An ALC study of spin exchange of a muoniated cosurfactant in lamellar phase surfactant dispersions

The Avoided Level Crossing muon spin resonance (ALC-μSRμSR) technique has been used to measure the Heisenberg spin exchange rate between the Mu adducts of 2-phenylethanol (PEA) and Ni2+Ni2+ in a concentrated lamellar phase dispersion composed of the dichain cationic surfactant 2,3-diheptadecyl ester ethoxypropyl-1,1,1-trimethylammonium chloride (DHTAC) and water. Ni2+Ni2+ is only dissolved in the aqueous phase, therefore information about the local environment of the PEA can be extracted from the spin exchange rate. In the high-temperature (Lα)(Lα) phase the spin exchange is very slow, revealing that PEA preferentially resides in the headgroup regime of the surfactant. In the low-temperature (Lβ)(Lβ) phase the spin exchange is diffusion controlled, because the PEA is expelled into the water region between the bilayers.