Self-Assembly of Nonionic Surfactants
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The self-assembly of nonionic surfactants in aqueous solution has been extensively investigated because of its various applications. The nonionic surfactants under research here are all Guerbet hydrophobic C10 branched alkyl chain, with different lengths of poly(ethylene oxide) (PEO) and with or without propylene oxide units. Lutensol® surfactants XP, XL series and ES series are supplied from BASF. XL, and ES series incorporate propylene oxide (PO) units in the surfactant chain Their micellization properties are investigated in aqueous solution in this thesis. The critical micellization concentration (CMC) was determined by pyrene fluorescence spectroscopy at 22 and 50°C. The Gibbs free energy, enthalpy and entropy of micellization were calculated from the CMC data and used to analyze the contributions of the surfactant chemistry. The nonionic surfactants in this research were all slightly temperature sensitive. Compared with compositionally similar surfactants, branched alkyl chain CiEOj and CiPOnEOj surfactants had higher CMC than linear CiEOj and CiPOnEOj surfactants. The PO group drives for micellization in self-assembly process of branched alkyl chain CiEOj and CiPOnEOj surfactant. Cloud point and relative viscosity experiments were supplied to investigate the thermodynamic properties.