The microstructure of U-type systems (9), as well as Proton NMR measurements were conducted on a U-type model the structure of micellar solutions, have been treated quite quaternary nonionic microemulsion containing varying amounts successfully by NMR methods (10)(12). The application of of water and having a fixed weight ratio of surfactant [octaethyl-NMR techniques to micellar systems stems from the fact that ene glycol mono-n-dodecylether; C 12 (EO) 8 ], cosurfactant (pentathe formation of organized surfactant structures in solution is nol), and oil (dodecane). Chemical shift and T 1 relaxation time accompanied by changes in NMR parameters (13). Chemidata were used to obtain information about the microemulsion cal shift experiments were done in early studies while nowaproperties and structure. A slow exchange was observed between the hydroxyls of water, C 12 (EO) 8 , and pentanol in microemulsions days additional parameters (like T 1 , T 2 relaxation times and containing up to 10 wt% water. This is precedence of the hydroxylself-diffusion coefficients) are also being measured ( ). water interaction over hydration of the ethylene oxide (EO) NMR techniques can provide information about solubilizagroups of the surfactant. The fraction of bound water was calcution equilibria, aggregate size and shape, hydration of polar lated from the chemical shift and T 1 data. For the model system, heads, solution structure, etc. (15). Special attention has chemical shift measurements indicated an inversion from W/O to been paid to the investigation of the structure and state of O/W microemulsion at about 55-60 wt% water, in agreement water in microemulsions, using NMR techniques (16)(17)(18) with the microviscosity values evaluated from T 1 data: 1.1 cP ( as well as FTIR (20) and calorimetric methods 21,. 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 We are currently engaged in studying water solubilization the chemical shifts on water content in the microemulsion at 18 in microemulsions, with the intention of developing a miand 55 wt% water were interpreted to possibly reflect structural croemulsion-based fire-resistant hydraulic fluid (23). The Uchanges that took place in solution. ᭧ 1997 Academic Press type system n-dodecane/C 12 (EO) 8 /1-pentanol/ water was Key Words: nonionic microemulsions; C 12 (EO) 8 ; pentanol; 1 H chosen by us as a model because of its typical features, NMR; proton water; chemical shifts; self-diffusion coefficients; T 1 common with successful formulations of the designed hyrelaxation; microviscosity. draulic fluid: 1. Use of an alcohol as a cosurfactant in a nonionic for the degree of Doctor in Applied Chemistry of The Hebrew University of study and show that in certain circumstances a great deal of Jerusalem, Israel.