The electric conductivity of the lamellar smectic, the micellar nematic, and the isotropic micellar solution of ammonium perfluorononanoate in water

Abstract

We present electric conductivity measurements on a mixture of 25 wt. % ammonium perfluorononanoate in H₂O. The system shows a lamellar smectic phase up to 26.3 °C, followed by a nematic phase consisting of disk‐like aggregates, which at 34.2 °C transforms to an isotropic micellar solution. The relative anisotropy of the conductivity increases from ∼0.07 at 34 °C to ∼0.29 at 26.3 °C. There is no discontinuity, but a small change in slope occurs at the nematic–smectic transition. The experimental results, interpreted in terms of structural models for the two anisotropic phases, shows that the aggregates in the nematic phase have diameter to thickness ratios, decreasing from about 8.3 at the lamellar to nematic transition, to about 4.0 at the transition to the isotropic phase. We estimate that about 30% of the total area are disrupted by holes or channel‐like defects. The results are in agreement with previous studies on a mixture of decylammonium chloride/NH₄Cl/H₂O. It is also indicated that increasing the size of the aggregates increases the binding of the counterions to the aggregates.