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Electrical charging of colloidal particles in nonpolar liquids due to surfactant additives is investigated intensively, motivated by its importance in a variety of applications. Most methods rely on average electrophoretic mobility measurements of many particles, which provide only indirect information on the charging mechanism. In the present work, we present a method that allows us to obtain direct information on the charging mechanism, by measuring the charge fluctuations on individual particles with a precision higher than the elementary charge using optical trapping electrophoresis. We demonstrate the capabilities of the method by studying the influence of added surfactant OLOA 11000 on the charging of single colloidal PMMA particles in dodecane. The particle charge and the frequency of charging events are investigated both below and above the critical micelle concentration (CMC) and with or without applying a DC offset voltage. It is found that at least two separate charging mechanisms are present below the critical micelle concentration. One mechanism is a process where the particle is stripped from negatively charged ionic molecules. An increase in the charging frequency with increased surfactant concentration suggests a second mechanism that involves single surfactant molecules. Above the CMC, neutral inverse micelles can also be involved in the charging process. [ABSTRACT FROM AUTHOR]

Abstract: Electrophoretic image displays (EPIDs) are a very promising solution in the search for low-power, paper like reflective displays. While the technology is already mature, little is known about the internal physical properties. In this paper, we will describe which elements contribute to the charge transport and give an explanation of the steady state current. The contribution of the surfactant molecules to the generation current is proven. For the first time temperature dependent measurements on EPIDs were performed. [Copyright &y& Elsevier]

Abstract: In this paper we describe electrophoresis of charged particles in a thin layer of a nonpolar liquid between two insulating substrates because this configuration is common in recently developed in-plane electronic paper. In the in-plane electrophoresis experiments a model system of charged inverse micelles in dodecane has been used which is well understood from studies of out-of-plane electrophoresis. The transient current due to drift and diffusion of charged inverse micelles is measured in thin in-plane devices upon application of a voltage step. For the modelling of the transient dynamics of charged inverse micelles without chemical reactions or convection a 1-dimensional approximation of the Poisson–Nernst–Planck (PNP) equations is developed. This approximation is valid for a sufficiently thin in-plane device and allows much faster calculations. Firstly, it is verified in the case of a sufficiently thin in-plane device and high applied voltage that the 1-dimensional approximation is in good agreement with the solution of the full 2-dimensional PNP equations with finite elements implementation. Then, the 1-dimensional approximation is used to study the transient current and trajectories of trace amounts of charged colloidal particles in different regimes depending on the screening of the electric field. Also a comparison is made to the well-studied case of out-of-plane electrophoresis. Finally, it is verified that for voltages much larger than the thermal voltage the experimental results are in good agreement with the 1-dimensional approximation, indicating that the charge transport dynamics of charged inverse micelles in the bulk are described well by the model. [Copyright &y& Elsevier]

Abstract: A complete model for the internal particle distribution of electrophoretic image displays (EPIDs) is presented. From this model, simulation formulas for electrical and optical properties are calculated. These formulas incorporate both time dependence and voltage dependence. They make it possible to optimize display properties since the model is built up with physical parameters. Results are shown that prove that this model is indeed capable of complete optical and electrical transient simulation. The importance of centrifugation during display manufacturing is proven as a way to improve the switching speed of the display. [Copyright &y& Elsevier]

Abstract: The transport of charges in non-polar media is governed by drift and diffusion in an electric field. In addition there may be generation and recombination processes that modify the number of charged species in the liquid. When the electrodes are covered with an insulator layer, the field distribution between the electrodes can be changed considerably. Especially for high concentrations of charges, the voltage drop over the insulator layers may be important. This leads to a faster decay of the transient current and a stronger screening of the electric field in the steady state. In this work we present the results of numerical simulations that combine drift, diffusion, generation, recombination and the voltage drop over the insulator layer. [Copyright &y& Elsevier]