Interfacial microrheology: characteristics of homogeneous and heterogeneous interfaces

Two-point microrheology was applied to a homogeneous (DPPC monolayers) and a heterogeneous (asphaltene films) interface. For DPPC monolayers, both the longitudinal and transverse-correlated motions showed a purely diffusional regime at different surface pressures. A good agreement between the single particle and two particle mean square displacements was observed. For asphaltene films, a transition from viscous to viscoelastic regime was observed as the interface aged. The thermal cross-correlations of particles showed a strong scattering over the particle distances evidence of the heterogeneity of the asphaltene films. This heterogeneity was also reflected in the mean square displacements where discrepancies are observed between results from one particle and two particle microrheology. Choosing one single particle as reference, a map of the spatial heterogeneity of asphaltene films was developed. The novel methodology provides insights into local micromechanics of complex interfaces that is not accessible with classical interfacial rheometry.

两点微流变学被应用于均相（二棕榈酰磷脂酰胆碱单分子层）和非均相（沥青质膜）界面。对于二棕榈酰磷脂酰胆碱单分子层，在不同的表面压力下，纵向和横向相关运动都呈现出纯扩散状态。观察到单粒子和双粒子均方位移之间有良好的一致性。对于沥青质膜，随着界面老化，观察到从粘性状态到粘弹性状态的转变。粒子的热交叉相关性在粒子间距上显示出强烈的散射，这证明了沥青质膜的非均质性。这种非均质性也反映在均方位移上，其中单粒子和双粒子微流变学的结果之间存在差异。选择一个单粒子作为参考，绘制了沥青质膜空间非均质性的图谱。这种新方法为复杂界面的局部微观力学提供了深入了解，这是传统界面流变测量无法实现的。