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    Synthesis, Characterization, and Physicochemical Performance of Nonionic Surfactants via PEG Modification of Epoxides of Alkyl Oleate Esters
    (Washington, DC : ACS Publ., 2023) Ogunjobi, Joseph K.; Farmer, Thomas J.; Clark, James H.; McElroy, Con Robert
    The synthesis of surfactants from fatty acid esters via epoxide chemistry has been known for its accompanying challenges, which usually involve the use of toxic homogeneous catalysts in the ring-opening reaction step and generation of many side reaction products. This paper presents environmentally benign routes to a library of nonionic surfactants via a three-step synthesis involving transesterification of methyl oleate to alkyl oleates, epoxidation of the oleate alkene, and solventless heterogeneously catalyzed ring opening of the epoxides with poly(ethylene glycols) of varying chain length under a short reaction time (60 min). The processes were highly atom efficient and afforded a minimum surfactant yield of 80% with limited or negligible side reaction products. The intermediate molecules and synthesized surfactants were purified and comprehensively characterized, including physicochemical measurements: dynamic surface tension and equilibrium surface tension. Additionally, the hydrophilic-lipophilic balance (HLB) concept was used to comprehensively scan through the polarity behaviors of the surfactants’ head and tail in solution as a prediction of their end use. The results showed that surfactants have a critical micelle concentration (CMC) lower than 0.1 mg/ml as the alkyl oleate increases in length from ethyl to decyl and that the lower-molecular-weight surfactants reached equilibrium faster than the higher-molecular-weight surfactants. HLB results showed that the surfactants can be applied as oil-in-water emulsifiers, detergents, solubilizers, and wetting agents. In general, the synthesized surfactants potentially possess switchable properties for use in industrial formulations, as the alkyl chain length and the ethylene oxide number in the surfactant’s structure are varied.
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    Cure kinetics of epoxy nanocomposites affected by MWCNTs functionalization: A review
    (Boynton Beach, Fla. : Hindawi, 2013) Saeb, M.R.; Bakhshandeh, E.; Khonakdar, H.A.; Mäder, E.; Scheffler, C.; Heinrich, G.
    The current paper provides an overview to emphasize the role of functionalization of multiwalled carbon nanotubes (MWCNTs) in manipulating cure kinetics of epoxy nanocomposites, which itself determines ultimate properties of the resulting compound. In this regard, the most commonly used functionalization schemes, that is, carboxylation and amidation, are thoroughly surveyed to highlight the role of functionalized nanotubes in controlling the rate of autocatalytic and vitrification kinetics. The current literature elucidates that the mechanism of curing in epoxy/MWCNTs nanocomposites remains almost unaffected by the functionalization of carbon nanotubes. On the other hand, early stage facilitation of autocatalytic reactions in the presence of MWCNTs bearing amine groups has been addressed by several researchers. When carboxylated nanotubes were used to modify MWCNTs, the rate of such reactions diminished as a consequence of heterogeneous dispersion within the epoxy matrix. At later stages of curing, however, the prolonged vitrification was seen to be dominant. Thus, the type of functional groups covalently located on the surface of MWCNTs directly affects the degree of polymer-nanotube interaction followed by enhancement of curing reaction. Our survey demonstrated that most widespread efforts ever made to represent multifarious surface-treated MWCNTs have not been directed towards preparation of epoxy nanocomposites, but they could result in property synergism.