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Main Title: Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy
Author(s): Füllbrandt, Marieke
Klitzing, Regine von
Schönhals, Andreas
Type: Article
Language Code: en
Abstract: Aqueous solutions of linear poly(N-isopropylacrylamide) (pNIPAM) with different polymer concentrations are investigated using dielectric spectroscopy in a frequency range of 10−1 Hz to 106 Hz at temperatures from 15 °C to 50 °C. The phase transition of pNIPAM is monitored by both the temperature (T) and the frequency (f) dependence of the conductivity spectra σ*(f, T). First, the T-dependence of the DC conductivity σ′DC is investigated and the phase transition (“coil-to-globule” transition) at the lower critical solution temperature (LCST) of pNIPAM is deduced by a change in the T-dependence of σ′DC. The observed hysteresis between heating and cooling runs is discussed in detail in dependence on both the polymer concentration and the rate. Second, for the first time a pronounced f-dependence of the real part of conductivity σ′ is observed at temperatures above the LCST whereas at temperatures below the LCST the conductivity spectra are more or less similar to that of water (frequency independent). This f-dependence of σ′ is assigned to the formation of a kind of soft particle (“globular structure”) at the LCST which is more or less impermeable to water and ions therefore giving rise to Maxwell–Wagner–Sillars (MWS) polarization effects (blocking of charges at the soft particle). The dependence on the concentration is studied in detail.
Issue Date: 2012
Date Available: 28-Jun-2016
DDC Class: 530 Physik
Journal Title: Soft matter
Publisher: Royal Society of Chemistry
Publisher Place: Cambridge
Volume: 8
Issue: 48
Publisher DOI: 10.1039/c2sm26826d
Page Start: 12116
Page End: 12123
EISSN: 1744-6848
ISSN: 1744-683X
Notes: Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.
Appears in Collections:Inst. Chemie » Publications

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