Effect of Nanoparticle Size on the Morphology of Adsorbed Surfactant Layers

Abstract

The surface aggregates structure of dimethyldodecylamine-N-oxide (C 12 DAO) in three silica dispersions of different particle sizes (16 -42 nm) was studied by small-angle neutron scattering (SANS) in a H 2 O/D 2 O solvent mixture matching the silica. At the experimental conditions (pH 9) the surfactant exists in its nonionic form and the structure of the adsorbed layer is not affected by added electrolyte. It is found that C 12 DAO forms spherical surface micelles of 2 nm diameter on the 16 nm silica particles, but oblate ellipsoidal surface micelles are formed on the 27 and 42 nm particles. The dimensions of these oblate surface aggregates (minor and major semi-axes R n and R lat ) are similar to those of C 12 DAO micelles in the aqueous solutions. It is concluded that the morphological transition from spherical to ellipsoidal surface aggregates is induced by the surface curvature of the silica particles. A comparison of the shape and dimensions of the surface aggregates formed by C 12 DAO and C 12 E 5 on the 16 nm silica particles demonstrates that the nature of the surfactant head group does not determine the morphology of the surface aggregates, but has a strong influence on the number of surface aggregates per particle, due to the different interactions of the head groups with the silica surface.2

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

“…According to these data no significant variations of the size and f-potential of nanoparticles are observed at the concentration of TX-100 lower and something above the critical micelle concentration (CMC) of TX-100 (CMC = 0.2 mM according to [31]). This is in good agreement with literature data [13,[32][33][34][35][36], indicating that at such concentration conditions nonionic surfactants tend to form island-like aggregates with the thickness no more than 5 nm at the silica/water interface. The growth of the nanoparticles size becomes rather significant at 5 mM of TX-100 (Table 1).…”

Aggregation of Silica Nanoparticles Directed by Adsorption of Lysozyme

“…This yields a ratio of the two areas a BET /a geom = 1.45. This is a typical value for silica nanoparticles in this size range and can be attributed to surface roughness [39].…”

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

“…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.…”