Directly probing surfactant adsorption on nanoscopic trenches and pillars

Abstract

HypothesisConfinement causes a change in the amount of surfactant adsorbed and adsorption morphology. ExperimentsTwo cationic surfactants, tetradecyltrimethylammonium bromide (TTAB) and cetylpyridinium chloride (CPC) were adsorbed at the silica-water interface. Atomic force microscopy (AFM) force curves were measured on 50 nm and 80 nm wide trenches. Force curves were also measured on silica pillars, and the results were quantified based on distance from the edge. FindingsTrenches: Adsorbed surfactants films in 50 nm and 80 nm trenches showed the same breakthrough values. However, compared to unconfined values, TTAB in trenches had decreased break-through and adhesion forces while CPC in trenches had increased break-through and adhesion forces, indicating that surfactant identity varies the confinement effect.Pillars: Near the edge, few surfactants adsorb, and those that do stretch in the direction normal to the surface. While the experimental data agree qualitatively with previous coarse-grained molecular dynamic simulations, the length scales at which the phenomena are detected differ by ~ half-order of magnitude. Specifically, experimental data show measurable effects on adsorbed surfactant morphology at a distance from the edge 10-20 times the length of a surfactant molecule after accounting for the ~8 nm size of the probe.

Lyotropic Liquid Crystal (LLC)-Templated Nanofiltration Membranes by Precisely Administering LLC/Substrate Interfacial Structure

“…Numerous studies have investigated surfactant mesophases formed on solid substrates, and it has been demonstrated that the surface properties of substrates, including hydrophilicity and heterogeneity, can modify the interfacial curvature of surfactant mesophases formed on them [ 18 ]. Moreover, Grady et al [ 106 ] directly probed the surfactant mesophases on nanoscopic trenches and pillars using an atomic force microscope. They found that the effect of surface physical heterogeneity on the structure of surfactant mesophases extends to lengths much longer than those of individual surfactant molecules (approximately 50 nm vs. 2 nm).…”