Gradient porous materials for reliable structured adhesivesPart of:
Hierarchical structures have been involved in natural creatures to realize reliable functions, such as reversible adhesions. For instance, hierarchical seta in geckos and material gradient in beetle’s seta, which have an elegant balance between the structure stability and the formation of intimate contact with counterpart surface, are believed to play a significant role in their reliable adhesions. While the hierarchical seta-inspired structures need complex fabrication processes and are easy to be destroyed, the gradient design for structured adhesives may hold the key for reliable structural adhesions. Here, gradient porous materials were designed to meet the requirements for structured adhesives. By changing the local pore size and density with several techniques, porous pillar arrays with gradient elastic modulus were achieved. The combination of microphase separation of block copolymer and directional selective swelling was used to fabricate continuous porous gradient, while the particle assembled in controlled manner served as sacrificial templates for gradient isolated pores. The gradient porous designs were then applied to the seta-inspired adhesive pillar arrays. Enhanced adhesions, structure stability and reliability were achieved at the same time on these gradient, porous structured adhesives.