Conformation of dilute poly(vinyl alcohol)-borax complex by asymmetric flow field-flow fractionation

Complexation between poly(vinyl alcohol) (PVA) and borax in aqueous solution yields a dynamic polyelectrolyte. Study of chain conformation of such a polyelectrolyte is challenging due to the difficulty in separating different macromolecular species. In this study, we investigated conformation of dilute PVA chains complexed with borax in a wide concentration range between 0.02 and 78.6 mM using asymmetrical flow field-flow fractionation (AF4). We find that elution of the complexes is strongly influenced by the borax concentration owing to (1) the charged complex is repelled electrostatically by the charged bottom membrane of the AF4 channel, and (2) the Debye screening length reduces with increasing a charge density. The chain conformation of PVA-borax complexes depends on both polymer molar mass and borax concentration. At low borax concentrations of 0.02~0.5 mM, a transition from random coil to rod-like conformation is observed with increasing the chain size. At borax concentrations of 1 mM and higher, all chains become random coil owing to a reduced screening length of the electrostatic repulsion.