Figure 21.

Opto-thermophoresis of nanomotors. (a) Schematic (upper) of a NIR-light-powered Janus mSiO₂ nanomotor and calculated steady-state temperature distribution (lower) of a representative nanomotor under 3 W cm^–2 irradiation. Reprinted with permission from ref (539). Copyright 2016 American Chemical Society. (b) Snapshots (left) and schematics (right) showing the mechanism of the motion of a PbS-nanoparticle-filled vial propelled by a NIR laser (indicated by a red arrow). The proposed mechanism of the photomechanical effect contains four steps: (1) thermophoretic motion of the PbS nanoparticles toward the laser source; (2) brutal force release induced by Jeans’ instability; (3) explosive growth of a bubble, which disperses the accumulated PbS nanoparticles; and (4) collapse of the bubble and return to the initial state. The temperature gradient is represented by the red color. Reprinted with permission from ref (561). Copyright 2020 Kavokine et al., published under the CC BY 4.0 license http://creativecommons.org/licenses/by/4.0/. (c) Schematic showing the trapping of a single polystyrene nanosphere in an open gold structure on a glass substrate. The inset shows the trajectory points of a 200 nm polystyrene sphere trapped within a hexagonal lattice of triangular Au pads by a moving laser with a rotation frequency of 18.9 Hz. Reprinted with permission from ref (573). Copyright 2013 American Chemical Society. (d) Schematic and two representative examples of the opto-thermophoretic assembly of colloidal matter of diverse sizes (from the subwavelength to micrometer scale) and materials (polymeric, dielectric, metal) with versatile configurations. A bright-field optical image of a 2D hybrid superlattice of 2 mm polystyrene spheres, 0.96 mm polystyrene spheres, 2 mm silica beads, and 1 mm silica beads and a dark-field optical image of a heterogeneous dimer of a 500 nm polystyrene sphere bead and a 200 nm Au nanosphere are shown on the right panel. Reprinted with permission from ref (575). Copyright 2017 Lin et al., published under the CC BY 4.0 license http://creativecommons.org/licenses/by/4.0/.