Adhesion Mechanism Of Bio-mimetic Micro&Nano Structures

Gecko-inspired adhesive micro&nano structures have been demonstrated to own high adhesion strength, reusable and self-cleaning features and have a broad application prospects in the fields of MEMS devices, biomedical devices and bio-mimetic robots. Deeply understanding the adhesion mechanism of the structures is of great importance for their design and application. In this thesis, we propose a self-consistently theo-retical adhesion model from intermolecular forces and study the adhesion mechanism of small particles and two excellent adhesion microstructures:film-terminated fibrillar microstructure and mushroom-shaped micro structure.First, we give the equilibrium equations and general expression of adhesive force for an arbitrary shaped rigid particle contacting with a semi-infinite incompressible e-lastic substrate based on finite deformation theory. With the theoretical model, we in-vestigate the adhesion mechanism of spherical particle, cylindrical particle and a two-dimensional rigid block contacting with a semi-infinite incompressible elastic substrate. Numerical results indicate that the classical Derjaguin approximation is still valid for the particle size small enough to the scale of the intermolecular interaction in the pull out process when contacting leaning angle is small. In addition, we also find out that:the real shape function for spherical particle should be adopted to obtain the right adhesive force rather than using parabolic approximation as classical models; the critical size of saturated adhesion strength for cylindrical particle from our model is smaller than the value of the classical Kendall model by one order; the leaning angle has great effect on the pull force of the two-dimensional rigid block especially for large ones.Applying the Derjaguin approximation theory to the adhesion of film-terminated fibrillar microstructure system, we study the effect of the terminated film on the ad-hesion properties of the microstructure. Ignoring the deformation of the fibers and the backing layer, we show that the adhesion behavior is dominated by a dimensionless parameter A which is related to the bending stiffness, size of the film and the interface adhesion strength. When λ>0.4, the approach-retraction process is reversible; when λ<0.4the approach-retraction process contains one or multiple hysteresis loops which greatly increase the specific separation work of the system.Finally, we study the effect of annular plate on adhesion property of mushroom-shaped microstructure. Introducing Tvergaard-Hutchinson cohesive zone model to char-acterize the interface interaction, and nonlinear Foppl-von Karman equation to represent the deformation of annular plate, we use finite element method to solve the problem in the case of the plate without instability happening. Results indicate that there are two kinds of delamination modes:one delamination mode with the whole microstructure delaminating suddenly before delamination boundary arriving at the outer boundary of the annular plate, the other delamination mode happening at the outer boundary of the annular plate. The conditions for the two modes happening are controlled by the thick-ness, size and stiffness of the annular plate. Also the friction property of the interface has great effect on the two delamination modes.