- 4:35 PM

Fabrication of Speckled Spheres

Neetu Chaturvedi, Chemical Engineering, The Pennsylvania State University, 175 Fenske Laboratory, University Park, PA 16802 and Darrell Velegol, Department of Chemical Engineering, The Pennsylvania State University, University Park, PA 16802.

We use the “particle lithography” technique to fabricate randomly-speckled spheres. Nanoscale regions of one chemistry (size ~100 to 400 nm) are placed on micron size, core colloidal particles. In the speckling technique, parts of positively-charged 3.3 µm polystyrene microspheres are masked off with negatively charged 0.9 µm silica particles, and then negatively-charged 60 nm polystyrene nanoparticles are introduced to cover the remaining portion of the microspheres. The masking particles are then removed to form speckles on the larger core particle. The effectiveness of this process is demonstrated by electron and confocal microscopy. The diameter of the circular speckles is reliable and predictable, following predictions from simple geometry. The number of speckles formed on the core polystyrene particle can be controlled by adhering various quantities of the masking silica particles onto the larger core particles. The process used is reliable and general in possible materials (e.g., polymer particles, as well as metals, oxides, or even semiconductors). The process is useful for applications requiring localized, high density regions, such as for drug delivery, where the precise placement of the regions is not important.