Wetting of Polyamide Film Surfaces with Electrospun Nanofibers
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Wetting of Polyamide Film Surfaces with Electrospun Nanofibers Urszula Stachewicz 1 Chantal Benett2 and Asa H. Barber 1,2 1 Nanoforce Technology Ltd. Queen Mary, University of London, Joseph Priestley Building, Mile End Road, London, E1 4NS, U. K. 2 School of Engineering and Materials Science, Queen Mary, University of London, , Mile End Road, London, E1 4NS, U. K. ABSTRACT The wetting behavior of polyamide films was modified by depositing electrospun nanofibers manufactured from the same polyamide material. Glycerol contact angles on the film surfaces with low coverage of electrospun nanofibers were successfully predicted using a CassieBaxter relationship but could not be predicted for high electrospun nanofiber coverage. INTRODUCTION The surface properties of electrospun nanofibers have been measured predominantly on macroscopic samples using wetting experiments where the organization of the fibrous network defines overall behavior. Usually the sessile drop method in static water contact angle measurement is used for the characterization of nanofibrous membranes [1] but the effect of surface porosity using Cassie-Baxter and Wenzel theories need to be employed when considering these contact angles [2]. Measurement of contact angle between liquids of differing surface tensions and an individual electrospun fiber is therefore the most direct method for understanding the inherent surface properties of the fiber. The surface free energy of electrospun polyamide 6 (PA6) nanofibers have been measured directly using a Wilhelmy based method using atomic force microscopy (AFM). Specifically, the surface free energy of the electrospun fibers were found to be 47.0 ± 2.8 mJm-2, which is higher than a surface free energy of 40.3 ± 1.7 mJm-2 for a corresponding solution processed PA6 film [3]. Owens-Wendt plots highlighted how the surface free energy increase for electrospun nanofibers is predominantly from an increased polar component at the nanofiber surface. X-ray photoelectron spectroscopy (XPS) analysis supported these results and indicated an increase in polar oxygen groups at the nanofiber surface relative to the film [3]. In this study we use previous literature describing the surface properties of individual PA6 nanofibers to describe the macroscopic liquid droplet contact angles on PA6 nanofibers network. These electrospun fibers were prepared on PA6 films and highlighted how the wetting behavior of polymer films are modified by the presence of electrospun fibers. EXPERIMENTS Polyamide 6 (PA6, Mw=24000 gmol-1, BASF, Ultramid B33 L, Germany) was dissolved in a mixture of acetic acid (99.7%, Sigma Aldrich, U.S.A.) and formic acid (98%, Sigma Aldrich, U.S.A.) (50/50 mass ratio) to produce a resultant polymer concentration of 24 % by
47
weight in solution. PA6 films were prepared by placing approximately 5 ml of polymer solution onto a glass slide rotating in a spin coater (SCS G3 Spin Coater, U.S.A.) operating at 800 rpm for 1 min. The electrospinning of nanofibers was performed using single nozzle setup with a distanc
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