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The objective of this research was to characterize the seawater transport and its effect on the transverse tensile strength of a carbon/vinylester composite. The moisture contents of neat vinylester and unidirectional carbon/vinylester composite panels immersed in seawater were monitored until saturation. A model for moisture up-take was developed based on superposition of Fickian diffusion, and Darcy’s law for capillary transport of water. Both the predicted and measured saturation times increased with increasing panel size, however the diffusion model predicts much longer times while the capillary model predicts shorter time than observed experimentally. It was also found that the saturation moisture content decreased with increasing panel size. Testing of macroscopic and miniature composite transverse tensile specimens, and SEM failure inspection revealed more fiber/matrix debonding in the seawater saturated composite than the dry composite, consistent with a slightly reduced transverse tensile strength. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

The gas transport properties of side-chain crystalline poly(n-alkyl acrylate) and poly(m-alkyl acrylate) blends are determined as a function of temperature for varying side-chain lengths, n and m, and blend compositions. The side chains of poly(n-alkyl acrylate)s crystallize independently of the main chain for n [is greater than or equal to] 10 which leads to an extraordinary increase in the permeability at the melting temperature of the crystallites. The compatibility of these polymers are examined and macroscopic homogeneity is observed for a small range of n and m when the difference /n - m/ is between 2 - 4 methylene units. Thermal analysis shows that the blend components crystallize independently of one another; at the same time, the crystallization of each component is hindered by the presence the other component. The permeation responses of these blends show two distinct permeation jumps as the crystallites from each component melt at their respective melting temperatures. Blends with continuous permeation responses are found to have higher effective activation energies than observed for common polymers. Thermal analysis proved to be a useful tool to help predict the permeation response for poly(alkyl acrylates); thus the thermal behavior of poly(n-alkyl acrylate) blended with n-aliphatic materials and random copolymers of poly(n-alkyl acrylates) are briefly examined. A bulk modified atmospheric storage design is proposed where produce is stored in a rigid chamber that is equipped with both selective and non-selective membrane modules that help regulate the oxygen entering and the carbon dioxide leaving the produce compartment. The design enables control of the atmosphere inside the chamber by modulating gas flow, i.e. the gas flow rate and composition, through the non-selective membrane by delivering fresh air upstream of the non-selective membrane. The model shows that the choice of materials for the selective and non-selective membranes dictate the range of concentrations achievable; however, the air flow rate allows the control between these ranges. The method to design a practical chamber from this model is also described.

Carbon capture and related gas separation processes are critical tools in our efforts to combat climate change. While polymer membranes are seen as a central construct to achieve these goals, their performance needs further improvement to meet current sustainability objectives. It is in this context that membranes composed of polymer-grafted nanoparticles (GNPs) become highly germane. Chemically tethering the available polymer to the nanoparticle (NP) surface in GNP systems helps mitigate difficulties controlling nanoparticle dispersion common when incorporating inorganic filler NPs into polymer (i.e., mixed matrix membranes (MMMs)). Previous work has shown that gas transport in pure GNP membranes can be strongly enhanced relative to that in the corresponding neat polymer. Additionally, we demonstrated that larger gases display greater degrees of permeability enhancement than smaller ones. This work explores the underlying mechanisms governing the unique gas transport behavior observed in GNPs, with the goal of designing materials possessing superior transport properties that can be known and manipulated a priori. We begin with the identification of transport mechanisms for penetrants of different sizes through an exploration of the heterogenous nature of GNPs. In the limit of moderate-to-high grafting density (the number of chains tethered per unit surface area), the chains are overcrowded near the surface and assume extended conformations termed “polymer brushes”. These brushes comprise two regimes: (1) a dry zone of higher polymer stretching closer to the NP surface and (2) the interstitial spaces in the multibody packing of lower polymer density. We find that larger penetrants such as CH₄, with low solubilities, preferentially sorb into the interstitial spaces in the NP packing prior to diffusing through stretched chains in the dry brush region. The nature of small gas permeability enhancement, on the other hand, is due primarily to enhancements in penetrant diffusion through the stretched chain region close to the NP surface – this is because these gases have high enough solubilities to be present everywhere in the polymer layer. Such solubility differences enable the direct control over penetrant transport through the disparate regions of the polymer brush in mixed-gas environments relevant to operation. Elevated CO₂ content, through increasing feed concentrations at higher pressures, yields increased CH₄ permeability and an associated reduction in mixed-gas selectivity relative to ideal gas analogs. Additionally, high-pressure conditioning with CO₂ evidently dilates the material (due to gas adsorption) in a manner that is apparently not recoverable after a pressure decrease. An alternative handle to control penetrant transport is to manipulate the physical brush structure. Such morphological control is accomplished through variations in preparation methodology; in particular, the rate of solvent evaporation in solution-cast samples plays a significant role in dictating the final structure of the jammed colloidal glass. Utilizing high-pressure conditioning in CO₂ as a concentration quench, we combine morphological control over the brush structure with selective penetrant manipulation to dilate the overcrowded brush regime and enhance gas transport performance. Leveraging the colloidal glass nature of GNPs in this way enables the formation of quasi-equilibrium structures with even greater amounts of “free volume”. The remaining chapters focus on employing our knowledge of the gas transport mechanisms in these materials to aid in future experimental design and to form mechanically resilient materials. Implementing a simulated design-of-experiments loop, we find that a surprisingly minimal amount of experimental data is necessary to effectively model the transport properties of new materials to within practical experimental error. Selectively altering the chemistry of specific chain regions achieved slight enhancement in membrane selectivity while significantly improving material toughness and ultimate utility. Our enhanced understanding of gas transport mechanisms in polymer-grafted nanoparticle membranes will aid in the design and implementation of membranes with tunable separation performance through direct control of how penetrants transport and via morphological changes to the brush structure.