ESR LINE-SHAPES IN LYOTROPIC SYSTEMS - THE MICELLAR AND LIQUID-CRYSTALLINE PHASES OF THE DODECYLTRIMETHYLAMMONIUM CHLORIDE WATER-SYSTEM

ESR spectra of a paramagnetic spin probe, 5-doxylstearic acid, solubilized in the micellar and lyotropic liquid-crystalline phases of the dodecyltrimethylammonium chloride (C12TACl)/water system have been recorded and analyzed by employing spectral line shape simulation techniques. The partial averaging of the magnetic interactions by fast local anisotropic motions in the aggregates has been accounted for by the introduction of scaled magnetic interactions, quantified by an order matrix. The effects of aggregate rotation and amphiphile surface diffusion in phases with curved aggregates are simulated by rotational diffusion models. The spectra from the micellar phase are well reproduced with an isotropic rotational diffusion model, giving reasonable estimates of the micellar size. In the hexagonal phase, with increasing water content and temperature, the ESR spectrum undergoes a transition from a static limit, similar to the spectrum from the lamellar phase, through an intermediate motional region, to a new static limit consistent with rapid lateral diffusion around the cylinder aggregates. The transition in line shape of the hexagonal phase spectra is qualitatively reproduced by the rotational diffusion of a highly anisotropic prolate symmetric top. © 1990 American Chemical Society.