Effect of Side-Chain on Conformation of Poly(acrylic acid) and Its Dielectric Behaviors in Aqueous Solution: Hydrophobic and Hydrogen-Bonding Interactions and Mechanism of Relaxations

摘要

Dielectric behaviors of poly(acrylic acid) (PAA), poly(acrylic acid)-graft-dodecyl (PAA-g-dodecyl), and poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) solutions were investigated from 40 Hz to 110 MHz at the solution temperature of 26 °C. For PAA and PAA-g-dodecyl solutions, two dielectric relaxations at about 5 MHz and 150 kHz were observed, whose mechanisms were proved to be the fluctuation of free counterions and condensed counterions, respectively. While for PAA-g-PEO solutions; an extra relaxation around 30 kHz was observed, including the two relaxations just mentioned, and it is related to the hydrogen-bonding aggregates in PAA-g-PEO solutions and was attributed to the rotation of the whole molecule. And no relaxation processes caused by dodecyl or PEO side-chains were detected in our measuring frequency range. Based on Mandel's model, some parameters characterizing the structure of polyelectrolyte chain, such as radius of gyration and ICuhn segment length, were obtained. Both PAA-g-PEO and PAA-g-dodecyl molecules adopt a more compact conformation than PAA, owing to the formation of hydrogen-bonding aggregates and hydrophobic microdomains, respectively. The introduction of dodecyl and PEO side-chains weakens the intramolecular hydrogen-bonding interactions in PAA molecule and makes the flexibility of PAA-g-PEO and PAA-g-dodecyl chains greater than PAA chains.