The Patterning Mechanism And Fabrication Research Of Microstructure On Curved Surfaces Based On The Electrostatic-induced Lithography

Electrostatic-Induced Lithography(EIL) is a novel and practical microstructure formation method which makes use of the electrohydrodynamic instability of the film to realize the fabrication of periodic or hierarchic micro/nanostructures, so knowing how to control their morphology are very important for theoretical research and technological application. This dissertation mainly studies morphological instability and ordered structures formation in films driven by spatially modulated electric fields.The thin film instability can be triggered by a variety of intermolecular interactions such as the long-range attractive van der Waals force or by the externally applied triggers such as a temperature gradient or an electric field. Within the framework of the finite element, this dissertation is focused on the instability and pattern formation in confined thin dielectric liquid films are subjected to electrostatic forces by using the theoretical approaches and nonlinear simulations. In addition, experimental studies of the replication of microstructures on planar or curved surfaces by the electrohydrodynamic instability process have been reported in this paper. Numerous theoretical and experimental works have been carried out to better understanding this phenomenon in such deformation and instability.First of all, we study the fabrication limit of electrostatic-induced lithography, where the film is driven by the spatially modulated electric fields generated through a periodically patterned electrode. Based on a commercial software package-COMSOL Multiphysics, the transient analysis model of electrically induced microstructure is developed to look at the evolution of structure due to the electrostatic force and surface tension at the interface of the liquid polymer. The interface between the immiscible polymer film and air phases is tracked by using the level set method.The characteristics of morphology which tend to emerge on the surface are examined. Based on the transition of morphology from non-uniform shape to uniform shape during the transfer process of the surface morphology of the electrode on to the film surface, this paper reports how to define the period limit LP, i.e. the fabrication limit of the periodic nanostructures using finite element analysis. The numerical simulation method based on finite element analysis method is employed to investigate the influence on Lp of the filling factor, aspect ratio, the initial mean film thickness, the electrode spacing and applied voltage between the two electrodes. By the proper control of EHDIP process parameters, it is demonstrated that hierarchical structures and hollow structures can be realized in one step. The influences of operational parameters such as the width and height of master electrode, electrodes spacing, the period of master electrode and initial film thickness has been studied in detail to realize the formation of hierarchical structures.An electrohydrodynamic technique is proposed to create hierarchic and hollow micro/nanostructures.And then, we demonstrate a simple yet cost-effective process to form the hierarchical structures by capillary force lithography(CFL). In our process, the simple principle that the time needed for the fluid to fill up the cavity in the mould is different if the contact angle of the mould or the width of the cavity in the mould is different. Based on this principle, two methods are developed to achieve hierarchical structures by CFL. One is to selectively modify the PDMS mould by UV or Oxygen plasma treatment to change its wettability in different areas. The other is to make patterns with variable dimensions in the mould. By using the PDMS mould with wettability selectively modified or with patterns with different lateral dimensions, hierarchical structures of convex/concave microlens array or stripes with convex/concave surfaces have been manufactured successfully.In addition, we present the generic method for analyzing the surface stability of a thin film resting on curved substrate subjected to electric field. We report the numerical study of the one-step faithful replication of micro/nano-scale structures on a cylinder surface using the electrohydrodynamic instability patterning(EHDIP) process. By employing a rigorous numerical analysis method, conditions are revealed under which the faithful replication of a pattern can be achieved from a master electrode. It is found that the radius of curvature of the fiber plays an important role in determining the final morphology of the pattern when the destabilizing electric field is dominant in both the flat and patterned template cases. In addition, it is shown by theoretical analysis and experimental works that high aspect ratio micro/nanostructures can be obtained on curved surfaces by using a master with a much lower aspect ratio. The results demonstrated in this work aims to provide guidelines for the faithful fabrication of micro/nano-structures on curved surfaces by the EHDIP process.Finally, based on long-wave approximation theory, we have presented a theoretical study of electric field induced instabilities and pattern formation in thin liquid films. The problem about the faithful transfer of patterns with a high aspect ratio onto a polymer film via electrohydrodynamic instabilities for a given patterned grating mask is analyzed theoretically, numerically and experimentally. In particular, the influence of the material properties(initial film thickness、applied voltage、dielectric constant 、 surface tension 、 the viscosity) of the polymer on pattern replication is discussed in detail.A series of 3D simulations are performed to study the electrostatic field induced thin film instability process,we observe either perfect grating pattern with no flaws or stripe structure where the grating emerges partially ruptured along the same line and merged with a neighboring grating.This evolution phenomenon is confirmed by our experimental observation.