Issue 48, 2012

Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

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 σDC 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 σDC. 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.

Graphical abstract: Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

Article information

Article type
Paper
Submitted
07 Aug 2012
Accepted
25 Sep 2012
First published
15 Oct 2012

Soft Matter, 2012,8, 12116-12123

Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

M. Füllbrandt, R. von Klitzing and A. Schönhals, Soft Matter, 2012, 8, 12116 DOI: 10.1039/C2SM26826D

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements