Associate Professor, Graduate School of Science and Technology, Hirosaki University, Japan

Speech Title: Unique Aggregation Behavior and Functions of Amphiphiles Having Mesogenic and Ethoxylated Alkyl tails in Water
Abstract: Amphiphiles form various kinds of micelles and liquid crystals (i.e. lyotropic assemblies) in solvents, depending on its solvophobic and solvophilic interactions. Introducing thermotropic liquid crystal mesogens as a hydrophobic moiety into amphiphiles often generates unique Lyotropic assemblies and functions by incorporating specific mesogen-mesogen interactions with solvophobic one. This study reports recent results about unique aggregation behavior and properties of a new class of hybrid surfactant, CB-B2ES having mesogenic units (6-[4-(4-cyanophenyl)phenyloxy]hexyl) and temperature-sensitive oxyethylated (butoxyethoxyethyl) tails. CB-B2ES formed lamellar aggregates in water at concentrations higher than 5 wt%. Some of the lamellar aggregates were found to undergo repeat formation/breakdown periodically at 30 ˚C, with an average domain lifetime of ~ 10 seconds. Fluorimetric measurements suggested that the polarity of CB-B2ES bilayers increased with decreasing temperature, in contrast to the small decrease in polarity observed for analogous non-ethoxylated bilayers. The periodic formation/breakdown and the cooling-induced hydrophilicity of the CB-B2ES lamellar aggregates, did not appear in the non-hybrid and/or non-ethoxylated surfactant systems. Therefore, the combination of two unsymmetrical tails, one containing oxyethylene units and the other cyanobiphenyl terminal tips, must play an important role to promote this unusual behavior.
Keywords: Mesogen; Lamellar aggregates; Oxyethylene; Surfactant; Temperature-response.