Manipulation of Elastic Deformation in Bio-inspired Wet Adhesion

控制附着力的材料的选择取决于所需的应用。例如，在机器人技术中，多个粘合循环对于运动、抓取和操作是必要的。基于壁虎脚垫的合成分层结构在空气中展示了这些能力。然而，在流体环境（例如水下）中实现这些可逆粘附的要求更具挑战性。在流体中，阻力和膨胀等动态效应会在接触之前使表面结构变形，从而防止粘附。这项工作的目的是发展对创造结构表面的基本理解，这些结构表面可以作为液体中的可逆粘合剂。要遵循的策略是制造多孔软材料薄膜，其表面形貌受到青蛙脚趾垫的启发。这些薄膜将被用来研究孔隙度和变形对附着力的影响。可逆水下粘附涂层的开发将推动机器人部件、绷带和伤口密封剂的制造，并有助于了解生物污染的机制。除了用于机器人和更大规模应用的水下粘附，更好地了解柔顺材料的孔隙弹性可以带来更好的性能材料来代替关节软骨。拓展工作包括高中和本科生在实验室的参与。参与该项目的学生将被鼓励在会议上发言，并参与当地小学的额外推广工作。由于传输、变形和粘附是高度耦合的，因此多孔柔顺材料的摩擦、粘附和断裂动力学涉及的现象很少被理解。为了解决这一问题，将开发新的仪器来研究软涂层和多孔涂层的力学性能，同时测量耗散力和时空变形。研究了用三种不同类型的各向异性柱制备的聚合物涂层的性能（如附着力和孔隙弹性松弛），并将结果与相同材料的均匀涂层进行比较。特别是，将进行流体中的耗散力测量，以确定非接触变形改变粘附的大小和方向所起的作用。在整个项目中，实验将与现有的基于多孔介质润滑、弹性和输运的弹性流体动力学和孔隙弹性的理论和连续数值有限元模型进行比较。多尺度孔隙度（如网格尺度、柱间距和表面粗糙度）、模量和表面形貌的方向各向异性的贡献将根据其在潮湿环境中可逆粘附的应用能力来表征。

The choice of materials to control adhesion depends on the desired application. In robotics, for example, multiple adhesive cycles are necessary for locomotion, gripping, and manipulation. Synthetic hierarchical structures based on the gecko toe pads demonstrated these capabilities in air. Fulfilling these requirements for reversible adhesion in fluid environments (for example underwater), however, is more challenging. In fluids, dynamic effects such as drag and swelling can deform surface structures prior to contact and prevent adhesion. The objective of the work is to develop the fundamental understanding in mechanics necessary for the creation of structured surfaces that can act as reversible adhesives in liquids. The strategy to be followed is the fabrication of porous soft material films with a surface topography inspired by the frog toe pads. These films will be employed to investigate the role played by porosity and deformation on adhesion. The development of coatings for reversible underwater adhesion will advance the manufacturing of robotic components, bandages and wound sealants, and could help understand the mechanisms of biofouling. Beyond underwater adhesion for robotic and larger scale applications, a better understanding of poroelasticity in compliant materials could lead to better performing materials to replace joint cartilage. Outreach efforts include participation of high school and undergraduate students in the laboratory. Students participating in the project will be encouraged to present at conferences and be involved with additional outreach efforts at local elementary schools.The dynamics of friction, adhesion, and fracture of porous compliant materials involve poorly understood phenomena because transport, deformation, and adhesion are highly coupled. To address this issue, new instrumentation will be developed to study the mechanical performance of soft and porous coatings to measure simultaneously dissipative forces and spatiotemporal deformation. The performance (e.g. adhesion and poroelastic relaxation) of polymer coatings fabricated with three different type of anisotropic pillars will be investigated and results will be compared with uniform coatings of the same material. In particular, dissipative force measurements in fluids will be performed to determine the role played by out-of-contact deformation alter the magnitude and directionality of adhesion. Throughout the project, experiments will be compared to existing theories and continuum numerical finite element models for elastohydrodynamics and poroelasticity that are based on lubrication, elasticity, and transport in porous media. The contributions of multi-scale porosity (e.g. mesh scale, pillar spacing, and surface roughness), modulus, and directional anisotropy in surface topography will be characterized in terms of their ability to be engineered toward applications in reversible adhesion in wet environments.