PHASE-DIAGRAM OF THE TETRAMETHYLAMMONIUM HEPTADECAFLUORONONANOATE (TMAHFN) D2O SYSTEM AS DETERMINED BY H-2 AND N-14 NMR/

The high resolution phase diagram of the tetramethylammonium heptadeca fluorononanoate (TMAHFN)/D2O system has been mapped out using H-2 and N-14 NMR spectroscopy. The N-14 quadruple splittings are more than an order of magnitude larger than corresponding H-2 splittings, while the line widths are only two to three times larger. Thus, N-14 NMR offers an order of magnitude improvement over H-2 NMR in the resolution of t he spectra from coexisting phases. The H-2 spectra of samples in bipha sic regions are often complicated by chemical exchange of D2O molecule s between coexisting phases, particularly at low TMAHFN concentrations . Analysis of the H-2 line shapes of a TMAHFN/D2O sample with a weight fraction of TMAHFN of 0.230 obtained at various times following cooli ng of the sample into the isotropic/nematic biphasic region shows that the mean diameter for the dispersed nematic droplet grows from about 7 to about 26 mum over a period of 2 h. At a mean droplet size of 7 mu m the exchange of TMA+ ions between the coexisting phases is slow on t he NMR time-scale and exchange effects are not observed in N-14 spectr a. The TMAHFN/D2O phase diagram exhibits the generic form of those of the CsPFO/water and APFO/D2O systems, which are the only other systems composed of stable discotic micelles for which high resolution phase diagrams are currently available, but the nematic phase is displaced t o smaller TMAHFN concentrations. Specifically, a discotic nematic phas e N(D)+, intermediate between an isotropic micellar phase I and a lame llar phase L, exists for weight fractions of TMAHFN between 0.149 (the ta = 0.105) and 0.420 (theta = 0.325) and temperatures between 277.3 a nd 327.6K.