Proton longitudinal and transverse magnetic relaxation in dilute aqueous solutions of poly(oxyethylene) alkyl ethers

Abstract

¹ H longitudinal and transverse relaxation times have been measured for dilute aqueous micellar solutions of a series of poly(oxyethylene) alkyl ethers of general formula CH₃(OCH₂CH₂)_mOC_nH_2n+1 with m= 27 and 53 and n= 12, 14, 16, 18 and 21. The C₁₈ and C₂₁ members showed line broadening and intensity loss in the alkyl signals attributed to a liquid/solid transition of the micelle core. For liquid cores the alkane relaxation times were analysed in terms of two motions, a ‘fast’ segmental motion (correlation time ca. 40 ps) and a ‘slow’ molecular diffusion around the micelle surface (correlation time ca. 5 ns). The diffusion rate is consistent with a micelle radius of the order of 1 nm.