Publications

Abstract not provided.

The impact of humidity and temperature on a zinc oxide based transparent conducting oxide (TCO) was assessed under accelerated aging conditions. An in situ electroanalytical method was used to monitor the electrical properties for a conducting zinc oxide under controlled atmospheric (humidity, temperature and irradiation) conditions. A review of thin film photovoltaic (PV) literature has shown one major failure mode of cells/modules is associated with the ingress of water into modules in the field. Water contamination has been shown to degrade the performance of the TCO in addition to corroding interconnects and other conductive metals/materials associated with the module. Water ingress is particularly problematic in flexible thin film PV modules since traditional encapsulates such as poly(ethyl vinyl acetate) (EVA) have high water vapor transmission rates. The accelerated aging studies of the zinc oxide based TCOs will allow acceleration factors and kinetic parameters to be determined for reliability purposes.

The purpose of this project is to develop multi-layered co-extrusion (MLCE) capabilities at Sandia National Laboratories to produce multifunctional polymeric structures. Multi-layered structures containing layers of alternating electrical, mechanical, optical, or structural properties can be applied to a variety of potential applications including energy storage, optics, sensors, mechanical, and barrier applications relevant to the internal and external community. To obtain the desired properties, fillers must be added to the polymer materials that are much smaller than the end layer thickness. We developed two filled polymer systems, one for conductive layers and one for dielectric layers and demonstrated the potential for using MLCE to manufacture capacitors. We also developed numerical models to help determine the material and processing parameters that impact processing and layer stability.

Abstract not provided.

Microencapsulation is the process of placing a shell composed of a synthetic or biological polymer completely around another chemical for the purpose of delaying or slowing its release. We report that Sandia National Laboratories was interested in microencapsulating concentrated sulfuric for a specific application. Historically, acids have been encapsulated many times using various techniques. However, the encapsulation of mineral acids has proven difficult due to the lack of a shell material robust enough to prevent premature leakage of the capsule. Using the Polymer-Polymer Incompatibility (PPI) technique, we screened a variety of shell materials and found our best results were with Derakane® 411-350, an epoxy vinyl ester resin (EVER) polymer.

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Silsesquioxanes have been the subject of intensive study in the past and are becoming important again as a vehicle for introducing organic functionalities into hybrid organic-inorganic materials through sol-gel processing. Depending on the application, the target hybrid material may be required to be a highly cross-linked, insoluble gel or a soluble polymer that can be cast as a thin film or coating. The former has applications such as catalyst supports and separations media; the latter is an economically important method for surface modification or compatiblization for applying adhesives or introducing fillers. Polysilsesquioxanes are readily prepared through the hydrolysis and condensation of organotrialkoxysilanes, though organotriaminosilane and organotrihalosilane monomers can also be used. This paper explores the kinetics of the preparation route.

Polysilsesquioxane xerogels were prepared by the sol-gel polymerization of organotrialkoxysilanes, RSi(OR′)3, with R′ = Me: R = H, Me, vinyl, chloromethyl, chloromethylphenyl, hexadecyl, and octadecyl and R′ = Et: R = H, Me, Et, cyanoethyl, chloromethyl, vinyl, dodecyl, and hexadecyl. The majority of the gels were opaque and colloidal in appearance. The porosity of the xerogels was characterized by nitrogen porosimetry and scanning electron microscopy. Many of the remaining organotrialkoxysilanes formed porous polymeric gels, but the surface areas were lower and the mean pore sizes larger. Some of the xerogels, especially those prepared under acidic conditions were non-porous.

Polymerization of organotrialkoxysilanes is a convenient method for introducing organic functionality into hybrid organic-inorganic materials. However, not much is known about the effects of the organic substituent on the porosity of the resulting xerogels. In this study, we prepared a series of polysilsesquioxane xerogels from organotrialkoxysilanes, RSi(OR{sup 1}){sub 3}, with different organic groups (R = H, Me, Et dodecyl, hexadecyl, octadecyl, vinyl, chloromethyl, (p-chloromethyl) phenyl, cyanoethyl). Polymerizations of the monomers were carried out under a variety of conditions, varying monomer concentration, type of catalyst, and alkoxide substituent. The effect of the organic substituent on the sol-gel process was often dramatic. In many cases, gels were formed only at very high monomer concentration and/or with only one type of catalyst. All of the gels were processed as xerogels and characterized by scanning electron microscopy and nitrogen sorption porosimetry to evaluate their pore structure.

Polymerizations of aryltrialkoxysilanes generally afford soluble oligomeric or polymeric aryl-substituted silsesquioxanes. This is in spite of being based on trifunctional precursors capable of forming highly crosslinked and insoluble network polymers. In this study, soluble phenyl, benzyl, and phenethyl-substituted silsesquioxane oligomers and polymers were prepared by hydrolyzing their respective triethoxysilyl precursor with water or aqueous acid. Additional samples of the polymers were prepared by heating the materials at 100 C or 200 C under vacuum in order to drive the condensation chemistry. One sample of polybenzylsilsesquioxane was heated at 200 C with catalytic NaOH. The resulting materials were characterized using solution {sup 1}H, {sup 13}C, and {sup 29}Si NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry. Of particular interest was the effect of the aryl substituent, and processing conditions on the molecular weight and glass transition temperatures of the polysilsesquioxanes.

Polymerization of phenyl-, benzyl-, and phenethyltroalkoxysilanes formed soluble oligo- and polysilsesquixanes. No gels of any of the monomers were observed to form. The molecular weights of the materials prepared and dried at room temperature were near 2K, but would continuously increase with heating at 100°C to between 5-15K. The polymers were structurally characterized by 1H, 13C, and 29Si NMR.

We have measured, by {sup 1}H and {sup 13}C nuclear magnetic resonance (NMR), the percent deuteration, the tacticity and the purity of several polymers and one solvent used in the preparation of microcellular foams. The percent deuteration was measured for polystyrene, polyacrylonitrile and polyethylene. The tacticities of polystyrene and polyacrylonitrile were determined. The purity and degradation products of polyacrylonitrile and maleic anhydride were examined. This report documents the experimental procedures and results of these measurements.