Wetting and aging behaviors for several O 2 and NH 3 plasma treated nanofibrous and flat film polymer materials: A comparison

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 O 2 and NH 3 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.