Hybrid-Supported Bilayers Formed with Mixed-Charge Surfactants on C18-Functionalized Silica Surfaces
Year: 2020
Type: article
Abstract: Mixtures of cationic–anionic surfactants have been shown to spontaneously form ordered monolayers at hydrophobic–hydrophilic boundaries, including air–water and oil–water interfaces. In this work, confocal Raman microscopy is used to investigate the structure of hybrid-supported surfactant bilayers (HSSBs) formed by deposition of a distal leaflet of mixed cationic–anionic surfactants onto a proximal leaflet of n -alkane (C 18 ) chains on the interior surfaces of chromatographic silica particles. The surface coverage of the two surfactants in a hybrid bilayer was determined from carbon analysis and the relative Raman scattering of their respective head-groups. Within the measurement uncertainty, the stoichiometric ratio of the two surfactants is one-to-one, equivalent to mixed-charge-surfactant monolayers at air–water and oil–water interfaces and consistent with the role of the head-group electrostatic interactions in their formation. When self-assembled on the hydrophobic surface, pairs of oppositely charged n- alkyl chain surfactants resemble a phospholipid (phosphatidylcholine) molecule, with its zwitterionic head-group and two hydrophobic acyl chain tails. Indeed, the structure of these hybrid-supported surfactant bilayers on C 18 -modified silica surfaces is similar to that of hybrid-supported lipid bilayers (HSLBs) on the same supports, but with denser and more-ordered n -alkyl chains. Hybrid-supported surfactant bilayers exhibit a melting phase transition (gel to liquid-crystalline phase) with structural and energetic characteristics similar to those of hybrid-supported bilayers prepared from a zwitterionic phospholipid of the same alkyl chain length. These mixed-charge surfactants on n -alkane-modified silica are stable in water over time (months), results that suggest the potential use of these hybrid bilayers for generating supported lipid-bilayer-like surfaces or for separation applications.
Source: Langmuir
Authors: Maryam Zare, Jay P. Kitt, Joel M. Harris
Institution: University of Utah
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W3033157639