MODELING SUSTAINABILITY IN RENEWABLE ENERGY SUPPLY CHAIN SYSTEMS

This dissertation aims at modeling sustainability of renewable fuel supply chain systems against emerging challenges. In particular, the dissertation focuses on the biofuel supply chain system design, and manages to develop advanced modeling framework and corresponding solution methods in tackling challenges in sustaining biofuel supply chain systems. These challenges include: (1) to integrate \u27environmental thinking\u27 into the long-term biofuel supply chain planning; (2) to adopt multimodal transportation to mitigate seasonality in biofuel supply chain operations; (3) to provide strategies in hedging against uncertainty from conversion technology; and (4) to develop methodologies in long-term sequential planning of the biofuel supply chain under uncertainties. All models are mixed integer programs, which also involves multi-objective programming method and two-stage/multistage stochastic programming methods. In particular for the long-term sequential planning under uncertainties, to reduce the computational challenges due to the exponential expansion of the scenario tree, I also developed efficient ND-Max method which is more efficient than CPLEX and Nested Decomposition method. Through result analysis of four independent studies, it is found that the proposed modeling frameworks can effectively improve the economic performance, enhance environmental benefits and reduce risks due to systems uncertainties for the biofuel supply chain systems

Theoretical and Experimental Studies of Polymer Adsorption and Polymer Mediated Interactions

Polyelectrolyte adsorption and polymer mediated interactions in different colloidal polymer systems have been studied in this work. Theoretical methods and experimental techniques are combined, in order to obtain more general reliable results, as well as a deep understanding of the molecular mechanisms that are responsible for the observed behaviors. Two different types of highly charged cationic polyions have been used to explore the adsorption onto oppositely charged surfaces. The adsorption varies with concentration of simple salt and the adsorption dependence on molecular weight have been considered. Polymer density functional theory and null ellipsometry have been utilized to study the adsorption. Various colloidal polymer systems have also been investigated in order to scrutinize polymer mediated interactions. For systems containing charged colloidal particles and non-adsorbing polyethylene oxide (PEO) chains, we studied gelation and constructed a coarse-grained model, to quantitatively compare predicted structure factors with corresponding experimental data. We have devoted some extra efforts to predict and understand the temperature response of polymer mediated interactions, in systems where the pure polymer solution display an local critical solution temperature (LCST). This has, for instance, resulted in predictions that such colloidal particle + polymer dispersions can display a phase behavior that responds on a nonmonotonic manner to temperature change (specifically: flocculated - dispersed - flocculated). these predictions are in qualitative agreement with experiments, and achieved without any assumptions of temperature-dependentinteractions. Another prediction from our studies on LCST polymer solutions, is that these may undergo phase separations in porous environments, even though there is only one phase for all compositions in the bulk solution