Influence of the volume fraction on the electrokinetic properties of maghemite nanoparticles in suspension

Abstract

Special issue in Honour of Pierre TURQInternational audienceWe used several complementary experimental and theoretical tools to characterise the charge properties of well-definedmaghemite nanoparticles in solution as a function of the volume fraction. The radius of the nanoparticles is equal to 6 nm.The structural charge was measured from chemical titration and was found high enough to expect some counterions tobe electrostatically attracted to the surface, decreasing the apparent charge of the nanoparticle. Direct-current conductivitymeasurements were interpreted by an analytical transport theory to deduce the value of this apparent charge, denoted here by‘dynamic effective charge’. This dynamic effective charge is found to decrease strongly with the volume fraction. In contrast,the ‘static’ effective charge, defined thanks to the Bjerrum criterion and computed from Monte Carlo simulations turns outto be almost independent of the volume fraction. In the range of Debye screening length and volume fraction investigatedhere, double layers around nanoparticles actually interact with each other. This strong interaction between nanocolloidalmaghemite particles is probably responsible for the experimental dependence of the electrokinetic properties with the volumefraction

Surface Charge Density Determination in Water Based Magnetic Colloids: a Comparative Study

“…In this method, in agreement with the literature. In this way, according to table 1, the saturation value of the surface charge density determined with the two methods show excellent agreement with each other and they are consistent with previous determinations in similar magnetic colloids 10,14,15,24 proving that both are effective. Nevertheless, the methods exhibit a significant different profile of the pH dependence of the surface charge density as shown in figure 4.…”

“…In the SPM 14,15 the pH of the magnetic colloid sample is adjusted to the PZC inducing rapid coagulation. Then, the coagulated nanoparticles are washed thoroughly with distilled water to ensure the particles are uncharged and the solvent is free of ions.…”

Can charged colloidal particles increase the thermoelectric energy conversion efficiency?

“…4, and is comparable to the dynamic electrical charge that has been measured in ref. 35 as the electrostatic repulsion created by the already adsorbed nanoparticles prevents additional particles from approaching, resulting in a plateau for f 4 0.1%. In a ferrofluid similar to ours, nanoparticles adsorption on mercury and gold electrodes has been observed in ref.…”

Eletrostática em sistemas coloidais carregados

“…O solvente geralmente é a água, e a nanopartícula é carregada com uma densidade superficial de carga elétrica, que depende do pH do meio: positiva em meio ácido, negativa em meio básico e nula em região de neutralidade. O processo de carregamento envolve reações ácido-base de Brönsted, nas quais, grupos superficiais são protonados ou desprotonados [22,23]. Outros solventes polares como o e5408-3 dimetilsulfóxido (DMSO) também têm sido empregados na elaboração de fluidos magnéticos iônicos [24].…”