Catalytic micromotor generating self-propelled regular motion through random fluctuation

Abstract

Most of the current studies on nano∕microscale motors to generate regular motion have adapted the strategy to fabricate a composite with different materials. In this paper, we report that a simple object solely made of platinum generates regular motion driven by a catalytic chemical reaction with hydrogen peroxide. Depending on the morphological symmetry of the catalytic particles, a rich variety of random and regular motions are observed. The experimental trend is well reproduced by a simple theoretical model by taking into account of the anisotropic viscous effect on the self-propelled active Brownian fluctuation.

Figure 1

SEM image of Pt particles used in our experiments.

Figure 2

Trajectory of the motion of primary particles in (a) pure water and (b) and (c) 1% hydrogen peroxide water for 1 min. Insets show the expanded figure. The particles in (a) and (b) have almost the same diameter, while the particle in (c) is larger. (d) Relationship between time and mean square displacement obtained from the trajectory of (a)–(c). Solid lines and the dotted line show approximate lines of slope 1.0 and 1.4, respectively.

Figure 3

Trajectory and snapshots of (a) translation, (b) spin, and (c) rotation motions of Pt aggregates in 1% hydrogen peroxide water. The scale bar indicates 10 μm.

Figure 4

Typical example of quantitative analysis of particle morphology [using the particle from Fig. 3a]. Top: (left) schematic representation of quantitative analysis of particle morphology and (right) profiles of R(θ) (−π ≤ θ ≤ π) from an axis tilted at angle ψ (ψ = π/3). Bottom: calculation result for f(ψ) of an arbitrary axis at various angles ψ (0 ≤ ψ ≤ π).

Figure 5

Calculated result of trajectory t (0 ≤ t ≤ 1.5 × 10⁴) for (a) translation, (b) spin, and (c) rotation motions of Pt aggregates based on Eqs. 7, 8. Blue arrows represent particles with the angular displacement of rotation (ϕ) [see the insets in (a)–(c)]. All parameters, excluding drag, η_v, and η_ω, are fixed as follows: ⟨|F(t)|²⟩ = 1/6, ⟨N(t)²⟩ = 1/3, x(0) = y(0) = v_x(0) = v_y(0) = ϕ(0) = ω(0) = 0, m = 0.5, and I = 1.0. Values of direction-dependent drag are described in the insets of (a)–(c).