Revealing New Structural Insights from Surfactant Micelles through DLS, Microrheology and Raman Spectroscopy
Date
2015-06-19
Journal Title
Journal ISSN
Volume Title
Publisher
MDPI AG
Abstract
The correlation between molecular changes and microstructural evolution of
rheological properties has been demonstrated for the first time in a mixed
anionic/zwitterionic surfactant-based wormlike micellar system. Utilizing a novel
combination of DLS-microrheology and Raman Spectroscopy, the effect of electrostatic
screening on these properties of anionic (SLES) and zwitterionic (CapB) surfactant mixtures
was studied by modulating the NaCl concentration. As Raman Spectroscopy delivers
information about the molecular structure and DLS-microrheology characterizes viscoelastic
properties, the combination of data delivered allows for a deeper understanding of the
molecular changes underlying the viscoelastic ones. The high frequency viscoelastic
response obtained through DLS-microrheology has shown the persistence of the Maxwell
fluid response for low viscosity solutions at high NaCl concentrations. The intensity of the
Raman band at 170 cm−1 exhibits very strong correlation with the viscosity variation. As this
Raman band is assigned to hydrogen bonding, its variation with NaCl concentration
additionally indicates differences in water structuring due to potential microstructural
differences at low and high NaCl concentrations. The microstructural differences at low and
high NaCl concentrations are further corroborated by persistence of a slow mode at the
higher NaCl concentrations as seen through DLS measurements. The study illustrates the
utility of the combined DLS, DLS-optical microrheology and Raman Spectroscopy in
providing new molecular structural insights into the self-assembly process in complex fluids.
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Citation
Amin, Samiul, et al. "Revealing new structural insights from surfactant micelles through DLS, microrheology and Raman spectroscopy." Materials 8.6 (2015): 3754-3766.