Chemistry Weekly Seminar - PhD Candidate Jeveria Rehman

Title:

Physical Chemistry of Gemini Surfactant Monolayers

Abstract:

In this seminar, I report on the effect of cation (Na+, Ca2+, and Fe3+) binding on the structure of monolayers prepared from two newly synthesized anionic gemini surfactants that belong to the N,N-dialkyl-N-N’-diacetate ethylenediamine class of compounds.  Furthermore I have investigated the interactions of Ace(n)-2-Ace(n) with perfluorotetradecanoic acid (C13F27COOH; PF) in monolayers at the air-water and air-solid interface. Surface active properties of the monolayers were investigated using a combination of monolayer characterization methods including, π-area isotherms, Brewster angle microscopy, and atomic force microscopy measurements while molecular level details of the films were inspected by my other group members using grazing incidence X-ray scattering, X-ray reflectivity and total reflection X-ray fluorescence studies. The anionic surfactant monolayers underwent significant expansion in response to Na+ and Ca2+cations in the sub-phase while with the Fe3+ in the sub-phase markedly compact films were observed. Apparent association constants (Kapp) for Ace(n)-2-Ace(n) were smaller than those found with comparator phospholipids systems reported in the literature, and gemini-cation binding stoichiometries of  2:1, 1:1 and 1:2 for Ca2+, Na+, and Fe3+ respectively, were found. For Ace(n)-2-Ace(n) –PF mixed systems, films were miscible for the shorter chain (n = 12) gemini and PF while phase separation was observed in longer chain gemini (n = 18)-PF mixed system. Overall this study provides an insight into the fundamental chemistry of interaction of EDTA based gemini with metal cations in monolayers. Furthermore it also provides an understanding of the physical and chemical factors that control the mixing behavior in mixed Ace(n)-2-Ace(n)-PF mixed monolayers.