Encapsulation and Permeability Characteristics of Plasma Polymerized Hollow Particles

Summary

We have used plasma enhanced chemical vapor deposition to deposit thin films ranging from a few nm to several 100 nm on nano-sized particles of various materials. We subsequently etch the core material to produce hollow nanoshells whose permeability is controlled by the thickness of the shell. We characterize the permeability of these coatings to small solutes and demonstrate that these barriers can provide sustained release of the core material over several days.

Abstract

In this protocol, core-shell nanostructures are synthesized by plasma enhanced chemical vapor deposition. We produce an amorphous barrier by plasma polymerization of isopropanol on various solid substrates, including silica and potassium chloride. This versatile technique is used to treat nanoparticles and nanopowders with sizes ranging from 37 nm to 1 micron, by depositing films whose thickness can be anywhere from 1 nm to upwards of 100 nm. Dissolution of the core allows us to study the rate of permeation through the film. In these experiments, we determine the diffusion coefficient of KCl through the barrier film by coating KCL nanocrystals and subsequently monitoring the ionic conductivity of the coated particles suspended in water. The primary interest in this process is the encapsulation and delayed release of solutes. The thickness of the shell is one of the independent variables by which we 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 release profile shows a characteristic 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.

Protocol

1. Preparation of Silica Nanoparticles for Deposition

1. Starting with dry silica powder, prepare the sample for coating by first eliminating large aggregates.
2. Wash silica particles (diameter of 200 nm, purchased from Gel-Tec Corp.) with ethanol (190 proof pure) and leave the sample under a fume hood till all the moisture evaporates with ethanol.
3. Sift particles through a series of metallic meshes (US # 100-400) in order to break any remaining agglomerations.
4. Place particles and a small magnetic stirrer bar in the tubular reactor, as shown in Figure 1. Particles should be placed inside the plasma zone.
5. S....

Discussion

One of the biggest challenges in coating nanoparticles is to provide a compatible chemistry between coating and the substrate ^1,2. The methodology described here has the advantage that it is not material-specific. Plasma polymers show excellent adhesion on a variety of substrates, including hard metals (Figure 2(c)), silica (Figure 2(c)), silicon, or soft materials (e.g., polymers) without the need for any special surface modification ^3,4,5. The technique has the fu.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Silica particles	Geltech Inc.
Potassium chloride (crystals)	EMD Chemicals Inc.
Isopropyl alcohol (99.9%)	Sigma-Aldrich
Hydrofluoric acid (48-51%)	VWR
Pipes and flanges	Swagelok		diameter of ¼ and 1 inch
roughing pump	Edwards
liquid nitrogen trap	A&N Corporation