Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 14, Issue 5, Pages 7340-7349Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.1c22683
Keywords
polypeptoids; ambient pressure XPS; restructuring; amphiphile; hydration; poly(ethylene oxide); polydimethylsiloxane
Funding
- Office of Naval Research (ONR) [N00014-17-1-2047, N00014-13-1-0633]
- Center for Materials for Water and Energy Systems (M-WET), an Energy Frontier Research Center - U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) [DE-SC0019272]
- Early Career Award in the Condensed Phase and Interfacial Molecular Science Program in the Chemical Sciences Geosciences and Biosciences Division of the Office of Basic Energy Sciences of the DOE [DE-AC02-05CH11231]
- National Defense Science and Engineering Graduate Fellowship Program
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC0205CH11231]
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Polymers are widely used in various applications that involve water exposure, and understanding the surface chemistry of polymers in these conditions is crucial. This study investigates the effects of surface-active side chains on polymer surface chemistry and water sorption using synchrotron ambient pressure X-ray photoelectron spectroscopy. The results show that different types of side chains, as well as the polymer backbone and environmental conditions, influence the water sorption behavior of the polymers.
Polymers are commonly used in applications that require long-term exposure to water and aqueous mixtures, serving as water purification membranes, marine antifouling coatings, and medical implants, among many other applications. Because polymer surfaces restructure in response to the surrounding environment, in situ characterization is crucial for providing an accurate understanding of the surface chemistry under conditions of use. To investigate the effects of surface-active side chains on polymer surface chemistry and resultant interactions with interfacial water (i.e., water sorption), we present synchrotron ambient pressure X-ray photoelectron spectroscopy (APXPS) studies performed on poly(ethylene oxide) (PEO)- and poly(dimethylsiloxane) (PDMS)-based polymer surfaces modified with amphiphilic polypeptoid side chains, previously demonstrated to be efficacious in marine fouling prevention and removal. The polymer backbone and environmental conditions were found to affect polypeptoid surface presentation: due to the surface segregation of its fluorinated polypeptoid monomers under vacuum, the PEO-peptoid copolymer showed significant polypeptoid content in both vacuum and hydrated conditions, while the modified PDMS-based copolymer showed increased polypeptoid content only in hydrated conditions due to the hydrophilicity of the ether monomers and polypeptoid backbone. Polypeptoids were found to bind approximately 2.8 water molecules per monomer unit in both copolymers, and the PEO-peptoid surface showed substantial water sorption that suggests a surface with a more diffuse water/polymer interface. This work implies that side chains are ideal for tuning water affinity without altering the base polymer composition, provided that surface-driving groups are present to ensure activity at the interface. These types of systematic modifications will generate novel polymers that maximize bound interfacial water and can deliver surface-active groups to the surface to improve the effectiveness of polymer materials.
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