Doctor of Philosophy (PhD)
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This study focuses on developing non-aqueous high internal phase emulsions (HIPEs) based on ionic liquid analogues, deep-eutectic solvents (DES), through a green approach and by a free-radical polymerization mechanism. The inclusion of different monomer types either (meth)acrylates: methacrylate (MMA), stearyl methacrylate (SMA), and lauryl acrylate (LA); or styrene divinylbenzene (StDvB), as continuous phases conferred different structural features leading to different bulk properties. Several parameters that affect DES-based HIPEs morphology and stability were explored including monomer tail lengths (C1-C18) and chemical nature (methacrylic-acrylic), internal phase viscosity mediated by different types of DESs, and surfactant type and quantity used. The use of DESs enabled the development of a greener process and allowed for DESs’ component recyclability. Additionally, the absence of water through the synthesis of poly(HIPEs) opens access to new synthetic routes that were once limited due to water sensitivity or temperature requirements including HIPE in vacuo polymerization. Detailed knowledge of HIPE flow properties and their reaction kinetics are necessary to ensure their adequate processing and scalability while mantaining optimum material properties. A second portion of the study delves into HIPE stability,that is the ability of a HIPE to withstand phase separation unperturbed and under ambient conditions, based on the type of monomer’s chemistry and using rheology as a defining tool. In this case, methacrylic monomers presented a higher yield point over acrylic monomers. Similarly, monomers with long hydrocarbon tails exhibited higher yield points than those with shorter tails. Stress-sweep studies enabled HIPE surfactant optimization increasing mechanical properties and decreasing potential production costs. Polymerization was quantified through chemorhelogical analysis presenting three regimes; an induction period, polymerization, and final curing. Activation energies were in agreement with expected values for specific monomers where acrylic monomers had greater reactivity than methacrylic monomers. Initiation energy was estimated to be 160 ± 8 KJ mol-1, which is higher than acrylic bulk polymerization, but within the range of polymerization on a solid matrix. This difference in energies is hypothesized to be the composite effect of initiator confinement within a thin continuous phase, a highly viscous internal phase, and a decrease in surfactant cloud point due to DES’s ionicity.
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Carranza, Arturo, "Deep-Eutectic Solvents as Delivery Vehicles in The Synthesis of Non-Aqueous high Internal Phase Emulsion Templated Functional Macroporous Nanocomposites and Their Application as Selective fuel Sorbents and tissue Scaffolds" (2016). LSU Doctoral Dissertations. 4366.
Pojman, John A.