(119b) Assembly of Binary Colloidal Particles with Opposite Charge

Large silica colloidal spheres of 1.78µm in diameter were modified with APS (aminopropyltriethoxysilane), then the modified silica spheres with positive charges were self-assembled into 2D orderly colloidal crystal monolayer on air-water interface, after that the crystal film was transferred onto a glass substrate with negative charges, which was treated in a Piranha solution (H₂SO₄/H₂O₂=70:30(v/v)) for 2hr at boiling condition and then washed ultrasonically in di-distilled water prior to use. The glass substrate loading silica monolayer was immersed in dilute suspension of polystyrene colloidal particles of 120nm in diameter with negative charges, which are synthesized with emulsion polymerization. The SEM photograph (Fig. 1) of the resulting sample indicates that little PS particles deposited onto the surfaces of large silica particles owing to attraction of opposite charges, surprisingly, in a larger void area around silica particle, some little PS particles self-assembled into orderly lattice by themselves, not depositing onto the surface of silica particles, the reason may be the colloidal particles self-assembling owing to capillary force on the substrate with same charges.