Thesis (Ph. D.)--State University of New York at Buffalo, 2007. / Title from PDF title page (viewed Nov. 20, 2007). Available through UMI ProQuest Digital Dissertations. Thesis adviser: Higbie, Carolyn. Includes bibliographical references.

SiO2 solutions were prepared from tetraethylortho-silicate (TEOS) by using the sol-gel process to fabricate dielectric materials of the insulator. We weighed different weight of TEOS in the solution and looked for the suitable conditions which easily fabricate the thin film. Then, we tried to add organic dispersants ( Octyl Phenol Ethoxylate ) in the SiO2 solution for the purpose of making molecules dispersed in the solution uniformly. After being a membrane, it could improve the roughness to make it more smooth. We used AFM to measure the root-mean square (RMS). The purpose of measurement was less than 1nm. Then we used these materials to make metal-insulator-metal (MIM) structures. And the measurement showed the leakage current was 10 times less than that without adding it in the solution. After that, we applied the thin film to the insulator of the thin film transistor (TFT). Pentacene of the semiconductor layer was thermally deposited and the thickness was about 50nm. Because the interface between the insulator and the semiconductor could change the arrangement of Pentacene, so we used O2 plasma to improve the interface. The process could make the molecules arrange regularly and influence the carrier mobility, and that can let us get the characteristic of the TFT.

Grafting polymeric chains on the surface of nanoparticles is an effective way to enhance particle-matrix interaction and their homogeneous dispersion within the matrix, leading to improved physical and mechanical properties. However, current methods for grafting polymeric chains onto nanoparticles have not produced well-defined polymers with high grafting density. Here, we employed anionic polymerization high vacuum techniques to synthesize in-situ grafted silica nanoparticles with either polystyrene (PS), polystyrene-b-polyisoprene (PS-b-PI) or 3- miktoarm star polymers (3-µ stars polymer) ((PS)2PS, (PS)2PI, and (PS)2PI-b-PS) by hydrolysis/condensation of ω-tetraethyl orthosilicate (TEOS) of PS, PS-b-PI and 3-µ star polymers. The molecular characteristics of the precursors PS-TEOS, PS-b-PI-TEOS, and 3-µ star polymer-TEOS were determined by 1H NMR, SEC, and MALDI-ToF. The synthesis of PS (PS@SiO2 NPs), PS-b-PI (PS-b-PI@SiO2 NPs), and 3-µ star polymer ((PS)2PS)@SiO2, (PS)2PI)@SiO2, and (PS)2PI-b-PS@SiO2 NPs) nanoparticles was verified by FT-IR, 29Si solid-state NMR, TEM, TGA, and DLS. Blends of PS@SiO2 with commercially available PS and PS-b-PI@SiO2 and 3-µ star polymer@SiO2 with anionically synthesized thermoplastic elastomer (PS-b-PI-b-PS), were obtained either in melt by extrusion or in solution by evaporation. The role of polymer@SiO2 on the mechanical and morphological properties was examined by tensile testing and SEM. In the fifth chapter, a high grafting density of polymer on the surface of SiO2 NPs approach that may also be employed in industry was presented. TEOS will be present in every repeating unit in the second block rather than simply the end group as it was in the first three chapters. First, anionic polymerization of PS functionalized with bromide group to utilize as a macroinitioter. Then, the macroinitioter (PS-Br) will initiate the polymerization of VTES (vinyltriethoxysilyl), ATMS (alyltrimethoxysilyl), and SETMS (styrene ethyltrimethoxysilyl) via atom transfer radical polymerization (ATRP) to form PS-b-PVTES, PS-b-PATMS, and PS-b-SETMS. SEC, 1H NMR, FT-IR, 29Si solid-state NMR, TEM, and DLS were used to confirmed copolymer grafting on SiO2 NPs. Lastly, a tensile test was used to study the mechanical properties of the nanocomposite. The proposed method controls the molecular weight, chemical composition, particle size and grafting density of nanoparticles and effectively improves the mechanical characteristics of the two families of PS-based nanocomposites.

A series of PMMA/silica hybrid composites were prepared by a sol-gel process in different catalytic and drying. Their thermal properties were analysized by DSC and TGA, the micro-structures by SEM, and the chemical reactions by FTIR. The highest decomposed temperature of these hybrid composites were found for samples prepared at low pH due to the hydrogen bonding. DSC data indicated the samples cured at 25 and 140 oC existed a higher Tg due to unhydrolyzed TEOS. The heat-treated hybrid composites exhibited more compact structures. The size of SiO2 particles from SEM increases with increasing drying temperature and pH value. The hybrid composites prepared in acid condition showed more Si-O-Si bonding than Si-O-C bonding in FTIR. In addition, in FTIR spectra the shifts have been observed from a non-hydrogen-bonded C=O at 1733cm-1 to a hydrogen-bonded carbonyl at 1725cm-1.

Τα λεπτά υμένια οξειδίων του πυριτίου (SiOx) χρησιμοποιούνται σήμερα ευρέως στην μικροηλεκτρονική και στη βιομηχανία συσκευασίας τροφίμων ενώ τα τελευταία χρόνια υπάρχει έντονο ερευνητικό ενδιαφέρον για την εφαρμογή τους στην προστασία μετάλλικών επιφανειών από την διάβρωση. Η χημική εναπόθεση SiOχ με τη χρήση πλάσματος χαμηλής πίεσης του τετρααιθοξυσιλανίου (TEOS) παρουσιάζει μερικά σημαντικά πλεονεκτήματα όπως εναπόθεση σε χαμηλές θερμοκρασίες, ομοιόμορφη κάλυψη της επιφανείας και μεγάλους ρυθμούς εναπόθεσης. Από την άλλη πλευρά, η ιδιαιτερότητα της εναπόθεσης μέσω πλάσματος ΤΕΟS, έγκειται στο γεγονός ότι η δομή, οι ιδιότητες και η χημική σύσταση των παραγόμενων υμενίων εξαρτώνται σημαντικά από τις παραμέτρους της διεργασίας, λόγω της πολυπλοκότητας του πλάσματος του ΤΕΟS. Είναι χαρακτηριστικό ότι ανάλογα με τις συνθήκες εναπόθεσης μπορούν να παραχθούν υλικά που η χημική τους σύσταση ποικίλλει μεταξύ σιλικόνης (SiOxCyHz) και σχεδόν στοιχειομετρικού SiO2. Στην παρούσα εργασία εξετάζεται η επίδραση διαφόρων παραμέτρων της διεργασίας (ολική πίεση, καταναλισκώμενη ισχύς, προεπεξεργασία επιφανείας) στο ρυθμό εναπόθεσης και στη σύσταση των παραγόμενων υμενίων που εναποτέθηκαν σε επιφάνειες διαφόρων κραμάτων του μαγνησίου. Για τη μέτρηση του ρυθμού εναπόθεσης χρησιμοποιήθηκε ανακλαστική συμβολομετρία με λέιζερ και για το προσδιορισμό της χημικής σύστασης φασματοσκοπία υπερύθρου (FTIR). Όσον αφορά τα διαγνωστικά τεστ του πλάσματος, χρησιμοποιήθηκε φασματογραφία μάζας για τον προσδιορισμό της κατανάλωσης της πρόδρομης ένωσης στην εκκένωση και φασματοσκοπία εκπομπής (OES) για την ανίχνευση και ταυτοποίηση των διεγερμένων ειδών στην αέρια φάση. Η αντοχή στη διάβρωση εκτιμήθηκε με τη βοήθεια της ηλεκτροχημικής φασματοσκοπίας εμπέδησης (ΕΙS) και ο χαρακτηρισμός της επιφανείας με μικροσκοπίες SEM και AFM. Οι συνθήκες που παρουσιάζονται τα βέλτιστα αποτελέσματα αντοχής στη διάβρωση, συζητούνται με βάση τη δομή και τη χημική σύσταση των υμενίων καθώς και τις μεταβολές των ιδιοτήτων του πλάσματος. / The silicon oxide (SiOx) thin films are used in microelectronics, in food packaging industry and in the recent years there is an increasing interest of using them as protective coatings for metallic surfaces. The plasma chemical vapor deposition of these films (PECVD) has several advantages, like the deposition at low temperatures, the uniform cover of the surface and the high deposition rates. On the other hand the thing that distinguishes this technique (PECVD) using TEOS as the precursor, is that the structure, the properties and the chemical composition of the deposited films are strongly depended on the variables of the process, because of the complexity of the chemistry of TEOS. The chemical composition of the deposited film can vary from almost total inorganic SiO2 to silicone like (SiOxCyHz). In the present essay, it is examined the effect of various parameters as the consumed power, the total pressure and the surface pre-treatment to the deposition rate and to the chemical composition and structure of the thin film. The films were deposited on aluminium and magnesium alloys. The technique used for measuring the deposition rate was Laser Reflective Interferometry and for the determination of the chemical composition the FTIR Spectroscopy. The evaluation of the corrosion resistance was made by using Electrochemical Impedance Specroscopy (ΕΙS), and the examination of the surfaces by SEM and AFM. The conditions that provided the best results for the corrosion protection of the metallic surfaces are presented according the structure and the chemical composition of the thin film and the changes of plasma properties.

Hybrid membranes represent a promising alternative to the limitations of organic and inorganic materials for high productivity and selectivity gas separation membranes. In this study, the previously developed concept of emulsion-polymerized mixed matrix (EPMM) membranes was further advanced by investigating the effects of surfactant and compatibilizer on inorganic loading in poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based EPMM membranes, in which inorganic part of the membranes originated from tetraethylorthosilicate (TEOS). The polymerization of TEOS, which consists of hydrolysis of TEOS and condensation of the hydrolyzed TEOS, was carried out as (i) one- and (ii) two-step processes. In the one-step process, the hydrolysis and condensation take place in the same environment of a weak acid provided by the aqueous solution of aluminum hydroxonitrate and sodium carbonate. In the two-step process, the hydrolysis takes place in the environment of a strong acid (solution of hydrochloric acid), whereas the condensation takes place in weak base environment obtained by adding excess of the ammonium hydroxide solution to the acidic solution of the hydrolyzed TEOS. For both one- and two-step processes, the emulsion polymerization of TEOS was carried out in two types of emulsions made of (i) pure trichloroethylene (TCE) solvent, and (ii) 10 w/v% solution of PPO in TCE, using different combinations of the compatibilizer (ethanol) and the surfactant (n-octanol). The experiments with pure TCE, which are referred to as a gravimetric powder method (GPM) allowed assessing the effect of different experimental parameters on the conversion of TEOS. The GPM tests also provided a guide for the synthesis of casting emulsions containing PPO, from which the EPMM membranes were prepared using a spin coating technique. The synthesized EPMM membranes were characterized using 29Si nuclear magnetic resonance (29Si NMR), differential scanning calorimetry (DSC), inductively coupled plasma mass spectrometry (ICP-MS), and gas permeation measurements carried out in a constant pressure (CP) system. The 29Si NMR analysis verified polymerization of TEOS in the emulsions made of pure TCE, and the PPO solution in TCE. The conversions of TEOS in the two-step process in the two types of emulsions were very close to each other. In the case of the one-step process, the conversions in the TCE emulsion were significantly greater than those in the emulsion of the PPO solution in TCE. Consequently, the conversions of TEOS in the EPMM membranes made in the two-step process were greater than those in the EPMM membranes made in the one-step process. The latter ranged between 10 - 20%, while the highest conversion in the two-step process was 74% in the presence of pure compatibilizer with no surfactant. Despite greater conversions and hence the greater inorganic loadings, the EPMM membranes prepared in the two-step process had glass transition temperatures (Tg) only slightly greater than the reference PPO membranes. In contrast, despite relatively low inorganic loadings, the EPMM membranes prepared in the one-step process had Tgs markedly greater than PPO, and showed the expected trend of an increase in Tg with the inorganic loading. These results indicate that in the case of the one-step process the polymerized TEOS was well integrated with the PPO chains and the interactions between the two phases lead to high Tgs. On the other hand, this was not the case for the EPMM membranes prepared in the two-step process, suggesting possible phase separation between the polymerized TEOS and the organic phase. The latter was confirmed by detecting no selectivity in the EPMM membranes prepared by the two-step process. In contrast, the EPMM membranes prepared in the one-step process in the presence of the compatibilizer and no surfactant showed 50% greater O2 permeability coefficient and a slightly greater O2/N2 permeability ratio compared to the reference PPO membranes.

Sol-gel process was utilized to produce organic/inorganic composite in this research, and the effect of mixing time¡]of polymer¡¦s and silica¡¦s precursor¡^ and coupling agent were investigated. To get low к materials was also the important objective. TMA, TGA, SEM, FT-IR, and RF impedance were used to investigate thermal properties, chemical bonding, morphology, and dielectric constant, respectively. The experiments showed that mixing time influence little to thermal stability but a lot to morphology and к. When mixing time was nearer to reaction time, the particle of silica was larger and the surface was flatter. The materials with coupling agent didn¡¦t show the same tendency as one without coupling agent. Regardless of coupling agent, it got larger к when mixing time was nearer to reaction time. Comparing with pure polymer, the modified materials got lower к. The lowest к got in this research was 2.36 which was lower than other materials.

Abstract This study focused on the structure of the particles developed in the PMMA matrix as a function of (a) coupling agent (£^-MPS) and (b) TEOS content. We investigated the difference of using TEOS monomer directly added to silica particles. The polymer precursors are catalyzed using acidic catalysts and undergo the sol-gel reaction to form a hybrid sol-gel material. This composite shows that highly optical transparency and microphase separation at the molecular level. The characteristics and properties of the polymer precursors and their hybrid materials were characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimogravimetic analysis (TGA). As for the influence of chemistry structure on morphology and thermal properties, experimental evidence form observations by scanning electron microscopy (SEM), mulitpoints analysis, and transmission electron microscopy (TEM). TEM was used to study the phase separation as well as the fractal structure of these particles present in the system. According to some result, it was found the compatibility between PMMA and silica mainly comes form incorporating the polymer with silica chemical bonding. This chemical bonding not only restrains silyl ester groups form hydrolyzing but also reduces silanol aggregation. Moreover, the thermal properties of the organic¡Vinorganic hybrid are improved as silica content increases.

Hybrid membranes represent a promising alternative to the limitations of organic and inorganic materials for high productivity and selectivity gas separation membranes. In this study, the previously developed concept of emulsion-polymerized mixed matrix (EPMM) membranes was further advanced by investigating the effects of surfactant and compatibilizer on inorganic loading in poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based EPMM membranes, in which inorganic part of the membranes originated from tetraethylorthosilicate (TEOS). The polymerization of TEOS, which consists of hydrolysis of TEOS and condensation of the hydrolyzed TEOS, was carried out as (i) one- and (ii) two-step processes. In the one-step process, the hydrolysis and condensation take place in the same environment of a weak acid provided by the aqueous solution of aluminum hydroxonitrate and sodium carbonate. In the two-step process, the hydrolysis takes place in the environment of a strong acid (solution of hydrochloric acid), whereas the condensation takes place in weak base environment obtained by adding excess of the ammonium hydroxide solution to the acidic solution of the hydrolyzed TEOS. For both one- and two-step processes, the emulsion polymerization of TEOS was carried out in two types of emulsions made of (i) pure trichloroethylene (TCE) solvent, and (ii) 10 w/v% solution of PPO in TCE, using different combinations of the compatibilizer (ethanol) and the surfactant (n-octanol). The experiments with pure TCE, which are referred to as a gravimetric powder method (GPM) allowed assessing the effect of different experimental parameters on the conversion of TEOS. The GPM tests also provided a guide for the synthesis of casting emulsions containing PPO, from which the EPMM membranes were prepared using a spin coating technique. The synthesized EPMM membranes were characterized using 29Si nuclear magnetic resonance (29Si NMR), differential scanning calorimetry (DSC), inductively coupled plasma mass spectrometry (ICP-MS), and gas permeation measurements carried out in a constant pressure (CP) system. The 29Si NMR analysis verified polymerization of TEOS in the emulsions made of pure TCE, and the PPO solution in TCE. The conversions of TEOS in the two-step process in the two types of emulsions were very close to each other. In the case of the one-step process, the conversions in the TCE emulsion were significantly greater than those in the emulsion of the PPO solution in TCE. Consequently, the conversions of TEOS in the EPMM membranes made in the two-step process were greater than those in the EPMM membranes made in the one-step process. The latter ranged between 10 - 20%, while the highest conversion in the two-step process was 74% in the presence of pure compatibilizer with no surfactant. Despite greater conversions and hence the greater inorganic loadings, the EPMM membranes prepared in the two-step process had glass transition temperatures (Tg) only slightly greater than the reference PPO membranes. In contrast, despite relatively low inorganic loadings, the EPMM membranes prepared in the one-step process had Tgs markedly greater than PPO, and showed the expected trend of an increase in Tg with the inorganic loading. These results indicate that in the case of the one-step process the polymerized TEOS was well integrated with the PPO chains and the interactions between the two phases lead to high Tgs. On the other hand, this was not the case for the EPMM membranes prepared in the two-step process, suggesting possible phase separation between the polymerized TEOS and the organic phase. The latter was confirmed by detecting no selectivity in the EPMM membranes prepared by the two-step process. In contrast, the EPMM membranes prepared in the one-step process in the presence of the compatibilizer and no surfactant showed 50% greater O2 permeability coefficient and a slightly greater O2/N2 permeability ratio compared to the reference PPO membranes.

Made available in DSpace on 2014-06-11T19:25:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-07-30Bitstream added on 2014-06-13T19:32:41Z : No. of bitstreams: 1 portella_ja_me_rcla.pdf: 606945 bytes, checksum: 60e97ae179f482319dab6311d8920b54 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho tem como objetivo o estudo das modificações estruturais em sonogéis de sílica preparados a partir da sonohidrólise do tetraetilortosilicato (TEOS) em função das diferentes adições de álcool polivinílico (PVA) em solução aquosa (5,5%). Os géis são estudados em estágios que vão desde o estado saturado (gel úmido) até o estado seco do gel (aerogel) resultante do processo de secagem supercrítica. As caracterizações estruturais das amostras são feitas através das técnicas de Termogravimetria (TG), densidade aparente, espalhamento de raios-X a baixo ângulo (SAXS), análise de distribuição de tamanho de poros e área superficial por Adsorção de Nitrogênio. A razão molar água/TEOS e o volume da mistura dos reagentes foram mantidos constantes no processo de sonohidrólise para todas as adições de PVA. Os sóis foram diluídos em quantidades proporcionais de água depois da hidrólise, a fim de obter a mesma concentração de sílica nos géis depois da geleificação e envelhecimento sob condições saturadas. A estrutura dos géis úmidos pode ser descrita como um fractal de massa com dimensão D essencialmente igual a 2,0 em praticamente todo o domínio de comprimentos característicos experimentalmente explorado por SAXS, de ~0.3 nm até ~15 nm. Para os sonogéis com TEOS puro e com baixa adição de PVA, há um afastamento da lei de espalhamento por um fractal de massa na região de baixos q’s devido ao tamanho finito do comprimento característico ξ da estrutura fractal de massa. O efeito fundamental das adições de PVA na estrutura dos géis úmidos é aumentar o comprimento característico ξ da estrutura fractal de massa, sem mudar a dimensão fractal D. Este resultado foi atribuído a efeitos estéricos do polímero na estrutura do gel... / The objective of this work is study the structural modification in silica sonogels prepared from the sonohydrolysis of tetraethoxysilane (TEOS) with different additions of Poly (vinyl alcohol) (PVA) in water solution (5,5%). The gels are studied in different stages since the satured conditions until the dried conditions how result of the supercritical process. The structural characteristics of the samples are measurement by Termogravimetry (TG), Density, Small-angle X-ray scattering (SAXS) and nitrogen adsorption. How these gels were prepared from the sonohydrolysis of tetraethoxysilane (TEOS) with different additions of PVA, the water/TEOS molar ratio and the reactant mixture volume were kept constant in the sonohydrolysis step for all the PVA additions. The sols were diluted in a proportionated water quantity after the hydrolysis in order to obtain the same silica concentration in the gels after gelation and aging under sealed conditons. The structure of wet gels can be described as a mass fractal with dimension D equal to 2.0 on the whole length The objective of this work is scale experimentally probed by SAXS, from ~0.3 to ~15 nm. Pure and low-PVA-addition wet gels exhibit an upper cutoff accounting for a finite characteristic length ξ of the mass fractal structure. The main effect of the addition of PVA on the structure of the wet gels is to increase the characteristic length ξ of the mass fractal structure, without changing the mass fractal dimension D. This result was attributed to steric effects of the polymer in the structure of the gel. Aerogels were obtained by CO2 change and supercritical extraction. The pore volume fraction of the aerogels diminishes typically about 11% with respect to that of the wet gels, although nitrogen adsorption could be underestimating some porosity. The mass fractal structure of the original wet gels seems to evolve to a mass/surface fractal...(Complete abstract, click electronic access below)