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

Füllbrandt, Marieke; Klitzing, Regine von; Schönhals, Andreas

doi:10.1039/c2sm26826d

Cited by 29 publications

(50 citation statements)

References 37 publications

(66 reference statements)

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“…31. Besides small electrode polarization effects at low frequencies s 0 is independent of frequency and increases monotonously with temperature.…”

Section: Dielectric Response Of Pnipam Microgelsmentioning

confidence: 93%

“…27,28 They cannot be observed in the selected frequency range as characteristic relaxation processes. However, as shown in our recent paper, 31 interfacial polarization effects such as Maxwell-Wagner-Sillars (MWS) polarization can be detected. Therefore the data are expressed as complex conductivity s*(u) since the focus is on the mobility of charges in order to monitor structural changes.…”

Section: Dielectric Response Of Pnipam Microgelsmentioning

confidence: 99%

“…31 However, as reported by us 31 the hysteresis effect (DLCST) depends on the heating and cooling rate and vanishes if the rate is around 0.1 K min À1 . These ndings explain the fact that no remarkable hysteresis effect is observed for DLS measurements where the heating-cooling rate is approximately 0.1 K min À1 .…”

mentioning

confidence: 99%

“…Although some of their arguments should be discussed in greater detail the latter was used to differentiate different structures of microgels. In a recent dielectric study on linear pNIPAM in water 31 we proved that the phase transition behaviour can be monitored by both the temperature (T) and frequency ( f ) dependence of the complex conductivity s*( f, T). In the present contribution, pNIPAM microgels with different crosslinking densities are analysed at different temperatures in a frequency range from 10 À1 Hz to 10 6 Hz.…”

mentioning

confidence: 99%

“…The same approach as in ref. 31 is used, which is to take charges as a probe to investigate the internal structure of the microgels. No extra charge carriers have been added to the samples, only remaining charges coming from the polymerization process (e.g.…”

mentioning

confidence: 99%

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The dielectric signature of poly(N-isopropylacrylamide) microgels at the volume phase transition: dependence on the crosslinking density

2013

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Temperature sensitive poly(N-isopropylacrylamide) (pNIPAM) microgels are prepared and investigated using dielectric spectroscopy in a frequency range from 10 À1 Hz to 10 6 Hz at temperatures from 15 C to 50 C. The microgels were synthesized with different crosslinker molar ratios resulting in microgels with structural differences. From the dielectric response of the pNIPAM microgels the swelling/ deswelling behaviour is monitored by both the temperature (T) and the frequency ( f ) dependence of the conductivity spectra s*(f, T). The volume phase transition (VPT) at the lower critical solution temperature (LCST) is deduced by a change in the T-dependence of the DC conductivity s 0 DC . It can be explained by a decrease in the effective charge mobility and a reduction in the effective charge number contributing to s 0 DC at T > LCST. Addressing the f-dependence of the real part of the conductivity s 0 , a pronounced frequency dependence at temperatures above the LCST can be observed whereas at temperatures below the LCST the conductivity spectra resemble that of the pure solvent (water) which is frequency independent. The f-dependence of s 0 at T > LCST is assigned to the collapse of the microgel particles. At the interfaces of the collapsed particles charge carriers are blocked and/or entrapped giving rise to Maxwell-Wagner-Sillars (MWS) polarization effects. The dependence of the MWS effect on the crosslinker amount is studied in detail and conclusions concerning the internal structure of the microgels with respect to their crosslinking density are drawn. Moreover the dielectric data are related to dynamic light scattering data. A correlation between the MWS polarization effect and the swelling/ deswelling ratio expressed by the hydrodynamic radius R h at different temperatures is established for the first time.

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“…31. Besides small electrode polarization effects at low frequencies s 0 is independent of frequency and increases monotonously with temperature.…”

Section: Dielectric Response Of Pnipam Microgelsmentioning

confidence: 93%

Section: Dielectric Response Of Pnipam Microgelsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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The dielectric signature of poly(N-isopropylacrylamide) microgels at the volume phase transition: dependence on the crosslinking density

2013

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One‐step preparation of poly(NIPAM‐pyrrole) electroconductive composite hydrogel and its dielectric properties

Şarkaya

Yıldırım

Allı

2021

J of Applied Polymer Sci

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Conductive polymers and hydrogels are two of the hot prospect polymer types that are used for new stimuli responsive materials. In this study, one‐step preparation of electroconductive composite hydrogels containing polypyrrole (PPy) and N‐isopropylacrylamide (NIPAM) using free radical polymerization technique was achieved with N,N‐methylenebisacrylamide as a crosslinker and ammonium peroxy disulphate (APS) as initiator, in mixture of water/isopropyl alcohol. The equilibrium swelling degree of the poly(NIPAM)‐pyrrole) electroconductive composite hydrogel was 9.88 g of H2O/g dry polymer. According to TGA results, the thermal stability of the prepared composite poly(NIPAM‐PPy) conductive hydrogel (700°C) hydrogel is higher than that of pure poly(NIPAM) hydrogel (600°C). Furthermore, prepared samples were characterized by FTIR, and SEM analyzes. Later, the samples were pressured into pellets so that electrical impedance spectroscopy (EIS) measurements were taken between 10 and 10 MHz at room temperature. The dielectric constant value of composite poly(NIPAM‐PPy) hydrogel at 10 Hz is almost 10 times higher than that of poly(NIPAM) hydrogel. Both samples' real and imaginary parts of dielectric constant decreased with increased frequency. Samples exhibited non‐Debye relaxation since experimental data fit into dielectric model of Havriliak‐Negami. Moreover, low frequency data yielded d.c. conductivity of the pure and composite samples as 3.74 × 10−11 and 1.02 × 10−8 S/cm, respectively. Real part of impedance at low frequencies also points out ~103 times lower resistance values at 10 Hz for composite poly(NIPAM‐PPy) hydrogel. Therefore, EIS results support that electroconductive composite hydrogel fabrication was achieved using free radical polymerization technique.

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Thermodriven Micrometer‐Scale Aqueous‐Phase Separation of Amphiphilic Oligoethylene Glycol Analogues

Kawasaki¹,

Muraoka²,

Obara³

et al. 2014

Chemistry An Asian Journal

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Thermoresponsive materials with a lower critical solution temperature (LCST) are receiving growing attention, of which examples of non-polymeric small molecules are limited. Monodisperse oligoethylene glycol amphiphiles that contain aromatic units with a LCST in water have been developed and applied to peptide extraction. Concentration-dependent hysteretic transmittance changes were observed in response to temperature elevation and reduction. Dynamic light scattering measurements and phase contrast microscopy revealed the formation of micrometer-sized aggregates upon heating at a concentration above 5.0 mM; these aggregates self-assembled to form larger aggregates upon cooling before dissolution. The "interaggregate" interactions are likely to cause the hysteretic behavior. As an application of this thermodriven phase separation, selective extraction of peptide fragments containing high percentages of hydrophobic and aromatic amino acid residues was successfully demonstrated.

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

Abstract: Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy Marieke F€ ullbrandt, a Regine von Klitzing b and Andreas Sch€ onhals * a

Cited by 29 publications

References 37 publications

The dielectric signature of poly(N-isopropylacrylamide) microgels at the volume phase transition: dependence on the crosslinking density

The dielectric signature of poly(N-isopropylacrylamide) microgels at the volume phase transition: dependence on the crosslinking density

One‐step preparation of poly(NIPAM‐pyrrole) electroconductive composite hydrogel and its dielectric properties

Thermodriven Micrometer‐Scale Aqueous‐Phase Separation of Amphiphilic Oligoethylene Glycol Analogues

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