Dispersity and spinnability: Why highly polydisperse polymer solutions are desirable for electrospinning

Abstract

We develop new criteria that describe the minimum concentration limits controlling the spinnability of dilute and semi-dilute flexible polymer solutions with high molecular weight and varying polydispersity. By asserting that the finite and bounded extensional viscosity of the solution is the key material property determining the stability of a filament during spinning, we propose a new scaling relating the minimum necessary concentration of a polymer c spin to its molecular weight M and the quality of the solvent (through the excluded volume exponent n) of the form c spin ⇠ M (n+1) . This new scaling differs from the classical interpretation of the coil overlap concentration c ⇤ or entanglement concentration c e as the minimum concentration required to increase the viscosity of the spinning dope, and rationalizes the surprising spinnability of high molecular weight polymers at concentrations much lower than c e .Furthermore, we introduce the concept of an extensibility average molecular weight M L as the appropriate average for the description of polydisperse solutions undergoing an extensiondominated spinning process. In particular it is shown that this extensibility average measure, and thus the solution spinnability, is primarily determined by the extensibility of the highest molecular weight fractions. For highly polydisperse systems this leads to an effective lowering of the minimum required concentration for successful fiber spinning (in comparison to narrowly distributed polymer solutions of similar weight average molecular weights). These predictions are validated with experimental observations of the electrospinnablity of monoand polydisperse poly(methyl methacrylate) (PMMA) solutions as well as a model bimodal blend, and through comparison to published literature data on the minimum spinnable polymer concentration for a variety of flexible long chain polymers over a range of molecular weights.

The relevance of extensional rheology on electrospinning: the polyamide/iron chloride case

“…The polymer concentration in the studied system is around e c and thus it is above the concentration set as minimum value for the solution to be spun [23]. Nevertheless, when a critical threshold of salt content exceeds, a good spinnability condition cannot be achieved anymore, despite the polymer concentration should be in principle high enough.…”

“…The critical overlap concentration which is typically found to be ten times above viscosity, the solution of 15 wt% PA6 in formic acid is expected to lead to successful fibre electrospinning [23].…”

Nanofiber formation in the presence of an external magnetic field in electrospinning

“…To do so, a lower bound of the Newtonian viscosity was associated with the critical entanglement concentration to sufficiently resist the capillary breakup. However, there are several evidences that the capillary instability can be suppressed even for solutions with concentrations lower than critical entanglement concentration [43]. Among different intricate models, a relatively workable one has been introduced by Helgeson et al to address the issue [37].…”

“…This helps to perform a scaling analysis to find the minimal necessary polymer concentration required to determine the spinnability of a given polymer solution. This approach interestingly addressed the effect of the molecular weight distribution of polymers on their spinnability and resulting morphology of the produced fibers [43].…”

Electrospinning predictions using artificial neural networks

“…The influence of polydispersity (or molecular weight distribution) on viscosity (and hence fibre diameter) is moderate [50][51][52]. As this information is often not known it will not be directly included in this work and will provide a known source of error.…”