Physics and Physical Chemistry of Foods, Wageningen University, Bornse Weilanden 9, 6708 WG, Wageningen, The Netherlands.
ETH Zurich, Department of Materials, Polymer Physics, Leopold-Ruzicka-Weg 4, 8093, Zurich, Switzerland.
Sci Rep. 2019 Feb 27;9(1):2938. doi: 10.1038/s41598-019-39761-7.
Complex interfaces stabilized by proteins, polymers or nanoparticles, have a much richer dynamics than those stabilized by simple surfactants. By subjecting fluid-fluid interfaces to step extension-compression deformations, we show that in general these complex interfaces have dynamic heterogeneity in their relaxation response that is well described by a Kohlrausch-Williams-Watts function, with stretch exponent β between 0.4-0.6 for extension, and 0.6-1.0 for compression. The difference in β between expansion and compression points to an asymmetry in the dynamics. Using atomic force microscopy and simulations we prove that the dynamic heterogeneity is intimately related to interfacial structural heterogeneity and show that the dominant mode for stretched exponential relaxation is momentum transfer between bulk and interface, a mechanism which has so far largely been ignored in experimental surface rheology. We describe how its rate constant can be determined using molecular dynamics simulations. These interfaces clearly behave like disordered viscoelastic solids and need to be described substantially different from the 2d homogeneous viscoelastic fluids typically formed by simple surfactants.
由蛋白质、聚合物或纳米粒子稳定的复杂界面，其动力学比由简单表面活性剂稳定的界面要丰富得多。通过对流体-流体界面进行阶跃延伸-压缩变形，我们表明，通常情况下，这些复杂界面在弛豫响应中具有动态异质性，可以很好地用 Kohlrausch-Williams-Watts 函数来描述，对于延伸，拉伸指数β在 0.4-0.6 之间，对于压缩，β在 0.6-1.0 之间。β在扩展和压缩之间的差异表明动力学存在不对称性。使用原子力显微镜和模拟，我们证明了动态异质性与界面结构异质性密切相关，并表明拉伸指数弛豫的主要模式是体相和界面之间的动量传递，这一机制在实验表面流变学中基本上被忽视了。我们描述了如何使用分子动力学模拟来确定其速率常数。这些界面明显表现为无序粘弹性固体，需要用与通常由简单表面活性剂形成的二维均匀粘弹性流体大不相同的方式来描述。
