Loosli Frédéric, Najm Matthieu, Chan Raymond, Oikonomou Evdokia, Grados Arnaud, Receveur Mathieu, Berret Jean-François
Matière et Systèmes Complexes, UMR 7057 CNRS, Université Denis Diderot Paris-VII, Bâtiment Condorcet, 10 rue Alice Domon et Léonie Duquet, 75205, Paris, France.
Chemphyschem. 2016 Dec 15;17(24):4134-4143. doi: 10.1002/cphc.201601037. Epub 2016 Nov 15.
Viscoelastic liquids are characterized by a finite static viscosity and a yield stress of zero, whereas soft solids have an infinite viscosity and a non-zero yield stress. The rheological nature of viscoelastic materials has long been a challenge and is still a matter of debate. Here, we provide for the first time the constitutive equations of linear viscoelasticity for magnetic wires in yield-stress materials, together with experimental measurements by using magnetic rotational spectroscopy (MRS). In MRS, the wires were subjected to a rotational magnetic field as a function of frequency and the motion of the wire was monitored by using time-lapse microscopy. The studied soft solids were aqueous dispersions of gel-forming polysaccharide (gellan gum) at concentrations above the gelification point. It was found that soft solids exhibited a clear and distinctive signature compared with viscous and viscoelastic liquids. In particular, the average wire rotation velocity equaled zero over a broad frequency range. We also showed that the MRS technique is quantitative. The equilibrium elastic modulus was retrieved from the wire oscillation amplitudes, and agrees with polymer-dynamics theory.
粘弹性液体的特征是具有有限的静态粘度和零屈服应力,而软固体具有无限粘度和非零屈服应力。粘弹性材料的流变性质长期以来一直是一个挑战，至今仍是一个有争议的问题。在这里，我们首次给出了屈服应力材料中磁性丝的线性粘弹性本构方程，并通过磁旋转光谱法（MRS）进行了实验测量。在MRS中，将丝置于随频率变化的旋转磁场中，并使用延时显微镜监测丝的运动。所研究的软固体是浓度高于凝胶化点的成胶多糖（结冷胶）的水分散体。结果发现，与粘性和粘弹性液体相比，软固体表现出清晰独特的特征。特别是，在很宽的频率范围内，丝的平均旋转速度等于零。我们还表明，MRS技术是定量的。从丝的振荡幅度中获取平衡弹性模量，其与聚合物动力学理论相符。
