Nanoparticles can be used as building blocks of materials. Properties of such materials depend on the organization of the constituent particles. Thus, control over particle organization enables control over material properties. However, robust and scalable methods for arranging nanoparticles are still lacking. This dissertation explores the use of an externally applied magnetic field to organize magnetic nanoparticles into microstructures of desired shape. It extends to proofs of concept towards applications in material design and tissue engineering. First, external control over dipolar self-assembly of magnetic nanoparticles (MNPs) in a liquid dispersion is investigated experimentally. Scaling laws are derived to explain experimental observations, correlating process control variables to microstructure morphology. Implications of morphology on magnetic properties of such structures are then explored computationally. Specifically, a method is proposed wherein superparamangetic nanoparticles, having no residual magnetization, can be organized into anisotropic structures with remanence. Another application explores the use of magnetic forces in organizing human cells into three-dimensional (3D) structures of desired shape and size. When magnetized cells are held in place for several days, they are seen to form inter-cellular contacts and organize themselves into tight clusters. This provides a method for 3D tissue culture without the use of artificial scaffolding materials. Finally, a method to pattern heterogeneities in the stiffness of an elastomer is developed. This makes use of selective inhibition of the catalyst of crosslinking reactions by magnetite nanoparticles. The last chapter discusses future possibilities. / Ph. D.

With the development of controlled and predictable nanoparticle fabrication, assembling multiple nano-objects into larger functional nanostructure has attracted increasing attention. As the most basic structure, assembly of one-dimensional (1D) structures is a good model for investigating the assembly mechanism of a nanostructure's formation from individual particles. In this dissertation, the dynamics and the growth mechanism of anisotropic 1D nanostructures is investigated. In our first study, we demonstrate a simple method for assembling superparamagnetic nanoparticles (SPIONs) into structure-controlled 1D chains in a rotating magnetic field. The length of the SPION chains can be well described by an exponential distribution, as is also seen in SPION chains in a static field. In addition, the maximum chain length is limited by the field's rotational speed, as is seen in micro-sized beads forming chains in a rotating field. However, due to a combination of thermal fluctuations and hydrodynamic forces, the chain length in our case is shorter than either limit. In addition to chain length, the disorder of chains was also studied. Because of the friction between particles, kinetic potential traps prevent relaxation to the global free energy minimum. The traps are too deep to be overcome through thermal fluctuations, and assemblies captured by the kinetic traps therefore form disordered chains. We demonstrate that this disorder gradually heals over a timescale of tens of minutes and that the healing process can be promoted by increasing particle concentration or solution ionic strength, suggesting that the chain growth process provides the energy required to overcome the kinetic trapping. Next, we introduce a novel optical technique we term Quantitative Optical Anisotropy Imaging (QOAI). A fast and precise single-particle characterizing technique for anisotropic nanostructures, QOAI allows real-time tracking of particle orientation as well as the spectroscopic characterization of polarizabilities of nanoparticles on a microsecond timescale. The abilities of QOAI are demonstrated by the detection and the characterization of single gold nanorods. We also show that single particle diffusions and the process of particle binding to a wall can be tracked through QOAI. The rotational diffusivities of gold nanorods near the wall were determined by autocorrelation analysis, which shows that the diffusivity in the polar direction is slightly smaller than in the azimuthal direction. This result demonstrates that a detailed correlation analysis with QOAI may provide the opportunity to analyze both the translational and rotational motion of particles simultaneously, enabling true 3-dimensional orientation tracking. Finally, optical methods including QOAI are applied to the investigation of magnetic assembly, demonstrating that optical anisotropy is generated during particle binding, which can be used as a probe of the magnetic assembly process. QOAI is employed to track the dynamics of magnetic clusters in real time, attempting to capture insights on the self-assembly of the magnetic nanoparticles. By turning the external magnetic field on and off, the processes of combining superparamagnetic colloidal nanoparticle clusters into chain assemblies are monitored along with the chain growth. This fast and orientation-sensitive single-particle measurement opens the door to detailed studies of self-assembly away from equilibrium. / Doctor of Philosophy / Nanotechnology is the study and application of phenomena at the nanoscale, which is between 1 and 100 nm. Due to quantum effects, nanomaterials exhibit many interesting properties that cannot be found in bulk materials and are highly influenced by the shape of the nanostructures. One of the most promising strategies for forming complex nanostructures is to use smaller nanoparticles as building blocks. Therefore, significant efforts have been spent on the studies of the fabrication and modeling of the assembly of nanostructures. As a good starting point for analyzing the mechanism of self-assembly, we focus on the most basic structure, one-dimensional (1D) nanowires and chains. First, we demonstrate a simple method to fabricate one-dimensional magnetic chains from spherical magnetic nanoparticles in a rotating magnetic field. The growth mechanism of the nanochains is investigated, indicating the theory developed for chains formed with larger beads is not applicable at the nanoscale, and additional factors, such as the effect of temperature, need to be considered. Second, we introduce a fast, sensitive optical technique for characterizing anisotropic nanostructures. Because of their unique optical properties, gold nanorods are used to demonstrate the capabilities of the optical system. Not only static properties (orientation, aspect ratio), but also dynamics properties (rotational motion), of single gold nanorods are characterized quantitatively. Finally, this optical technique is extended to preliminary work on characterizing magnetic chain assembly. The processes of magnetic cluster binding and dissociation in a magnetic field are monitored and analyzed.

This thesis identifies a facile and versatile technique for creating multi-scale porous titania with tunable meso-scale morphology. Three templating approaches were simultaneously utilized in achieving this; namely, soft-templating by template-free self-assembly of an aligned macroporous structure, freeze-casting for the preservation of particle dispersion found in suspension, and hard-templating by the use of cellulose nanocrystals (CNCs) as sacrificial material. A systematic study was conducted wherein three synthesis parameters (water content, alcohol solvent content, and drying method) were varied in the hydrolysis of titanium tetra-isopropoxide (TTIP) by the sol-gel method to determine their contribution to the formation of multi-scale porous titania exhibiting aligned macrochannels and mesoporosity. The optimal synthesis settings for producing multi-scale porous titania were identified as H2O/TTIP molar ratio of 30, without any isopropanol (acting as solvent), and freeze-drying after freezing at -40°C. Subsequently, CNCs were added in various quantities (0-50vol%) to the hydrolysis of TTIP using these optimized settings to achieve more direct and precise control of the final titania meso-structure. Morphological studies revealed that the final titania bodies maintained the formation of macrochannels 1-3 μm in diameter as a result of hydrolysis in excess water in the absence of an organic solvent and exhibited successful templating mutually affected by CNC addition and freeze-casting. Freeze-drying preserved particle dispersion in the colloid suspension, hindering agglomeration otherwise found after oven-drying and enhanced the CNCs' role of disrupting titania aggregation and increasing interconnectivity. Thus, meso-structured multi-scale porous titania was prepared by a combined templating strategy using template-free self-assembly, freeze-casting, and CNC hard-templating. / MS / Titanium dioxide (TiO₂) has been shown to exhibit desirable properties including physical and chemical stability and biocompatibility making it a material of great interest in a variety of fields including pigments and biomedicine. Furthermore, the material’s photocatalytic activity (i.e. ability to absorb light energy to generate usable charge) has led to its implementation in solar cells, in the production of hydrogen as an eco-friendly fuel, and in decontaminating water from organic pollutants. While TiO₂ has shown great promise in these applications, there remains a need to identify a simple strategy to synthesize TiO₂ with a tunable multi-scale porous structure with pores of different sizes and shapes to improve its performance. To this end, a facile and versatile procedure was used to prepare multi-scale porous TiO₂ with tunable morphology. In investigating the effect of water content, alcohol content and drying method on the final morphology, a multi-scale structure was achieved by synthesizing TiO₂ in the absence of an alcohol solvent and within a new moderate range of water content that had not been previously explored. Lacking an effective and easy strategy to further manipulate the multi-scale morphology, this self-assembly technique was modified by incorporating cellulose nanocrystals (CNCs) into the synthesis procedures to further tune the structure on the nanometric scale by altering the final porosity and surface area. The final TiO₂ samples exhibited multi-scale porous structures that could be manipulated by combining the self-assembly and CNC-templating techniques in an adaptable strategy to tailor the TiO₂ morphology for its various uses in photocatalysis and biomedicine.

Stent is one of the coronary angioplasty techniques that expands the narrowed coronary arteries due to the accumulation of fat, cholesterol and other substances in the lumen of the arteries. The major complication of stent is restenosis. Current development of drug-eluting stents shows successfully reduce the occurrence of restenosis. Other than using drugs, electrostatic self assembled (ESAd) thin films may be the potential candidates to prevent restenosis. ESA is a process to fabricate thin films bases on the electrostatic attraction between two oppositely charges. We used this technique to fabricate four PVP films and four PEI films. All films were examined by XPS and AFM. XPS data showed our coatings were successfully fabricated on substrates. AFM images revealed PVP coating was uniform, but PEI coatings had different morphologies due to diffusion and pH during the process. Three preliminary hemocompatibility testes were performed to evaluate the hemocompatibility of the coatings. Platelet adhesion study showed the thin films inhibited platelet adhesion. All thin films were able to inhibit coagulation and were less cytotoxic. The studies suggested the ESA films were potentially hemocompatible. / Master of Science

Surface modification of colloidal nanoparticles is essential for broadening the scope of nanotechnology. In this dissertation, we discuss novel approaches to functionalize the surface of nanoparticles to tailor their properties for applications including radical polymerization inhibitors, supported heterogeneous catalysts, and building blocks for plasmonic devices. First, we investigate the interaction of hydrogen-terminated silicon nanoparticles (H-SiNPs) with Karstedt's catalyst and report a room‑temperature synthesis of Pt-coated SiNPs with highly tunable Pt loading. Analysis of the Pt on-Si ensemble reveals surface-bound Pt(II) on SiNPs which can undergo ligand exchange. Upon calcination, Pt-loaded SiNPs catalyze the hydrogenation of phenyl acetylene, and the SiNP scaffold enables efficient recovery and reuse of the catalyst. Conditions that favor the reductive elimination of the catalyst and efficient hydrosilylation of olefins are also discussed. Next, we report H-SiNPs as inhibitors for anerobic thermal autopolymerization of methacrylates. Prior to use, these solid-state inhibitors can be easily removed from the methacrylic monomers by low-speed centrifugation, offering great advantage to the traditionally used phenols and quinones. Analysis of SiNPs isolated after heating in methacrylates reveals the grafting of ester groups. As such, thermal hydrosilylation is presented as a powerful yet facile route to attach ester and allyl ester groups onto the surface of SiNPs. Finally, we report a method to rapidly and uniformly assemble gold nanoparticles (AuNPs) and their clusters on cm‑scale unmodified substrates. Cetyltrimethylammonium (CTAC) capped AuNPs were conjugated to a sparse coating of poly(ethylene glycol) and extracted into dichloromethane. The clustered patterns were deposited on hydroxyl terminated surfaces from stable dispersions using centrifugal force. The degree of clustering on substrates was tuned by varying a single parameter, the concentration of CTAC in the deposition dispersion. This approach bridges the gap between methods for depositing isolated AuNPs (typically using electrostatic interactions) and AuNP clusters (using covalent or electrostatic binders) and enables large-scale uniform deposition of isolated AuNPs, as well as clusters with tunable size. The non‑covalent assembly onto the substrate provided a means for depositing AuNPs into nanowells in topographically patterned substrates: after uniform deposition onto these substrates, the AuNPs on the surface were selectively removed using mechanical rubbing. This facile approach enabled large-scale selective deposition of AuNPs into patterned substrates that are attractive as SERS substrates and refractive index sensors.

No / The relationship between molecular self-assembly processes and nucleation during crystallization from solution is an important issue, both in terms of fundamental physical chemistry and for the control and application of crystallization processes in crystal engineering and materials chemistry. This contribution examines the extent to which the occurrence of crystal polymorphism can be used as an indicator of the nature of molecular aggregation processes in supersaturated solutions. For the specific case of 2,6-dihydroxybenzoic acid a combination of solubility, spectroscopic, crystallization, and molecular modeling techniques are used to demonstrate that there is a direct link between the solvent-induced self-assembly of this molecule and the relative occurrence of its two polymorphic forms from toluene and chloroform solutions.

Yes / 2D materials such as graphene, LAPONITE® clays or molybdenum disulfide nanosheets are of extremely high interest to the materials community as a result of their high surface area and controllable surface properties. While several methods to access 2D inorganic materials are known, the investigation of 2D organic nanomaterials is less well developed on account of the lack of ready synthetic accessibility. Crystallization-driven self-assembly (CDSA) has become a powerful method to access a wide range of complex but precisely-defined nanostructures. The preparation of 2D structures, however, particularly those aimed towards biomedical applications, is limited, with few offering biocompatible and biodegradable characteristics as well as control over self-assembly in two dimensions. Herein, in contrast to conventional self-assembly rules, we show that the solubility of polylactide (PLLA)-based amphiphiles in alcohols results in unprecedented shape selectivity based on unimer solubility. We use log Poct analysis to drive solvent selection for the formation of large uniform 2D diamond-shaped platelets, up to several microns in size, using long, soluble coronal blocks. By contrast, less soluble PLLA-containing block copolymers yield cylindrical micelles and mixed morphologies. The methods developed in this work provide a simple and consistently reproducible protocol for the preparation of well-defined 2D organic nanomaterials, whose size and morphology are expected to facilitate potential applications in drug delivery, tissue engineering and in nanocomposites. / University of Warwick, Materials GRP, EPSRC, The Royal Society, ERC

Yes / We report on the use of non-equillibrium biocatalytic self-assembly and gelation to guide the reductive synthesis of gold nanoparticles. We show that biocatalytic rates simultaneously dictate supramolecular order and presentation of reductive phenols which in turn results in size control of nanoparticles that are formed. / BBSRC funding (BB/K007513/1); European Research Council under the European Union’s Seventh Framework Programme, ERC (Starting Grant EMERgE) grant agreement no. 258775.

Yes / The synthesis of nucleobase-containing polymers was successfully performed by RAFT dispersion polymerization in both chloroform and 1,4-dioxane and self-assembly was induced by the polymerizations. A combination of scattering and microscopy techniques were used to characterize the morphologies. It is found that the morphologies of self-assembled nucleobase-containing polymers are solvent dependent. By varying the DP of the core-forming block, only spherical micelles with internal structures were obtained in chloroform when using only adenine-containing methacrylate or a mixture of adenine-containing methacrylate and thymine-containing methacrylate as monomers. However, higher order structures and morphology transitions were observed in 1,4-dioxane. A sphere-rod-lamella-twisted bilayer transition was observed in this study. Moreover, the kinetics of the dispersion polymerizations were studied in both solvents, suggesting a different formation mechanism in these systems. / University of Warwick, Swiss National Science Foundation, EPSRC, Birmingham Science City, Advanatfe West Midlands (AWM), European Regional Development Fund (ERDF), Science City Research Alliance, Higher Education Funding Council for England (HEFCE)

Yes / The possibility of using differential pre‐heating prior to supramolecular gelation to control the balance between hydrogen‐bonding and aromatic stacking interactions in supramolecular gels and obtain consequent systematic regulation of structure and properties is demonstrated. Using a model aromatic peptide amphiphile, Fmoc‐tyrosyl‐leucine (Fmoc‐YL) and a combination of fluorescence, infrared, circular dichroism and NMR spectroscopy, it is shown that the balance of these interactions can be adjusted by temporary exposure to elevated temperatures in the range 313–365 K, followed by supramolecular locking in the gel state by cooling to room temperature. Distinct regimes can be identified regarding the balance between H‐bonding and aromatic stacking interactions, with a transition point at 333 K. Consequently, gels can be obtained with customizable properties, including supramolecular chirality and gel stiffness. The differential supramolecular structures also result in changes in proteolytic stability, highlighting the possibility of obtaining a range of supramolecular architectures from a single molecular structure by simply controlling the pre‐assembly temperature. / FP7 Ideas: European Research Council. Grant Number: 258775