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A Study of Dewetting during Solvent-Assisted Vapor Deposition of Polymer Films

Xichong Chen, University of Rochester, Department of Chemical Engineering, 206 Gavett Hall, Rochester, NY 14627 and Mitchell Anthamatten, Chemical Engineering, University of Rochester, 206 Gavett Hall, Rochester, NY 14627.

Initiated chemical vapor deposition (iCVD) is a technique to produce polymeric thin films from gaseous reagents.[1-3] At low pressures, monomers and initiator molecules are fed into a vacuum reactor. Once inside, initiator molecules are thermally activated to create free radicals, and they diffuse to a target substrate and initiate a polymerization reaction with adsorbed monomer. We have recently designed and built an axisymmetric iCVD vacuum reactor. Using this reactor, smooth poly (methyl methacrylate) (PMMA) films can be grown from vapor feeds of methyl methacrylate and t-butyl peroxide. Prior studies focused on understanding how polymer film growth rates are related to reactor operating parameters including reagent flowrates, reactor pressure, and hot-zone temperature.[2] The polymer deposition rate was also affected by the presence of solvent vapor (a third gas feed). Under certain operating conditions, solvent vapor leads to dewetting of polymer films from target substrates.

The objective of our current study is to understand and predict the deposition conditions that result in dewetting. We performed several depositions on different substrates including silicon wafers, glass slides, and PMMA-coated surfaces. Solvent vapors with different solubility parameter and vapor pressure including t-butanol, water, and isopropanol were also used. Scanning electron microscopy (SEM) and white light interferomety were used to investigate dewetted structures following deposition. The feature size of the dewetted structures depends on the film thickness, the film growth rate, and the type of solvent. A kinetic model will be discussed that compares rates of film growth, polymerization, and phase separation to explain dewetting behavior.

1. Chan, K. and K.K. Gleason, Initiated CVD of poly(methyl methacrylate) thin films. Chemical Vapor Deposition, 2005. 11(10): p. 437-443.

2. Chen, X.C. and M. Anthamatten, Vapor Deposition Polymerization of Poly(Methyl Methacrylate) in an Axisymmetric Vacuum Reactor. Polymer, 2008. 49: p. 1823-1830.

3. Lau, K.K.S. and K.K. Gleason, Initiated chemical vapor deposition (iCVD) of poly(alkyl acrylates): A kinetic model. Macromolecules, 2006. 39(10): p. 3695-3703.