Fig. 1
From: Experimental observation of flow fields around active Janus spheres
Experimental measurements of the flow field around an active Janus sphere. (a) Sketch of the Pt-PS Janus particle and notations. \({\hat{\mathbf{e}}}\) is the direction of swimming. The red arrows represent the current loops that start at the equator of the particle and end at its pole13,16,17. (b) Inset: First five coefficients in the expansion of v(θ) in Legendre polynomials, obtained as fitting parameters of the experimental radial and tangential velocities, in the cases where the colloid is stuck or freely moving (blue: stuck, red: moving; triangle: radial, square: tangential). The averages are shown as black dots, and the error bars correspond to the standard deviations. Main: Plot of the slip velocity \(\tilde v(\theta )\) reconstructed from the averages of the Legendre coefficients obtained from the fit (dashed) compared with the simplified expression for v(θ) we use for further analysis. (c–f) Streamlines around the Janus particles obtained experimentally (c, d) and analytically (e, f), in the two situations where the particle is stuck (c, e) and freely moving (d, f). The background colours represent the magnitude of the velocity \(u = |{\mathbf{u}}|\) rescaled by the swimming velocity of the Janus particle when it is freely moving
