Growney David J, Mykhaylyk Oleksandr O, Middlemiss Laurence, Fielding Lee A, Derry Matthew J, Aragrag Najib, Lamb Gordon D, Armes Steven P
Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
Technology Centre, BP Formulated Products Technology , Whitchurch Hill, Pangbourne RG8 7QR, U.K.
Langmuir. 2015 Sep 29;31(38):10358-69. doi: 10.1021/acs.langmuir.5b02017. Epub 2015 Sep 16.
Soot formation in diesel engines is known to cause premature engine wear. Unfortunately, genuine diesel soot is expensive to generate, so carbon blacks are often used as diesel soot mimics. Herein, the suitability of a commercial carbon black (Regal 250R) as a surrogate for diesel soot dispersed in engine base oil is examined in the presence of two commonly used polymeric lubricant additives. The particle size, morphology, and surface composition of both substrates are assessed using BET surface area analysis, TEM, and XPS. The extent of adsorption of a poly(ethylene-co-propylene) (dOCP) statistical copolymer or a polystyrene-block-poly(ethylene-co-propylene) (PS-PEP) diblock copolymer onto carbon black or diesel soot from n-dodecane is compared indirectly using a supernatant depletion assay technique via UV spectroscopy. Thermogravimetric analysis is also used to directly determine the extent of copolymer adsorption. Degrees of dispersion are examined using optical microscopy, TEM, and analytical centrifugation. SAXS studies reveal some structural differences between carbon black and diesel soot particles. The mean radius of gyration determined for the latter is significantly smaller than that calculated for the former, and in the absence of any copolymer, diesel soot suspended in n-dodecane forms relatively loose mass fractals compared to carbon black. SAXS provides evidence for copolymer adsorption and indicates that addition of either copolymer transforms the initially compact agglomerates into relatively loose aggregates. Addition of dOCP or PS-PEP does not significantly affect the structure of the carbon black primary particles, with similar results being observed for diesel soot. In favorable cases, remarkably similar data can be obtained for carbon black and diesel soot when using dOCP and PS-PEP as copolymer dispersants. However, it is not difficult to identify simple copolymer-particle-solvent combinations for which substantial differences can be observed. Such observations are most likely the result of dissimilar surface chemistries, which can profoundly affect the colloidal stability.
众所周知，柴油发动机中碳烟的形成会导致发动机过早磨损。不幸的是，纯正的柴油碳烟生产成本高昂，因此炭黑常被用作柴油碳烟的模拟物。在此，研究了一种商用炭黑（Regal 250R）在两种常用聚合物润滑剂添加剂存在的情况下，作为分散在发动机基础油中的柴油碳烟替代物的适用性。使用BET表面积分析、透射电子显微镜（TEM）和X射线光电子能谱（XPS）评估了两种基质的粒径、形态和表面组成。通过紫外光谱法，采用上清液耗尽测定技术间接比较了聚（乙烯 - 共 - 丙烯）（dOCP）统计共聚物或聚苯乙烯 - 嵌段 - 聚（乙烯 - 共 - 丙烯）（PS - PEP）二嵌段共聚物从正十二烷中吸附到炭黑或柴油碳烟上的程度。热重分析也用于直接测定共聚物的吸附程度。使用光学显微镜、TEM和分析离心法检查分散程度。小角X射线散射（SAXS）研究揭示了炭黑和柴油碳烟颗粒之间的一些结构差异。测定的柴油碳烟的平均回转半径明显小于炭黑计算得到的平均回转半径，并且在没有任何共聚物的情况下，与炭黑相比，悬浮在正十二烷中的柴油碳烟形成相对松散的质量分形。SAXS为共聚物吸附提供了证据，并表明添加任何一种共聚物都会将最初紧密的团聚体转变为相对松散的聚集体。添加dOCP或PS - PEP不会显著影响炭黑初级颗粒的结构，柴油碳烟也观察到类似结果。在有利的情况下，当使用dOCP和PS - PEP作为共聚物分散剂时，炭黑和柴油碳烟可以获得非常相似的数据。然而，不难确定能观察到显著差异的简单共聚物 - 颗粒 - 溶剂组合。这些观察结果很可能是由于不同的表面化学性质导致的，这会深刻影响胶体稳定性。
