Studies on Structures and Ultrahigh Permeability of Novel Polyelectrolyte Complex Membranes

Abstract

This work studies the aggregation structures and free volumes of novel polyelectrolyte complex membranes (PECMs) and correlates the two with their ultrahigh permeability to water. Solution-processable PECs between poly(2-methacryloyloxy ethyl trimethylammonium chloride) (PDMC) and sodium carboxymethyl cellulose (CMCNa) were prepared in a two-step method, i.e., precipitation in HCl and redispersion in NaOH. PECMs were subsequently made in a solution casting method. Chemical and aggregation structures of PECs solids were characterized by FT-IR, element analysis (EA), zeta potential, transmission electron microscopy (TEM), and dynamic light scattering (DLS). Surface and cross-section structures of PECMs were characterized by a field emission scanning microscopy (FESEM) and an atomic force microscopy (AFM). Free volume of PECMs was characterized by positron annihilation lifetime spectroscopy (PALS). The free volume of PECMs is larger than that of component polyelectrolyte and is ascribed to the unique aggregation structures of PECMs. Moreover, PALS shows that a long lifetime component (tau(4)) exists with PECMs, indicating that there are water channels in PECMs. Due to these channels, PECMs showed ultrahigh permeability and selectivity.