Friction-directed self-assembly of Janus lithographic microgels into anisotropic 2D structures

Abstract

We present a method for creating ordered 2D structures with material anisotropy from self-assembling micro-sized hydrogel particles (microgels). Microgel platelets of polygonal shapes (hexagon, square, rhombus), obtained by a continuous...

Hydrogel Microrobots Self‐Assembled into Ordered Structures with Programmable Actuation

“…Additionally, packing occurred also at much lower inclines. Even a small tilt of the surface (≈2°) cause the discs to slide since there is no static friction (as we described previously) [ 48 ] and, once set in motion, these arrange into the packing. Hence, densely packed structures could be obtained on flat inclined plane under tilts between ≈2° and 10° (Figure S2B,C, Supporting Information) (higher tilt angles lead to structure collapse and formation of multiple layers).…”

“…For a system comprising multiple discs, the total potential energy equals the sum of the potential energies of individual discs (being constrained by contact); hence, the more densely the discs are packed around the well center, the lower the potential energy of the system. Although the discs do not exhibit any random motion (thermal or agitation) and, hence, cannot explore their phase space, [ 48 ] we observed the ordering of the discs into the minimum potential energy state—hexagonal packing—at the bottom of the depression. The crawling and assembly of the first 10 discs and the final assembly after 24 discs crawled into the well and assembled is depicted in Figure 2A,B, respectively, and Video S1, Supporting Information.…”

“…The sliding is purely passive, induced by gravity, and does not require actuation (more on sliding platelet microgels in ref. [48]). The potential energy of each disc in the depression is defined by its elevation, dictated by its distance from the depression center.…”

“…[42] Note that microrobots are typically too large to exhibit Brownian motion (>2 μm) and so cannot explore their phase space to overcome local maxima at their free-energy hyperplane. [43] Still, simple ordered structures can be assembled at these lengthscales, [43][44][45][46][47][48] which may be useful for microrobotics applications. Self-assembly at these lengthscales is typically restricted to two spatial dimensions, due to the positive buoyant mass of the building blocks in the media and their rapid sedimentation.…”

Photocontrollable liquid-crystalline block copolymers: design, photo-directed self-assembly and applications

“…132 The gravitational field is determined by the relative position of the solid centre of mass and the earth. 133 The electric field can polarize small objects and attract them. 134 In addition, the changing electric field can control small objects to move along with the real-time distribution of the electric field.…”