Size-Dependent Interaction of Silica Nanoparticles with Different Surfactants in Aqueous Solution

摘要

The size-dependent interaction of anionic silicannanoparticles with ionic (anionic and cationic) and nonionicnsurfactants has been studied using small-angle neutronnscattering (SANS). The surfactants used are anionic sodiumndodecyl sulfate (SDS), cationic dodecyltrimethyl ammoniumnbromide (DTAB), and nonionic decaoxyethylene n-dodecylethern(C12E10). The measurements have been carried out fornthree different sizes of silica nanoparticles (8, 16, and 26 nm) at fixed concentrations (1 wt % each) of nanoparticles andnsurfactants. It is found that irrespective of the size of the nanoparticles there is no significant interaction evolved between likechargednnanoparticles and the SDS micelles leading to any structural changes. However, the strong attraction of oppositelyncharged DTAB micelles with silica nanoparticles results in the aggregation of nanoparticles. The number of micelles mediatingnthe nanoparticle aggregation increases with the size of the nanoparticle. The aggregates are characterized by fractal structurenwhere the fractal dimension is found to be constant (D ≈ 2.3) independent of the size of the nanoparticles and consistent withndiffusion-limited-aggregation-type fractal morphology in these systems. In the case of nonionic surfactant C12E10, micelles interactnwith the individual silica nanoparticles. The number of adsorbed micelles per nanoparticle increases drastically whereas thenpercentage of adsorbed micelles on nanoparticles decreases with the increase in the size of the nanoparticles.