First-Principles Studies of Structure-Property Relationships: Enabling Design of Functional Materials

First-principles calculations based on quantum mechanics have been proved to be powerful for accurately regenerating experimental results, uncovering underlying myths of experimental phenomena, and accelerating the design of innovative materials. This work has been motivated by the demand to design next-generation thermionic emitting cathodes and techniques to allow for synthesis of photo-responsive polymers on complex surfaces with controlled thickness and patterns. For Os-coated tungsten thermionic dispenser cathodes, we used first-principles methods to explore the bulk and surface properties of W-Os alloys in order to explain the previously observed experimental phenomena that thermionic emission varies significantly with W-Os alloy composition. Meanwhile, we have developed a new quantum mechanical approach to quantitatively predict the thermionic emission current density from materials perspective without any semi-empirical approximations or complicated analytical models, which leads to better understanding of thermionic emission mechanism. The methods from this work could be used to accelerate the design of next-generation thermionic cathodes. For photo- responsive materials, we designed a novel type of azobenzene-containing monomer for light-mediated ring-opening metathesis polymerization (ROMP) toward the fabrication of patterned, photo-responsive polymers by controlling ring strain energy (RSE) of the monomer that drives ROMP. This allows for unprecedented remote, noninvasive, instantaneous spatial and temporal control of photo-responsive polymer deposition on complex surfaces.This work on the above two different materials systems showed the power of quantum mechanical calculations on predicting, understanding and discovering the structures and properties of both known and unknown materials in a fast, efficient and reliable way

Nora Coal Corporation v. M.T. McArthur

Supreme Court of Appeals of Virginia at Wythevillehttps://scholarlycommons.law.wlu.edu/va-supreme-court-records-vol153/1000/thumbnail.jp

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Publicació alternativa: FanzineDescripció basada en: No. 5 (jun. 1983

Acute Degradation of Surface-Bound Unsaturated Polyolefins in Common Solvents under Ambient Conditions

We describe the detachment of covalently grafted polybutadiene and polynorbornene chains, which were prepared by surface-initiated ring-opening metathesis polymerization (SiROMP), from Si/SiO2 substrates upon brief exposure to common solvents in air. Degradation and disappearance of grafted polybutadiene films after successive rinses with dichloromethane were monitored by ellipsometry. Changes in surface topography were analyzed by atomic force microscopy. The rapid auto-oxidation of allylic carbon−hydrogen bonds renders these thin films extremely susceptible to degradation under ambient conditions. Polymers in the tethered state suffer more acute degradation (on the time scale of seconds) compared to those dissolved in solution (not detectable after days). To prevent degradation, unsaturated polymers prepared by SiROMP and the subsequent conversion (of unsaturated groups) need to be carried out under inert atmosphere. For example, smooth polybutadiene thin films of ∼100 Å thickness were covalently attached to silicon substrates via SiROMP of cyclooctadiene in the vapor phase. Solvent rinsing to remove unreacted monomers and free oligomers/polymers was carried out prior to the conversion of double bonds to epoxide groups. When these steps were carried out under nitrogen, negligible film loss was observed, and surface topography of the thin films was preserved. Once the unsaturation was removed from polybutadiene, the epoxidized and hydroxylated polybutadiene films were stable toward solvent exposure in air

Surface-initiated ring opening metathesis polymerization from the vapor phase to prepare compositionally versatile thin films

Functional polymer films provide the ability to tailor the properties of surfaces. Ring opening metathesis polymerization (ROMP) is a powerful polymerization technique that provides rapid kinetics and substantial control over the polymerization. However, the development of functional polymer films by surface-initiated ROMP (SiROMP) is limited because of the relatively low number of available monomers. Thus, finding accessible new methods that can impart multiple functionalities to polymer films grown by SiROMP is critical. This dissertation describes the work that I have performed in introducing multiple functionalities and properties into polymer thin films prepared by SiROMP. I report the SiROMP of trans-5-norbornene-2,3-dicarbonyl chloride (NBDAC) from the vapor phase as a versatile platform to achieve many functional polymer films via simple exposure of the pNBDAC film to reagents. This modification strategy owes to the fast and high-yield reactions of acyl chlorides with alcohols, amines, water, and other molecules. The compositionally versatile platform is applied to produce polynorbornene films that contain pendant hydroxamic acid groups, which show ability to chelate transition metal ions and can be used in metal ion caption from aqueous solutions. The chelated metals within the polymer film act as cross-linkers, which remarkably enhance the pH stability, thermal stability, and resistance against ion transfer of the original film. Another application of this compositionally versatile pNBDAC platform is to produce pH-responsive, ester/carboxylic acid random copolymer films, which demonstrate the ability of these films to have multiple functionalities introduced. The magnitude and range of the pH-responsive performance are controllable by designing the ester/carboxylic acid composition in the film. Part of the dissertation examines another compositionally versatile platform through the preparation of polymer/ionic liquid (IL) composite films. Instead of chemically modifying the polymer films, the film properties can also be altered by the physical or electrostatic incorporation of other materials within the polymer framework. A polymer/ IL gel film can be prepared by incorporating ILs into surface-initiated poly(dicyclopentadiene)(pDCPD) films using a simple immersion method. This novel processing approach is proven to be feasible in preparing polymer/IL gel films with various IL species