Microencapsulation by Vapor Deposition

Summary

Encapsulation of particulate solids and of liquid droplets is commonly done for purposes of controlled release, environmental protection or rendering inert reactive, toxic, or hazardous materials. Coating of pharmaceuticals, pesticides, catalysts and discrete electronic elements are some specific examples of applications involving microencapsulation techniques. While most microencapsulation methods use liquid techniques, vapor-phase deposition of polymeric coatings using poly-p-xylylene is accomplished dry in vacuum environment. Encapsulation of substrates is accomplished by tumbling the particulate charge within an evacuated cylinder. Liquids are formed in droplets, frozen, and held at temperatures below their melting point during the subsequent coating operation. Deposition of poly-p-xylylene polymer from the reactive xylylene vapors uniformly coats and encapsulates the tumbling particles. Any desired thickness may be attained, from a few angstroms to over 1 mil if required for specific end-use. Examples will be discussed illustrating use and performance of encapsulated liquid and solid chemical materials.