Space charge limited release of charged inverse micelles in non-polar liquids

Charged inverse micelles (CIMs) generated during a continuous polarizing voltage between electrodes in the model system of polyisobutylene succinimide in dodecane do not populate a diffuse double layer like CIMs present in equilibrium (regular CIMs), but instead end up in interface layers. When the applied voltage is reversed abruptly after a continuous polarizing voltage step, two peaks are observed in the transient current. The first peak is due to the release of regular CIMs from the diffuse double layers formed during the polarizing voltage step, which is understood on the basis of the Poisson-Nernst-Planck equations. The second peak is due to the release of a small fraction of generated negative CIMs from the interface layer. A model based on space charge limited release of the generated negative CIMs from the interface layer is presented and the results of the model are compared with several types of measurements. For the situation in which the bulk is deprived of regular CIMs and neutral inverse micelles, the results of the model are in agreement with the experimental results. However, for the situation in which regular CIMs and neutral inverse micelles are present, the model shows discrepancies with the experiment for high voltages and high charge contents. These discrepancies are attributed to electrohydrodynamic flow caused by local variations in the electric field at the vicinity of the electrodes, which occur during the reversal voltage. Also the long term decrease of the amount of released generated CIMs is studied and it is found that the presence of regular CIMs and neutral inverse micelles speeds up the decrease. This study provides a deeper insight in the electrodynamics of CIMs and is relevant for various applications in non-polar liquids

A Straightforward Journey? Discovering Belgium's Refugee Policy through Its Central Government Archives (1945-1957)

When looking at the “management” of refugee crises or violence induced mobility in Western Europe since the 1930s, one cannot help but notice that Belgium offers an interesting case study. In the second half of the 1940s, it recruited over 22,000 displaced persons (DPs) from Germany to work as miners, and by early 1954, it had become the first country to delegate its national competence for recognizing refugees on its territory to the representative of an international body - the Belgian delegate of the United Nations High Commissioner for Refugees (UNHCR). This historical evolution is of course only of interest in as much as it is reflected in the archives which, in the case of Belgium, are well preserved. This contribution uses the records of the Aliens Police and of various Belgian branches of international refugee organizations over the years 1945-1957. The aim is to analyze how their archive production bears the traces of the evolving refugee mobility and Belgium’s asylum regime. Interestingly, these archives have a dynamic of their own, which makes them much more than passive witnesses of the policy-making in the past. I will argue that the latter aspect is of crucial importance for a good understanding and efficient use of such archival sources

Impact of diffusion layers in strong electrolytes on the transient current

Transient currents of electrolytes in response to a voltage step can reveal a lot about the behavior of charges present in an electrolyte. In this paper, electrolytes with high ionic strength are considered. In the limit of small voltage steps, the interpretation is straightforward as the equations describing the transient can be linearized. However, when high ion concentrations and voltage steps of the order of kT/q are considered, we find higher-order effects that occur simultaneously with the diffuse double layer charging. In this case, the diffuse double layer and the transient diffusion layer are coupled because of the screening of the field, leading to a -3/2 power law for the transient current

Axial electrokinetic trapping of single particles at kHz feedback rates

Anti-Brownian Electrokinetic (ABEL) trapping has proven to be a valuable novel tool for analysis at the single-nanoparticle level. In previous work, we explored axial (in the z-direction only) ABEL trapping with planar ITO electrodes based on video image analysis. In this work, we improved the method by using total-internal-reflection (TIR) in combination with a single-photon-counting module. This allows us to axially trap single nanoparticles with a homogeneous field at feedback rates of several kHz such that screening of the electric field becomes negligible