Amphiphiles, molecules that possess both hydrophilic and hydrophobic moieties, are architecturally simple molecules that can spontaneously self-assemble into complex hierarchical structures from lower to higher dimensions either in the bulk phase or at an interface. Recent developments in multifunctional nanostructure design using the advanced concept of nanoarchitectonics utilize this simple process of assembly. Amphiphilic self-assemblies involving lipids or proteins mimic the structure of biological systems, thus highlighting the necessity of a fundamental physical understanding of amphiphilic self-assembly towards a realization of the complex mechanisms operating in nature. Herein, we describe self-assembled microstructures of biocompatible and biodegradable tetraglycerol lauryl ether (C12G4) nonionic surfactant in an aqueous solvent system. Temperature-composition analyses of equilibrium phases identified by using small-angle x-ray scattering (SAXS) provide strong evidence of various spontaneously self-assembled mesostructures, such as normal micelles (Wm), hexagonal liquid crystal (H1), and reverse micelles (Om). In contrast to conventional poly(oxyethylene) nonionic surfactants, C12G4 did not exhibit the clouding phenomenon at higher temperatures (phase separation was not observed up to 100 °C), demonstrating the greater thermal stability of the self-assembled mesophases. Generalized indirect Fourier transformation (GIFT) evaluation of the SAXS data confirmed the formation of core-shell-type spherical micelles with a maximum dimension ca. 8.7 nm. The shape and size of the C12G4 micelles remained apparently unchanged over a wide range of concentrations (up to 20%), but intermicellar interactions increased and could be described by the Percus-Yevick (PY) theory (after Carnahan and Starling), which provides a very accurate analytical expression for the osmotic pressure of a monodisperse hard sphere.

We report the percolation behavior of nonionic surfactant reverse micelles (RMs) composed of sorbitan laurate (Span20) and poly(oxyethylene) sorbitan monooleate (Tween80) in isopropyl myristate (IPM) in presence of a trace amount of water and electrolyte (KCl). Abrupt increase of conductivity above 20°C for oil/surfactant = 8/2 and Span20/Tween80 = 3/2 composition is an indication of the typical percolation behavior. The dynamic percolation behavior was suggested based on the scaling analysis of the conductivity change around the percolation temperature. Contrary to the ionic surfactant RMs, conductivity maxima was observed in the present nonionic RM system. Small-angle X-ray scattering (SAXS) data showed sphere-to-rod-type RM microstructure transition with increasing temperature in the lower temperature region. On the other hand, RM shrunk in the high temperature region due to dehydration of poly(oxyethylene) chains. It is anticipated that this characteristic feature of nonionic surfactant led to the depercolation at high temperatures.Keywords: Reverse micelle | Percolation | Conductivity Self-assembly has been recognized as a ubiquitous aspect of modern chemistry. 13 Reverse micelle (RM) or w/o microemulsion formed in nonpolar solvents, which is one of the surfactant self-assembled structures, has not been as extensively studied as the normal micelles in aqueous systems, in spite of several promising applications such as reaction media for nanomaterial preparation, chemical and biological reactions. Among the RM studies, electrical percolation behavior in ionicsurfactant-based systems has been extensively studied.46 Although RMs in nonaqueous systems show limited conductivity at low temperature or at low water concentration, the conductivity abruptly increases after a threshold temperature or water content. It is generally believed that such electrical percolation occurs because of clustering or transient fusion of RMs,7,8 which allows transfer of ions in the water pool of RMs. Percolation behavior in ionic surfactant (especially Aerosol OT) RM systems has been broadly investigated over the decades. However, percolation in nonionic surfactant RMs have been sparsely studied. 9,10 We have extensively studied the shape, size, and internal structure of nonionic surfactant RMs in surfactant/ oil system for the last ten years. We have successfully underlined the fundamental understanding of the microstructure and morphology control of nonionic surfactant RMs. 1113 Based on a decade-long experience on RMs, we aimed to study electrical percolation behavior of nonionic surfactant RM systems.Nonionic surfactants used in the present study, poly(oxyethylene) sorbitan monooleate (Tween80) and sorbitan laurate (Span20), were purchased from Sigma-Aldrich Co., and Tokyo Chemical Industry (TCI) Co., respectively. We chose those surfactants because it has been reported that nonionic reverse micelles or microemulsions can be formed using those surfactants.14,15 Isopropyl myristate (IPM) and potassium chloride (KCl) were purchas...