Effects of processing parameters on jet diameter profile in electrospinning of poly(N-isopropylacrylamide) solutions in dimethylformamide

  • 王 煜

Student thesis: Doctoral Thesis


The electrospinning of poly(N-isopropylarylamide)/dimethylformamide (PNIPAM/DMF) solutions with various concentrations was performed at room temperature Prior to electrospinning the rheological properties were investigated which used to determine the relaxation time solution viscosity overlap and entanglement concentrations In this study we reveal the effects of solution properties and processing parameters on the morphologies of Taylor cone/jet/as-spun fibers Light scattering technique with He-Ne laser source was carried out to measure the jet diameter (dj(z)) at different positions (z) from needle-end to the jet-end position The jet diameter profile was constructed from the magnitude of scattering vector of first intensity maximum (qm 1) which obtained from the equatorial intensity profiles by R G B theory: dj(z)=10 22/qm 1 Based on the assumption that no solvent evaporation took place in the cone-jet region the jet velocity (vj(z)) could be calculated by mass balance (vj(z)=4Q/?dj(z)2) The slope in the jet velocity profiles represent the strain rate that applied on the electrospinning jet According to the derived strain rate three distinct regions could be identified Regime I is from the needle-end to the initial jet section The liquid element was stretched significantly by the highest strain rate in the straight jet section thus the jet diameter decreased significantly in this region Due to the high strain rates in regime I the chain orientation even chain stretch may occur Along the jet dj keep decreasing as a scaling law: dj(z)~z-n in this range which named region II The derived exponent n is a function of solution viscosity not a function of flow-rate and applied voltage Near the jet-end position jet diameter finally reached an asymptotic value (dj e) despite of the parameters applied named region III Because the derived strain-rate in region III is around 0 s-1 the chain relaxation process would occur The jet diameter on the jet-end (dj e) is a function of flow-rate but independent of solution viscosity The existence of regime III could be explained by the force balance between air drag stress and electrical stress which induced by the surface charges on the jet in the electrical field The derived result dj e~Q0 41 was consistent with our experimental results Based on our finding the resistant force by air friction is not negligible at the straight jet-end and progressively becomes the key factor in determining dj e and the initial jet whipping behavior In the last section we used a high speed camera to study the effect of solution viscosity on the vibration process of electrospinning jet in the initial jet whipping region for 7 9 and 17 wt% solutions There are wave-like morphologies for electrospinning jet in the initial jet whipping region despite of solution concentration But only 17 wt% solution has a periodicity motion which composed by high frequency and low frequency vibrations The effects of solution viscosity on the jet velocities on the lateral and axial directions and vibration frequency were investigated by the measurement of wavelength in wave-like motion and the jet velocity in the axial direction
Date of Award2018 Jan 10
Original languageEnglish
SupervisorChi Wang (Supervisor)

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