Dielectric relaxations of poly(acrylic acid)-graft-poly(ethylene oxide) aqueous solution: Analysis coupled with scaling approach and hydrogen-bonding complex

摘要

Dielectric properties of poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) aqueous solution werenmeasured as a function of concentration and temperature over a frequency range of 40 Hz to 110 MHz. Afternsubtracting the contribution of electrode polarization, three relaxation processes were observed at about 20 kHz,n220 kHz, and 4 MHz, and they are named low-, mid- and high-frequency relaxation, respectively. The relaxationnparameters of these three relaxations (dielectric increment u0002ε and relaxation time τ ) showed scaling relationsnwith the polyelectrolyte concentration. The mechanisms of the three relaxations were concluded in light ofnthe scaling theory: The relaxations of low- and mid frequency were attributed to the fluctuation of condensedncounterions, while the high-frequency relaxation was ascribed to the fluctuation of free counterions. Based onnthe dielectric measurements of varying temperatures, the thermodynamic parameters (enthalpy change u0002H andnentropy change u0002S) of the three relaxations were calculated and these relaxation processes were also discussednfrom the microscopic thermodynamical view. In addition, the impacts of PEO side chains on the conformationnof PAA-g-PEO chains were discussed. PEO side chains greatly strengthen the hydrogen-bonding interactionsnbetween PAA-g-PEO chains, resulting in the chains overlapping at a very low concentration and the formationnof a hydrogen-bonding complex. Some physicochemical parameters of PAA-g-PEO molecules were calculated,nincluding the overlap concentration, the effective charge of the chain, the friction coefficient, and the diffusionncoefficient of hydrogen counterions.