Polymeric encapsulation of liquids via plasma surface polymerization

Abstract

ABSTRACTThis study introduces a new approach of liquid encapsulation using an atmospheric pressure plasma (APP). The technique is similar to interfacial polymerization, though here one phase is liquid (that contains unsaturated C═C bonds) and the other phase is plasma (that contains free radicals). When combined, the atmospheric plasma can induce surface polymerization of an acrylate‐based liquid, resulting in a thin polymeric skin on top of the liquid. Measurements with an atomic force microscope and a spectroscopic ellipsometer estimate the thickness of the skin formed on top of di(ethylene glycol) diacrylate to be 40–50 nm. To demonstrate an application of this method, we encapsulated hemispherical capsules of reactive adhesives on a glass substrate. These adhesives are based on thiol‐acrylate and thiol‐acrylate‐epoxy systems that react in the presence of a strong base catalyst. Plasma‐induced polymerization can encapsulate, immobilize, and isolate separate droplets of resin and the catalyst in a latent (nonreactive) state. These capsules remain latent until they rupture in response to physical contact. A tensile testing machine reports an adhesive strength of ~ 2 MPa for the formulated resins after curing. The capsules reported here may be useful for storing functional liquids for just‐in‐time release, such as contact‐sensitive adhesives, on‐demand lubricants, or self‐healing agents. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48880.