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Concentration dependent phase behavior and collapse dynamics of PNIPAM microgel by dielectric relaxation

Abstract

The dielectric behavior of thermo-sensitive poly-(N-isopropylacrylamide) (PNIPAM) microgel with three different concentrations was investigated over the frequency from 40 Hz to 110 MHz as a function of temperature from 10-60oC. Two remarkable and temperature-dependent relaxation processes were observed. The slow relaxation originates from the segmental motion in the whole temperature range. The fast relaxation is due to the fluctuation of counterions below the lower critical solution temperature (LCST) and to the interfacial polarization above LCST. It was concluded from the temperature dependent dielectric parameters that the microgel concentration will not influence the LCST but affects the phase behavior of microgel suspension: the dense system experienced the colloidal crystal-to-liquid transition and volume phase transition, while the dilute system only underwent a volume phase transition. Based on the interfacial polarization theory, the electrical parameters for the constituent phases (the permittivity, conductivity and volume fraction of the microgel (εp, κp, ϕ) and the conductivity of water κa) and the water content in microgel (fw) was calculated by Hanai equation. In addition, the thermodynamics parameters of the two relaxations were calculated from Eyring equation. The electrical and thermodynamic parameters indicate that the microgel concentration influence the volume, charge density, thickness of electric double layer and the freedom degree of the segments of microgel, thus results in the differences in collapse dynamics.

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Publication details

The article was received on 03 Mar 2017, accepted on 05 May 2017 and first published on 11 May 2017


Article type: Paper
DOI: 10.1039/C7CP01378G
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    Concentration dependent phase behavior and collapse dynamics of PNIPAM microgel by dielectric relaxation

    M. Yang, C. Liu and K. Zhao, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP01378G

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