Department of Physical-Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, 13084-862 Campinas, SP, Brazil.
Langmuir. 2010 Feb 2;26(3):1482-6. doi: 10.1021/la903683e.
The hydrodynamic drag reduction phenomenon, also termed the Toms effect, is an unusual case involving macromolecules in solution in which the resistance to flow is reduced comparatively to that of the pure solvent. Although the effect is relatively well characterized, it is still unclear from the molecular viewpoint. The presence of some amount of a polymer with high molecular weight can produce large levels of drag reduction in turbulent flow as a result of the interactions of the long structures with the small vortices developed during the flow. For this reason, the effect is very attractive in the pumping process because a significant amount of energy can be saved. In aqueous systems, giant micelles can be spontaneously formed, driven by the hydrophobic effect, and are effective drag reducers. Giant micelles are interesting in promoting drag reduction because the noncovalent and reversible aggregation of the surfactant molecules avoids mechanical degradation, which typically occurs with classical polymers, due to irreversible scission of the backbone. In this letter, we present the first hydrodynamic drag reducer for hydrocarbons based on a self-assembled polymer formed from the reversible aggregation of bis-urea monomers. This system forms two competitive polymeric structures--the tube (T) and the filament (F) forms--which are in equilibrium with each other. Our rheology results in octane and toluene are fully consistent with calorimetry data and show that only the longest form, T, is able to promote the drag reduction effect.
流体动力阻力减少现象，也称为汤姆效应，是一种涉及溶液中大分子的不寻常情况，其中流动阻力相对于纯溶剂而言降低。尽管该效应已经得到了相对较好的描述，但从分子角度来看，它仍然不清楚。由于长链结构与流动过程中产生的小涡流相互作用，高分子量聚合物的存在会在湍流中产生大量的阻力减少。出于这个原因，该效应在泵送过程中非常有吸引力，因为可以节省大量能量。在水基体系中，由于疏水效应，巨大胶束可以自发形成，并且是有效的阻力减少剂。巨大胶束在促进阻力减少方面很有趣，因为表面活性剂分子的非共价和可逆聚集避免了机械降解，而机械降解通常会发生在经典聚合物中，因为主链的不可逆断裂。在这封信中，我们提出了第一个基于双脲单体可逆聚集形成的自组装聚合物的烃类流体动力阻力减少剂。该系统形成两种竞争性聚合物结构——管（T）和丝（F）形式——它们彼此处于平衡状态。我们在辛烷和甲苯中的流变学结果与量热学数据完全一致，表明只有最长的形式 T 才能促进阻力减少效应。
