High-pressure solution behavior such as density and phase behavior is a critical fundamental property for the design and optimization of various chemical processes, such as distillation and extraction in the production and purification of oils, polymers, and other natural materials. In this PhD study, solution behavior data are experimentally determined and equation of state (EoS) modeled for n-hexadecane, n-octadecane, n-eicosane, methylcyclohexane, ethylcyclohexane, cis-1,2-dimethylcyclohexane, cis-1,4-dimethylcyclohexane, trans-1,4-dimethylcyclohexane, o-xylene, m-xylene, p-xylene, and 2-methylnaphthalene at temperatures to 525 K and pressures to 275 MPa. A variable-volume view cell coupled with a linear variable differential transformer is used for the high-pressure determination. The reported density data are less than 0.4% of available literature data, which is within the estimated accumulated experimental uncertainty, 0.75%. Special attention is paid to the effect of architectural differences on the resultant high-pressure solution behavior. The reported data of low molecular weight hydrocarbons are modeled with Peng-Robinson (PR) equation of state (EoS), high-temperature high-pressure volume-translated cubic (HTHP VT-cubic) EoS, and perturbed-chain statistical fluid theory (PC-SAFT) EoS. The three pure-component parameters in PC-SAFT EoS can be either obtained from literature or from a group contribution (GC) method. Generally, PR EoS gives the worst predictions and HTHP VT-cubic EoS provides modest improvements over the PR EoS, but both of the equations underpredict the densities at high pressures. On the other hand, PC-SAFT EoS, with parameters from the literature or from a GC method, gives the improved density predictions with respect to PR EoS and HTHP VT-cubic EoS, although an overprediction of densities is found at high pressures. Model calculations also highlight the capability of these equations to account for the different densities observed for the hydrocarbon isomers. However, none of the EoS investigated in this study can fully account for the effect of isomeric structural differences on the high-pressure densities. For a better prediction of densities at high pressures, a new set of PC-SAFT pure-component parameters are obtained from a fit of the experimental density data obtained in this study and the mean absolution percent deviation is within 0.4%. The experimental technique and PC-SAFT EoS modeling method are extended to a star polymer-propane mixture. Star polymers with a fixed number of arms have a globular structure that does not promote chain entanglements. Star polymers can be synthesized with a large number of functional groups that can be readily modified to adjust their physical properties for specific applications in the areas of catalysis, coatings, lubrication, and drug delivery. In this study, a star polymer with a divinylbenzene core and statistically random methacrylate copolymer arms is synthesized with reversible addition-fragmentation-transfer method and fractionated with supercritical carbon dioxide and propane to obtain fractions with low molecular weight polydispersity. The phase behavior and density behavior are experimentally determined in supercritical propane for fractionated star polymers and the corresponding linear copolymer arms at temperatures to 423 K and pressures to 210 MPa. Experimental data are presented on the impact of the molecular weight, the backbone composition of the lauryl and methylmethacrylate repeat units in the copolymer arms, and the DVB core on the polymer-propane solution behavior. The star polymer is significantly more soluble due to its unique structure compared with the solubility of the linear copolymer arms in propane. The resultant phase behavior for the two homopolymers and the copolymers in propane are modeled using the PC-SAFT and copolymer PC-SAFT EoS, which give reasonable predictions for both phase behavior and density behavior. Model calculations are not presented for the phase behavior of the star polymers in propane since the PC-SAFT approach is not applicable for star polymer structures.

The objective of this research is to investigate three classes of block copolymers, the vesicle structures they form, their response to stimuli in solution and their capabilities for use in biomimicry. The self-assembled structures of all classes of polymers will be used as a basis for templating hydrogel materials, in the interior of the vesicles, and the resulting particles will be designed to show the structural and mechanical properties similar to living cells. The synthetic block copolymers are a poly(ethylene glycol) and poly(butadiene) (PEO-b-PBd) copolymer, a poly(ethylene glycol) and a poly(dimethyl siloxane) (PEO-b-PDMS) copolymer and the polypeptide block copolymer is a lysine and glycine (K-b-G) copolymer. Investigation using the synthetic block copolymers will focus on whether the polymer can form vesicles, size limitations of vesicle structures, and the formation of internal polymer networks. Subsequent investigations will look at the needed steps for biomimicry. The PDMS copolymer is a novel entrant into amphiphilic block copolymers. Although characterization of the copolymer solution behavior is known, the mechanical properties of the polymer are not known. PDMS was investigated along with the PBd polymer due to the similar chemical structure and nature. The lysine-glycine copolymers are a new system of materials that form fluid vesicle structures. Therefore, characterization of how K-b-G assembly behavior and investigations of how K-b-G responds to solution conditions are needed before incorporating this copolymer into a cellular mimic. The size and mechanical behavior of the lysine-glycine vesicles are measured to compare and contrast to the synthetic systems. The goals in creating a biomimic are a hollow sphere structure with a fluid bilayer, a vesicle that has controllable mechanical properties, and with a controllable surface chemistry and density. Overall, these experiments were successful; the various properties are easily controllable: the size of vesicles created, the material properties of the vesicle interior and shell, as well as the surface chemistry of the vesicles. Investigations into the novel block copolymers were conducted, and the polypeptide block copolymer showed the ability to create vesicles that are responsive to changing salt and pH concentrations. The PDMS block copolymer system offers a new material system that will perform as well as the PBd system, but without some of the inherent drawbacks.

Energy efficient purification of hydrogen is an important technological challenge with broad applications in the chemical, petrochemical, metallurgical, pharmaceutical, textile and energy industries. Palladium-alloy membranes are particularly suited to this problem due to their high hydrogen permeability, thermal stability, and virtually infinite selectivity. In current systems hydrogen flux is observed to be inversely proportional to membrane thickness which is indicative of the interstitial diffusion mechanism of hydrogen permeation. This observation, along with the high cost of palladium, has motivated continuous efforts to decrease membrane thickness. Theoretical modeling of membrane performance predicts that as membrane thickness continues to decrease, eventually the permeation rate will no longer be limited by diffusion through the bulk Pd but will become limited by desorption from the permeate surface. If it exists, this is a vital transition to pinpoint due to the fact that below this thickness membrane operating conditions will have a drastically different effect on hydrogen permeation behavior and no additional performance enhancements will result from further decreasing thickness. A handful of experimental results in the open literature contradict these modeling predictions. A new model is developed in this work to explain these contradictions by considering the non-ideal behavior of hydrogen solution into metals which has been neglected in previous models. Additionally, it has been demonstrated that hydrogen permeation through bulk Pd depends on membrane microstructure, making deposition conditions and post-deposition thermal treatment important issues for repeatable performance. The interplay of these issues on the performance of ultra-thin, Pd-Ag alloy hydrogen separating membranes is experimentally investigated. It is demonstrated that the hydrogen permeation behavior of sub-micrometer thick Pd-Ag alloy membranes exhibits diffusion-limited behavior in the context of the new model. The microstructure evolution during annealing is characterized and a correlation is drawn with the observed transient hydrogen permeation behavior during initial testing of a new membrane. In addition, two distinct failure modes of the microfabricated membranes are observed and the implications for future Pd-based membrane research are discussed.