### Abstract

Structure and transport properties of an oil-in-water microemulsion of weakly charged spherical micelles were studied experimentally using viscosity, NMR self-diffusion, and static and dynamic light scattering as well as theoretically by Brownian dynamics and Monte Carlo simulations and the Poisson-Boltzmann equation. The micelles contain decane covered by the nonionic surfactant pentaethylene glycol dodecyl ether (C_{12}E_{5}) and the ionic surfactant sodium dodecyl sulfate. The system has a constant surfactant-to-oil ratio, and the total volume fraction of surfactant and oil, Φ, is varied between 0.01 ≤ Φ ≤ 0.46. The micelles were made weakly charged by replacing a small fraction (0.01, 0.04, and 0.06) of the nonionic surfactant with ionic surfactant, retaining the micellar size. Comparison between self-diffusion and viscosity coefficients measured as a function of concentration showed that the system obeys the generalized Stokes-Einstein relation at lower micellar concentrations. At higher micellar concentrations, a slightly modified equation can be used upon the addition of an extra frictional factor due to stronger interactions. The collective diffusion coefficient shows a maximum as a function of the volume fraction. This result is in good agreement with predictions based on a charged hard-sphere model with hydrodynamic interactions. Other static and dynamic properties such as osmotic pressure, osmotic compressibility, and self-diffusion coefficient were obtained theoretically from simulations based on a charged-sphere model. The static and dynamic properties of the charged hard-sphere model qualitatively describe the behavior of the charged microemulsion micelles. At high volume fractions, Φ > 0.1, the agreement is quantitative, but at Φ < 0.1 the effect of the charge is smaller than what is predicted from the model.

Original language | English (US) |
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Pages (from-to) | 1043-1053 |

Number of pages | 11 |

Journal | Langmuir |

Volume | 17 |

Issue number | 4 |

DOIs | |

State | Published - Feb 20 2001 |

Externally published | Yes |

### ASJC Scopus subject areas

- Materials Science(all)
- Condensed Matter Physics
- Surfaces and Interfaces
- Spectroscopy
- Electrochemistry

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## Cite this

*Langmuir*,

*17*(4), 1043-1053. https://doi.org/10.1021/la0011883