Wetting of nanofiber yarns

• We developed a model of wetting of nanofiber yarns.
• The effect of nanofiber tilt was analyzed.
• We electrospun yarns from cellulose acetate and poly(methyl methacrylate).
• Contact angles were rigorously measured and analyzed.
• Wetting properties of nanofiber yarns are significantly different from those of films.

In order to probe and interpret the wetting properties of nanofiber yarns, a modification of the original Cassie–Baxter model of apparent contact angle was developed. The model includes the effect of fiber tilt: on the surface of tilted fiber the contact line describes an elliptical arc rather than a circular. With this new interpretation of the capillary rise experiments we studied the wetting properties of nanofiber yarns made of cellulose acetate (CA), poly(methyl methacrylate) (PMMA), and their blends. Wetting properties of nanofiber yarns were compared with those of the films. The Zisman plot was created to show that the critical interfacial tensions of CA and PMMA films are very close to each other. However, the contact angles of water droplets placed on the films casted from the CA/PMMA blends appeared significantly smaller than those obtained on the pure CA and PMMA films. Inspection of the film morphology revealed a bumpy structure of the CA/PMMA films leading to their enhanced hydrophilicity. In contrast, the nanofibers that were electrospun form the CA/PMMA blends had smooth surface. We were able to confirm that the contact angles of water with the CA/PMMA nanofibers are similar to those of water with the pure CA and PMMA films.

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