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Journal Article

Characterization of active matter in dense suspensions with heterodyne laser Doppler velocimetry


Fischer,  Peer       
Max Planck Institute for Medical Research, Max Planck Society;

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Sachs, J., Kottapalli, S. N., Fischer, P., Botin, D., & Palberg, T. (2021). Characterization of active matter in dense suspensions with heterodyne laser Doppler velocimetry. Colloid and Polymer Science, 299(2), 269-280. doi:10.1007/s00396-020-04693-6.

Cite as: https://hdl.handle.net/21.11116/0000-000B-3A30-E
We present a novel approach for characterizing the properties and performance of active matter in dilute suspension as well as in crowded environments. We use Super-Heterodyne Laser-Doppler-Velocimetry (SH-LDV) to study large ensembles of catalytically active Janus particles moving under UV illumination. SH-LDV facilitates a model-free determination of the swimming speed and direction, with excellent ensemble averaging. In addition, we obtain information on the distribution of the catalytic activity. Moreover, SH-LDV operates away from walls and permits a facile correction for multiple scattering contributions. It thus allows for studies of concentrated suspensions of swimmers or of systems where swimmers propel actively in an environment crowded by passive particles. We demonstrate the versatility and the scope of the method with a few selected examples. We anticipate that SH-LDV complements established methods and paves the way for systematic measurements at previously inaccessible boundary conditions.