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Nonlinear electrical and rheological spectroscopies identify structural and supramolecular relaxations in a model peptide

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Abstract

Supercooled liquid secondary amides display an electrical absorption peak characterized by an almost Debye-like shape, indicative of a close-to-exponential polarization response. This response, believed to be supramolecular in nature, is so enormously intense that the amide's structural process, contributing only a few percent to the total relaxation strength, is hard to resolve reliably using standard dielectric spectroscopy. To overcome this issue, nonlinear dielectric spectroscopy involving field-induced structural recovery and temperature-induced physical aging, was applied near the calorimetric glass transition of a mixture of N-methylformamide and N-ethylacetamide. Without the need to rely on cumbersome deconvolution procedures, it is thus demonstrated that the supramolecular response is by a factor of 6 slower than the structural relaxation. Conversely, in linear rheological experiments only the structural relaxation could be resolved, but not the supramolecular one. However, medium-amplitude oscillatory shear experiments carried out at 160 K do reveal the supramolecular process. Hence, the combination of linear and nonlinear mechanical measurements corroborates the dielectrically uncovered spectral separation of the two processes.

Graphical abstract: Nonlinear electrical and rheological spectroscopies identify structural and supramolecular relaxations in a model peptide

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Publication details

The article was received on 28 Feb 2019, accepted on 24 Apr 2019 and first published on 10 May 2019


Article type: Paper
DOI: 10.1039/C9SM00434C
Soft Matter, 2019, Advance Article

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    Nonlinear electrical and rheological spectroscopies identify structural and supramolecular relaxations in a model peptide

    G. Honorio, S. P. Bierwirth, C. Gainaru and R. Böhmer, Soft Matter, 2019, Advance Article , DOI: 10.1039/C9SM00434C

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