a competing modified mean-field theory shows excellent agreement. Finally, the putative field-dependent critical parameters for the condensation transition are obtained and compared against existing simulation results for the Stockmayer fluid. Dipolar hard spheres do not undergo the transition, but the presence of isotropic attractions, as in the Stockmayer fluid, gives rise to condensation even in zero field. A comparison of the relative changes in critical parameters with increasing field strength shows excellent agreement between theory and simulation, showing that the theoretical treatment of the dipolar interactions is robust.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermodynamics of ferrofluids in applied magnetic fields

2013

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“…The knowledge about the microstructure of ferrofluids is not only valuable by itself, but also is directly linked to thermodynamic properties such as pressure, compressibility factors and heat capacity which alter together with the microstructure [20,[24][25][26][27][28][29][30]. To our knowledge, nobody has studied isothermal compressibility of ferrofluids by means of computer simulations despite it has a strong implication for thermodynamics and dynamics of ferrofluids [31].…”

Section: Introductionmentioning

confidence: 99%

Compressibility of ferrofluids: Towards a better understanding of structural properties

et al. 2018

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This paper addresses a computational method aimed at obtaining the isothermal compressibility of ferrofluids by means of molecular dynamics (MD) simulations. We model ferrofluids as a system of dipolar soft spheres and carry out MD simulations in the NPT ensemble. The obtained isothermal compressibility computed via volume fluctuations provides us with a strong evidence that dipolar interactions lead to a higher compressibility of dipolar soft sphere systems: the stronger the dipolar interactions, the bigger is the deviation of the compressibility from the one of a system with no dipoles. Furthermore, we use the isothermal compressibility to calculate the structure factor of ferrofluids at low values of wave vectors, i.e. in the range where it is difficult to predict its behaviour because of a problem with accounting for long-range particle correlations that give the main contribution to the structure factor in this range. Our approach based on the interpolation of the structure factor and the computed isothermal compressibility allows us to obtain the smooth structure factor in the range of low wave vectors and the reliable fractal dimension of the clusters formed in the system.

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“…Один из при-меров таких сред -феррожидкости -устойчивые взвеси наноразмерных однодоменных частиц ферро-и ферримагнитных материалов в жидких носителях [1]. Свойства феррожидкостей широко изучаются эксперимен-тальными методами [2] - [8], теоретически [9] - [15] и с помощью ком-пьютерного моделирования [14] - [19]. Для эффективного применения феррожидкостей ключевой характеристикой является микроструктура этих материалов.…”

Section: Introductionunclassified