Abstract
Proton NMR measurements were conducted on a U-type model quaternary nonionic microemulsion containing varying amounts of water and having a fixed weight ratio of surfactant [octaethylene glycol mono-n-dodecylether; C12(EO)8], cosurfactant (pentanol), and oil (dodecane). Chemical shift and T, relaxation time data were used to obtain information about the microemulsion properties and structure. A slow exchange was observed between the hydroxyls of water, C12(EO)8, and pentanol in microemulsions containing up to 10 wt% water. This is precedence of the hydroxyl-water interaction over hydration of the ethylene oxide (EO) groups of the surfactant. The fraction of bound water was calculated from the chemical shift and T1 data. For the model system, chemical shift measurements indicated an inversion from W/O to O/W microemulsion at about 55-60 wt% water, in agreement with the microviscosity values evaluated from T1 data: 1.1 cP (55 wt% water) compared to 4.7 cP (30 wt% water) and 12.7 cP (10.7 wt% water). The irregularities in the monotonic dependence of the chemical shifts on water content in the microemulsion at 18 and 55 wt% water were interpreted to possibly reflect structural changes that took place in solution.
Original language | English |
---|---|
Pages (from-to) | 282-295 |
Number of pages | 14 |
Journal | Journal of Colloid and Interface Science |
Volume | 188 |
Issue number | 2 |
DOIs | |
State | Published - 15 Apr 1997 |
Keywords
- H NMR
- C(EO)
- Chemical shifts
- Microviscosity
- Nonionic microemulsion
- Pentanol
- Proton water
- Self-diffusion coefficients
- T relaxation