Authors
Henri C G De Cagny
Bart E. Vos
Mahsa Vahabi
Nicholas A. Kurniawan
Masao Doi
Gijsje H. Koenderink
F. C. MacKintosh
Daniel Bonn
Date (dd-mm-yyyy)
2016-11-18
Title
Porosity governs normal stresses in polymer gels
Journal
Physical Review Letters
Volume
117
Publication Year
2016-11-18
Issue number
21
Document type
Article
Faculty
Faculty of Science (FNWI)
Amsterdam University College (AUC)
Institute
Van der Waals-Zeeman Institute (WZI)
Institute for High Energy Physics (IHEF)
Institute of Physics (IoP)
Abstract

When sheared, most elastic solids including metals, rubbers, and polymer gels dilate perpendicularly to the shear plane. This behavior, known as the Poynting effect, is characterized by a positive normal stress. Surprisingly, fibrous biopolymer gels exhibit a negative normal stress under shear. Here we show that this anomalous behavior originates from the open-network structure of biopolymer gels. Using fibrin networks with a controllable pore size as a model system, we show that the normal-stress response to an applied shear is positive at short times, but decreases to negative values with a characteristic time scale set by pore size. Using a two-fluid model, we develop a quantitative theory that unifies the opposite behaviors encountered in synthetic and biopolymer gels.

URL
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Permalink
https://hdl.handle.net/11245.1/061a92cc-dafe-4663-a38a-80a28a8ff17c