This dissertation presents the development of a modeling scheme that is developed to model the membrane potentials and ion currents through a bilayer network system. The modeling platform builds off of work performed by Hodgkin and Huxley in modeling cell membrane potentials and ion currents with electrical circuits. This modeling platform is built specifically for cell mimics where individual aqueous volumes are separated by single bilayers like the droplet-interface-bilayer. Applied potentials in one of the aqueous volumes will propagate through the system creating membrane potentials across the bilayers of the system and ion currents through the membranes when proteins are incorporated to form pores or channels within the bilayers. The model design allows the system to be divided into individual nodes of single bilayers. The conductance properties of the proteins embedded within these bilayers are modeled and a finite element analysis scheme is used to form the system equations for all of the nodes. The system equation can be solved for the membrane potentials through the network and then solve for the ion currents through individual membranes in the system. A major part of this work is modeling the conductance of the proteins embedded within the bilayers. Some proteins embedded in bilayers open pores and channels through the bilayer in response to specific stimuli and allow ion currents to flow from one aqueous volume to an adjacent volume. Modeling examples of the conductance behavior of specific proteins are presented. The examples demonstrate aggregate conductance behavior of multiple embedded proteins in a single bilayer, and at examples where few proteins are embedded in the bilayer and the conductance comes from a single-channel or pore. The effect of ion gradients on the single channel conductance example is explored and those effects are included in the single-channel conductance model. Ultimately these conductance models are used with the system model to predict ion currents through a bilayer or through part of a bilayer network system. These modeling efforts provide a modeling tool that will assist engineers in designing bilayer network systems. / Ph. D.

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Thesis (Masters)--California Institute of Technology, 1974. / Advisor name found in the Acknowledgements pages of the thesis. Title from home page. Viewed 12/02/2009. Includes bibliographical references.

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acase@tulane.edu / This work embraces the fabrication of functional materials through the interactions at interfaces and covers two topics. First, we investigate the assembly of hydrophobically modified polypeptoids (HMPs) with lipid bilayers and the structural transition of lipid bilayers induced by HMPs. Polypeptoids are a class of pseudo-peptidic polymers. Properties such as biocompatibility, biodegradability, enzymatic resistance, and good processibility make polypeptoid a promising material for biotechnological applications. With decyl groups as hydrophobic side chains, HMPs interact with lipid bilayers by inserting the hydrophobes into the lipid bilayers through hydrophobic interaction. The hydrophobe insertion results in the disruption of lipid bilayers and the formation of lipid bilayer fragments containing HMPs and HMP-lipid complexes depending on HMP-to-lipid ratio. These polymer-lipid “rafts” can attach to the bare lipid bilayers forming close-spaced multilamellar structures, with HMPs connecting across the adjacent lipid bilayers. Also, HMP-lipid rafts can significantly increase the solubility of sorafenib in aqueous solution through hydrophobic interaction. The ability to assemble to lipid bilayers and to encapsulate hydrophobic drugs demonstrate the promise of HMP-lipid rafts in the application of drug delivery. The second topic is the rapid fabrication of hollow and yolk-shell functional materials through an aerosol assisted synthesis. Materials with hollow and yolk-shell structures have potentials in many applications, such as catalysis and energy storage. But the fabrication of such materials often suffers time-consuming and tedious procedures, which limits the practical application of these materials. We first demonstrated the rapid fabrication of hollow and yolk-shell Fe2O3 microspheres for enhanced photo-Fenton reactions. The placement of iron salts on the external surface of a carbonaceous microsphere generated from an aerosol droplet allows the formation of a Fe2O3 capsule by calcination, where colloid particles can be encapsulated. The Fe2O3 microspheres show significant enhancement in the photo-Fenton reaction. We then illustrated the fabrication of hollow and cage-like mesoporous Fe2O3/SiO2 microspheres. Through salt bridge effect, iron salts and cationic surfactants form colloidal aggregates which are locked within a rapidly formed SiO2 shell during the aerosol process. Sucrose as a pore generating agent leads to the formation of mesopores in the shell, which was proven favored features for CO2 capture. / 1 / Yueheng Zhang

With the need for the development of renewable sources of energy, organic photovoltaic (OPV) has been attracting researchers’ interest for the past decades. This solar technology utilizes carbon-based semiconductors instead of conventional inorganic materials which enables inexpensive, lightweight and flexible roll-to-roll fabrication of large area solar panels with a very short energy payback time. Device efficiencies have rapidly increased to above 18% within the last few years, becoming competitive with solar technologies available on the market. However, research has been focused on the maximization of efficiencies at all cost leading to synthetically challenging materials and processes with negligible commercial scalability. In this thesis, silicon phthalocyanines (SiPcs), synthetically facile molecules most known for their extensive use as dyes and pigments in the industry, were employed as low-cost and scalable active materials for OPV devices. We also report the use of layer-by-layer deposition of the donor and acceptor layer providing a more scalable process compared to the conventional blended heterojunction morphology. Different SiPc derivatives, both soluble and non-soluble, were used as acceptors, paired with different donor polymers (P3HT, PCDTBT, and PBDB-T) and integrated into hybrid evaporation-solution and all-solution layer-by-layer OPV devices. Significant device engineering and optimization was performed through the investigation of several processing conditions such as solvent choice, spin-speed, concentration and annealing temperature/time. In particular, all-solution processed SiPc-based bilayer OPV devices achieved PCEs above 3% with Voc above 1 V, which was similar to performances of corresponding BHJ OPVs. SiPc derivatives also demonstrated their ability to act as electron transport layers in perovskite solar cells. These results further establish the potential of SiPc derivatives as active materials in different solar technologies, while promoting the use of the bilayer structure in OPV devices.

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