No description available.

No description available.

A series of hybrid component based on reactive polyhedral oligomeric silsesquioxane(POSS) precusors and its reactive copolymers of PGMA were synthesized and utilized to nanobuild in epoxy. Reactive POSS and copolymer dispersed in homogenous in matrix, overcomed POSS-POSS interaction, which resulted in macroscale phase separation. The nanocomposites obtained were analyzed by Scanning electron microscopy, Transmission electron microscopy, X-ray scattering and dynamic mechanical. An analogue of POSS (denoted as POSSMOCA) was synthesized via addition reaction, which had reactive amino group bonding into epoxy network and improved the thermostability, because of the structural silicon, nitrogen and halogen. Epoxy/polyhedral oligomeric silsesquioxanes (POSS) hybrid composites were prepared from prereaction between trifunctional silanol POSS-OH and diglycidyl ether of bisphenol A (DGEBA) via silanol and the oxirane group. Reactive POSS-PGMA was polymerized via Reversible addition-fragmentation transfer polymerization. It was easy to tail the compatibility of the epoxide block copolymer with a step-growth polymerized matrix, to form nanostructure via reaction with PGMA segements. In the case of inert POSS-PMMA copolymers modified epoxy, topology of copolymer defined the final morphology and interaction between epoxy and them, because of directional hydrogen bonding and dilution effect. Tg of different epoxide conversion, obeyed of Gordon-Taylor equation and Kwei equation, k which reflected the interaction of modifier and DGEBA/MEDA and epoxy/amine oligomers, was consistent of the rheology and dynamic results.

No description available.

No description available.

Single wavelength ellipsometry measurements at Brewster's angle provide a powerful technique for characterizing ultrathin polymeric films. By conducting the experiments in different ambient media, multiple incident media (MIM) ellipsometry, simultaneous determinations of a film's thickness and refractive index are possible. Poly(tert-butyl acrylate) (PtBA) films serve as a model system for the simultaneous determination of thickness and refractive index (1.45 at 632 nm). Thickness measurements on films of variable thickness agree with X-ray reflectivity results. The method is also applicable to spincoated films where refractive indices of PtBA, polystyrene and poly(methyl methacrylate) are found to agree with literature values within experimental error. Likewise, MIM ellipsometry is utilized to simultaneously obtain the refractive indices and thicknesses of thin films of trimethylsilylcellulose (TMSC), regenerated cellulose, and cellulose nanocrystals where Langmuir-Blodgett (LB) films of TMSC serve as a model system. Ellipsometry measurements not only provide thickness and optical constants of thin films, but can also detect thermally induced structural changes like surface glass transition temperatures (Tg) and layer deformation in LB-films. Understanding the thermal properties of the polymer thin films is crucial for designing nanoscale coatings, where thermal properties are expected to differ from their corresponding bulk properties because of greater fractional free volume in thin films and residual stresses that remain from film preparation. Polyhedral oligomeric silsesquioxane (POSS) derivatives may be useful as a nanofiller in nanocomposite formulations to enhance thermal properties. As a model system, thin films of trisilanolphenyl-POSS (TPP) and two different molar mass PtBA were prepared as blends by Y-type Langmuir-Blodgett film deposition. For comparison, bulk blends were prepared by solution casting and the samples were characterized via differential scanning calorimetry (DSC). Our observations show that surface Tg is depressed relative to bulk Tg and that magnitude of depression is molar mass dependent for pure PtBA films. By adding TPP as a nanofiller both bulk and surface Tg increase. Whereas, bulk Tg shows comparable increases for both molar masses, the increase in surface Tg for higher molar mass PtBA is greater than for lower molar mass PtBA. These studies show that POSS can serve as a model nanofiller for controlling Tg in nanoscale coatings. / Ph. D.

Thin film bilayers and blends composed of polymers and nanoparticles are increasingly important for technological applications that range from space survivable coatings to novel drug delivery systems. Dewetting or spontaneous hole formation in amorphous polymer films and phase separation in multicomponent polymer films can hinder the stability of these systems at elevated temperatures. Hence, fundamental understanding of dewetting and phase separation in polymer/nanoparticle bilayer and blend films is crucial for controlling transport and thermomechanical properties and surface morphologies of these systems. This dissertation provides studies on morphological evolution driven by phase separation and/or dewetting in model polymer/nanoparticle thin film bilayers and blends at elevated temperatures. Morphological evolution in dewetting bilayers of poly(t-butyl acrylate) (PtBA) or polystyrene (PS) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP) is explored at elevated temperatures. The results demonstrate unique dewetting morphologies in both PtBA/TPP and PS/TPP bilayers that are significantly different from those typically observed in dewetting polymer/polymer bilayers. Upon annealing the PtBA/TPP bilayers at 95°C, a two-step dewetting process is observed. PtBA immediately diffuses into the upper TPP layer leading to hole formation and subsequently the holes merge to form interconnected rim structures in the upper TPP layer. Dewetting of both the TPP and PtBA layers at longer annealing times leads to the evolution of scattered holes containing TPP-rich, fractal aggregates. The fractal dimensions of the TPP-rich, fractal aggregates are ~2.2 suggesting fractal pattern formation via cluster-cluster aggregation. Dewetting in PS/TPP bilayers also proceeds via a two-step process; however, the observed dewetting morphologies are dramatically different from those observed in PtBA/TPP bilayers. Cracks immediately form in the upper TPP layer during annealing of PS/TPP bilayers at 200°C. With increasing annealing times, the cracks in the TPP layer act as nucleation sites for dewetting and aggregation of the TPP layer and subsequent dewetting of the underlying PS layer. Complete dewetting of both the TPP and PS layers results in the formation of TPP encapsulated PS droplets. Phase separation in PtBA/TPP thin film blends is investigated as functions of annealing temperature and time. The PtBA/TPP thin film blend system exhibits an upper critical solution temperature (LCST) phase diagram with a critical composition and temperature of 60 wt% PtBA and ~70°C, respectively. Spinodal decomposition (SD) is observed for 60 wt% PtBA blend films and off-critical SD is seen for 58 and 62 wt% PtBA blend films. The temporal evolution of SD in 60 wt% PtBA blend films is also explored. Power law scaling for the characteristic wavevector with time (q ~ t^n with n = -1/4 to -1/3) during the early stages of phase separation yields to domain pinning at the later stages for films annealed at 75, 85, and 95°C. In contrast, domain growth is instantly pinned for films annealed at 105°C. Our work provides an important first step towards understanding how nanoparticles affect polymer thin film stability and this knowledge may be utilized to fabricate surfaces with tunable morphologies via controlled dewetting and/or phase separation. / Ph. D.

For over a century, Langmuir films have served as excellent two-dimensional model systems for studying the conformation and ordering of amphiphilic molecules at the air/water (A/W) interface. With the equipment of Wilhelmy plate technique, Brewster angle microscopy (BAM), and surface light scattering (SLS), the interfacial phase and rheological behavior of Langmuir films can be investigated. In this dissertation, these techniques are employed to examine Langmuir films of polyhedral oligomeric silsesquioxane (POSS), polymer blends, and magnetic nanoparticles (MNPs). In a first time, SLS is employed to study POSS molecules. The interfacial rheological properties of trisilanolisobutyl-POSS (TiBuP) indicate that TiBuP forms a viscoelastic Langmuir film that is almost perfectly elastic in the monolayer state with a maximum dynamic dilational elasticity of around 50 mNâ m-1 prior to film collapse. This result suggests that TiBuP can serve as model nanofiller with polymers. As an interesting next step, blends of TiBuP and polydimethylsiloxane (PDMS) with different compositions are examined via surface pressure (surface pressureâ surface area occupied per molecule (A) isotherms and SLS. The results show that TiBuP, with its attendant water, serves as a plasticizer and lowers the dilational modulus of the films at low surface pressure. As surface pressure increases, composition dependent behavior occurs. Around the collapse pressure of PDMS, the TiBuP component is able to form networks at the A/W interface as PDMS collapse into the upper layer. Blends of non-amphiphilic octaisobutyl-POSS (OiBuP) and PDMS are also studied as an interesting comparison to TiBuP/PDMS blends. In these blends, OiBuP serves as a filler and reinforces the blends prior to the collapse of PDMS by forming "bridge" structure on top of PDMS monolayer. However, OiBuP is non-amphiphilic and fails to anchor PDMS chains to the A/W interface. Hence, OiBuP/PDMS blends exhibit negligible dilational viscoelasticity after the collapse of PDMS. Furthermore, the phase behavior of PDMS blended with a trisilanol-POSS derivative containing different substituents, trisilanolcyclopentyl-POSS (TCpP), is also investigated via the Wilhelmy plate technique and BAM. These TCpP/PDMS blends exhibit dramatically different phase behavior and morphological features from previously studied POSS/PDMS blends, showing that the organic substituents on trisilanol-POSS have considerable impact on the phase behavior of POSS/PDMS blends. The interfacial rheological behavior of tricarboxylic acid terminated PDMS (PDMS-Stabilizer) and PDMS stabilized MNPs are investigated and compared with "regular" PDMS containing non-polar end groups. The tricarboxylic acid end group of the PDMS-Stabilizer leads to a different collapse mechanism. The PDMS stabilized MNPs exhibit viscoelastic behavior that is similar to PDMS showing all the tricarboxylic acid end groups are bound to the magnetite cores. Studying the interfacial behavior of different Langmuir films at the A/W interface provides us insight into the impact of molecule-molecule and molecule-subphase interactions on film morphology and rheology. These results are able to serve as important guides for designing surface films with preferred morphological and mechanical properties. / Ph. D.

This work is generally aimed to synthesize POSS based BCPs via RAFT polymerization, to study their self-assembly behaviors, to research on the effect of POSS self-assembly structure on the bulk properties and to prepare nanostructured hybrid epoxy via self-assembly of POSS based copolymer. In Chapter1, We studied the RAFT polymerization of POSS macromers and capable to synthesize well defined POSS based BCPs with high POSS fraction and different topology such as AB，BAB and (BA)3. The vertex group and the morphology effect on thermo-mechanical properties of POSS based BCPs as well as the structure-property relationship was investigated. Dispersion RAFT polymerization in apolar solvent was applied and various aggregates with different morphology in Chapter2. Cooling induced reversible micelle formation and transition was found and the pathway selection in vesicle formation was investigated. Nano-construction of O/I hybrid epoxy materials based on POSS based copolymers was investigated in Chapter4. The effect of functional group content on miscibility of POSS based statistic copolymer and epoxy was investigated. A novel method to nanostructure epoxy hybrid involving self-assembly of POSS based BCPs in epoxy was presented. High homogeneity and well size/morphology control of core-corona structure containing rigid POSS core and soluble PMMA corona in networks were obtained.

Une série de composant hybride basée sur réactives polyédriques oligomères silsesquioxane (POSS) precusors et ses copolymères réactifs de PGMA ont été synthétisés et utilisés pour nanobuild en époxy. POSS réactifs et de copolymères en dispersion dans la matrice homogène dans, au délà de POSS-POSS interaction, ce qui a entraîné la séparation de phase macroscopique. Les nanocomposites obtenus ont été analysés par microscopie électronique à balayage, microscopie électronique à transmission, diffusion des rayons X et l'analyse mécanique dynamique. Un analogue de POSS (notée POSSMOCA) a été synthétisé par réaction d'addition, qui a réactive liaison groupe amino dans le réseau époxy et d'améliorer la stabilité thermique, en raison du silicium, d'azote et un atome d'halogène structurel. Époxy / polyédriques silsesquioxanes oligomères (POSS) composites hybrides ont été préparés à partir de pré-réaction entre l'éther de silanol POSS-OH et diglycidylique trifonctionnel de bisphénol A (DGEBA) par l'intermédiaire du silanol et un groupe oxiranne. Réactif POSS-PGMA a été polymérisé par polymérisation par transfert de réversible par addition-fragmentation. Il est facile à queue de la compatibilité du copolymère séquencé époxyde avec une matrice de l'étape de croissance-polymérisé, pour former par réaction avec nanostructure segements PGMA. Dans le cas d'inertes POSS-PMMA copolymères modifiés époxy, topologie de copolymère défini la morphologie finale et l'interaction entre époxy et entre eux, en raison de la liaison hydrogène directionnelle à effet de dilution. Tg de conversion époxyde différente, obéi de Gordon-Taylor équation et l'équation Kwei, k qui reflète l'interaction de modificateur et les oligomères DGEBA / MEDA et époxy / amine, était cohérente de la rhéologie et les résultats dynamiques. / A series of hybrid component based on reactive polyhedral oligomeric silsesquioxane(POSS) precusors and its reactive copolymers of PGMA were synthesized and utilized to nanobuild in epoxy. Reactive POSS and copolymer dispersed in homogenous in matrix, overcomed POSS-POSS interaction, which resulted in macroscale phase separation. The nanocomposites obtained were analyzed by Scanning electron microscopy, Transmission electron microscopy, X-ray scattering and dynamic mechanical. An analogue of POSS (denoted as POSSMOCA) was synthesized via addition reaction, which had reactive amino group bonding into epoxy network and improved the thermostability, because of the structural silicon, nitrogen and halogen. Epoxy/polyhedral oligomeric silsesquioxanes (POSS) hybrid composites were prepared from prereaction between trifunctional silanol POSS-OH and diglycidyl ether of bisphenol A (DGEBA) via silanol and the oxirane group. Reactive POSS-PGMA was polymerized via Reversible addition-fragmentation transfer polymerization. It was easy to tail the compatibility of the epoxide block copolymer with a step-growth polymerized matrix, to form nanostructure via reaction with PGMA segements. In the case of inert POSS-PMMA copolymers modified epoxy, topology of copolymer defined the final morphology and interaction between epoxy and them, because of directional hydrogen bonding and dilution effect. Tg of different epoxide conversion, obeyed of Gordon-Taylor equation and Kwei equation, k which reflected the interaction of modifier and DGEBA/MEDA and epoxy/amine oligomers, was consistent of the rheology and dynamic results.