Date of Award
Doctor of Philosophy (PhD)
Chemical and Biomolecular Engineering
Hierarchical, multifunctional materials hold important keys to numerous advanced technologies, including electronics, optics, and medicine. This thesis encompasses generation of hierarchical structures with novel morphologies and functions through self-assembly directed by lithographically fabricated templates. Here, two soft materials, amphiphilic random copolymers of photopolymerized acryloyl chloride (ranPAC) and smectic-A liquid crystal (SmA-LC) molecule, 4'(5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heptadecaflu-orododecyloxy)-biphenyl-4-carboxylic acid ethyl ester, are synthesized as model systems to investigate the governing principles at the topographic surface/interface.
The ranPAC can self-organize into nanomicelles with high regularity and stability, typically not possible in random copolymer systems. The morphology can be controlled by the photopolymerization conditions and solvent; the crosslinked shell makes the micelles robust against drying and storage. Using SU-8 micropillar arrays with spatially controlled surface chemistry as templates, we construct hierarchical microporous structures with tunable pore size and symmetry (e.g. square array), and uncover a new evaporative assembly method. By functionalizing the ranPAC nanovesicles with cationic poly(ethyleneimines), we encapsulate the anticancer drug, doxorubicin hydrochloride, and mRNA at a high payload, which are delivered to HEK 293T cells in vitro at a low cytotoxicity level.
SmA-LC are characterized by arrangement of molecules into thin layers with the long molecular axis parallel to the layer normal, forming a close-packed hexagonal array of topological defects known as focal conic domains (FCDs) in a thin film. Using a series of SU-8 micropillar arrays with different size, shape, height, and symmetry as topological templates, we investigate the epitaxial and hierarchical assemblies of FCDs; whether the system favors confinement or "pillar edge-pinning" depends on balance of the elastic energy of LCs and the surface energy imposed by the template. The conservation of toric FCD (TFCD) textures over large LC thickness manifests a remarkably unique outcome of the epitaxial growth of TFCDs. On shorter pillars, however, the system favors the "pinning" of FCD centers near pillar edges while avoiding the opposing effect of confinement, leading to the break of the underlying symmetry of the pillar lattice, exhibiting tunable eccentricity, and a nontrivial yet organized array of defects balancing the elastic energy of LCs and the surface energy imposed by the template.
Honglawan, Apiradee, "Hierarchical Assemblies of Soft Matters From Polymers and Liquid Crystals on Structured Surfaces" (2013). Publicly Accessible Penn Dissertations. 642.