Fig. 3: Aligning torque as the mechanism for path reuse.
From: Environmental memory boosts group formation of clueless individuals
a, b Time sequence of a light-activated Janus particle experiencing a torque that aligns it to openings in a crowded environment at a density of SiO2 passive particles of ρp = 37.5%. The effect of this torque on the particle’s trajectory is evident in the frames at a t = 34 s and b t = 58 s, where the particle has turned clockwise (towards a void in the structure formed by the passive colloids) and counter-clockwise (towards an open path), respectively. In each image, 24-s-long trajectories are shown for both active (red colour scale) and passive (blue colour scale) particles; t represents the time of each frame and τ the time along each trajectory. Scale bar: 10 μm. c Probability P(δ) that a Janus particle moving at a velocity v is deflected by an angle δ from its direction of approach to an obstacle due to a torque Ω (inset). The deflection angle δ is defined between the active particle’s direction of approach to the obstacle (at a distance between the two particles' surfaces equal to one diameter d) and its direction of motion after having passed it (after travelling a 2d distance); we calculated δ at low density of passive particles (ρp = 12.5%) to primarily consider interactions with single obstacles for active particles' approaches within a narrow angular cone (±π/8 excluding near head-on approaches, which contribute symmetrically around δ = 0). Positive δ values indicate deflection away from the obstacles (as shown in the inset), while negative δ values indicate initial deflections towards the obstacles. The solid line is a Gaussian fit (centred at δ ≈ 0.23 rad, dashed vertical line) around the position of the peak. Source data are provided as a Source Data file.
