We analyzed each polymer film by atomic force microcopy (AFM; Agilent Technologies 5550 Scanning Probe Microscope, Agilent Technologies, Inc., Santa Clara, CA). The maximum scan range was approximately 10 μm × 10 μm using a cantilever with a force constant of 21–78 N/m, resonance frequency of 250–390 kHz, and tip height of 10–15 μm (NCH-10, Nano World, Zurich, Switzerland). AFM was performed in air acoustic AC mode. AFM image analysis was performed using Pico Image Software (Agilent Technologies).
The wettability of the polymer surfaces was characterized by contact angle measurement [15 (link)]. The static contact angle on each polymer surface was measured using the sessile drop method at room temperature. For the sessile drop method, 2 μL of deionized water was dropped on a dried polymer film using a microsyringe. The static contact angle was observed 30 s later under a microscope (G-1-1000; ERMA Inc., Tokyo, Japan). After at least five readings which were obtained for different areas of the polymer, the measurements were averaged to arrive at a final contact angle (n = 6).
The wettability of the polymer surfaces was characterized by contact angle measurement [15 (link)]. The static contact angle on each polymer surface was measured using the sessile drop method at room temperature. For the sessile drop method, 2 μL of deionized water was dropped on a dried polymer film using a microsyringe. The static contact angle was observed 30 s later under a microscope (G-1-1000; ERMA Inc., Tokyo, Japan). After at least five readings which were obtained for different areas of the polymer, the measurements were averaged to arrive at a final contact angle (n = 6).