<p> Mesoporous silicate have widespread potential applications, such as drug delivery, supports for catalysis, selective adsorption and host to guest molecules. Most important in the area of scientific research and industrial applications is their demand due to its extremely high surface areas (> 800<i>m</i>²<i>g</i>^&minus;1) and larger pores with well defined structures. </p><p> Mesoporous silicate (MCM-41) samples were prepared by hydrothermal method under various chemo-physical conditions and various experimental methods such as small angle X-rays scattering (SAXS), Nitrogen adsorption-desorption analysis at 77 K, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were employed to investigate the changes in the structural morphology and subtle lattice parameter changes. With regards to the subtle changes in the structural characteristics of the synthesized mesoporous silicate, we seek to understand the electron density function changes as the synthesis parameter are varied from low molar concentration of ATAB/Si to higher concentration, the system becoming more acidity due to increase in the hydrolysis time of pH regulator as a result of increased production of ethanol and acetic acid and the changes due to extended reaction time. </p><p> This Ph.D. research tries to understand the influence of various parameters like surfactant-Si molar ratio, reaction time, and the hydrolysis of the pH regulator on the orderliness/disorderliness of the lattice order, lattice spacing and electron density function. The stages during synthesis are carefully selected to better understand where the greater influence on the overall structural morphology exist so as to be able to ne tune this parameter for any desired specification and application. </p><p> The SAXS measurement were conducted on a HECUS S3-Micro X-ray system at Rensselaer Polytechnic Institute, Troy, NY. while the data evaluation and visualization were carried in 3DView 4.2 and EasySWAXS software. The electron density functions were generated with a proprietary software called edens. </p><p> In this dissertation, the following observations have been revealed resulting from SAXS measurement. </p><p> 1. As one increases the hydrolysis duration of ethyl acetate, a gradual collapse of the lattice spacing of the mesoporous silcate MCM-41 is observed. We found from SAXS that there is a slight right shift of the spectra toward the higher q-values indicating that we are gradually losing orderliness in the lattice spacing and hexagonal structure of the mesoporous silica. Also, the intensity of the peak of second and third peaks are diminutive when compared to sample with shorter hydrolysis time. </p><p> 2. A comparison of the SAXS spectra for the different molar concentration sample reveals that the 0:5M samples shows a deteriorating structural characteristics as compared to the 0:25 and 0:75M samples respectively and a clear decrease in the (100) reflection planes. Also noticed is the slight rightward shift in the overall spectrum prole. This observation suggest that further analysis is needed so as to better understand the result. </p><p> 3. We establish that during MCM-41 synthesis, longer reaction time is needed to produce quality sample with well defined structurally characteristic for its intended application because according to spectrum for the sample with a longer reaction time (aging), a shift towards the lower q-values indicates that a sample with a larger lattice parameter and wall thickness but the intensities of its peak are diminishing when compared to the other of relatively shorter reaction time. </p><p> Other complementary techniques were used to corroborated the result obtained from SAXS. Nitrogen adsorption-desorption analysis at 77K was used to generate the isotherms while B.E.T method was used in conjunction with the isotherms to obtained the very important surface area information. SEM provide a visual structural morphology of the samples and FTIR gave the fingerprint detail of the bonds and vibration types between particle present.</p>

<p> Characterization of magnetic domain structure is essential to understand and manipulate the magnetic properties of materials. In this thesis, we have utilized Lorentz Transmission Electron Microscopy (LTEM) in combination with image simulations based on micromagnetic models, to investigate the magnetic domain structure of a unique nano-chessboard structure consisting of L1<i> 0</i> and L1₂ phases in a Co₄₀Pt₆₀ alloy. We have shown high-resolution LTEM images of nano-size magnetic features acquired through spherical aberration correction in Lorentz Fresnel mode. Phase reconstructions based on the transport of intensity equation has been carried out to fully understand the magnetic domain structure and to extract quantitative information, including direction of magnetic induction and magnetic domain wall width, from the Lorentz TEM images. The experimental Fresnel images of the nano-chessboard structure show zig-zag shaped magnetic domain walls at the inter-phase boundaries between L1<i>0</i> and L1₂ phases. A circular magnetization distribution with vortex and anti-vortex type arrangement is evident in the phase reconstructed magnetic induction maps as well as simulated maps. The magnetic contrast in experimental LTEM images has been properly interpreted with the help of magnetic induction maps simulated for various relative electron beam-sample orientations inside TEM. Apart from the nano-chessboard structure, this alloy shows other interesting microstructural features such as anti-phase boundaries, tweed structure, coarse L1<i>0</i> plates, and macro-twins all of which have been characterized using conventional bright field/dark field TEM imaging and compared with their respective Lorentz TEM images. The magnetic domain wall widths obtained for each microstructure has been compared and the influence of microstructure and the particle size on wall widths has been discussed.</p><p>

<p> Carbon nanotubes are a relatively new area of research which has gained significant attention in published literature. One reason for this interest is their use in multi-phase composites, specifically where they can enhance traditional polymer matrices. Many authors have attempted to adapt conventional micromechanical analyses reserved for microfibers to the nano scale. A review of these works is presented. In depth analysis is provided on one of these two phase (nanotube and matrix) models, the Anumandla-Gibson model, originally published in 2006. A discussion of its strengths and sensitivities is given, with numerical data to support the conclusions. It is extended to three-phase composites through the use of classical laminated plate theory. A literature survey is conducted to gather published two and three-phase experimental results for comparison. Two phase experimental results agree well with the present model, whereas three phase data was limited, but initial comparisons were promising.</p>

<p> In light of their escalating exposure to possible environmental toxicants, there are many biological systems that need to be evaluated in a resource and time efficient manner. Understanding how toxicants behave in relation to their physicochemical properties and within complex biological media is especially important toward developing a stronger scientific foundation of these systems so that adequate regulatory decisions may be made. While there are many emerging methods available for the detection and characterization of these chemicals, nanotechnology has presented itself as a promising alternative toward creating more efficient assays. In particular, metallic nanoparticles and thin films exhibit unique optical properties that allow for highly sensitive and multiplexed studies to be performed. These plasmonic materials often preclude the use of molecular tags and labels, enabling direct characterizations and enhancing the throughput of biomolecular studies. However, their lack of specificity toward certain targets and potential toxicity has thus far precluded their widespread use in toxicity testing.</p><p> The cell membrane, a natural signal transducer, represents one of the fundamental structures for biological recognition and communication. These interfaces principally function as a selective barrier to exogenous materials, including ions, signaling molecules, growth factors, and toxins; therefore, understanding interactions at membrane interfaces is a vital step in elucidating how biological responses are effected. Supported lipid bilayers, which may easily be tailored in composition and complexity, are ideal interfaces for coupling to plasmonic assays since they may be supported in close proximity to metallic nanoparticles and thin films, where measurements are most sensitive. This research will focus on the coupling of plasmonic materials and biomimetic interfaces to increase the sensitivity, efficiency, and throughput of conventional toxicity assays. The fabrication of new plasmonic materials for membrane-based assays is presented, as well as method developments in membrane array formation and opportunities for hyphenation with complementary analytical techniques. </p><p>

<p> Our need to reduce global energy use is well known and without question, not just from an economic standpoint but also to decrease human impact on climate change. Emerging advances in this area result from the ability to tailor-make materials and energy-saving devices using solution&ndash;phase chemistry and deposition techniques. Colloidally synthesized nanocrystals, with their tunable size, shape, and composition, and unusual optical and electronic properties, are leading candidates in these efforts. Because of recent advances in colloidal chemistries, the inventory of monodisperse nanocrystals has expanded to now include metals, semiconductors, magnetic materials, and dielectric materials. For a variety of applications, an active layer composed of a thin film of randomly close-packed nanocrystals is not ideal for optimized device performance; here, the ability to arrange these nano building units into mesoporous (2 nm &lt; d &lt; 50 nm) architectures is highly desirable. Given this, the goal of the work in this dissertation is to determine and understand the design rules that govern the interactions between ligand-stripped nanocrystals and polymeric materials, leading to their hierarchical assembly into colloidal nanocrystal frameworks. I also include the development of quantitative, and novel, characterization techniques, and the application of such frameworks in energy efficiency devices such as electrochromic windows.</p><p> Understanding the local environment of nanocrystal surfaces and their interaction with surrounding media is vital to their controlled assembly into higher-order structures. Though work has continued in this field for over a decade, researchers have yet to provide a simple and straightforward procedure to scale across nanoscale material systems and applications allowing for synthetic and structural tunability and quantitative characterization. In this dissertation, I have synthesized a new class of amphiphilic block copolymer architecture-directing agents based upon poly(dimethylacrylamide)-b-poly( styrene) (PDMA-b-PS), which are strategically designed to enhance the interaction between the hydrophilic PDMA block and ligand-stripped nanocrystals. As a result, stable assemblies are produced which, following solution deposition and removal of the block copolymer template, renders a mesoporous framework. Leveraging the use of this sacrificial block copolymer allows for the formation of highly tunable structures, where control over multiple length scales (e.g., pore size, film thickness) is achieved through the judicious selection of the two building blocks. I also combine X-ray scattering, electron imaging, and image analysis as novel quantitative analysis techniques for the physical characterization of the frameworks. </p><p> Last, I demonstrate the applicability of these porous frameworks as platforms for chemical transformation and energy efficiency devices. Examining the active layer in an electrochromic window, I show a direct comparison between, and improved performance for, devices built from both randomly close-packed nanocrystals and those arranged in mesoporous framework architectures. I show that the framework also serves as a scaffold for in-filling with a second active material, rendering a dual&ndash;mode electrochromic device. These results imply that there may exist a broad application space for these techniques in the development of ordered composite architectures.</p><p>

Microphase separated block copolymers (BCPs) are emerging as promising templates and scaffolds for the fabrication of nanostructured materials. To achieve the desired nanostructures, it is necessary to establish convenient approaches to control the morphology of BCPs. It remains challenging to induce morphological transitions of BCPs via external fields. Click chemistry, especially alkyne/azide click chemistry, has been widely used to synthesize novel functionalized materials. Here, we demonstrate that alkyne/azide click chemistry can be used as an efficient approach to chemically modify BCPs and therefore induce morphological transitions. Alkyne-functionalized diblock copolymers (di-BCPs) poly(ethylene oxide)- block-poly(n-butyl methacrylate-random-propargyl methacrylate) (PEO-b-P(nBMA-r-PgMA)) have been successfully synthesized. When the di-BCP is blended with an azide additive Rhodamine B azide and annealed at elevated temperatures, click reaction occurs between the two components. With the Rhodamine B structure attached to the polymer backbone, the di-BCP shows dramatic change in the interactions between the two blocks and the volume fraction of each block. As a result, morphological transitions, such as disorder-to-order transitions (DOTs) and order-to-order transitions (OOTs), are observed. The reaction kinetics and morphology evolution during the click chemistry induced DOTs have been investigated by in-situ and ex-situ characterizations, and fast kinetics properties are observed. Microphase separated morphologies after the DOTs or OOTs are dictated by the composition of neat di-BCPs and the mole ratio between the alkyne and azide groups. The DOTs of PEO-b-P(nBMA-r-PgMA) di-BCPs induced by alkyne/azide click chemistry have also been achieved in thin film geometries, with comparable kinetics to bulk samples. The orientation of the microdomains is dependent on the grafting density of Rhodamine B structure as well as film thickness. At higher grafting densities, a perpendicular orientation of the microdomains can be obtained. For di-BCPs with certain compositions, the microphase separated morphologies in thin films deviate from the corresponding bulk morphologies, which is probably due to the interfacial interactions and confined geometries arising from film thickness.

Magnetic mesoscopic and nano-sized structures have promising applications such as high-density data storage, magnetic field sensors, and microwave devices. Patterned magnetic structures are especially interesting because their constitutive material, sizes and geometry are easily adjustable in fabrication. This makes manipulation of electromagnetic properties possible and creates many novel features never discovered in conventional bulk materials. The artificial magnetic structures that can be engineered to meet specific application purposes are called magnetic metamaterials. This thesis aims to investigate magnetic materials nanostructured to produce high permeability and low loss performance at gigahertz (GHz) frequency region. Such property is highly desired for communication devices with miniaturized size, reduced energy consumption and enhanced signal detection sensitivity. Antennas, microwave field sensors are the examples of applications. We first analyze the single domain model for ac magnetization to get theoretical understanding and prediction. Then we evaluate all free energy terms for a magnetic dipole to know which energies (or fields) are contributing to the effective magnetic field in our real experiments. Secondly experiment work including fabrication, dc characterization and ac characterization of Permalloy and cobalt nanoscale magnetic structures, as well as FePt nanoparticles are covered. Different microwave techniques regarding sensitive magnetic permeability measurements are discussed in detail for comparison. In the last chapter, micromagnetic simulations are performed to obtain broadband ac magnetization response spectrum for a single Permalloy nanowire and two interacting Permalloy nanowires.

One of the current challenges in materials science is establishing a simple way to generate an ultradense arrays of addressable nanoscopic elements on macroscopic scales. The addressability of nanomaterials is essential for many applications, ranging from high-density magnetic storage to high-density, ultrahigh resolution displays to photovoltaics. Among the strategies available, "photocombing" has been proposed as a promising route to create long-range ordered nanostructures in self-assembled block copolymers (BCPs) over macroscopic distances through a photocontrollable ordering transition. In this process, bands of light act as a "comb" to sweep across BCP thin films unidirectionally, reversibly bringing the BCPs through an ordering transition, like the disorder-to-order transition (DOT) and the order-to-order transition (OOT). Thus, defects are "combed" out, forming arrays of highly ordered BCP microdomains on a macroscopic length scale. It is similar in principle to the classic zone refining method, which is used to produce large single crystals of metals and semiconductors. In this dissertation, I will focus on three systems to investigate photocombing. System I is the supramolecular assembly of poly(2-vinylpyridine)-block-poly(n-butyl methacrylate) and polystyrene-block-poly(2-vinylpyridine) di-BCPs with azobenzene-containing 2-(4-hydroxyphenylazo)benzoic acid chromophores. In these systems, an ordering transition from lamellae to hexagonally packed cylinders was observed after one hour of UV radiation at 150 °C. System II is the deuterated polystyrene-block-poly(n-butyl methacrylate) BCPs with photoisomerizable azobenzene functionalities. They exhibit an entropy-driven lower DOT, the characteristic of "compressibility", similar to their parent BCPs. System III is anthracene-functionalized tri-BCPs containing deuterated polystyrene (d8-PS) and poly(methyl methacrylate) (PMMA) blocks, as well as a small middle block of poly(2-hydroxyethyl methacrylates) that is randomly functionalized by anthracene. Under UV exposure, the junction between d8-PS and PMMA blocks in the tri-BCPs is joined together through anthracene photodimers, thereby resulting in a significantly increase in the total molecular weight of the tri-BCPs. As a consequence, the tri-BCPs undergo an ordering transition from a disordered state to an ordered state, when it is phase-mixed but close to the boundary of the ordering transition.

<p> Polymer blending facilitates the combination of the attractive attributes of two or more polymers while compensating for the unfavorable ones. Most polymers are thermodynamically incompatible with one another, and their blending yields a two-phase microstructure. This morphology generally determines the mechanical and rheological properties of the blend system which then determine its applications. Morphology development typically involves deformation of the dispersed phase followed by drop breakup. However, drop coalescence competes with this process, and ultimately a balance must be reached between these two competing processes. Extensional flow fields are known to promote drop breakup and are especially important for blends with high viscosity ratios, that is for blends where the viscosity of the dispersed phase is at least about 3.8 times greater than that of the matrix phase. Coalescence may be attenuated by compatibilizers that modify the interface between the polymer phases. Nanoparticles with tuned surface chemistry may also be used as compatibilizers. A combination of extensional flow and nanoparticle stabilization should, therefore, result in a fine, stable morphology. </p><p> To begin the investigation toward the effects of extensional flow blending with and without the incorporation of nanoparticles, preliminary results were obtained using two different polymer blend systems: polycarbonate (PC)/styrene acrylonitrile (SAN) and polystyrene (PS)/linear low-density polyethylene (LLDPE). However, the majority of the presented results involve blends of high-density polyethylene (HDPE) dispersed in PS. With this blend system, with the material grades selected, the viscosity ratio exceeded 3.8 over the entire domain of deformation rates anticipated in the processing used. Coarse blends of various compositions were formulated using shear flow in an internal mixer or in a twin-screw extruder. These blends were subjected to extensional flow in converging dies of different geometries and where more than one stretching episode was possible; the temperature, total strain, and flow rate were varied, among other factors, in a systematic manner. Experiments were repeated in the presence of various grades of fumed nanosilica of different sizes and surface treatments, which imparted different surface tension and relative surface polarity (hydrophilic versus hydrophobic) for the nanoparticles. The mixing sequence was varied including premixing the nanosilica into the thermodynamically non-preferred polymer phase. </p><p> Scanning electron microscopy (SEM) was used to determine the size and size distribution of the dispersed polymer phase. The material was typically sectioned in the flow direction, but sectioning in the direction perpendicular to flow and etching, or selectively dissolving, one phase or the other was also investigated. The primary effect of extensional flow blending was to reduce the volume-average diameter of the dispersed polymer phase, especially with increasing strains and flow rates, or strain rates, which is directly dependent on both. Finding suitable conditions for the nanoparticles to selectively localize at the HDPE/PS interface was challenging, but relatively small amounts of nanoparticles dispersed in the PS matrix decreased the volume-average diameter of HDPE drops. When the nanosilica was preloaded into the HDPE dispersed phase, very coarse initial blends were produced which then exhibited dramatic decreases in phase size with extensional flow. These and other results are properly organized and presented.</p>

Can organic semiconducting nanoparticles be used as building blocks for fabricating electronic devices? The first half of this dissertation focuses on addressing this question and the associated research challenges for attaining morphological control pertaining to organic photovoltaic devices by nanoparticle assembly. Conjugated polymer nanoparticles were synthesized using miniemulsion technique and their optical, charge transfer and charge transport properties were studied. Some degree of control in polymer chain packing within the nanoparticle was also demonstrated. The optical, charge transfer and charge transport properties of these nanoparticles were found to be similar to that of parent conjugated polymer irrespective of the surface charge. From the initial photovoltaic measurements, it is shown that these nanoparticles are potential candidates for fabricating future photovoltaic devices. The second half of this dissertation is focused on developing a novel and viable strategy for sensing aqueous based nitroaromatic compounds. Nitroaromatic compounds are commonly used as explosives and possess serious health hazards. Thiophene-based conjugated polymer nanoparticles were synthesized and were shown to effectively detect aqueous based nitroaromatic explosives.