Self-assembly of nanoscale materials to form intriguing structures has garnered considerable attention due to their potential applications in optical, electronic, magnetic and information storage devices. Among all the efforts to pattern functional polymers and nano materials, flow-enabled self-assembly (FESA) stands out as a lithography-free evaporation-induced self-assembly technique to construct large-scale 0D, 1D and 2D periodic structures in a simple, robust and cost effective manner. In the first part of the thesis, flow-enabled self-assembly of polystyrene is chosen as the model system, and systematic experiments have been conducted to reveal intrinsic and external variables that lead to 3 possible FESA patterns (i.e., coffee ring induced spoke pattern, fingering instability induced strip pattern, and their intermediate network-like structures). In the second part of the thesis, applications of FESA in patterning electrochromic polymers and fabricating PS-PMMA strips as etching mask of Si microchannels are demonstrated. Both applications convincingly illustrate the advantages of cost effective, large yield and flexible control of flow-enabled self-assembly.

No description available.

The objective of my MSc thesis is to study the self-assembly process of macrocyclic complexes, as well as the properties that affect the obtained supramolecular architectures. The possibility of substrate recognition within the cavity of these complexes is also of interest. Preparation of three new ligands based on the triazole-pyridine chelating units connected through variable spacer groups, as well as the complexes formed with octahedral metal ions, are described herein. The first ligand contained a naphthalene spacer region, which was longer than the previously examined xylene spacer. This extension increases the distance between metal ions in the complex, as well as the size of the cavity. More work is required to obtain the unsaturated double-stranded complex, which could potentially bind substrate molecules within its cavity. The triple-stranded saturated complexes with [Fe(H2O)6](BF4)2 and [Ni(H2O)6](BF4)2 both gave insight into the process of self-assembly. The next two ligands were designed to probe the effect that increasing the length of an aliphatic spacer had on complex self-assembly. Both ethyl and propyl spacer units had been previously studied, so butyl and pentyl spacer groups were the natural next step to analyze. The length of the alkyl spacer was found to be very important in the nature of the obtained complex. As the length of the alkyl chain, and the corresponding flexibility increased, so too did the complexity of the resulting supramolecular architectures. / Thesis (Master, Chemistry) -- Queen's University, 2013-09-03 12:21:39.581

acase@tulane.edu / 1 / hong zhang

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Darrin J. Pochan, Dept. of Materials Science & Engineering. Includes bibliographical references.

This dissertation focuses on investigating the morphologies, optical and photoluminescence properties of porphyrin nanostructures prepared by the self-assembly method. The study is divided into three main parts. In the first part, a large variety of porphyrin nanostructures, including nanoplates, nanofibers, nanoparticles and nanowires, were obtained through direct acidification of tetra(p-carboxyphenyl)porphyrin (TCPP) in aqueous solution. Protonation of the carboxylate groups of TCPP resulted in the formation of nanoplates through the J-aggregation of the porphyrin. Further protonating the core nitrogens of TCPP formed the porphyrin diacids which organized into well-defined structures through their interactions with counter-anions in the solution. The structures of the resulting assemblies were found to be counterion dependent. In the second part of this work, we explored the optical memory effect of the porphyrin thin film. We found that the morphology and the emission of the porpyrin thin film on Si can be changed by varying the pH of its surrounding solution. The changing in morphology and light emission of the thin film resulted from the protonation or deprotonation of TCPP'S core nitrogens. By selectively deprotonating the TCPP dications in a confined region utilizing the water meniscus between an AFM tip and the surface, Fluorescence patterns can be generated on the thin film. The fluorescence patterns can be easily erased by re-protonating the porphyrin. In the third part of this study, porphynoid nanoparticles were deposited on a surface energy gradient, and then characterized by AFM in order to investigate how the surface energy influences thier morphologies. The surface energy gradient was prepared by selectively oxidizing a self-assembly monolayer of octadecyltrichlorosilane (OTS) by UV-ozone. The nanoparticles disassemble into smaller nanoparticles with narrower size distribution on the surface with higher surface energy. Lastly, we engaged in characterizing the morphologies of polymer nanocomposites prepared by layer-by-layer assembly for wettability control. The surface roughness of the nanocopmosite in air and in salt solutions was also measured to study the correlation between the wettability of the polymer surface and its surface roughness.

The objective of this research is to investigate synthetic and polypeptide block copolymers, the structures they form, their response to various stimuli in solution and their capabilities for use in biomimicry. The self-assembled structures of both polymers will be used as a basis for the templating of hydrogels materials, both in the interior and on the surface of the vesicles. The resulting particles will be designed to show the structural and mechanical properties of living cells. The synthetic block copolymers are a polyethylene glycol and polybutadiene (PEO-b-PBd) copolymer and the polypeptide block copolymers are Lysine and Glysine (K-b-G) copolymers. Investigation of the structures synthetic block copolymers will focus on whether the polymer can form vesicles, how small of a vesicle structure can be made, and the formation of internal polymer networks. Subsequent investigations will look at the needed steps for biomimicry, using the synthetic block copolymers as a starting point and transitioning to a polypeptide block copolymer. The Lysine-Glysine copolymers are a new system of materials that form fluid vesicle structures. Therefore, we must characterize its assembly behavior and investigate how it responds to solution conditions, before we investigate how to make a cellular mimic from it. The size and mechanical behavior of the K-G vesicles will be measured to compare and contrast with the synthetic systems. The goals for creating a biomimic include a hollow sphere structure with a fluid bilayer, a vesicle that has controllable mechanical properties, and a vesicle with controllable surface chemistry. Overall, these experiments were a success; we showed that we can effectively control the size of vesicles created, the material properties of the vesicles, as well as the surface chemistry of the vesicles. Investigations into a novel polypeptide block copolymer were conducted and the block copolymer showed the ability to create vesicles that are responsive to changing salt and pH concentrations.

The possibility of using residual stresses favorably as a means of self-assembling MEMS during material deposition is experimentally investigated. Two atomic force microscope cantilevers are placed in contact at their free ends. Material is isothermally electroplated onto one (the deposition) cantilever, but no material is deposited onto the other (spring) cantilever. The deposited layer contains residual stresses that deform the deposition cantilever. The deposition cantilever in turn deforms the spring cantilever, thereby doing work in the spring cantilever and proving that the two structures can selfassemble during deposition processing. An insoluble nickel electroplating process and an all-sulfate nickel solution are used for the deposition. The deflection of the selfassembled cantilevers is measured in-situ as a function of the deposited thin film thickness through the optical method of atomic force microscopy. The experimental results are compared to an analytical model which consists of Euler-Bernoulli beam theory that is modified to account for moving boundaries as the material is deposited. The model accounts for the through-thickness variation of the intrinsic strain during the electroplating. Closed-form solutions are not possible, but numerical solutions are plotted for the cantilever deflection and work on the spring cantilever as functions of the deposition thickness.

The use of spontaneous self-assembly as a lithography free means to construct well-ordered, often intriguing structures has received much attention for its ease of producing complex, centimeter-scale structures with small feature sizes. These self-organized structures promise new opportunities for developing miniaturized optical, electronic, optoelectronic, and magnetic devices. One extremely simple route to intriguing structures is the evaporative self-assembly of nonvolatile solutes from a sessile droplet on a solid substrate. However, flow instabilities during the evaporation process often result in non-equilibrium and irregular dissipative structures (e.g., randomly organized convection patterns, stochastically distributed multi-rings, etc.). Therefore, in order to fully control the evaporative self-assembly of solutes, two strategies, namely, controlled evaporative self-assembly (CESA) and flow-enabled evaporative-induced self-assembly (FESA) were developed to create ordered structures of various nanomaterials. First, hierarchical assemblies of amphiphilic diblock copolymer (i.e., polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP)) micelles were crafted by FESA. The periodic threads comprising a monolayer or a bilayer of PS-b-P4VP micelles were precisely positioned and patterned over large areas. Second, highly aligned parallel DNA nanowires in the forms of nanostructured spokes over a macroscopic area were created via evaporative self-assembly (CESA) by subjecting DNA aqueous solution to evaporate in a curve-on-flat geometry composed of a spherical on a flat substrate. Third, large-scale aligned metallic nanowires templated by highly oriented DNA were produced by flow-enabled self-assembly (FESA). A simple yet robust swelling-induced transfer printing (SIT-Printing) technique was developed to transfer ultralong DNA nanowires onto the desirable substrate. Subsequently, the resulting DNA nanowires were exploited as templates to form metallic nanowires by exposing DNA nanowires preloaded with metal salts under oxygen plasma. Moreover, DNA nanowires were also employed as scaffold for aligning metal nanoparticles and nanorods. Fourth, colloidal microchannels (i.e., cracks) on a large scale were yielded by fully controlling the drying process of colloidal suspensions via flow-enabled self-assembly (FESA). The influence of chemically patterned substrate (i.e., hydrophobic stripes on a hydrophilic substrate) on the formation of colloidal microchannels was explored. In addition, such colloidal microchannels with tunable center-to-center distance between the adjacent cracks, λ_(c-c) was exploited as template for aligning inorganic nanoparticles. Importantly, theoretical study of the formation mechanism of parallel stripes of solutes by FESA was conducted. The relationship between the characteristic spacing of adjacent stripes λ_(c-c) and other experimental parameters such as the stripe width, the stop time and the moving speed of lower substrate were scrutinized. Such theoretical modeling would provide guidance for the precise design and crafting of ordered structures composed of nanomaterials by FESA in the future study. Interestingly, during the preparation of Au nanorods, the formation of ultrathin gold nanowires were unexpectedly observed. Based on conventional synthetic route to Au nanorods using CTAB as soft-templates, we discovered that the addition of a small amount of hydrophobic solvent (e.g., toluene or chloroform) to the Au growth solution entailed the formation of ultrathin Au nanowire, rather than Au nanorods. The growth mechanism of such intriguing water-soluble ultrathin Au nanowires, differed from those formed by using oleylamine (i.e., non-water-soluble Au nanowires), was explored. In general, the ability to craft ordered structures comprising nanomaterials by FESA and CESA provides new opportunities for organizing nanomaterials for use in electronics, optics, optoelectronics, sensors, nanotechnology and biotechnology.

Self-assembling materials have gained attention in the field of nanotechnology due to their potential to be used as building blocks for fabricating complex nanoscale devices. The biological world is abundant with examples of functional self-assembling biomolecules. Proteins are one such example, found in a variety of geometries and shapes. This research is focussed on the use of ring-shaped self-assembling proteins, called Lsm proteins, as componentary for applications in bionanotechnology. Lsm proteins were used because of their spontaneous association into stable rings, tolerance to mutations, and affinity to RNA. This thesis primarily focussed on the thermophilic Lsmα (from Methanobacterium. thermoautotrophicum) that assembles as heptameric rings. The oligomeric state of the heptameric protein, and hence the diameter of its central cavity, was manipulated by judiciously altering appropriate residues at the subunit interface. Lsmα presented a complex set of interactions at the interface. Out of the mutations introduced, R65P yielded a protein for which SEC and SAXS data were consistent with a hexameric state. Moreover, key residues, L70 and I71, were identified that contribute to the stability of the toroid structure. Covalent linking of rings provided nanotubular structures. To achieve this, the surface of the Lsmα ring scaffold was modified with Cys residues. This approach led to the formation of novel Lsmα nanotubes approximately 20 nm in length. Importantly, the assembly could be controlled by changing the redox conditions. As an alternative method to manipulate the supramolecular assembly, His6-tags were attached at the termini of the Lsmα sequence. The higher-order organisation of the constructs was influenced by the position of the His6-tag. The N-terminally attached His6-tag version of Lsmα showed a metal-dependent assembly into cage-like structures, approximately 9 nm across. This organisation was highly stable, reproducible, and reversible in nature. The results presented in this thesis aid the understanding of generating complex nanostructures via in vitro self-assembly. The Lsmα rings were assembled into higher-order architectures at the quaternary level by employing protein engineering strategies. Future work is necessary to functionalise these supramolecular structures; however, this study confirms the potential role of Lsmα proteins as a molecular building block in bionanotechnology.