Interaction of Surfactants with Hydrophobic Surfaces in Nanopores

Abstract

Surfactant-induced wetting of hydrophobic nanopores is investigated. SDS micelles interact with the C18 layer on the nanopore walls with their hydrophobic tails, creating a charged wall lining with their head groups and inducing a breakthrough of the aqueous solution to wet the pores. The surface coverage of the surfactant molecules is evaluated electrophoretically. A surprising discovery is that pore wetting is achieved with 0.73 μmol/m(2) coverage of SDS surfactant, corresponding to only 18% of a monolayer on the walls of the nanopores. Clearly, the surfactant molecules cannot organize as a compact uninterrupted monolayer. Instead, formation of hemimicelles is thermodynamically favored. Modeling shows that, to be consistent with the experimental observations, the aggregation number of hemimicelles is lower than 25 and the size of hemimicelle is limited to a maximum radius of 11.7 Å. The hydrophobic tails of SDS thus penetrate into and intercalate with the C18 layer. The insight gained in the C18-surfactant interactions is essential in the surfactant-induced solubilization of hydrophobic nanoporous particles. The results have bearing on the understanding of the nature of hydrophobic interactions.

Polymer Free Volume Effects on Protein Dynamics in Polystyrene Revealed by Single-Molecule Spectroscopy

“…17 Previous work shows that hydrophobics can also play a large role in 3D transport dynamics in porous media. 85 Here, a more careful look at single protein tracking results suggests that the underlying microstructure of PS yields similar effects without the introduction of new charge carrying chemistries to PS. 17 Although similar results and driving forces are at play in both cases, here we uncover a structure−function relationship present in Lys dynamics at PS without modifying the overall hydrophobicity of the thin PS film (Figures 1−3).…”

A criterion to assess the impact of confined volumes on surfactant transport to liquid–fluid interfaces

“…2,3 Depletion is a well-known phenomenon, arising in a variety of situations that involve finite solution volumes, small bulk surfactant concentrations, or large surface areas. Examples include multiphase flow in porous media, 4 emulsification and coalescence, 5,6 biological processes, 7 surface tension studies, [8][9][10][11][12][13][14][15][16][17] tipstreaming, 18,19 wetting, [20][21][22] and Marangoni flows. 23,24 Depletion is properly accounted for by using a global surfactant mass balance in conjunction with the governing equations for transport and equilibrium.…”

Biomedical applications of mesoporous silica particles

“…sulfate head groups into the aqueous phantom matrix [121], selectively solubilizing the outer surface and preventing particle aggregation. Gentle agitation by hand was sufficient to achieve visual homogeneity ( Figure 5-11).…”