Permeability characteristics of hollow nanoparticles fabricated by low-pressure plasma deposition

Summary form only given. Hollow nanoparticles are of interest for several potential applications, ranging from drug delivery, to catalyst, to fertilizers. We have developed a plasma-based process for depositing plasma coatings by plasma polymerization of hydrocarbon molecules (e.g., isopropyl alcohol and cyclohexane) onto micro-and nanoparticles of various materials (silica, sodium chloride, and potassium chloride). Film deposition is conducted in a tubular reactor driven by a radio frequency, RF, generator at low pressure. Hollow nanoparticles are fabricated in a two-step process. First particles that serve as the core are exposed to the hydrocarbon plasma where it becomes coated, and then the thickness of the coating is determined by the deposition time that ranges from few nm to more than 100 nm. The particles are collected after this process and the core material is dissolved in a suitable solvent. The resulting hollow nanoshells are characterized with several techniques. TEM and FESME images confirm the thickness and uniformity of the plasma coatings and Thermogravimetric analysis (TGA) shows nanoshells to be thermally stable up to 250 °C. The etching of the particle core indicates that nanoshells are permeable to small molecules. To study the rate of permeation, KCl particles were coated in the plasma and then placed in an aqueous solution to dissolve the core. The rate of dissolution was then measured by monitoring the conductivity of the solution as a function of time. Release profiles were obtained for shell thicknesses between 20 and 100 nm. Generally, about 60% of the core material is released within 10-20 minutes while the rest of the material showing a slow release over several days, up to 30 days, for the thickest shells.