Recording IR spectra for individual electrospun fibers using an in situ AFM-synchrotron technique

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Recording IR spectra for individual electrospun fibers using an in situ AFM-synchrotron technique Urszula Stachewicz 1, Fei Hang2, Russell J. Bailey2, Himadri S. Gupta2, Mark D. Frogley3, Gianfelice Cinque3 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 Material Science, Queen Mary, University of London, Mile End Road, London, E1 4NS, U. K. 3 Diamond Light Source Ltd, Diamond House, Harwell Science and Innovation Campus, Didcot, OX11 0DE, U.K. Abstract A setup is described where an individual electrospun polyamide fiber is attached to an atomic force microscope (AFM) tip and structural information collected with synchrotron micro Fourier transform infrared spectroscopy (μFT-IR). The combination of AFM and synchrotron μFT-IR therefore highlights the potential for recording structure-mechanical property relationships simultaneously in materials with sub-micron dimensions. INTRODUCTION Electrospun fibers with sub-micron diameters are known to have improved mechanical properties when compared to their bulk polymeric equivalents, suggesting polymer chain alignment from the electrospinning process [1, 2]. Previous work from our group has measured the mechanical properties of individual electrospun fibers directly using atomic force microscopy (AFM) [3], with recent experiments allowing direct tensile testing along the principal fiber axis. Since the polymer chain organization during this tensile testing defines the mechanical properties of the fiber, structural investigations during mechanical deformation can elucidate the origin of the improved electrospun fiber mechanical performance. However, information on changes in the electrospun fiber structure during mechanical deformation is generally lacking. Micro Fourier transform infrared spectroscopy ( FT-IR) therefore presents a considerable opportunity to examine the development of structural changes in individual electrospun fibers during tensile deformation, especially as the spatial resolution of FT-IR can resolve sub-micron electrospun fiber diameters when compared to less coherent desktop FT-IR techniques. Additionally, IR spectroscopy has been used to show improvements in the mechanical properties of fibrous materials due to size effects [4], thus highlighting further advantages of evaluating electrospun fiber mechanics with FT-IR. This work describes methodology to obtain IR spectrum from individual fibers using FT-IR from a synchrotron source. EXPERIMENTS Polyamide 6 (PA6, 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.)

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(50/50 mass ratio) to produce a resultant polymer concentration of 24 %wt. in solution. The PA6 polymer solution was electrospun using a single nozzle electrospinning setup with a distance between the metal needle and the grounded collector of 15 cm. The applied voltage was 15 kV and the solution flow rate to the

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