Slipping friction of an optically and magnetically manipulated microsphere rolling at a glass-water interface

Abstract

The motion of submerged magnetic microspheres rolling at a glass-water interface has been studied using magnetic rotation and optical tweezers combined with bright-field microscopy particle tracking techniques. Individual microspheres of varying surface roughness were magnetically rotated both in and out of an optical trap to induce rolling, 2 along either plain glass cover slides or glass cover slides functionalized with polyethylene glycol. It has been observed that the manipulated microspheres exhibited nonlinear dynamic rolling-while-slipping motion characterized by two motional regimes: At low rotational frequencies, the speed of microspheres free-rolling along the surface increased proportionately with magnetic rotation rate; however, a further increase in the rotation frequency beyond a certain threshold revealed a sharp transition to a motion in which the microspheres slipped with respect to the external magnetic field resulting in decreased rolling speeds. The effects of surface-microsphere interactions on the position of this threshold frequency are posed and investigated. Similar experiments with microspheres rolling while slipping in an optical trap showed congruent results.

Propulsion of microspheres in fluids using rotating magnetic fields

“…Since the speed of motion is largest near f c , the total distance that a microsphere moves during a fixed time interval (here ∆t = 10 s) will also be largest near f c , and therefore, this zigzag pattern of motion will be most easily observed just above f c . Agayan et al [15] observed similar effects in rotating fields for both free microspheres on a glass surface, as well as for microspheres that were trapped by optical tweezers at the surface, and found shifts in the direction of motion relative to the plane of the rotating field of up to 10 • for field rotation frequency above a critical value f c ≈ 2.5 Hz. This was interpreted as a tilt of the direction of the magnetic moment away from the plane of rotation into the third dimension.…”

“…Optical tweezers have been used to trap magnetic microspheres near a surface [15], and the particles were then exposed to rotating magnetic fields. Due to the rotation of the particles, the equilibrium trapping position of the particles was displaced relative to the center of the optical trap.…”

“…The authors of Ref. [15] then studied how the rolling and slipping of the microsphere depended on the magnetic rotation rate and surface properties. Martinez-Pedrero and Tierno [8] have shown that carpets of magnetically driven rotating beads can be used to carry cargo such as cells.…”

Approximate steering of a plate-ball system under bounded model perturbation using ensemble control

“…Studies by Ding et al on rolling friction of microspheres [20] demonstrate that even on the micro-scale spheres can roll with little slip. A study by Agayan et al of the slipping friction of optically and magnetically manipulated microspheres on a glass-water interface demonstrate techniques for manipulation that may benefit from our methodology [21].…”

Coulombically Driven Rolling of Nanorods on Water

“…This is also seen in S obtained in the STO regime for the AT and related CG rollers, with even larger " s . The overall increase of S with " s is caused by the decreased slipping and increased traction of the roller [29].…”