Evolution of and Disparity among Biomimetic Superhydrophobic Surfaces with Gecko, Petal, and Lotus Effect.

It is desirable to turn one kind of superhydrophobic (SHPO) surfaces into another by changing surface topography alone and attaining solid surfaces with tunable properties. Herein, gecko-, petal-, and lotus-like SHPO surfaces, composed of ZnO tetrapods and polydimethylsiloxane, are realized by adjusting the roughness factor and length scale of roughness, while keeping the surface chemistry the same. Afterward, water droplet sliding and impacting are investigated. The surfaces behave similarly in spreading but deviate from each other in sliding, receding, jetting, and rebounding due to their different adhesive properties. Moreover, the disparity between surfaces with petal and lotus effects is well explained by Furmidge's and Young-Dupre equations. On the other hand, these formulas fail to elucidate the surface with gecko effect because of its inside sealed air that produces negative pressure upon droplet motion. This paper provides a facile topography evolution path and a manifest correlation between topography and performance in water droplet dynamics for SHPO surfaces with gecko, petal, and lotus effects.

Topological alternation from structurally adaptable to mechanically stable crosslinked polymer.

Stimuli-responsive polymers with complicated but controllable shape-morphing behaviors are critically desirable in several engineering fields. Among the various shape-morphing materials, cross-linked polymers with exchangeable bonds in dynamic network topology can undergo on-demand geometric change via solid-state plasticity while maintaining the advantageous properties of cross-linked polymers. However, these dynamic polymers are susceptible to creep deformation that results in their dimensional instability, a highly undesirable drawback that limits their service longevity and applications. Inspired by the natural ice strategy, which realizes creep reduction using crystal structure transformation, we evaluate a dynamic cross-linked polymer with tunable creep behavior through topological alternation. This alternation mechanism uses the thermally triggered disulfide-ene reaction to convert the network topology - from dynamic to static - in a polymerized bulk material. Thus, such a dynamic polymer can exhibit topological rearrangement for thermal plasticity at 130°C to resemble typical dynamic cross-linked polymers. Following the topological alternation at 180°C, the formation of a static topology reduces creep deformation by more than 85% in the same polymer. Owing to temperature-dependent selectivity, our cross-linked polymer exhibits a shape-morphing ability while enhancing its creep resistance for dimensional stability and service longevity after sequentially topological alternation. Our design enriches the design of dynamic covalent polymers, which potentially expands their utility in fabricating geometrically sophisticated multifunctional devices.

Light-Induced Topological Patterning toward 3D Shape-Reconfigurable Origami.

Shape-reconfigurable materials are crucial in many engineering applications. However, because of their isotropic deformability, they often require complex molding equipment for shaping. A polymeric origami structure that follows predetermined deformed and non-deformed patterns at specific temperatures without molding is demonstrated. It is constructed with a heterogeneous (dynamic and static) network topology via light-induced programming. The corresponding spatio-selective thermal plasticity creates varied deformability within a single polymer. The kinematics of site-specific deformation allows guided origami deployment in response to external forces. Moreover, the self-locking origami can fix its geometry in specific states without pressurization. These features enable the development of shape-reconfigurable structures that undergo on-demand geometry changes without requiring bulky or heavy equipment. The concept enriches polymer origamis, and could be applied with other polymers having similar chemistries. Overall, it is a versatile material for artificial muscles, origami robotics, and non-volatile mechanical memory devices.