Role of particle clusters on the rheology of magneto-polymer fluids and gels
Journal
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
ISSN
1471-2962
Date Issued
2020-04-13
Author(s)
William R. Suarez-Fernandez
Giuseppe Scionti
Juan D. G. Duran
Andrey Yu. Zubarev
Modesto T. Lopez-Lopez
Abstract
<jats:p>Even in the absence of cross-linking, at large enough concentration, long polymer strands have a strong influence on the rheology of aqueous systems. In this work, we show that solutions of medium molecular weight (120 000–190 000 g mol<jats:sup>−1</jats:sup>) alginate polymer retained a liquid-like behaviour even for concentrations as large as 20% w/v. On the contrary, solutions of alginate polymer of larger (and also polydisperse) molecular weight (up to 600 000 g mol<jats:sup>−1</jats:sup>) presented a gel-like behaviour already at concentrations of 7% w/v. We dispersed micrometre-sized iron particles at a concentration of 5% v/v in these solutions, which resulted in either stable magnetic fluids or gels, depending on the type of alginate polymer employed (medium or large molecular weight, respectively). These magneto-polymer composites presented a shear-thinning behaviour that allowed injection through a syringe and recovery of the original properties afterwards. More interestingly, application of a magnetic field resulted in the formation of particle clusters elongated along the field direction. The presence of these clusters intensely affected the rheology of the systems, allowing a reversible control of their stiffness. We finally developed theoretical modelling for the prediction of the magnetic-sensitive rheological properties of these magneto-polymer colloids.</jats:p><jats:p>This article is part of the theme issue ‘Patterns in soft and biological matters'.</jats:p>