Investigation of the hygroscopic growth of self-assembled layers of N-alkyl-N-methylpyrrolidinium bromides at the interface between air and organic salt

April 1, 2008

Journal Article

Investigation of the hygroscopic growth of self-assembled layers of N-alkyl-N-methylpyrrolidinium bromides at the interface between air and organic salt

Abstract

We report on the hygroscopic growth of self-assembled lamellae, composed of N-alkyl-N-methylpyrrolidinium bromide (CnMPB; n = 10, 12, 14, 16, 18) surfactant molecules, spontaneously formed at the interface between ambient air and the low-melting organic salt tetrabutylammonium acetate (TBAAc). The organization process to form well-defined hygroscopic bilayer patterns at the air/TBAAc interface was investigated using a combination of time-dependent X-ray diffraction (XRD) and carbon-13 cross-polarization magic angle spinning nuclear magnetic resonance (13C CP/MAS NMR) spectroscopy. CnMPB surfactants containing the highest alkyl chain lengths studied (n = 16, 18) formed highly ordered, fully-interdigitated bilayer patterns with an all-trans conformation of interior methylene carbons. In contrast, CnMPB surfactants with shorter alkane chains (n = 10, 12, 14) in this series formed less-ordered bilayer arrangements with mixed trans/gauche aliphatic character. The lamellar patterns became increasingly ordered with longer exposure to humid air at the air/salt interface.

Revised: April 16, 2009 | Published: April 1, 2008

Citation

Shin Y., G.A. Baker, L.Q. Wang, and G.J. Exarhos. 2008. Investigation of the hygroscopic growth of self-assembled layers of N-alkyl-N-methylpyrrolidinium bromides at the interface between air and organic salt. Colloids and Surfaces. A, Physicochemical and Engineering Aspects 318, no. 1-3:254-258. PNNL-SA-51884. doi:10.1016/j.colsurfa.2007.12.045