Electrospinning Ethanol–Water Solutions of Poly(Acrylic Acid): Nonlinear Viscosity Variations and Dynamic Taylor Cone Behavior

Shameek Vats,Jan P.F Lagerwall,Francesco Basoli,Lawrence W Honaker,Margaret W Frey

doi:10.1002/mame.202100640

Abstract

AbstractElectrospinning of polymer solutions is a multifaceted process that depends on the careful balancing of many parameters to achieve a desired outcome, in many cases including mixtures of multiple solvents. A systematic study of how the solution viscosity —a good probe of solvent–polymer interactions—and the electrospinnability change when poly(acrylic acid) (PAA) is dissolved in ethanol–water mixtures at varying mixing ratio is carried out. A pronounced maximum is found in at a water‐to‐ethanol molar ratio of about 2:1, where the solvent mixture deviates maximally from ideal mixing behavior and partial deprotonation of carboxyl groups by water coincides synergistically with dissolution of the uncharged protonated PAA fraction by ethanol. The PAA concentration is tuned as a function of water–ethanol ratio to obtain a common value of for all solvent mixtures that is suitable for electrospinning. For high PAA content, the Taylor cone grows in volume over time despite minimum solution flow rate, even experiencing surface gelation for ethanol‐rich solutions. This is attributed to the hygroscopic nature of PAA, drawing excess water into the Taylor cone from the air during spinning.

Highlights

The maximum deviation from ideal mixing behavior can be seen in a maximum of viscosity of ethanol–water mixtures at xw ≈ 0.7.[57] this viscosity maximum is three orders of magnitude lower than that of the Poly(acrylic acid) (PAA) solutions studied here; the impact of the viscosity of the solvent itself is negligible in the context of our study
We note that the most common value xw ≈ 0.6[54] for maximum non-ideal water–ethanol mixing coincides rather well with xw ≈ 0.65 for maximum PAA solution viscosity seen in Figure 2, as well as with the minimum of solvent quality for PVP in ethanol–water mixtures studied by Guettari et al.[46]
We can conclude that the mole fraction where we find a maximum PAA solution viscosity corresponds to the conditions where the ethanol–water mixture is the furthest from ideal, with a microphase segregation of water and ethanol which is at its maximum

Summary

Introduction

W. Honaker Laboratory of Physical Chemistry and Soft Matter Wageningen University & Research Wageningen 6703 DE, The Netherlands phenomena such as phase separation and gelation can disrupt the electrospinning process.[6,40] A common strategy ( in single-phase spinning) is to use mixtures of solvents, but many papers report only a fix solvent composition, without including any systematic study of how the polymer solution properties change with solvent mixing ratio. Basoli Department of Engineering Università Campus Bio-Medico di Roma teractions, there is good reason to carry out such a systematic study In this context, poly(acrylic acid) (PAA, Figure 1) is interesting, as it is readily soluble in water as well as ethanol,[41,42] allowing a complete study of how mixing these two solvents af-

Results

Discussion

Conclusion