STRUCTURE OF THE ISOTROPIC AND LAMELLAR PHASE OF A SOLUTION OF TETRAMETHYLAMMONIUM PERFLUORONONANOATE IN D2O (REPRINTED FROM J PHYS CHEM, VOL 99, PG 14450-14467, 1995)

A 30% by weight solution of tetramethylammonium perfluorononanoate in D2O (TMAHFN; C8F17COON(CH3)(4)) is in a lamellar state below 33 degree s C. In this state the repeat distance and the thickness of the perflu oronated part of the micellar lamellae are around 7.11 and 2.14 nm, re spectively. in the presence of a strong magnetic field of 2.0 T a slow reduction of the sample temperature from 40 degrees C (isotropic phas e) via 34 degrees C (nematic phase) down to 25 degrees C gives a stron g alignment of the nematic and lamellar liquid crystalline phases. By small angle X-ray scattering (SAXS) experiments, the mean scattering l ength density across the lamellae, the structure factor related to the one-dimensionality of the lamellar crystal, and information about the perforation of the lamellae could be extracted. The scattering intens ity distribution of the isotropic phase can be described quite satisfa ctorily assuming disklike micelles, where the perfluoronated part of t he micelle has a thickness of 2.4 nm and a radius of about 3.0 nm.