(374a) Encapsulation and Permeability Characteristics of Amorphous Hydrogenated Carbon Films Formed by Plasma Enhanced Chemical Vapor Deposition Technique

We have used plasma enhanced chemical vapor deposition technique to coat the materials and control the rate of their release. This powerful technique coat nanoparticles and nanopowders ranging from 15 nm to 1 micron and we can control the thickness (from 1nm to upwards of 100 nm) of the film by controlling the duration of the deposition time. We present results with two different core materials, silica nanopheres and KCl nanoparticles.  By coating silica and etching the core in HF, we form hollow nanoshells whose dimensions depend on the size of the silica particle and the thickness of the shell. Permeation studies are conducted using KCl, whose release profile is measured easily by monitoring the conductivity of the solution. The thickness of the shell is one of the independent variables by which to control the rate of release. It has a strong effect on the rate of release, which increases from a six-hour release (shell thickness is 20 nm) to a long-term release over 30 days (shell thickness is 95 nm). The profile of release for any thickness follows a unique behavior: a fast release (35% of the final materials) during the first five minutes after the beginning of the dissolution, and a slower release till all of the core materials come out. In order to analyze this behavior a model based on an unsteady-state diffusion from sphere is developed. Very good agreement between experimental data and the model after half an hour from the beginning of the release is observed and based on that a diffusion coefficient for the shell is calculated. The diffusion coefficient of (3.5±0.5)* 10^-21 is obtained for four different samples with different shell thicknesses (20, 40, 75, 95 nm).