The Instability Of A Liquid-supported Inhomogeneous Film:A Mechanical Viewpoint

Thin film-substrate structures exist extensively in nature a nd engineering.The research on the surface instability of such structures helps to prevent the failure of related engineering structures,expand the application of membrane-substrate systems in modern science and technology,and reveal the formation of surface morphology of membrane-substrate composite structures in nature.In this paper,the elastic thin film-liquid substrate system was selected as the research object,and the instability behaviors of the film with defects under the plane compressive load and the evolution process of the morphology are studied systematically.Firstly,a theoretical model was established to analyze the initial buckling load of the inhomogeneous film instability,and the finite element method was used to simulate the dynamic buckling process of the inhomogeneous elastic film-liquid substrate system.The influence of the geometry and material properties of the defect part on the initial buckling load and the instability morphology were discussed in detail.The results show that the length,position and elastic modulus of the defect have an important influence on the initial buckling load.When the elastic modulus ratio is less than and greater than 1,the change of the length of the defect part has a diametrically opposite eff ect on the initial buckling load of the film instability.With the position of the defect part moving toward the center of the film,the initial buckling load decreases and gradually stabilizes.Within a certain range,the initial buckling load of the film instability also increases as the elastic modulus ratio increases.In addition,the above-mentioned changes in defect parameters also play an important role in the evolution of the instability morphology of inhomogeneous thin films.When the elastic modulus ratio is less than 1,the entire instability process only produces a local instability morphology at the location of the defect part,and the length of the defect part determines the symmetry and antisymmetry of the morphology.When the elastic modulus ratio is greater than 1,the initial global instability and the secondary local instability will occur during the entire instability process.The length of the defect part will affect the magnitude of the global instability morphology,and the secondary local instability morphology will occur at the end of the film which is far from the defect part.Secondly,the self-made experimental device was used to study the instability behavior of polyester film with prefabricated defects on the surface of the water,focusing on the influence of different defect parameters of the film on the instability morphology.The experimental results are basically consistent with the numerical simulation results.Finally,according to the principle of special surface morphology replication and the surface instabilities of stiff film-soft substrate system,a method for preparing a surface with a millimeter-micron instability morphology was proposed.At the same time,super-hydrophobic surface with multi-level morphology is successfully prepared by combining the surface sprayed nanoparticle method.The experimental results show that the hydrophobic properties of the surface of the sinusoidal silicone rubber sample with micro-morphology significantly improve,compared with the surface of the sample without micro-morphology,and due to the sinusoidal morphology of the sample,the micro-morphology formed on the surface is different.Thus,different hydrophobic contact angles are obtained at different positions on the sample surface.This work provides a guidance for the optimal design of the fluid-supported film instability morphology,help to better understand some biological tissue morphology phenomenon,and provide an approach for the preparation of films with specified special morphologies.