ma5016616_si_001.pdf (2.94 MB)
Core-Liquid-Induced Transition from Coaxial Electrospray to Electrospinning of Low-Viscosity Poly(lactide-co-glycolide) Sheath Solution
journal contribution
posted on 2015-12-17, 06:01 authored by C. J. Luo, M. EdirisingheCo-electrospinning has demonstrated
that polymer solutions below
the entanglement concentration can be made into fibers as an encapsulated
core in an electrospinnable sheath solution containing a carrier/template
polymer. The carrier polymer may require removal at a later stage.
This work shows for the first time that without increasing the polymer
concentration/molecular weight or needing a template polymer, simply
infusing a liquid in the core nozzle can cause the sheath polymer
solution (viscosity <20 mPa s) to electrospin instead of electrospray
in a coaxial electrified jet. Different from coelectrospinning, the
core liquid can be a common solvent such as water and does not require
a readily electrospinnable carrier polymer. The process was not limited
to one core liquid system; infusing solvents and nonsolvents with
different properties in the core generated either beaded fibers or
continuous fibers from the sheath solution. The process of fiber formation
instead of particle breakup was attributed to the relaxation time
of the elastic polymer sheath solution becoming longer than the growth
rate of the Rayleigh instability in the compound jet upon the infusion
of a second solvent in the core. Key parameters of the process included
high surface tension of the core liquid (e.g., water and glycerol),
high interfacial tension between the core and the sheath liquids,
and electrohydrodynamic operating parameters such as flow rate and
applied voltage. Given that charge was transferred from the sheath
solution to the core liquid, differences in the dielectric constant
and electrical conductivity of the core liquids showed little influence
on the process. Fibers also formed irrespective of the miscibility
and solubility of the solvent, though in the case of a nonsolvent,
a lower miscibility was desirable to minimize polymer precipitation
at the core–sheath interface. The process was investigated
using poly(lactide-co-glycolide) as a model system,
with polycaprolactone and polymethylsilsesquioxane systems presented
as two additional examples. This work documents new roles of solvents
in coaxial electrohydrodynamic processes and presents a useful method
to obtain micro- and nanofibers from low-viscosity solutions without
using a template polymer.