Wetting and aging behaviors for several O2 and NH3 plasma treated nanofibrous and flat film polymer materials: A comparison

• Published in: Plasma processes and polymers Vol. 20; no. 6
• Main Authors: Watson, Sean, Pattyn, Cedric, Mohseni Garakani, Mansoureh, Ajji, Abdellah, Reuter, Stephan, Wertheimer, Michael R.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.06.2023
• Subjects: aging; Aging (materials); Ammonia; Contact angle; flat film; Glow discharges; nanofibers; Photoelectrons; Polycaprolactone; Polylactic acid; Polymer films; Polymers; Spectrum analysis; surface modification; Time dependence; Time measurement; XPS
• ISSN: 1612-8850; 1612-8869
• DOI: 10.1002/ppap.202200224

Aging (or “hydrophobic recovery”) of plasma‐modified polymer surfaces has been known and documented in the literature over several decades; to the best of our knowledge, the present study appears to be the first in which this is done for two vastly different rough surface structures: (i) electrospun nanofibrous (NF) mats, and (ii) flat films (FF), for three polymers of well‐documented interest in biotechnological applications: poly(lactic acid); poly(urethane); and poly(caprolactone). Two different plasma treatments are applied: low‐pressure (LP) radio‐frequency (rf) glow discharges in flows of O2 and NH3 under mild power conditions. Measured time‐dependent surface compositions (from X‐ray photoelectron spectroscopy survey spectra) and water contact angles (WCA) were found to tend toward asymptotic limiting values after ca. 30 days of storage in clean air, as previously reported by these and other authors. An entirely novel aspect of this work is to examine and compare time‐dependent WCA behaviors of NF and FF samples in terms of Wenzel (W) and Cassie‐Baxter (C‐B) model behaviors, including possible transitions from C‐B to W and their interpretation. We report “hydrophobic recovery” of O2 and NH3 plasma modified (i) electrospun nanofibrous (NF) mat and (ii) flat film (FF) polymer surfaces: poly(lactic acid); poly(urethane); and poly(caprolactone). Time‐dependent surface compositions from X‐ray photoelectron spectroscopy survey spectra and water contact angles (WCA) tended toward asymptotic values after roughly 30 days of atmospheric storage. We compare time‐dependent WCAs of NF and FF samples in terms of Wenzel (W) and Cassie‐Baxter (C‐B) model behaviors, including possible transitions from C‐B to W and their interpretation.