Fabrication Of Ordered Microstructures By Dewetting On Patterned Surfaces

The widely application of functional materials has become more and more important for modern society. The realization of the functionalities of many materials relies on the development of miniaturization and patterning capability. Along with the traditional"top-down"photolithography technique showed its bottleneck, another kind of strategy, which is called"bottom-up"strategy steps into many scientists'sights. In former studies, researchers found that combing both"top-down"and"bottom-up"strategies showed enormous potential. On the other hand, dewetting phenomenon influences the quality of membrane preparation and thermal treatment in industry fields such as coating, lubrication, corrosion resistant and semiconductor. Thanks to the continuous development of surface patterning techniques, it now can also be applied for microstructure fabrication. Under this background, combing"top-down"and"bottom-up"strategy, applying dewetting effects to fabricate ordered microstructures that are hard or impossible manufactured by other techniques, has its practical contents in theory and clearly applicable prospects. In this thesis, we utilize"top-down"techniques such as microcontact printing to fabricate patterned surfaces, then we applied these surfaces to control the liquid dewetting process on it. Many ordered structures could be formed by this strategy. We believe this cheap, convenient, and widely applicable method will offer us a new way for micro-machining and functionality realization.In chapter 2, we exploited microcontact printing technique to fabricate patterned chemical heterogeneous surfaces, and combined these patterns varied in wettabilities with surface-induced vapor deposition to form templates with ordered water droplets arrays and wettability patterns together. After a dewetting process which was initiated by evaporation of the solvents during dip-coating process of applied materials solution, we fabricate binary patterns of organic electroluminescent small molecular (mdppy)BF in one step. Optical microscopy, SEM and AFM were used to analyze the ordered binary patterns. We suggested that two dewetting processes happened during the pattern formation, the second dewetting process, together with a selective wetting process, directly led to the formation of binary patterns. Considering the influences of solution concentration and underlying templates, we make a conclusion that this process is a surface-directed and concentration-controlled dewetting process. The dimension of the as-prepared patterns could be simply adjusted by experimental conditions.In chapter 3, we firstly fabricated ordered two-dimensional rings array, dots array and patterned porous film by integrating surface-induced vapor deposition and dewetting phenomenon. Then, we changed the solution viscosity, the size of the water droplets and recorded the dewetting process in-situ by video captured equipment. The results showed the formation of these three ordered morphologies intrinsically resulted from a surface-directed and solution viscosity controlled dewetting process. We put forward the formation mechanisms of these patterns respectively and subsequently extended the morphology diversities by delicate design of the underlying chemical patterns. This method could also be applied to other materials which could be dissolved or dispersed in organic solvents, for instance, polymeric materials, nanoparticles coated with polymers, functional organic molecules, inorganic salts, colloidal particles etc. The as-prepared morphologies could also be used as templates to fabricate more complex structures in the following treatment.In chapter 4, we applied thermal annealing process at a temperature higher than the Tg of the polymer we used to initiate a morphological transformation from circular pores into polygonal meshes by using patterned porous polymer films. 2D polymer latticeworks were finally fabricated after this process. AFM results of the samples before and after thermal annealing revealed that this morphological transition was a thermal-initiated, Gibbs free energy-controlled and self-organized anisotropic dewetting process. The speed of the film dewetting was faster at the directions pointing to the centers of arrangement cells resulted in the formation of latticeworks morphology. Following this strategy, we successfully fabricated multiform lattice shapes by simply changing the underlying chemical patterns. PS was used only as an model chemical here, the requirements for the applying materials are they could be solved in chloroform and kept stable in the thermal annealing process. We also established an empirical equation based on conservation of matter to guide the formation of final morphology. Therefore, the cross-sectional area of the meshes in the latticeworks could be controlled via the ordered arrays of the hydrophilic circles predesigned as well as the experimental parameters such as the concentration of solution. Moreover, after an etching process of the underlying Au layer, these"through"polymeric structures we fabricated could be peeled off and transferred to other substrates for further applications as single layer or multi-layers. It could also be used as templates in replicate molding and directly copy its morphology to the surface of another material.