Surface aggregate structure of nonionic surfactants on silica nanoparticles

Abstract

The self-assembly of two nonionic surfactants, pentaethylene glycol monododecyl ether (C 12 E 5 ) and n-dodecyl-ß-maltoside (ß-C 12 G 2 ), in the presence of a purpose-synthesized silica sol of uniform particle size (diameter 16 nm) has been studied by adsorption measurements, dynamic light scattering and small-angle neutron scattering (SANS) using a H 2 O/D 2 O mixture matching the silica, in order to highlight the structure of the surfactant aggregates. For C 12 E 5 strong aggregative adsorption onto the silica beads, with a high plateau value of the adsorption isotherm above the CMC was found. SANS measurements were made at a series of loadings, from zero surfactant up to maximum surface coverage. It is found that the spherical core-shell model nicely reproduces the SANS data up to and including the local maximum at q = 0.42 nm -1 but not in the Porod region of high q, indicating that the surface area of the adsorbed surfactant is underestimated by the model of a uniform adsorbed layer. A satisfactory representation of the entire scattering profiles is obtained with the model of micelle-decorated silica beads, indicating that C 12 E 5 is adsorbed as spherical micellar aggregates. This behaviour is attributed to the high surface curvature of the silica which prevents an effective packing of the hydrophobic chains of the amphiphile in a bilayer configuration. For the maltoside surfactant ß-C 12 G 2 very weak adsorption on the silica beads was found. The SANS profile indicates that this surfactant forms oblate ellipsoidal micelles in the silica dispersion, as in the absence of the silica beads.

Structuring of colloidal suspensions confined between a silica microsphere and an air bubble

“…The adsorption of b-C 12 G 2 to negatively charged silica has been shown to be weak. 35,36 The deformation of the bubble at the same nanoparticle concentration with varying b-C 12 G 2 concentration is illustrated in Fig. 4a , respectively.…”

Surfactant adsorption and aggregate structure at silica nanoparticles: Effects of particle size and surface modification

“…For instance, for the surfactant penta(ethyleneglycol) monododecylether (C 12 E 5 ) it was recently found that discrete surface micelles are formed on silica nanoparticles, 14,16 although flat bilayer aggregates are preferred at planar silica surfaces. 6,7 At even weaker anchoring energies, surface micelles may be disfavoured against micelles in solution, implying that little or no adsorption occurs, as in the case of dodecyl maltoside (b-C 12 G 2 ) at silica nanoparticles.…”

“…6,7 At even weaker anchoring energies, surface micelles may be disfavoured against micelles in solution, implying that little or no adsorption occurs, as in the case of dodecyl maltoside (b-C 12 G 2 ) at silica nanoparticles. 14 Here, we study the influence of particle size and surface modification on the adsorption of the surfactant C 12 E 5 at silica nanoparticles. The particles were synthesized by a modified St€ ober method 19 yielding particles of narrow size distribution down to the 10 to 50 nm size range which was of interest in this study.…”

“…As in the preceding studies, 14,15 SANS measurements were made with a H 2 O-D 2 O mixture that matches the scattering length density of the silica. In this contrast-match scenario the silica particles become invisible to the neutron beam.…”

Interaction between Surfactants and Colloidal Latexes in Nonpolar Solvents Studied Using Contrast-Variation Small-Angle Neutron Scattering

“…While the free volume between stabilizer chains would suggest that such an arrangement is not possible, such a form factor has recently been used to describe CV-SANS data measured for the adsorption of nonionic surfactant micelles on silica nanoparticles in water. 44 The scattering from AOT-D 34 with PMMA latexes in PMMA-matched solvent has been fit using a "raspberry" model, which is appropriate for Pickering emulsions or nanocomposite raspberry particles. 45 As in Figure 7, the core dimensions were fixed, and parameters describing the inverse micelles were allowed to vary (r; φ ; and χ, the fraction of interfacial area covered).…”