Fig. 2: Mechanism of optocapillarity-driven assembly.

(a) Three-dimensional diagram showing the air-water interface deformation generated by light-induced bending of two azo-LCP actuators. The right image is a schematic diagram of the finite element method. The inset is an optical photograph showing the air-water interface deformation generated by light-induced bending of an azo-LCP actuator. The interface rose near the ends of the bent actuator and depressed in the middle when it bent upwards. The deformed interface adopted a quadrupolar structure. (b–e) The total Gibbs free energy of the system composed of two actuators varies with the distance d (c, d) and the orientation angle α (b, e) in different conditions. As a reference, U₀ is the total Gibbs free energy of the system with two actuators end to end, i.e., Case 1. (b) The end of two actuators are always in contact at the peak-point during the rotation and с₁ = c₂ = 20 m⁻¹. (c, d) The horizontal axis denotes the ratio of the center-to-center distance d to the initial length of the actuator l. Here the orientation angle between two actuators is α = 0° (c) and α = 180° (d) respectively, the curvatures are set as с₁ = c₂ = 20 m⁻¹. (e) The center-to-center distance is fixed as d = 1.2 l, the curvatures are set as с₁ = 20 m⁻¹, c₂ = −20 m⁻¹. The green arrow represents the direction of capillarity in which the potential energy of the system decreases. The inset illustrations show the air-water surface morphology obtained by numerical calculation. The color bar represents the height from the horizontal plane, the same as in (f). (f) Three-dimensional air-water interface morphology and the corresponding iso-height contour diagrams of six typical stable assemblies of two actuators (Case 1, с₁ = c₂ = 20 m⁻¹; Case 2, с₁ = c₂ = −20 m⁻¹; Case 3, с₁ = c₂ = 20 m⁻¹; Case 4, с₁ = c₂ = −20 m⁻¹; Case 5, с₁ = −20 m⁻¹, c₂ = 20 m⁻¹; Case 6, с₁ = 20 m⁻¹, c₂ = −20 m⁻¹).