Converting water adsorption and capillary condensation in useable forces with simple porous inorganic thin films

This work reports an innovative humidity driven actuation concept based on Bangham effect using simple nanoporous sol-gel silica thin films as humidity responsive materials. Bilayer shaped actuators, consisting on a humidity-sensitive active nanostructured silica film deposited on a polymeric substrate (Kapton) were demonstrated as an original mean to convert water molecule adsorption and capillary condensation in useable mechanical work. Reversible silica surface energy modifications by water adsorption and the energy produced by the rigid silica film contraction, induced by water capillary condensation in mesopores, were finely controlled and used as the energy sources. The influence of the film nanostructure (microporosity, mesoporosity) and thickness, and of the polymeric support thickness, on the actuation force, on the movement speed, and on the amplitude of displacement are clearly evidenced and discussed. We show that the global mechanical response of such silica-based actuators can be easily adjusted to fabricate a humidity variation triggered tailor-made actuation systems. This first insight in hard ceramic stimulus responsive materials may open the door toward new generation of surface chemistry driven actuation systems.Comment: 17 pages, 7 figure

Layered Zeolite Materials And Methods Related Thereto

A novel oxide material (MIN-I) comprising YO2; and X2O3, wherein Y is a tetravalent element and X is a trivalent element, wherein X/Y=O or Y/X=30 to 100 is provided. Surprisingly, MIN-I can be reversibly deswollen. MIN-I can further be combined with a polymer to produce a nanocomposite, depolymerized to produce predominantly fully exfoliated layers (MIN-2), and pillared to produce a pillared oxide material (MIN-3), analogous to MCM-36. The materials are useful in a wide range of applications, such as catalysts, thin films, membranes, and coatings.Regents Of The University Of MinnesotaGeorgia Institute Of Technolog

Formation and characterization of inorganic membranes from zeolite-silica microcomposites

Small crystals of zeolites (500-1000 nm) with two- and three-dimensional channel systems (faujasite and ZSM-5 structures) were embedded in amorphous thin films derived from TEOS hydrolyzed in alcoholic solution. Scanning electron microscopy studies show that the zeolites can be quite evenly dispersed in the membrane, resulting in single layers of zeolite crystals protruding out of the amorphous matrix. In situ FT-IR studies with a series of probe molecules revealed that in most membranes the zeolites were 100% accessible from the gas phase. The membranes excluded molecules which are larger than the pore openings of the zeolite embedded in the composite

Electro-spinning/netting: A strategy for the fabrication of three-dimensional polymer nano-fiber/nets.

Since 2006, a rapid development has been achieved in a subject area, so called electro-spinning/netting (ESN), which comprises the conventional electrospinning process and a unique electro-netting process. Electro-netting overcomes the bottleneck problem of electrospinning technique and provides a versatile method for generating spider-web-like nano-nets with ultrafine fiber diameter less than 20 nm. Nano-nets, supported by the conventional electrospun nanofibers in the nano-fiber/nets (NFN) membranes, exhibit numerious attractive characteristics such as extremely small diameter, high porosity, and Steiner tree network geometry, which make NFN membranes optimal candidates for many significant applications. The progress made during the last few years in the field of ESN is highlighted in this review, with particular emphasis on results obtained in the author's research units. After a brief description of the development of the electrospinning and ESN techniques, several fundamental properties of NFN nanomaterials are addressed. Subsequently, the used polymers and the state-of-the-art strategies for the controllable fabrication of NFN membranes are highlighted in terms of the ESN process. Additionally, we highlight some potential applications associated with the remarkable features of NFN nanostructure. Our discussion is concluded with some personal perspectives on the future development in which this wonderful technique could be pursued

SYNTHESIS OF TITANIA THIN FILMS WITH CONTROLLED MESOPORE ORIENTATION: NANOSTRUCTURE FOR ENERGY CONVERSION AND STORAGE

This dissertation addresses the synthesis mechanism of mesoporous titania thin films with 2D Hexagonal Close Packed (HCP) cylindrical nanopores by an evaporation-induced self-assembly (EISA) method with Pluronic surfactants P123 and F127 as structure directing agents, and their applications in photovoltaics and lithium ion batteries. To provide orthogonal alignment of the pores, surface modification of substrates with crosslinked surfactant has been used to provide a chemically neutral surface. GISAXS studies show not only that aging at 4°C facilitates ordered mesostructure development, but also that aging at this temperature helps to provide orthogonal orientation of the cylindrical micelles which assemble into an ordered mesophase directly by a disorder-order transition. These films provide pores with 8-9 nm diameter, which is precisely the structure expected to provide short carrier diffusion length and high hole conductivity required for efficient bulk heterojunction solar cells. In addition, anatase titania is a n-type semiconductor with a band gap of +3.2 eV. Therefore, titania readily absorbs UV light with a wavelength below 387 nm. Because of this, these titania films can be used as window layers with a p-type semiconductor incorporated into the pores and at the top surface of the device to synthesize a photovoltaic cell. The pores provide opportunities to increase the surface area for contact between the two semiconductors, to align a p-type semiconductor at the junction, and to induce quantum confinement effects. These titania films with hexagonal phase are infiltrated with a hole conducting polymer, poly(3-hexylthiophene) (P3HT), in order to create a p-n junctions for organic-inorganic hybrid solar cells, by spin coating followed by thermal annealing. This assembly is hypothesized to give better photovoltaic performance compared to disordered or bicontinuous cubic nanopore arrangements; confinement in cylindrical nanopores is expected to provide isolated, regioregular “wires” of conjugated polymers with tunable optoelectronic properties, such as improved hole conductivity over that in bicontinuous cubic structure. The kinetics of infiltration into the pores show that maximum infiltration occurs within less than one hour in these films, and give materials with improved photovoltaic performance relative to planar TiO2/P3HT assemblies. These oriented mesoporous titania films are also used to develop an inorganic solar cell by depositing CdTe at the top using the Close Spaced Sublimation (CSS) technique. A power conversion efficiency of 5.53% is measured for heterostructures built using mesoporous titania films, which is significantly enhanced relative to planar TiO2/CdTe devices and prior reports in the literature. These mesoporous titania films have a great potential in inorganic solar cell development and can potentially replace CdS window layers which are conventionally used in inorganic CdS-CdTe solar cells. The last part of the dissertation addresses layer-by-layer synthesis to increase the thickness of mesoporous titania films with vertically oriented 2D-HCP nanopores, and their use in lithium ion batteries as negative electrodes because of advantages such as good cycling stability, small volume expansion (~3%) during intercalation/extraction and high discharge voltage plateau. The high surface area and small wall thickness of these titania films provide excellent lithium ion insertion and reduced Li-ion diffusion length, resulting in stable capacities as high as 200-250 mAh/g over 200 cycles

Immobilized photosensitizers for antimicrobial applications

Photodynamic antimicrobial chemotherapy (PACT) is a very promising alternative to conventional antibiotics for the efficient inactivation of pathogenic microorganisms; this is due to the fact that it is virtually impossible for resistant strains to develop due to the mode of action employed. PACT employs a photosensitizer, which preferentially associates with the microorganism, and is then activated with non-thermal visible light of appropriate wavelength(s) to generate high localized concentrations of reactive oxygen species (ROS), inactivating the microorganism. The concept of using photosensitizers immobilized on a surface for this purpose is intended to address a range of economic, ecological and public health issues. Photosensitising molecules that have been immobilized on solid support for PACT applications are described herein. Different supports have been analyzed as well as the target microorganism and the effectiveness of particular combinations of support and photosensitiser

DNA translocation through an array of kinked nanopores

Synthetic solid-state nanopores are being intensively investigated as single-molecule sensors for detection and characterization of DNA, RNA, and proteins. This field has been inspired by the exquisite selectivity and flux demonstrated by natural biological channels and the dream of emulating these behaviors in more robust synthetic materials that are more readily integrated into practical devices. To date, the guided etching of polymer films, focused ion beam sculpting, and electron-beam lithography and tuning of silicon nitride membranes have emerged as three promising approaches to define synthetic solid-state pores with sub-nanometer resolution. These procedures have in common the formation of nominally cylindrical or conical pores aligned normal to the membrane surface. Here we report the formation of kinked\u27 silica nanopores, using evaporation induced self-assembly, and their further tuning and chemical derivatization using atomic layer deposition. Compared to \u27straight-through\u27 proteinaceous nanopores of comparable dimensions, kinked nanopores exhibit a factor of up to 5x reduction in translocation velocity, which has been identified as one of the critical issues in DNA sequencing. Additionally we demonstrate an efficient two-step approach to create a nanopore array exhibiting nearly perfect selectivity for ssDNA over dsDNA. We show that a coarse-grained drift-diffusion theory with a sawtooth like potential can reasonably describe the velocity and translocation time of DNA through the pore. By control of pore size, length, and shape, we capture the major functional behaviors of protein pores in our solid-state nanopore system.\u2

SILICA NANOPOROUS CONFINEMENT EFFECTS ON IONIC LIQUID PROPERTIES FOR BETTER DESIGN OF SMALL MOLECULE SEPARATION, ELECTROCHEMICAL DEVICES AND DRUG DELIVERY

Silica nanoconfinement provides a high level of control of ionic liquids (ILs) in localizing catalysts, creating distinct environment for tuning reactivity and controlling the partition of solvents, reactants and products. Silica thin films with two different pore sizes (2.5 nm and 8 nm) were synthesized to study the effect of nanopore confinement on ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), and 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]). Silica thin films with accessible 8 nm pore diameters were synthesized using evaporation-induced self-assembly (EISA) with Pluronic P123 as templating surfactant on a chemically neutral modified substrate. The silica films with similar orthogonal aligned mesostructured but smaller pore size (2.5 nm) were produced through cetyltrimethylammonium bromide (CTAB) templated EISA. The perpendicularly oriented channels were achieved by doping the silica matrix with small amount of titania, which destabilized the nanoporous structure during calcination so that the isolated micelles connect with each other when the films go through thermal contraction during calcination. In situ grazing-incidence small angle X-ray scattering (GISAXS) was performed and it revealed this structure transformation. To broaden the application of this CTAB templated film, a sugar surfactant was added to bind with titania precursor and disperse titania on the pore surface instead of through out the entire matrix. The absorption of water by ILs is among the most concerning properties when they are utilized in catalysis systems for example, the dehydration of glucose to 5-(hydroxymethyl)furfural (HMF) using [BMIM][Cl] as solvent. Thus, [BMIM][Cl] confined in the 8-nm-pore-diameter silica thin films was investigated and compared to that of bulk ionic liquid. Transmission Fourier transform infrared spectra (FTIR) were collected in situ at room temperature while the relative humidity (RH) of the environment was changed. Pore confinement effects were interpreted from the C-H stretching bands shift and OH stretching band growth. Deconvolution of OH stretching bands shows that weakly coordinated water is promoted in confined [BMIM][Cl], which may affect mechanisms of solubilization and catalysis in confined ILs. To understand the effect of pore confinement on transport, the two silica thin films were modified with physically absorbed [BMIM][PF6], chemically tethered 3-methyl-1-[3-(trimethoxysilyl) propyl]-1-imidazolium group ([TMS-MIM]+) and with the presence of both. Electrochemical impedance spectroscopy (EIS) was performed to investigate the permeability of hydrophilic and hydrophobic redox groups through the thin films with different treatments and different pore sizes. Both films with chemically tethered IL possess much higher resistance to hydrophilic molecules than hydrophobic molecules with 14-fold lower permeability through 8-nm tethered films and 30-fold lower for 2.5-nm tethered films. This work successfully produced highly selective silica thin films for selective separation of hydrophilic and hydrophobic species. Crystallization of ILs is another attractive property of ILs to study but lack of direct characterization results. This dissertation work introduced in situ probing using grazing-incidence wide-angle X-ray scattering (GIWAXS) to characterize the crystallization behavior of [BMIM][PF6] and [BMIM][Cl] under confinement of the two silica thin films with and without ILs tethering as described above. While certain crystallization behavior can be predicted by the classic Gibbs-Thomson theory, confined ILs in most cases studied do not follow the predictions of Gibbs-Thomson theory. One extreme case is when [BMIM][PF6] were confined in [TMS-MIM] tethered 2.5-nm porous silica thin films, the composite did not melt at room temperature while [BMIM][PF6] in bulk melts around -11 °C. This work successfully demonstrates how different confining condition changes the crystallization behavior of the two ILs through the novel in situ GIWAXS characterization, which benefits further studies for drug delivery and battery research

Developing Metrology for Nondestructive Characterization of Buried Polymer Interfaces in Situ.

Polymers are widely used in modern microelectronics as adhesives, organic substrates, chip passivation layers, insulating dielectric materials, and photoresists in microlithography. The interfacial structures of polymer materials determine the interfacial properties of the materials. Weak adhesion or delamination at interfaces involving polymer materials can lead to failure of microelectronic devices. Therefore, it is important to investigate the molecular structures of such interfaces. However, it is difficult to study molecular structures of buried interfaces due to a lack of appropriate analytical techniques. This dissertation presents the development of the nonlinear optical technique sum frequency generation (SFG) vibrational spectroscopy into a metrology tool for nondestructive characterization of molecular structures at buried polymer interfaces in microelectronic packages in situ and the elucidation of relationships between buried molecular structures and interfacial properties such as adhesion strength. Buried polymer/epoxy, copper/epoxy, and silicon/organosilicate dielectric interfaces were investigated. SFG was used to directly probe molecular structures at buried adhesive interface in situ. Plasma treatment of polymer surfaces was found to alter the molecular structure at corresponding buried interfaces prepared using the plasma treated surfaces. Hygrothermal aging treatment was found to influence hydrophobic polymer/polymer interfaces less than hydrophilic interfaces, showing that hydrophobic materials can better resist delamination during qualification testing in high humidity environments. Copper/epoxy interfaces were found to delaminate near, but not exactly at, the metal/polymer interface and silane adhesion promoters were found to modify the interfacial region near the copper surface which suggests that the interfacial layer near copper needs to be modified to improve adhesion. Quantitative data analysis methodology was developed to simultaneously characterize the surface and buried interface of silicon-supported thin low-k polymer films nondestructively before and after microelectronic processing steps which provided a molecular level understanding of the effects of the processing. The general nature of the methodology enables it to be directly utilized to elucidate structure-property relationships at buried interfaces by correlating interfacial structures to interfacial properties. Structure-property relationships elucidated using this methodology can be used to guide the rational engineering of buried polymer interfaces with optimized properties in many practical applications such as polymer composites, optical fibers, paints, and anticorrosion coatings.PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133179/1/myersjn_1.pd

Functionalized silica nanostructures for biosensing applications

This work covers both two dimensional (2D) and three dimensional (3D) silica-based nanostructures for use in biomedical sensing applications. The first section of this study discusses the formation of 2D nanostructured surface plasmon resonance (SPR)-based biosensor substrates. The surface of these biosensors was nanostructured by adding sacrificial star polymers or block copolymers to a silicate precursor solution. Subsequent vitrification resulted in two distinct morphological patterns: random and ordered porosity. Amino groups on the surface of the biosensors enabled the installation of analyte receptors and antifouling agents such as oligo (ethylene oxide). The second section discusses the development of 3D core-shell silica nanoparticles (SNPs). For this work, star polymers were generated to provide hydrophobic interiors capable of sequestering large hydrophobic porphyrinoid dyes and hydrophilic exteriors capable of templating the growth of silica shells. The diameter of the SNPs (25-100 nm) varied depending on reaction time, template size, and reagent concentration. The shell thickness was also controlled in order to either release or retain the hydrophobic dyes. The SNPs were surface-functionalized with biocompatible stealth materials such as poly (ethylene oxide) to generate non-toxic, water-soluble nanoparticles for the in vivo delivery of various hydrophobic imaging and therapeutic materials