Designed Mushroom-Shaped Microstructures Based On Functional Applications And Mechanics Properties

Mushroom-shaped microstructures,which are considered to be one of the most desirable composite structural materials as adhesives in the future due to their excellent adhesion properties,are expected to be applied to a wide range of fields,for example,transfer-printing systems,soft crawling robots,biomedical instruments,and so on.As a biomimetic adhesive,the adhesion property of mushroom-shaped adhesive strongly depends on the geometry of the structure.In recent two decades,researchers have performed many experimental and theoretical studies on the adhesion mechanism of mushroom-shaped adhesives in terms of the influence of structural morphology on adhesion,the stress distribution at the adhesion interface,and the form of interfacial failure during detachment.With the structured design of mushroom-shaped adhesives,the stress at the adhesion interface changes from being concentrated at the edge position to being distributed at the center,and the failure form switches from edge crack failure to center crack failure,thus exhibiting stronger adhesion.However,adhesive with excellent adhesion is no longer sufficient to meet the engineering demand for fast adhesion switching in intelligent pick-and-place systems.Nature has provided a wealth of impressive practical examples,such as the micro-structures of geckos’ and frogs’ toes.Biologically inspired structures of smart and switchable adhesives have been actively developed to achieve reversibility by applying external stimuli,such as temperature,light,voltage,magnetic field,and force loading.Despite advances in artificial adhesives,it remains a technical and scientific challenge to achieve strategies for rapidly tunable adhesion in a noncontact manner.In addition to excellent adhesion,the mushroom-shaped microstructure may also be used as a support substrate for flexible and stretchable electronics due to its strain isolation effect.When electronics are subjected to large deformations,such as tensile,compression,bending,and torsion,most deformations are isolated on the substrate,ensuring the proper function of the electronics.However,the strain isolation effect of the mushroom-shaped substrate also depends heavily on the geometry of the structure.Exploring the influence of the geometry of mushroom-shaped substrate on the strain isolation effect may expand the potential applications of the mushroom-shaped substrate in the field of flexible and stretchable electronics.Therefore,in this work,the mushroom-shaped material made of polydimethylsiloxane(PDMS)is investigated to explore the influence of geometry on the adhesion property and strain isolation effect.According to the experimental and theoretical results,reasonable structured design strategies are suggested,respectively.Meanwhile,smart adhesives with fast,reversible,and switchable adhesion are proposed.The main contents of this work are briefly summarized as follows:(1)Based on the self-developed method of preparing mushroom-shaped microstructure,mushroom-shaped adhesives with the desired geometry(diameters of tip and stalk)were prepared.Systematic adhesion experiments were performed on mushroom-shaped adhesives to investigate the influence of loading conditions(preload displacement,holding time,and retraction speed)and geometry of the structure on the adhesion.The interfacial failure was observed and captured using a microscape during the detachment.By combining the Finite Element Method,the relationships among the geometries of the structure,the forms of interfacial failure,and the adhesion properties were analyzed to explain the adhesion mechanism of the mushroom-shaped materials.A structured design strategy was also suggested.(2)Base on the adhesion mechanism of mushroom-shaped adhesives,a strategy of smart adhesive with fast,reversible,and switchable adhesion was proposed via magnetic actuation.The structure and material of the smart adhesive were optimized to obtain the maximum magnetic actuation.With the self-developed method of preparing mushroom-shaped microstructure,the smart adhesives with structured design were prepared.Systematic adhesion experiments were carried out to verify the feasibility of smart adhesives in both selective pick and pick-and-place operations.Examples of smart adhesive in transfer technology illustrated its applicability.(3)Based on the excellent strain isolation effect,the mushroom-shaped microstructure was developed and applied to the field of flexible and stretchable electronics.Systematic numerical simulations have been carried out to investigate the influence of geometries on the strain isolation effect in Gallium Arsenide Photovoltaics.According to the strain isolation effect,the structure stability,and the preparation method,a reasonable structured design was suggested for the mushroom-shaped substrate.The mushroom-shaped microsubstrate was applied to a highly stretchable electronic skin which was suffered a uniaxial tensile load.The sensing capability was tested to further verify the strain isolation effect of the mushroomshaped microsubstrate.