Effects of colloidal particles on interfacial rheology

这项研究的重点是亚微米颗粒（或“纳米颗粒”）如何在油水界面积聚并改变其物理性质。这项研究的动机是一种被称为“微生物提高采收率”（MEOR）的工业工艺，在这种工艺中，对石油有“胃口”的细菌被注入油井，以帮助回收残余的碳氢化合物。过去在这项技术的生化方面已经做了很多工作。相比之下，很少或根本没有对充满微生物的油水界面的物理学研究。特别是，了解这些表面在外力作用下如何变形和流动是很重要的。与实际的细菌不同，我们建议创造一些小型的无生命的物体来模仿微生物。例如，这些可以是亚微米的玻璃球，其表面覆盖着长链糖分子（多糖）。然后允许“模型细菌”在油水界面积聚（例如在淹没的油滴表面），由此产生的表面机械性能将被量化。众所周知，界面上粒子的存在对界面张力没有影响。然而，我们关心的是高阶机械性能，如表面粘度和表面弹性（统称为“流变性能”）。这些特性将被量化使用技术，如振荡垂坠滴和微移液管。

The proposed study focuses on how submicron particles (or "nanoparticles") may accumulate at the oil-water interface and modify its physical properties.  This research is motivated by an industrial process known as "microbial enhanced oil recovery" (MEOR), where bacteria with "appetites" for petroleum are injected into oil wells to help recover residual hydrocarbon.  Much work has been done in the past on the biochemical aspects of this technology.  In contrast, there has been little or no research on the physics of oil-water interfaces that are laden with microorganisms.  In particular, it is important to understand how these surfaces will deform and flow under applied forces.  Instead of working with actual bacteria, we propose to create small inanimate objects that will mimic the microorganisms.  These, for example, can be submicron glass spheres whose surfaces are covered with long chain sugar molecules (polysaccharides).  The "model bacteria" will then be allowed to accumulate at oil-water interfaces (e.g. on the surfaces of submerged oil droplets), and the resulting surface mechanical properties will be quantified.  It is commonly-known that the presence of particles at interfaces can have no effect on their interfacial tensions.  We are, however, concerned with higher-order mechanical properties such as surface viscosities and surface elasticities (collectively known as "rheological properties").  These properties will be quantified using techniques such as the oscillating pendant drop and the micropipette.