STRUCTURE OF THE ISOTROPIC, NEMATIC, AND LAMELLAR PHASE OF A SOLUTIONOF TETRAMETHYLAMMONIUM PERFLUORONONANOATE IN D2O

A 30% by weight solution of tetramethylammonium perfluorononanoate in D2O (TMAHFN; C8F17COON-(CH3)(4)) is in a lamellar state below 33 degre es C. In this state the repeat distance and the thickness of the perfl uoronated part of the micellar lamellae are around 7.11 and 2.14 nm, r espectively, In the presence of a strong magnetic field of 2.0 T a slo w reduction of the sample temperature from 40 degrees C (isotropic pha se) via 34 degrees C (nematic phase) down to 25 degrees C gives a stro ng alignment of the nematic and lamellar liquid crystalline phases. By small angle neutron scattering (SANS) and small angle X-ray scatterin g (SAXS) experiments, an order parameter, the mean scattering length d ensity across the lamellae, the structure factor related to the one-di mensionality of the lamellar phase, and information about the perforat ion of the lamellae could be extracted. A model taking into account al l these effects quantitatively describes the experimental scattering i ntensity distribution in reciprocal space (($) over right arrow Q spac e) accessible in our experimental setup. Furthermore, for the nematic phase we can extract detailed data on the anisotropic correlation betw een neighboring discotic micelles. The scattering intensity distributi on of the isotropic phase can be described quite satisfactorily again assuming disklike micelles, where the perfluoronated part of the micel le has a thickness of 2.4 nm and a radius of about 3.0 nm.