Firmenich SA, Materials Science Department, Corporate Research Division, Meyrin 2, Genève, Switzerland.
Langmuir. 2012 May 22;28(20):7757-67. doi: 10.1021/la301023k. Epub 2012 May 7.
Foams and emulsions are often exposed to strong external fields, resulting in large interface deformations far beyond the linear viscoelastic regime. Here, we investigate the nonlinear and transient interfacial rheology of adsorption layers in large-amplitude oscillatory shear flow. As a prototypical material forming soft-solid-type interfacial adsorption layers, we use Acacia gum (i.e., gum arabic), a protein/polysaccharide hybrid. We quantify its nonlinear flow properties at the oil/water interface using a biconical disk interfacial rheometer and analyze the nonlinear stress response under forced strain oscillations. From the resulting Lissajous curves, we access quantitative measures recently introduced for nonlinear viscoelasticity, including the intracycle moduli for both the maximum and zero strains and the degree of plastic energy dissipation upon interfacial yielding. We demonstrate using in situ flow visualization that the onset of nonlinear viscoelasticity coincides with shear localization at the interface. Finally, we address the nonperiodic character of this flow transition using an experimental procedure based on opposing stress pulses, allowing us to extract additional interfacial properties such as the critical interfacial stress upon yielding and the permanent deformation.
泡沫和乳液经常受到外部强场的作用，导致界面发生远超线性粘弹范围的大变形。在这里，我们研究了在大幅度振荡剪切流中吸附层的非线性和瞬态界面流变学。作为形成软固态型界面吸附层的典型材料，我们使用金合欢胶（即阿拉伯树胶），一种蛋白质/多糖的混合物。我们使用双锥形盘界面流变仪在油水界面定量测量其非线性流动特性，并分析强制应变振荡下的非线性应力响应。从得到的李萨如图中，我们获取了最近引入的非线性粘弹性的定量测量，包括最大和零应变时的内循环模量，以及界面屈服时塑性能量耗散的程度。我们通过原位流动可视化证明，非线性粘弹性的出现与界面处的剪切局部化同时发生。最后，我们使用基于相反应力脉冲的实验程序解决了这种流动转变的非周期性特征，从而可以提取出屈服时的临界界面应力和永久变形等其他界面性质。
