Effects Of Surface Microstructures On The Instability Morphologies Of Hard Film/soft Substrate System

The behavior of instability of hard film/soft substrate systems exists widespread in nature and engineering,and has extensive application in the fields of biomedicine,aerospace,microelectronics and so on.Therefore,it is a hotspot around the scientists major in mechanics,biology,materials science and physics.In this thesis,by introducing quadrangular pyramidlike periodic micro-structures on the surface of hard film/soft substrate system,the influence of the center to center distance,the concavity and convexity,the size and the arrangement direction of the surface micro-structures on the instability morphologies have been systematically studied via experimental,theoretical and numerical simulation methods.Certain results have been obtained.The main content of this thesis includes the following aspects:(1)Firstly,convex and concave quadrangular pyramid-like micro-structures are prepared on the surface of polydimethylsiloxane(PDMS)via lithography,wet etching and casting.After that,by applying pre-strain and surface ultraviolet ozone(UVO)treatment to the PDMS polymer,a pre-strained hard film/soft substrate system is obtained.Then further release of prestrain causes instability in the hard film/soft substrate system.At last,3D laser microscope and optical microscope are used to characterize the surface morphologies of the system after instability.(2)Secondly,the influence of the surface micro-structures with large center to center distance on the instability morphologies is discussed.The systematic analysis of the experimental results is conducted to investigate the regulation effects of the center to center distance of micro-structures and the UVO treatment time on the instability morphologies is discussed in the condition of the center to center distance of micro-structures is greater than the intrinsic wavelength.Then the influence of elastic modulus and thickness of the film on the instability morphologies is discussed by finite element analysis.And also by the former results,the importance of normalized center to center distance of micro-structures to the instability morphologies is verified.Moreover,the quantitative relationship between the number of wrinkles and the normalized center to center distance of micro-structures is obtained.Furthermore,based on the principle of minimum energy,the quantitative relationship between the number of wrinkles and the normalized center to center distance of micro-structures is verified.(3)Afterwards,the influence of the surface micro-structures with small center to center distance on the instability morphologies is discussed.The influence of the center to center distance of micro-structures and the UVO treatment time on the surface instability morphologies is evaluated experimentally.And the influence of the elastic modulus and the thickness of the film on the surface instability morphologies is analyzed from the perspective of finite element analysis.Finally,the quantitative relationship between the normalized center to center distance of micro-structures and the number of micro-structures in a wrinkle period is obtained.What's more of the relationship between the size of the micro-structures and the instability morphologies is analyzed.(4)Finally,the influence of the arrangement direction of the surface micro-structures on the instability morphologies is discussed.The regulation effects of the angle between the arrangement direction of the micro-structures and the pre-strain direction,the center to center distance of micro-structures and the concavity of the micro-structures on the orientation of the wrinkles are analyzed by experimental methods.Then the method of finite element analysis is used to analyze the relationship between the angle between the arrangement direction of the micro-structures and the pre-strain direction and the orientation of wrinkles.In the end,the trend of the critical angle with respect to the normalized center to center distance of microstructures is obtained.