The self-assembled organization of partilces depends on the symmetry of their interactions, and strides are being made in producing nanoaparticles of controlled shape and functionalization. This paper describes the use of particles adsorption to control and detect surface modification, particle symmetry, and assembly shape. Charged polystyrene (PS) spheres (600 nm, and 1.2 micron in diameter) were spread as a monolayer on a charged film. A randomly adsorbed monolayer of particles was formed after moderate heating (80 ?C for 60 s). After coating the spheres with an oppositely charged polymer and releasing them for the charged film, they had a small charged area on their surface. This lithographic patch provided sufficient area to associate with only a single oppositely charged particle of comparable size, and resulted in the controlled formation of anisotropic doublets. Self aggregation of patchy particles depends on the ionic strength.At a high salt concentration (0.5 M NaCl or higher) doublets formed within 1 day, whereas formation required longer time (>3 d) at a low salt concentration (0.1 M or lower). Additionally, a strategy that added oppositely charged particles that were smaller than the uncoated surface area of the PS spheres was used to determine the size of this area. The size of the uncoated area was evaluated by counting the numbers of small charged particles that attached to it. For example, one to five 160 nm PS particles could attach to an uncoated area on a 1.2 micron PS sphere.
Pub Type: Journals
colloids, nanoparticles, patchy particles, self-assembly