Fibers were electrospun from a solution comprised of oppositely charged polyelectrolytes, in efforts to achieve highly confined macromolecular packaging. A stoichiometric ratio of poly(allylamine hydrochloride) and poly(acrylic acid) solution was mixed in an ethanol-water co-solvent. Differential scanning calorimetry (DSC) analysis of electrospun fibers demonstrated no indication of glass transition, Tg. Infrared spectroscopy (FTIR) analysis of the fibers as a function of temperature, demonstrated an amidation process at lower temperature compared to cast film. Polarized FTIR indicated a preference of the functional groups to be perpendicular to the fiber axis. These results imply formation of mixed phase fibers with enhanced conditions for intermolecular interactions, due to the highly aligned and confined assembly of the macromolecules. The tunable intermolecular interactions between the functional groups of the polyelectrolytes, impact pH-driven, reversible swelling-deswelling of the fibers. The degree of ionization of PAA at pH 5.5 and pH 1.8 varied from 85% to 18%, correspondingly, causing transformation of ionic interactions to hydrogen bonding between the functional groups. The chemical change led to a massive water diffusion of 500% by weight and to a marked increase of 400% in fiber diameter, at a rate of 0.50 μm s(-1). These results allow for manipulation and tailoring of key fiber properties for tissue engineering, membranes, and artificial muscle applications.

The macromolecular organization in system composed of anionic poly(acrylic acid) (PAA) and cationic chitosan (Cs), with different degrees of deacetylation (DD), under extensive elongational flow, is described. Cs/PAA nanofibers were obtained, and polyelectrolyte complexation only occurred when fibers were immersed in fluid media of a certain pH. Assembled polyelectrolytes complexes formed a pH-triggered system, as demonstrated by reversible change of the swelling degree, by 3 orders of magnitude, and a change on the elastic modulus, by 2 orders of magnitude. Both the swelling degree and the elastic modulus proved sensitive to the DD of Cs. Rheological measurements showed that increased DD of Cs resulted in a decrease in viscosity of both pure Cs and precursor Cs/PAA solutions, attributed to repulsive interactions between ionized amino groups in Cs. At the same time, a DD-dependent change in balance between hydrogen bonding and ion-dipole interactions between the components in Cs/PAA, was responsible for the more pronounced viscosity decrease in these solutions.

The behavior of a mixture of negatively charged cellulose nanocrystals (CNCs) and positively charged poly(allylamine) (PAAm) is examined in aqueous media. By modulating the pH, the acting Coulomb forces can be varied that can lead not only to adsorption of PAAm chains on the CNC surface but also to the development of a supermolecular structure by bridging of CNC rods by extended PAAm chains. This bridging can result in the formation of CNC clusters, which was demonstrated experimentally. Light scattering and rheological studies showed that these clusters begin to grow and merge, ultimately forming a global percolated network above a critical degree of PAAm ionization.The adsorption of PEs on oppositely charged nanoparticles (cNPs) influences their net charges; charge neutralization causes van der Waals forces to dominate and consequently leads to aggregation of cNPs, whereas charge reversal stabilizes the colloidal suspension upon sufficient PE adsorption. 28 Under specific conditions, PEs can simultaneously adsorb on two (or maybe more) cNPs, generating "attractive" bridging forces between these particles. 29 The probability of such bridging interactions depends on the interparticle distance, the PE and nanoparticle charge densities, the PE chain length and stiffness, and the ionic strength of the solution. 30 Simulations of interactions between a cNP and an oppositely charged weak PE showed induced ionization and modification of the charge distribution along the charged chain. [31][32][33][34][35] To date, only a few works [36][37][38][39] have experimentally demonstrated bridging of cNPs by PEs. However, the effect of PE charge density on bridging between cNPs to ultimately form a global percolated network consisting of weak PEs and cNPs is so far unknown.Additional Supporting Information may be found in the online version of this article.

Intermolecular interactions as well as macromolecular conformation affect the rheological and microstructural properties of polyelectrolyte complexes (PECs) solutions. The properties of semi-dilute solutions of weakly charged PECs can be controlled by the degree of ionization and solvent composition. In this work, we examined the effect of ethanol as a co-solvent on PECs composed of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) at low pH. The aqueous PECs solution was turbid, indicating formation of large aggregates, whereas PECs solution in water/ethanol (60:40 w/w) was transparent, implying no aggregation, and demonstrated higher relative viscosity than the aqueous solution, implying pronounced network formation. Imaging PECs solution by transmission electron microscopy (TEM) demonstrated aggregation, whereas the solution prepared with the mixed solvent revealed almost no phase contrast. Small-angle X-ray scattering (SAXS) of PECs in the aqueous solution indicated the presence of aggregates, while PECs in mixed solvent demonstrated a swelled macromolecular conformation with diminished aggregation. PECs with no ionic interactions in the mixed solvent assumes a homogenous network structure, which enables PECs solution processing by electrospinning.

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