Partitioning of Small Amphiphiles at Surfactant Bilayer/Water Interfaces:  An Avoided Level Crossing Muon Spin Resonance Study

Abstract

The temperature-dependent variation of local environment and reorientation dynamics of the small amphiphile 2-phenylethanol in lamellar phase dispersions of the dichain cationic surfactants, 2,3-diheptadecyl ester ethoxypropyl-1,1,1-trimethylammonium chloride (DHTAC) and dioctadecyldimethylammonium chloride (DODMAC), and the nonionic surfactant, tetra(ethylene glycol) n-dodecyl ether (C12E4), have been determined using avoided level crossing muon spin resonance spectroscopy (ALC-muSR). For cosurfactant radicals the hydrophobic or hydrophilic character of the surrounding media can be determined from their magnetic resonance signatures. Comparison of the three different bilayer-forming surfactant systems shows that the ALC-muSR technique is able to distinguish both major and subtle differences in the partitioning of the cosurfactant radicals between the different systems.

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

“…Such a dependence results in shifts of the resonance fields, as plotted in Figure 21 for the three isomers of the radicals derived from the n = 3 alcohol. The assignment of the lines to specific isomers is analogous to that of the radicals derived from 2-phenylethan-1-ol [84,98].…”

“…Such spin labelled tracer radicals have recently been used as probes of soft condensed matter [6,[83][84][85][86]. Adopted from [83].…”

“…Hence, the muon spin label is considered a nearly nonperturbing probe [84]. Such muoniated radicals act as spectators of their local environments, in particular of the polarity, and of the changes in the properties of the colloidal systems.…”

“…This system forms a simple (i.e., non-interdigitated) lamellar phase structure composed of lipid bilayers consisting of cationic dichain surfactant molecules DHTAC separated by water as determined by SAXS [84]. The surfactant amphiphiles aggregate to bilayers of ca.…”

“…They self-assemble into regularly spaced lamellar phase structures of ca. 30.2 ± 0.4 nm periodicity in the L β state [84]. This system was chosen because the solution state of the surfactant (and therefore bilayer properties) can be manipulated simply by changing the temperature.…”