Reconfigurable periodic porous membranes and nanoparticle assemblies

The thesis here will cover two parts of my research. The focus of the first part of the thesis will be using responsive hydrogel materials to manipulate the pattern transformation at microscale (Chapter 3-5), and meanwhile using the finite element method (FEM) to guide new designs of the periodic porous structures that can undergo controlled pattern transformation processes (Chapter 6). In beginning, I design fabrication methods of micro-structures from responsive hydrogel materials via micro-/nano- imprinting. The responsiveness of the hydrogels is introduced by incorporating responsive monomers into the hydrogel precursors. Here, the responsiveness of the hydrogel leads to the tunable swelling ratio of the hydrogel under external stimuli, e.g. pH, temperature, and variation of humidity, so that the imprinted nano-/micro- structures can be dynamically controlled. Later, upon using FEM simulation, we design and experimentally test the deformation and mechanical properties of the periodic porous membranes based on different collapsing modes of kagome lattices. The experiments are performed at macroscopic scale taking advantage of powerful 3D printing prototyping. As the deformation phenomenon is scale independent, the observed phenomenon is applicable to predict the deformation of the micro-structures. In the second part of the thesis, we investigate two colloidal assembly systems. First (Chapter 7-8), we utilize the new form of silica nanoparticles with chain-like morphology to generate sharp nanostructures on the coating surface that minimize the contact between liquid and solid phase, and thus improve dramatically the water repellency on the coating surfaces. The stability test of the superhydrophobicity against hydrodynamic/hydrostatic pressure, low surface tension liquid, and vapor phase condensation, are also investigated for a complete interpretation of the wetting behavior. Secondly (Chapter 9), I design colloidal suspensions matching the inter-particle interactions with those used in theoretical study of colloidal assembly within the confined the space. The beauty of the system is that the colloidal suspension can be cross-linked and lock the assembled structures, so that the assembled structure can be observed under electron microscope and compare to theory and simulation. So far, a good consistence has been observed, indicating a validated design of the systems