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Avoided level crossing muon spin resonance (ALC-μSR) has been used to study the reorientational dynamics of muon-spin-labelled 2,4,6-trimethylbenzoate (246TMB−) counterions and their interaction with DODMAC (dioctadecyldimethylammonium chloride) bilayers in the Lα and Lβ liquid crystalline states. The muoniated radical anion formed by the addition of muonium to the secondary carbons of the aromatic ring of 246TMB− is used as a local spin probe. The muon and methylene proton hyperfine parameters and the electron spin relaxation rate (λe) of the muoniated spin probe were determined as a function of temperature by modelling the ALC-μSR spectra with Monte Carlo numerical simulations. The observation of a Δ1 resonance indicates that 246TMB− is undergoing anisotropic motion and doesn't reside in the aqueous layer in either the Lα and Lβ phases. The lack of an abrupt change in the hyperfine parameters or λe when the system goes from the Lβ to the Lα lamellar liquid crystalline phases suggests that 246TMB− is located at the oil–water interface rather than within the bilayer. The hyperfine parameters indicate that 246TMB− is undergoing large amplitude reorientational motion about a preferred orientation resulting from the bilayer's electric field. The interaction between 246TMB− and the bilayer decreases and the amplitude of the wobbling-in-a-cone motion increases with increasing temperature. The temperature dependence of the electron spin relaxation rate indicates the barrier to reorientation is 41.7 kJ mol−1. [ABSTRACT FROM AUTHOR]

Avoided level-crossing muon spin resonance (ALC-μSR) has been used to study the dynamics and local environment of spin probes formed by muonium (Mu) addition to 2-phenylethanol (PEA) and limonene (1-methyl-4-(1-methylethenyl)-cyclohexene) in an aqueous dispersion of the nonionic surfactant C12E4 (tetra(ethylene glycol) n-dodecyl ether). The spin probes derived from both cosurfactants reside within the micelles in the L1 phase and the bilayers in the Lα phase rather than in the aqueous region. The local polarity measured by the different isomers of the Mu adducts of PEA suggests there is a water gradient within the micelles and bilayers. Slow rotation of the micelles broadened the Δ1 resonances with increasing temperature in the L1 phase while narrower Δ1 resonances were observed in the Lα phase due to the rapid rotation of the spin probes around a preferred axis, which was wobbling within a cone. [ABSTRACT FROM AUTHOR]

Avoided level crossing muon spin resonance (ALC-μSR) has been used to study the cyclohexadienyl-type radicals produced by the addition of muonium (Mu) to the discotic liquid crystal HAT6 (2,3,6,7,10,11-hexahexyloxytriphenylene) in the crystalline (Cr) phase, the hexagonal columnar mesophase (Colh) and isotropic (I) phase. In the Cr phase unpaired electron spin density can be transferred from the radical to neighboring HAT6 molecules depending on the overlap of their π-systems and hence on the relative orientation of the triphenylene rings. The two Δ1resonances in the ALC-μSR spectra of the Cr phase indicate that the neighboring HAT6 molecules have two preferred orientations with respect to the radical: one which results in negligible spin density transfer and a second where 17% of the unpaired spin density is transferred. The ALC-μSR spectra in Colhand I phases are substantially different from those of the Cr phase in that there are two narrow resonances superimposed on an extremely broad and intense resonance. The narrow resonances are due to highly mobile radicals located in the aliphatic region between the columns and the broad resonance is due to radicals incorporated within the columns of HAT6 molecules. The large width and amplitude of this resonance indicates that the radicals within the columns are undergoing rapid electron spin relaxation but the mechanism that causes this relaxation is unknown. [ABSTRACT FROM AUTHOR]