Abstract
Particles exposed to an electric field experience forces that influence their movement. This effect can be used for filtration of air, or for size classification of aerosols. The motion of charged particles in a non-uniform electric field is called electrophoresis. Two processes are involved in this phenomenon: 1) charging of particles and 2) electrical mobility separation. If fibres are exposed to electrophoresis, they are separated on the basis of two parameters: diameter and length. Regrettably, as naturally occurring fibres are polydisperse both in diameter and length, the electrophoresis is not very efficient in length classification. In contrast, dielectrophoresis is the motion of electrically neutral particles in a non-uniform electric field due to the induced charge separation within the particles. As deposition velocity of fibres induced by dielectrophoretic force strongly depends on length and only weakly on diameter, it can be used for efficient length classification. Principles of length classification of conducting and non-conducting fibres are presented together with design of a fibre classifier. Lastly, images of motion of fibres recorded by high-speed camera are depicted.
Highlights
The adverse health effects of inhaled fibres are known for decades [1]
Fibre classifiers are being used for in-situ selecting the fibres of specific length from polydisperse clusters [2,3]
Charged particles exposed to an electric field experience forces that cause motion of the particles
Summary
The adverse health effects of inhaled fibres are known for decades [1]. As fibre length is believed to be one of the important factors for an assessment of their toxicological impact [2], it is important to be able to produce batches of fibres of identical length for experiments. The principles that can be used for length-separation of fibres have been described by Baron [4]. Charged particles exposed to an electric field experience forces that cause motion of the particles. It has been demonstrated by Hochrainer [5] that electrostatically charged longer fibres have higher mobility in a non-uniform electric field compared to short fibres and isometric particles. This fact can be used for the size separation. There are two processes involved in this phenomenon: 1) charging of particles and 2) electrical mobility separation [4]. Classification of fibres based on the principle of electrophoresis is not very efficient [6]
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