Figure 4
From: Brownian fluctuations and hydrodynamics of a microhelix near a solid wall
The piezoelectric stage is driven back and forth along the x direction while the structure is held in optical traps. (a) Velocity of the stage measured by its capacitive sensor. (b) Trajectories in x (blue) and ϕ (green). Brownian noise is filtered out by computing the average trajectory of x and ϕ plotted respectively as blue and green tick lines. Dashed lines plot a fit to the curve based on Eqs. (11) and (12). (c–d) Drag coefficients Γxx and Γxϕ as a function of the distance between the coverglass and the helix axis. The same two quantities are computed using Rotne-Prager method and plotted as solid lines. Dashed line in (c) plots the best fit to the function γ∞/(1 − (9/16)a/z) (where a and γ∞ are free parameters and z is the distance of the helix center from the coverslip); the same function is used to fit data point in (d). Inset in (d) plots the predicted linear velocity of an helical structure that rotates with a constant torque (solid line) or a constant speed (dashed line) at different wall separations.
