Using spin polarised positive muons for studying guest molecule partitioning in soft matter structures

摘要: Fully polarised positive muons substituted for protons in organic free radicals can be used as spin labels which reveal information about the structure, dynamics and environment of these radicals. In applications via technique avoided-level-crossing muon resonance (ALC-μSR), has been to study partitioning phenyl alcohols lamellar phase colloidal dispersions a cationic dichain surfactant. Here we describe experimental permits highly sensitive spectroscopy previously demonstrated surfactant mixtures. We also demonstrate its capability cosurfactant molecules bilayers order elucidate main factors contribute ordering at interfaces. The takes advantage combining with an electron hydrogen-like atom that is called muonium. This attaches group, forming cyclohexadienyl-type radical contains label, providing excellent probe even very low alcohol concentrations. position one type resonance, on basis spectroscopic selection rules denoted Δ0, related solvent polarity radicals’ environment. results derived from Δ0 measurements systematic trend where increasing chain length deeper immersion ring into bilayer OH group anchored interface. addition, data suggest partial penetration water bilayer. Furthermore, ensuing second (called Δ1, dependent upon degree confinement within aggregate structure) indicates not only resides anisotropic environment, (i.e. host molecule unable undergo full 3-D reorientation timescale 50 ns), but line widths indicate are undergoing fast rotation particular axis, this instance first C–C substituent bond ring. Detailed analysis Δ1 shapes suggests other types motion involving above axis present. At room temperature, hydrocarbon chains double layers form state commonly referred Lβ phase, motions alkyl effectively frozen out. These melt heating over temperature range solution composition (ca. 51 67 °C), all cases leading liquid-like disordered regime whilst retaining overall structure (and termed Lα). Above Lα/Lβ transition tracer reside bilayer, below depending their water–oil solubility) they completely or partly expelled. interpretation further supported by Heisenberg exchange experiments. water–bilayer reflects both typical classical nonclassical hydrophobic solvation alcohols.