Allan Daniel B, Firester Daniel M, Allard Victor P, Reich Daniel H, Stebe Kathleen J, Leheny Robert L
Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Soft Matter. 2014 Sep 28;10(36):7051-60. doi: 10.1039/c4sm00484a.
We report experiments studying the mechanical evolution of layers of the protein lysozyme adsorbing at the air-water interface using passive and active microrheology techniques to investigate the linear and nonlinear rheological response, respectively. Following formation of a new interface, the linear shear rheology, which we interrogate through the Brownian motion of spherical colloids at the interface, becomes viscoelastic with a complex modulus that has approximately power-law frequency dependence. The power-law exponent characterizing this frequency dependence decreases steadily with increasing layer age. Meanwhile, the nonlinear microrheology, probed via the rotational motion of magnetic nanowires at the interface, reveals a layer response characteristic of a shear-thinning power-law fluid with a flow index that decreases with age. We discuss two possible frameworks for understanding this mechanical evolution: gelation and the formation of a soft glass phase.
我们报告了一系列实验，分别使用被动和主动微流变技术研究蛋白质溶菌酶在空气-水界面吸附层的力学演化，以探究线性和非线性流变响应。在新界面形成后，我们通过界面处球形胶体的布朗运动来研究的线性剪切流变学，会变成具有复模量的粘弹性，该复模量具有近似幂律频率依赖性。表征这种频率依赖性的幂律指数会随着吸附层年龄的增加而稳步下降。同时，通过界面处磁性纳米线的旋转运动探测到的非线性微流变学，揭示了一种剪切变稀幂律流体的层响应特性，其流动指数会随着年龄增长而降低。我们讨论了两种理解这种力学演化的可能框架：凝胶化和软玻璃相的形成。
