No abstract

Nonwoven fibrous membranes were formed from electrospinning lecithin solutions in a single processing step. As the concentration of lecithin increased, the micellar morphology evolved from spherical to cylindrical, and at higher concentrations the cylindrical micelles overlapped and entangled in a fashion similar to polymers in semi-dilute or concentrated solutions. At concentrations above the onset of entanglements of the wormlike micelles, electrospun fibers were fabricated with diameters on the order of 1 to 5 micrometers. The electrospun phospholipid fibers offer the potential for direct fabrication of biologically based, high-surface-area membranes without the use of multiple synthetic steps, complicated electrospinning designs, or postprocessing surface treatments.

The influence of polyelectrolyte rheological 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 rheological 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 3.75 ) 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 ).

Structure-property relationships for polymerized ionic liquids (PILs) relate chemical structure to ionic conductivity and reveal the importance of glass transition temperature ( T g ) and the energy associated with an ion-hopping mechanism for ion conduction for a series of alkyl-substituted vinylimidazolium PILs. The alkyl-substituted vinylimidazolium-based PILs with varying lengths of n -alkyl substituents provide diverse precursors with exchangeable anions to further enhance thermal stability and ionic conductivity. As the anion size increases, regardless of alkyl substituent length, T g decreases and the onset of weight loss, T D , increases. As the length of the alkyl substituent increases, T g decreases for PILs with Br − and BF 4 − counteranions. Ionic conductivity increases over an order of magnitude upon exchange of the counteranion from TfO − < Tf 2 N − . due to their unique combination of physical properties including high thermal stability, wide electrochemical window, negligible vapor pressure, and potentially high ionic conductivities. [3][4][5][6][7] Two particular classes of ILs are polymerizable ILs (PILs) that contain polymerizable functional groups and room temperature ILs (RTILs) with melting temperatures at or below room temperature. [ 8 ] Potential applications have included electrolytes in electromechanical transducers, artifi cial muscle fabrication, and non-volatile solvents for a myriad of chemical reactions. [ 9 ] Chen and Elabd investigated the solution properties and subsequent formation of electrospun fi bers of an imidazolium-containing methacrylate-based PIL. [ 10 ] This study revealed solution properties similar to polyelectrolyte solutions, and electrospun fi bers formed with intermediate fi ber diameters and onset of fi ber formation between polyelectrolyte and neutral polymers. The fi brous mats exhibited promising ionic conductivities at room temperature, and upon swelling with a RTIL, ionic conductivities were on the order of 10 mS cm − 1 . Long and co-workers also investigated the impact of counteranion on the solution and thermal properties of ammoniumbased polyelectrolytes. [ 11 ] Our study revealed the important infl uence of anion selection on the T g of the polyelectrolyte, and we observed polyelectrolyte electrospinning