Solution rheological behavior and electrospinning of cationic polyelectrolytes

The influence of polyelectrolyte theological behavior on the electrospinning process was determined for a series of poly(2-(dimethylamino) ethyl methacrylate hydrochloride) (PDMAEMA·HCl) aqueous solutions in the presence of added NaCl. Solution Theological studies revealed that PDMAEMA·HCl in an 80/20 w/w water/methanol cosolvent displayed polyelectrolyte behavior based on the scaling relationship between specific viscosity (η _sp) and concentration in the semidilute unentangled and semidilute entangled regimes. The entanglement concentration (C _e) increased with NaCl concentration due to screening of the electrostatic repulsive forces along the PDMAEMA·HCl backbone, which enabled the PDMAEMA·HCl chains to adopt a flexible, coillike conformation. Moreover, the scaling behavior in the semidilute entangled regime shifted from polyelectrolyte (η _sp ∼ C ^1.5) to neutral polymer behavior (η _sp ∼ C ^1.5) in the high salt limit. The electrospinning performance of PDMAEMA·HCl solutions was also dependent on NaCl concentration, and NaCl-free PDMAEMA·HCl solutions did not form fibers at concentrations less than 8C _e. The minimum concentration for fiber formation decreased as the level of NaCl was increased due to screening of the repulsive, electrostatic interactions between charged repeating units that served to stabilize the electrospinning jet. Moreover, because of the high electrical conductivity of the polyelectrolyte solutions, the electrospun polyelectrolyte fibers were 2-3 orders of magnitude smaller in diameter compared to fibers that were electrospun from solutions of neutral polymers of equal zero shear viscosity (η ₀) and normalized concentration (C/C _e).