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Paresh Chokshi - One of the best experts on this subject based on the ideXlab platform.

  • Electrospinning of polymer solutions an analysis of instability in a thinning Jet with solvent evaporation
    2020
    Co-Authors: Dharmansh Deshawar, Karan Gupta, Paresh Chokshi
    Abstract:

    Abstract The present study examines the stability of a thinning straight Jet in Electrospinning process. The linear stability analysis is carried out to obtain the growth/decay rate of axisymmetric disturbance imposed on the thinning Jet. The analysis captures the role of solvent evaporation in the stability behavior of the linear path of the Electrospinning Jet. In contrast to many prior stability analyses which consider the Jet as a cylindrical filament with uniform radius, the present study analyzes the stability of a Jet which exhibits thinning under realistic Electrospinning conditions. Two different polymeric solutions are considered: the poly-isobutene (PIB) Boger fluid with low electrical conductivity and the highly conductive poly-ethylene oxide (PEO) solution in ethanol/water. At low extensional deformation, the rheology of the unentangled PIB-based Boger fluid is described by the Oldroyd-B model. The PEO solution, on the other hand, experiences a very high elongation rate due to the development of strong axial electric stress. The nonlinear rheology of the entangled PEO solution is appropriately described by the eXtended Pom–Pom (XPP) model, a variant of the classical tube model. The analysis reveals that the instability in low conductivity fluid is driven by the capillary forces, whereas the high conductivity fluid exhibits oscillatory conducting mode of instability driven by the coupled effect of axial electric field and surface charges. For both the reference fluids, the increase in solvent evaporation tends to decrease the disturbance growth rate to the extent that the axisymmetric instability is completely suppressed for a strong enough evaporation. The stabilizing role of solvent evaporation is attributed to the enhancement in fluid viscosity and elasticity due to increased polymer concentration upon evaporation. Thus, by suppressing the onset of axisymmetric instability during the straight Jet path, solvent evaporation potentially helps produce smooth fibers without bead formation.

  • analysis of axisymmetric instability in polymer melt Electrospinning Jet
    2018
    Co-Authors: Dharmansh Deshawar, Paresh Chokshi
    Abstract:

    Abstract The linear stability analysis is carried out for the straight Jet of a polymer melt in an Electrospinning process. The stability of axisymmetric disturbances is examined in order to comprehend the onset of fiber morphology with diametric variations or bead formation along the fiber under non-isothermal Electrospinning conditions. As the polymeric fluid (polylactic acid melt) is a low conductivity fluid with unentangled polymer molecules, the viscoelasticity is described using the non-linear rheological Giesekus constitutive model assuming very small axial conduction current. The non-periodic axisymmetric disturbances are imposed on the non-uniform radius Jet, obtained as the solution of the 1-D slender filament governing equations and the eigenspectrum for the disturbance growth rate is constructed under the realistic melt Electrospinning conditions. The growth rate corresponding to the leading mode in the eigenspectrum is found to increase with increasing surface tension forces and decrease with the enhanced external electric field. Thus, the leading growth rate behavior suggests that the classical Rayleigh–Plateau instability dominates over the conducting mode of instability for melt Electrospinning. Further, the role of non-isothermal conditions in the stability behavior is examined. The convective heat transfer from electrified Jet to the cooling ambiance leads to thicker fibers with greater stability to axisymmetric disturbances. The stabilizing effect of heat transfer is attributed mainly to the temperature sensitive fluid rheology. In particular, the enhancement in polymer viscosity in the Jet propagation direction is responsible for the build up of stabilizing viscoelastic stress. The fluid elasticity, denoted by the flow Deborah number, also tends to stabilize the electrified Jet as temperature drop along the flow increases the relaxation time of the polymer chains leading to high polymeric stress associated with the stretched chains. As crystallization of polymeric chains under non-isothermal condition is not considered, the analysis holds for either amorphous polymers or polymers with slow crystallization kinetics compared to the short residence time during the spinning flow.

  • stability analysis of an Electrospinning Jet of polymeric fluids
    2017
    Co-Authors: Dharmansh Deshawar, Paresh Chokshi
    Abstract:

    Abstract The axisymmetric instability, which has a potential to cause bead formation along the fibers produced by Electrospinning technique, is examined with the help of linear stability theory. The stability of a straight Jet is analyzed under conditions corresponding to the Electrospinning of two types of polymeric fluids, the PIB-based Boger fluid with low electrical conductivity and the highly conductive PEO solution in ethanol/water. For the former, the rheology is described by the Oldroyd-B model, suitable for unentangled polymers under weak elongational flow. On the other hand, the highly conductive polymer solution experiences a strong elongational flow due to very high axial electric force, for which the viscoelasticity is appropriately described using the eXtended Pom-Pom (XPP) model, the nonlinear rheological model for entangled polymeric systems. Contrary to previous studies, which oversimplifies the electrified Jet as a cylindrical Jet with uniform radius and other Jet variables, we analyze the stability of the realistic non-uniform thinning Jet as observed in Electrospinning experiments. The stability of the thinning Jet profile, obtained using the 1D slender body model, is examined by imposing non-periodic axisymmetric disturbances and constructing the spectrum of disturbance growth rate. The thinning Jet is found to be relatively less unstable than the uniform Jet, which is attributed to the stabilizing role of extensional stresses, in addition to the axial variation in surface charge density and electric field, present in the non-uniform deforming Jet, but ignored in the analysis of the uniform Jet. For both the reference fluids considered, the polymer addition renders the Jet stable and thus, suppresses the bead formation during straight Jet path of Electrospinning. Also, the enhancement in fluid elasticity, characterized by the flow Deborah number, plays a stabilizing role for the thinning Jet of Oldroyd-B fluid. However, for the XPP fluid, the fluid elasticity shows a rich behavior with a stabilizing effect for moderate values of Deborah number, attributed to stretching of polymer chain between the branch points, and a destabilizing effect for highly elastic fluids, due to strain rate softening. Increasing the strain hardening effect in the polymer solution, achieved by increasing number of arms at the branch point in the XPP molecule, tends to stabilize the Electrospinning Jet against axisymmetric disturbances potentially producing smooth bead-less fibers. While the instability in low conductivity fluid is driven by capillary forces, the instability in highly conductive fluid is an oscillatory conducting mode driven by the coupling of the surface charges and the axial electric field.

Yanzhong Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Direct printing of patterned three-dimensional ultrafine fibrous scaffolds by stable Jet Electrospinning for cellular ingrowth.
    2015
    Co-Authors: Huihua Yuan, Qihui Zhou, Min Bao, Xiangxin Lou, Yanzhong Zhang
    Abstract:

    Electrospinning has been widely used to produce ultrafine fibers in microscale and nanoscale; however, traditional Electrospinning processes are currently beset by troublesome limitations in fabrication of 3D periodic porous structures because of the chaotic nature of the Electrospinning Jet. Here we report a novel strategy to print 3D poly(L-lactic acid) (PLLA) ultrafine fibrous scaffolds with the fiber diameter of approximately 2 μm by combining a stable Jet Electrospinning method and an X-Y stage technique. Our approach allows linearly deposited electrospun ultrafine fibers to assemble into 3D structures with tunable pore sizes and desired patterns. Process conditions (e.g., plotting speed, feeding rate, and collecting distance) were investigated in order to achieve stable Jet printing of ultrafine PLLA fibers. The proposed 3D scaffold was successfully used for cell penetration and growth, demonstrating great potential for tissue engineering applications.

  • Stable Jet Electrospinning for easy fabrication of aligned ultrafine fibers
    2012
    Co-Authors: Huihua Yuan, Shifang Zhao, Bei Feng, Hongju Peng, Yanzhong Zhang
    Abstract:

    Electrospinning has emerged as an attractive technique for the fabrication of ultrafine fibers in micro-/nano-scale fineness. However, it is still a huge technological challenge in achieving aligned fibers and arrays due to the inherent chaotic motion of an Electrospinning Jet. We report herein a novel spinning approach termed stable Jet Electrospinning to offer a facile solution to the noted issue. It involves judiciously using an ultrahigh molecular weight poly(ethylene oxide) to formulate the viscoelasticity of a spinning dope such that a very long and stable Jet can be formed during Electrospinning. This consequently allows for readily collecting and fabricating individual fibers, multi-filament yarns, well-aligned unidirectional fiber arrays in a large area, and ordered fiber patterns by controlling fiber placement. Our approach could thus open up the possibility of achieving continuous aligned ultrafine fibers and structures in a straightforward and scalable fashion, suitable for a variety of practical applications.

Dharmansh Deshawar - One of the best experts on this subject based on the ideXlab platform.

  • Electrospinning of polymer solutions an analysis of instability in a thinning Jet with solvent evaporation
    2020
    Co-Authors: Dharmansh Deshawar, Karan Gupta, Paresh Chokshi
    Abstract:

    Abstract The present study examines the stability of a thinning straight Jet in Electrospinning process. The linear stability analysis is carried out to obtain the growth/decay rate of axisymmetric disturbance imposed on the thinning Jet. The analysis captures the role of solvent evaporation in the stability behavior of the linear path of the Electrospinning Jet. In contrast to many prior stability analyses which consider the Jet as a cylindrical filament with uniform radius, the present study analyzes the stability of a Jet which exhibits thinning under realistic Electrospinning conditions. Two different polymeric solutions are considered: the poly-isobutene (PIB) Boger fluid with low electrical conductivity and the highly conductive poly-ethylene oxide (PEO) solution in ethanol/water. At low extensional deformation, the rheology of the unentangled PIB-based Boger fluid is described by the Oldroyd-B model. The PEO solution, on the other hand, experiences a very high elongation rate due to the development of strong axial electric stress. The nonlinear rheology of the entangled PEO solution is appropriately described by the eXtended Pom–Pom (XPP) model, a variant of the classical tube model. The analysis reveals that the instability in low conductivity fluid is driven by the capillary forces, whereas the high conductivity fluid exhibits oscillatory conducting mode of instability driven by the coupled effect of axial electric field and surface charges. For both the reference fluids, the increase in solvent evaporation tends to decrease the disturbance growth rate to the extent that the axisymmetric instability is completely suppressed for a strong enough evaporation. The stabilizing role of solvent evaporation is attributed to the enhancement in fluid viscosity and elasticity due to increased polymer concentration upon evaporation. Thus, by suppressing the onset of axisymmetric instability during the straight Jet path, solvent evaporation potentially helps produce smooth fibers without bead formation.

  • analysis of axisymmetric instability in polymer melt Electrospinning Jet
    2018
    Co-Authors: Dharmansh Deshawar, Paresh Chokshi
    Abstract:

    Abstract The linear stability analysis is carried out for the straight Jet of a polymer melt in an Electrospinning process. The stability of axisymmetric disturbances is examined in order to comprehend the onset of fiber morphology with diametric variations or bead formation along the fiber under non-isothermal Electrospinning conditions. As the polymeric fluid (polylactic acid melt) is a low conductivity fluid with unentangled polymer molecules, the viscoelasticity is described using the non-linear rheological Giesekus constitutive model assuming very small axial conduction current. The non-periodic axisymmetric disturbances are imposed on the non-uniform radius Jet, obtained as the solution of the 1-D slender filament governing equations and the eigenspectrum for the disturbance growth rate is constructed under the realistic melt Electrospinning conditions. The growth rate corresponding to the leading mode in the eigenspectrum is found to increase with increasing surface tension forces and decrease with the enhanced external electric field. Thus, the leading growth rate behavior suggests that the classical Rayleigh–Plateau instability dominates over the conducting mode of instability for melt Electrospinning. Further, the role of non-isothermal conditions in the stability behavior is examined. The convective heat transfer from electrified Jet to the cooling ambiance leads to thicker fibers with greater stability to axisymmetric disturbances. The stabilizing effect of heat transfer is attributed mainly to the temperature sensitive fluid rheology. In particular, the enhancement in polymer viscosity in the Jet propagation direction is responsible for the build up of stabilizing viscoelastic stress. The fluid elasticity, denoted by the flow Deborah number, also tends to stabilize the electrified Jet as temperature drop along the flow increases the relaxation time of the polymer chains leading to high polymeric stress associated with the stretched chains. As crystallization of polymeric chains under non-isothermal condition is not considered, the analysis holds for either amorphous polymers or polymers with slow crystallization kinetics compared to the short residence time during the spinning flow.

  • stability analysis of an Electrospinning Jet of polymeric fluids
    2017
    Co-Authors: Dharmansh Deshawar, Paresh Chokshi
    Abstract:

    Abstract The axisymmetric instability, which has a potential to cause bead formation along the fibers produced by Electrospinning technique, is examined with the help of linear stability theory. The stability of a straight Jet is analyzed under conditions corresponding to the Electrospinning of two types of polymeric fluids, the PIB-based Boger fluid with low electrical conductivity and the highly conductive PEO solution in ethanol/water. For the former, the rheology is described by the Oldroyd-B model, suitable for unentangled polymers under weak elongational flow. On the other hand, the highly conductive polymer solution experiences a strong elongational flow due to very high axial electric force, for which the viscoelasticity is appropriately described using the eXtended Pom-Pom (XPP) model, the nonlinear rheological model for entangled polymeric systems. Contrary to previous studies, which oversimplifies the electrified Jet as a cylindrical Jet with uniform radius and other Jet variables, we analyze the stability of the realistic non-uniform thinning Jet as observed in Electrospinning experiments. The stability of the thinning Jet profile, obtained using the 1D slender body model, is examined by imposing non-periodic axisymmetric disturbances and constructing the spectrum of disturbance growth rate. The thinning Jet is found to be relatively less unstable than the uniform Jet, which is attributed to the stabilizing role of extensional stresses, in addition to the axial variation in surface charge density and electric field, present in the non-uniform deforming Jet, but ignored in the analysis of the uniform Jet. For both the reference fluids considered, the polymer addition renders the Jet stable and thus, suppresses the bead formation during straight Jet path of Electrospinning. Also, the enhancement in fluid elasticity, characterized by the flow Deborah number, plays a stabilizing role for the thinning Jet of Oldroyd-B fluid. However, for the XPP fluid, the fluid elasticity shows a rich behavior with a stabilizing effect for moderate values of Deborah number, attributed to stretching of polymer chain between the branch points, and a destabilizing effect for highly elastic fluids, due to strain rate softening. Increasing the strain hardening effect in the polymer solution, achieved by increasing number of arms at the branch point in the XPP molecule, tends to stabilize the Electrospinning Jet against axisymmetric disturbances potentially producing smooth bead-less fibers. While the instability in low conductivity fluid is driven by capillary forces, the instability in highly conductive fluid is an oscillatory conducting mode driven by the coupling of the surface charges and the axial electric field.

Huihua Yuan - One of the best experts on this subject based on the ideXlab platform.

  • Direct printing of patterned three-dimensional ultrafine fibrous scaffolds by stable Jet Electrospinning for cellular ingrowth.
    2015
    Co-Authors: Huihua Yuan, Qihui Zhou, Min Bao, Xiangxin Lou, Yanzhong Zhang
    Abstract:

    Electrospinning has been widely used to produce ultrafine fibers in microscale and nanoscale; however, traditional Electrospinning processes are currently beset by troublesome limitations in fabrication of 3D periodic porous structures because of the chaotic nature of the Electrospinning Jet. Here we report a novel strategy to print 3D poly(L-lactic acid) (PLLA) ultrafine fibrous scaffolds with the fiber diameter of approximately 2 μm by combining a stable Jet Electrospinning method and an X-Y stage technique. Our approach allows linearly deposited electrospun ultrafine fibers to assemble into 3D structures with tunable pore sizes and desired patterns. Process conditions (e.g., plotting speed, feeding rate, and collecting distance) were investigated in order to achieve stable Jet printing of ultrafine PLLA fibers. The proposed 3D scaffold was successfully used for cell penetration and growth, demonstrating great potential for tissue engineering applications.

  • Stable Jet Electrospinning for easy fabrication of aligned ultrafine fibers
    2012
    Co-Authors: Huihua Yuan, Shifang Zhao, Bei Feng, Hongju Peng, Yanzhong Zhang
    Abstract:

    Electrospinning has emerged as an attractive technique for the fabrication of ultrafine fibers in micro-/nano-scale fineness. However, it is still a huge technological challenge in achieving aligned fibers and arrays due to the inherent chaotic motion of an Electrospinning Jet. We report herein a novel spinning approach termed stable Jet Electrospinning to offer a facile solution to the noted issue. It involves judiciously using an ultrahigh molecular weight poly(ethylene oxide) to formulate the viscoelasticity of a spinning dope such that a very long and stable Jet can be formed during Electrospinning. This consequently allows for readily collecting and fabricating individual fibers, multi-filament yarns, well-aligned unidirectional fiber arrays in a large area, and ordered fiber patterns by controlling fiber placement. Our approach could thus open up the possibility of achieving continuous aligned ultrafine fibers and structures in a straightforward and scalable fashion, suitable for a variety of practical applications.

Xiaohong Qin - One of the best experts on this subject based on the ideXlab platform.

  • controlled stretching of the first spiral in Electrospinning whipping Jet via surface charge
    2021
    Co-Authors: Sailing Lei, Chengdong Xiong, Zhenzhen Quan, Xiaohong Qin
    Abstract:

    Abstract Generally, the first spiral of whipping Jet (FSWJ) has the maximum motion velocity in the stretching and thinning of Electrospinning Jet. Accurate control of the stretching of FSWJ is vital to generate nanofibers with expected diameter and property, but it is still a technical bottleneck. Herein, a theoretical model has been established to quantitatively predict the diameter of FSWJ. It shows that the variation of radius with axial distance follows a power law with an exponent −1/4 for a fully charged Jet, while the exponent increases for a partly charged Jet. In addition, the stretching of FSWJ has been predicted by a scaling model of relation between stretch rate and axial distance, whose exponent gradually increases to −1/2 as the surface charge tends to saturation. Meanwhile, the experimental results achieved by a novel characterization method agreed well with the theoretical values calculated from the derived models. This work provides a new insight on controlling the Jet stretching as well as the fiber diameter, which can promote the morphological and functional design of electrospun nanofibers.

  • effect of licl on the stability length of Electrospinning Jet by pan polymer solution
    2005
    Co-Authors: Xiaohong Qin, Shanyuan Wang, Torres Sandra, David Lukas
    Abstract:

    Abstract Polyacrylonitrile(PAN) is used to study the effect of the instability on Electrospinning nanofibers by adding LiCl. The theoretical analysis showed that the electricity potential with high content of LiCl descends more sharply than low content of LiCl during the movement of charged fibers. The former caused Jet instability to occur earlier and also caused the stability length of Electrospinning Jet to decrease. The experimental data agreed very well with our theoretical analysis by a series of experiments.