Raman spectroscopic study of the conformational behaviour of the polymorphic non-ionic surfactant α-hexadecyl-ω-hydroxytris(oxyethylene)(C16E3)

Abstract

The conformational behaviour of α-hexadecyl-ω-hydroxytris(oxyethylene)(C₁₆E₃), which is one of the typical non-ionic surfactants, has been studied by Raman spectroscopy. The solid phase of this compound exhibits polymorphism; four distinct solid phases giving different Raman spectra have been found. The phase behaviour is not simple and most of the phase transitions are irreversible. The Raman spectra of these phases have been analysed in relation to the molecular conformation. The most stable crystalline phase comprises the alkyl chains in the extended conformation and the oxyethylene chains in the helical conformation. In the second crystalline phase, both the alkyl and oxyethylene chains take the extended conformation except for the terminal hydroxy-containing part. In the other phases, only the alkyl chains are ordered by taking the extended conformation and the oxyethylene chains are disordered. These results are consistent with previous findings by other techniques on the polymorphic phase structures of this compound.