Pattern Formation And Modulation In Soft Elastomers And Films

Understanding the mechanics of morphology formation in soft elastomers and films in daily life and practical application, and knowing how to control their morphology are very important for theoretical research and technological applications. This dissertation mainly studies pattern formation and modulation in soft elastomers and elastic films driven by electric field and eigenstrain. Soft elastomers may deform and buckle into ordered surface patterns, in the presence of various external forces; thin elastic film may also buckle into regular morphology driven by external forces. The structures with ordered morphology have been widely applied in industrial and practical applications. We expect to better understanding the phenomenon in such deformation and instability, and try to control these phenomena to make and design structures with desired morphology for practical applications.This dissertation mainly studies deformation and morphological instability in soft elastomers and elastic films induce by electric field and eigenstrain. In the part of electric-field induced instability, the soft elastomers are considered to be pre-stretched, so finite deformation theory is applied to analyze the deformation behaviors, and a linear stability analysis is carried out. In the part of eigenstrain induced instability in an elastic disk, nonlinear Von-Karman plate theory is used for performing deformation and stability analysis, and triangular network model is applied to simulate the post-buckling morphology numerically.Fist of all, we study the deformation and buckling of a uniaxially pre-stretched soft elastomers driven by spatially modulated electric fields. The film is adhered onto a rigid conductive substrate, and the electric field is generated through a periodically patterned electrode over the film. Deformation analysis and a linear stability analysis show that at low applied voltages the deformation of the film follows the pattern of the electrode, allowing for the transfer of the surface morphology of the electrode onto the film surface in opposite sign. However, when the voltage reaches a threshold, the film buckles to form stripped pattern parallel to the tensile direction. This newly resulting deformation is superposed on that before onset of buckling, leading to complicated and ordered topography of the film. By adjusting the related parameters such as the initial thickness of the film, the magnitude of pre-stretch and the pattern of the electrode, a great variety of ordered surface morphologies of the film can be formed in a controllable way.And then, we study electric-field driven surface instability in a conductive film capping a liquid layer resting on a pre-stretched soft elastic layer glued onto a rigid substrate. A linear stability analysis shows that, the capping film is always unstable, even for very small applied voltage. The undulation wavelength of the film is initially quite large, but undergoes a sharp transition when the voltage is increased to a critical value. In this case, well aligned winkles with considerably smaller wavelength appear in the fashion parallel to the tensile direction of the soft elastic layer. The magnitude of the wavelength is tunable by controlling the voltage and pre-stretch, thus providing a mechanism to control the wrinkling pattern of the capping film.Finally, we study morphological instability in a disk with inhomogeneous eigenstrain. A phase diagram is given out by a linear stability analysis, and dependence of morphology on the size of the disk and the eigenstrain is shown. The results demonstrate that the disk with expanding and shrinking eigenstrain buckle into dome morphology and the edge-wrinkled morphology, respectively. We perform nonlinear numerical simulation using triangular network model, and investigate the dependence of post-buckling morphology on eigenstrain, which corroborate the linear stability analysis.Understanding the phenomenon and mechanics in these systems can provide avenues for the morphology control of soft elastomers and films for specific applications.