Isotherm behavior studies of silica nanoparticles: Role of surfactant concentration and particle size

In the present work, the effect of the surfactant concentration and particle size on the 2D assembly and corresponding isotherms of the silica nanoparticles at the air/water interface is studied and reported using Langmuir-Blodgett (LB) technique. Silica nanoparticles (NPs) of different sizes (30 nm & 150 nm) were synthesized by Stöber´s method and were characterized to determine their sizes and dispersity using scanning electron microscopy. As-synthesized NPs were hydrophobized to varying extents through addition of varying amounts (0.5 mg to 1.5 mg) of cationic surfactant, cetyltrimethylammoniumbromide (CTAB). The lift off area (area/particle) and corresponding yield was found to be very low for 30 nm sized particles. The yield in case of 150 nm sized particles participating in monolayer formation is found to be much higher implying a more optimal interaction with surfactant in the studied concentration range. The low yield at small particle size can be attributed to the partial surface modification of particles.