Supramolecular Structure of Surfactants Confined to Interfaces

Abstract

The mounting evidence for the existence of surfactant aggregates at solid/solution interfaces prompts a re-examination of common experimental techniques for studying surfactant adsorption. The simple models of a surfactant monolayer or bilayer, while reasonable in the face of older experimental data, are now seen to be inadequate to describe the rich range of order seen by atomic force microscopy and other techniques. In this manuscript we review the results of atomic force microscopy which demonstrate the existence of surface micelles, look again at the experimental results which pointed towards surface aggregates, and also look ahead at how the existence of surface micelles requires us to revise the interpretation of other experimental studies and our entire picture of adsorbed films.

Temperature induced phase separation of luminescent silica nanoparticles in Triton X-100 solutions

“…According to literature data hydrogen bonding plays significant role in the adsorption of non-ionic surfactants at the silica/water interface [12]. To elucidate the role of the hydrogen bonding we used the dissociation of Si-OH groups in alkaline conditions to minimize the hydrogen bonding between polyoxyethylene chains of TX-100 and silanole groups at the silica surface.…”

“…Various ions or molecules can be solubilized into non-ionic micelles and thus extracted from the aqueous phase through the temperature induced phase separation [10,11]. The adsorption of non-ionic surfactants at a silica/water interface represents another well studied and widely applied phenomenon [12,13]. In recent decades the adsorption of various surfactants and polyelectrolytes at a silica/water interface has gained additional attention, because it represents promising alternative to a covalent modification of nanoparticles due to a lack of multistep purification procedures [14].…”

Silica nanoparticles with a substrate switchable luminescence

“…at the varied concentration of SDS at pH = 9.2. I 0 is the emission intensity without phenol red [18]. So, the "on-off-on" switching luminescent system was obtained.…”

“…The aggregation of cationic surfactants at the silica nanoparticles is exemplified in literature in most details by cetyltrimethylammonium bromide (CTAB) [7,15], which is monocationic surfactant. Amphiphilic cations cethyltrimethylammonium (CTA + ) form doubly charged bilayer at the silica/water interface, resulting in the recharging of the silica surface from minus to plus [7,18]. Taking into account that electrostatic interactions play the key role in the formation of the doubly charged bilayer, gemini surfactant with two cationic groups per molecule, namely hexalidene-bis(dimethylammonium) bromide (16-6-16, chart 1) was chosen to recharge silica surface.…”

Structure changes in micelles and adsorbed layers during surfactant polymerization

“…DTAB and C 14 TAB both form slightly aspherical micelles in solution [50][51][52] but long rods adsorbed on mica [14]. This is generally attributed to the high charge density of mica (where charged sites occupy an area of 49 Å 2 each), which reduces the surfactant head-group area, and increases in the packing parameter [59,60].…”