Synthesis of Nanocapsules via Miniemulsions Using Bio-derived Functional Surfactants
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This thesis focuses on the synthesis of nanocapsules via the miniemulsion approach using three different novel surfactants. Maleyl chitosan (MCS) was successfully synthesized with different degree of substitution. However, relative to chitosan, MCS only showed slight improvement on the surface activity, leading to the formation of nanocapsules with sizes around 210 nm. On the other hand, hydrophobically modified MCS, obtained by treatment of MSC with 1-dedocanethiol via thiol-ene reaction, could result in smaller nanocapsules with sizes of about 100 nm, indicating an increase in surface activity after incorporating hydrophobic hydrocarbon chains with MCS. Fatty acid functionalized sugar (FFS) surfactant was synthesized by linking linoleic acid and gluconolactone with an ethylenediamine-based spacer via two amidation reactions. The corresponding miniemulsions were prepared at 85 °C to fabricate nanocapsules due to the poor solubility of FFS at room temperature (21 °C). For miniemulsions without optimal amounts of surfactants, precipitants were observed after cooling miniemulsions to room temperature. However, miniemulsions with optimal amounts of surfactant would not form precipitants during cooling, and could lead to nanocapsules with sizes down to 128 nm. Nanodroplets with docoane (C 22 )-based as crystallized solid cores and hexadecane (C 16 )-based liquid cores were prepared via miniemulsions using monomer and cross-linker surfactants functionalized with vinyl groups, respectively. With the same total amounts of surfactants, nanodroplets with liquid cores showed smaller sizes because of the low viscosity of C 16 relative to C 22 , while the nanodroplets with solid cores demonstrated lower polydisperse index (PDI) suggesting the higher stability of crystallized miniemulsion possibly due to the reduced interfacial mobility of surfactant molecules resulting in inhibited destabilization of nanodroplets.