Ultrathin Free-Standing Polymer Films Deposited onto Patterned Ionic Liquids and Silicone Oil

Abstract

We studied the vapor deposition of polymers onto the surfaces of silicone oil and imidazolium-based ionic liquids (ILs). We found that the deposition of poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(N-isopropylacrylamide) (PNIPAAm) resulted in polymer particles on silicone oil whereas continuous polymer skins formed on 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4 ]), and 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF 4 ]). The silicone oil and ILs were patterned onto a common substrate by exploiting their different wetting properties. Ultrathin free-standing PHEMA and PNIPAAm films of different shapes were produced by confining the shape of the IL within a wax barrier, surrounding it with silicone oil, and then depositing the polymer. The silicone oil prevented the polymer film from connecting to the underlying substrate and maintained the shape of the polymer film during deposition. Our process allows for multidimensional control over the resulting free-standing film: the area of the shape can be controlled by patterning the IL, and the thickness of the film can be controlled by adjusting the duration of polymer deposition. The films are highly pure and do not contain any residual monomer or solvent entrapment which extends their potential applications to include in vivo biomedical research. ■ INTRODUCTIONThe initiated chemical vapor deposition (iCVD) technique is a one-step, solventless free radical polymerization process that can be used to deposit a wide range of polymer films such as poly(2-hydroxyethyl methacrylate) (PHEMA), 1 poly(4-vinylpyridine) (P4VP), 2 and poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA). 3 The iCVD technique is typically used to deposit polymer coatings onto solid substrates such as silicon wafers, 4 membranes, 5 wires, 6 carbon nanotubes, 7 and fibers. 8 We recently demonstrated the ability to deposit polymer coatings onto ionic liquids (ILs). 9 ILs are salts that are liquids at ambient temperatures, and they have recently attracted significant interest as environmentally friendly alternatives to traditional volatile organic solvents because they are nonvolatile, nonflammable, and can be easily recycled. 10,11 Our previous work examined the deposition of PHEMA and PPFDA in the presence of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) droplets. We found that polymerization occurred at the vapor−IL interface and/or within the bulk IL depending on the solubility of the monomer within the IL and the reaction conditions such as the duration of deposition and stage temperature.In this paper, we use iCVD to deposit polymers onto silicone oil for the first time. We observe different polymer morphologies on the silicone oil as compared to the ILs, and we exploit this difference to fabricate ultrathin free-standing polymer films of different shapes by combining the silicone oil and ILs onto a common substrate. The generality of our fabrication method is demonstrated for multiple po...

25th Anniversary Article: CVD Polymers: A New Paradigm for Surface Modifi cation and Device Fabrication

“…Besides solid substrates, Gupta and co‐workers have shown that iCVD is able to coat liquids with low vapor pressure, for example, ionic liquids (ILs) 145. Surfaces patterned with IL and silicone oil resulted in the selective encapsulation of IL, given that continuous iCVD films can only be deposited on ILs but not on silicone oil 146. In addition, marbles of IL were fully encapsulated within a polymer shell of p(PFDA‐ co ‐EGDA) 147.…”

“…Free‐standing p(PFDA) polymer films have been obtained by depositing the iCVD polymer over droplets of ionic liquid 146. The low surface energy p(PFDA) coatings have been applied on PDMS‐based micromold173 and microfluidic88 devices in order to create a barrier coating towards organic solvents.…”

The effects of iCVD film thickness and conformality on the permeability and wetting of MD membranes

“…They could also potentially be prepared using free-standing, iCVD polymer films [34]. This type of membrane could have permeability that increases with ro/rt according to Eq.…”

Vapor Deposition of Fluoropolymer Surfaces

“…Since porous substrates do not allow using physical mask, metal salts were printed on the membranes inhibiting the polymerization process and thus, creating the pattern [44]. Ionic liquids (IL) were also modified using iCVD p(PFDA) [45,46]. Due to the low vapor pressure of IL, the PFDA monomer is able to adsorb on its surface and encapsulate the IL.…”