The chain conformation, relaxation dynamics and thermodynamics of poly(acrylamide-co-diallyldimethylammonium chloride) solution: Dielectric analysis coupled with scaling approach

• We measured the dielectric data for the solution of poly(acrylamide-co-diallyldimethylammonium chloride), a copolymer having uncontrolled (i.e., statistical or random) comonomer sequence.
• The low- and high-frequency dielectric relaxations were all analyzed by scaling approach.
• The mechanism of these two relaxaitons can be described with the polarization of condensed or free counterions fluctuate within some certain lengths which relate to the chain conformation.
• The information of dynamics and thermodynamics for this copolymer solution were obtained from our dielectric analysis.

Dielectric properties of poly(acrylamide-co-diallyldimethylammonium chloride) (P(AAm-co-DADMAC)) aqueous solution have been measured as a function of concentration and temperature over a frequency range from 40 Hz to 110 MHz, respectively. Different from the dielectric behavior of homopolymers solutions (only one dielectric relaxation was observed in poly(diallyldimethylammonium chloride) (PDADMAC) solution around MHz, and no detectable dielectric relaxation is observed in polyacrylamide (PAAm) homopolymer solution), two dielectric relaxations are observed in P(AAm-co-DADMAC) solution around 700 kHz and MHz, and they are named low- and high-frequency relaxation, respectively. The relaxation parameters (dielectric increment and relaxation time, obtained by fitting the dielectric spectra with the Cole–Cole equation) of these two relaxations show scaling relations with the copolymer concentration. The information about the dynamics of copolymer solution are got from the discussion of the mechanisms of these two relaxations in light of the scaling theory: the low- and high-frequency relaxations are ascribed to the fluctuation of condensed and free counterions, respectively; the fluctuation ranges of these two kinds counterions reveal the different chain conformations exist in the copolymer solution. For the dependence of dielectric relaxation on temperature in P(AAm-co-DADMAC) solution, the thermodynamic parameters, activation enthalpies and entropies, of these two relaxations are calculated from the relaxation time by means of the Eyring equation. The temperature dependences of dielectric increments are also discussed. The comparison about the concentration and temperature dependences of dielectric properties between P(AAm-co-DADMAC) and PDADMAC solution are discussed from the perspective of the difference of molecular structure in the proper place of the text.

Figure optionsDownload as PowerPoint slideThe frequency dependences of the dielectric loss of poly(acrylamide-co-diallyldimethylammonium chloride) solution solution with (a) different concentrations and (b) different temperatures.