Ion Migration through a Polymer Solution: Microviscosity

The ion migration in polymer solutions of different molecular weights is investigated by conductometry for various inorganic salts. The electric conductivity κ declines with increasing the number concentration of polymer c_p at a given salt concentration c_s. All reduced conductivities for salts of the same valency type collapse into a single curve for a given polymer molecular weight and can be well represented by the simple exponential κ = κ_o(C_s) exp(-[κ]c _p). Here κO is the conductivity of the salt solution in the absence of polymers, and [κ] can be regarded as an intrinsic attenuation factor. Our result indicates that the reduction of the ion mobility is mainly attributed to hydrodynamic interactions between the probe ion and polymer segments, and the specific ion effect plays a minor role. The intrinsic attenuation factor is found to be independent of the salt concentration but to vary with polymer molecular weight M_w, [κ] ∞ M _w. This consequence reveals that the ion interacts with all segments of a polymer as it migrates through the coil or the network, and hence the conductivity reduction depends mainly on the polymer weight concentration.