Electrospinning Fibers from Oligomeric Complex Coacervates: No Chain Entanglements Needed

The electrospinning field is dominated by studies that investigate parameters, such as polymer concentration and chain length, to identify conditions where the polymer chains are sufficiently entangled to facilitate fiber formation. Here, we report the first demonstration that linear, nonentangled, oligomeric polyelectrolytes can be electrospun into fibers using a traditional single-nozzle setup. Previously, we have demonstrated that the associative phase separation phenomenon known as complex coacervation facilitates the electrospinning of polyelectrolyte complex fibers directly from water. In this work, we synthesized polycations and polyanions with degrees of polymerization ranging from ∼500 down to <10, representing average molecular weights on the order of 100 to 1 kg/mol. We then quantified the phase behavior and viscosity of our various coacervate samples as a function of both chain length and salt concentration. Our results confirm that the polymer concentration in all samples was near or above the estimated value for the overlap concentration and that only the longest polymer samples were expected to experience entanglements. However, we were able to electrospin fibers from all of our coacervate samples, even oligomers. Thus, the electrospinnability of coacervates is fundamentally different from the traditional electrospinning of linear, neutral polymers or solutions composed of polyelectrolytes mixed with neutral polymers. In the same way that coacervation represents a novel way to enable the electrospinning of polyelectrolytes from water, the associative interactions driving phase separation eliminate the need for entanglements by slowing the timescale for relaxation. Our results suggest an alternative route that enables the electrospinning of novel solutions by decoupling chain-length requirements from other length-dependent parameters.