Initiated Chemical Vapor Deposition of Polymers Onto Liquid Substrates

The initiated chemical vapor deposition process is typically used to deposit functional polymer coatings onto solid substrates. We were recently the first group to use this technique to deposit polymers onto liquid substrates. The use of liquid substrates adds complexity to the process because it introduces surface tension and solubility effects. We have shown that the surface tension interactions between the polymer and liquid dictate the thermodynamically stable morphology of polymer deposited at the liquid–vapor interface. Films form when it is energetically favorable for the polymer to spread on the liquid surface whereas polymer particles form when it is energetically favorable for the polymer to minimize its area of contact with the liquid. The monomer solubility in the liquid dictates the location of polymerization. If the monomer is not soluble in the liquid, polymerization only occurs at the liquid–vapor interface, whereas polymerization occurs at both the liquid–vapor interface and within the liquid if the monomer is soluble. In this article, we review the different structures that have been made by varying the surface tension and solubility including free-standing films, nanoparticles, encapsulated droplets, polymer–liquid gels, and heterogeneous films. The use of liquid substrates in the initiated chemical vapor deposition process enables us to fabricate novel polymer structures for a wide range of potential applications in optics, sensing, and separations. The fundamental insight gained from our research can also be extended to other vacuum processing techniques to make inorganic and hybrid materials.