We are interested in studying the mechanism and kinetics associated with initiated chemical vapor deposition (iCVD) of functional polymers onto structured materials and liquid surfaces. The iCVD process eliminates the need for organic solvents and thereby offers a safer and cleaner alternative to liquid phase polymer processing.
Deposition onto Liquid Substrates
We have recently demonstrated that we can deposit polymers onto liquids with low vapor pressures, including ionic liquids (ILs) and silicone oils. The liquid surface is mobile and unconstrained and thereby offers new initial conditions for growth and additional degrees of freedom which can be exploited to produce films and particles with desirable physical properties. We have found that the surface tension interaction between the polymer and the liquid plays a key role in determining the polymer morphology at the liquid-vapor interface. In addition, we have observed that the introduction of liquid substrates adds complexity because polymerization can now occur at both the liquid-vapor interface as well as within the liquid for cases in which the monomer is soluble within the liquid. We have demonstrated that we can form new polymeric structures such as ultra-thin polymer films, sub-micron particles, liquid/polymer composites, and core-shell particles by tuning solubility and surface tension interactions.
Macromolecules, 2011, 44, 2653, Macromolecules, 2012, 45, 165, Langmuir, 2012, 28, 10276, Langmuir, 2013, 29, 10448, Macromolecules, 2013, 46, 6852, Langmuir, 2013, 29, 11640, Macromolecular Rapid Communications, 2014, 35, 2000, Macromolecules, 2014, 47, 6657, Langmuir, 2015, 31, 7999, Langmuir, 2016, 32, 11014, Thin Solid Films, 2017, 635, 17, Langmuir, 2017, 33, 7701, Applied Physics Letters, 2018, 112, 201605, ACS Applied Nano Materials, 2018, 1, 6575, ACS Applied Polymer Materials, 2019, 1, 1930, Molecular Systems Design & Engineering, 2019, advance article.
Fabrication of Porous Membranes
We recently discovered that we can use extremely low substrate temperatures to make membranes with dual-scale porosity by simultaneous deposition of solid monomer and polymerization. Our process uses unconventional iCVD processing parameters: we increase the monomer partial pressure above the saturation pressure and we decrease the substrate temperature below the freezing point of the monomer. The solid monomer that deposits serves as both a porogen and a template for polymerization. Since our process is a bottom up approach, we can extend our method to make “porous-on-porous structures” with a wide range of chemical compositions and shapes. Our all-dry technique eliminates solvent-related issues and allows for the development of next-generation hierarchically structured materials for water purification and gas separation.
Macromolecules, 2013, 46, 2976, ACS Applied Materials & Interfaces, 2013, 5, 9714, Journal of Vacuum Science & Technology A, 2014, 32, 041514, Macromolecular Materials and Engineering, 2015, 300, 1079, Macromolecular Materials and Engineering, 2016, 4, 371, Macromolecular Materials and Engineering, 2016, 301, 1037, Polymer, 2017, 126, 463, Langmuir, 2018, 34, 9025, Macromolecules, 2018, 51, 10297, Industrial & Chemical Engineering Research, 2019, 58, 9908, Industrial & Chemical Engineering Research, 2019, 58, 15190.
Coatings for Microfluidic Devices and Structured Surfaces
The iCVD process is not a line-of-sight process and therefore we can uniformly coat a variety of structured materials such as filters, microfluidic devices, and pillars. We recently demonstrated that we can modify poly(dimethylsiloxane) microfluidic devices and paper-based microfluidic devices with thin layers of low surface energy fluoropolymer barrier coatings that enable these devices to resist absorption and swelling, allowing for use of organic solvents in these channels. We have also developed new methods to coat pillars to make responsive hierarchically structured surfaces and we have also developed new patterning methods to control the location of polymer growth on porous substrates for filtration and lab-on-a-chip applications.
Lab on a Chip, 2011, 11, 3049, Soft Matter, 2011, 7, 2428, Langmuir, 2011, 27, 10634, ACS Applied Materials & Interfaces, 2011, 3, 4201, ACS Applied Materials & Interfaces, 2012, 4, 3077, Analytical Chemistry, 2012, 84, 10129, ACS Applied Materials & Interfaces, 2012, 4, 6911, ACS Applied Materials & Interfaces, 2013, 5, 12701, ACS Applied Materials & Interfaces, 2015, 7, 23056, Nature Communications, 2016, 7, 10780, Industrial & Chemical Engineering Research, 2018, 57, 11675.
Coatings for Biomedical Implants
We collaborate with medical researchers at USC to develop functional coatings for biomedical implants. We work with Dr. Mark Humayun’s Biomimetic Microelectonic Systems (BMES) – Engineering Research Center (ERC) to develop thermoresponsive coatings for retinal implants. Our new collaboration with Prof. Ellis Meng and Prof. James Weiland involves developing antifouling coatings for wireless shunts to treat hydrocephalus, a disease which results in the accumulation of cerebrospinal fluid in the brain. Our goal is to develop coatings that prevent shunt malfunction.
Journal of Vacuum Science & Technology A, 2016, 34, 041403, Beilstein Journal of Nanotechnology, 2017, 8, 1629.