Atomic Force Microscopy Force Mapping Analysis of an Adsorbed Surfactant above and below the Critical Micelle Concentration.
Atomic Force Microscopy Force Mapping Analysis of an Adsorbed Surfactant above and below the Critical Micelle Concentration.
复制标题
DOI：
10.1021/acs.langmuir.8b00574
复制
发表时间：
2018-05
期刊：
影响因子：
--
通讯作者：
J. J. Hamon-J.;R. Tabor;A. Striolo;B. Grady
中科院分区：
文献类型：
--
作者：
J. J. Hamon-J.;R. Tabor;A. Striolo;B. Grady
力曲线收集使用原子力显微镜（AFM）在吸附的表面活性剂的存在下，经常被用来得出结论，吸附膜包装，刚度和厚度。然而，这种力曲线特性的一些值得注意的特征尚未被彻底研究和解释。在这项工作中，我们收集的力曲线从十四烷基三甲基溴化铵薄膜吸附在高度取向的热解石墨（HOPG），二氧化硅，二氧化硅已被疏水化的官能化与二氯二甲基硅烷。比较了几个不同试验的力曲线中的突破事件，结果表明，突破距离（通常报告为吸附膜厚度）随低于临界胶束浓度（CMC）的浓度增加而增加，但在2×和10× CMC之间的所有表面上均约为3.5 nm;由于三个表面的表面化学性质不同，这是一个意外结果。我们采用了不同的力常数（k）值的AFM探针，以及胶体探针和突破距离保持在所有情况下约3.5 nm。梯度映射，力映射的一个变种，也实现了在三个表面上，并导致在原位可视化吸附的表面活性剂的一种新技术。得到的地图显示吸附的表面活性剂低于CMC的补丁，并显示，随着浓度的增加，补丁的大小增加，导致在CMC附近和以上的完全覆盖。这些结果是，据我们所知，第一次力映射已被用于空间跟踪补丁的吸附表面活性剂。最后，表面活性剂层上的AFM针尖进行了研究，通过收集一个单独的AFM探针的尖端上使用的AFM针尖上的力图。在尖端之间观察到突破事件，表明表面活性剂层存在于至少一个尖端上，如果不是两个尖端的话。
Force curves collected using an atomic force microscope (AFM) in the presence of adsorbed surfactants are often used to draw conclusions about adsorbed film packing, rigidity, and thickness. However, some noteworthy features of such force curve characteristics have yet to be thoroughly investigated and explained. In this work, we collected force curves from tetradecyltrimethylammonium bromide films adsorbed on highly oriented pyrolytic graphite (HOPG), silica, and silica that had been hydrophobized by functionalization with dichlorodimethyl silane. Breakthrough events in the force curves from several different trials were compared to show that the breakthrough distance, often reported as the adsorbed film thickness, increased with concentration below the critical micelle concentration (CMC) but was approximately 3.5 nm on all surfaces between 2× and 10× CMC; an unexpected result because of the different surface chemistries for the three surfaces. We employed an AFM probe with a different force constant ( k) value as well as a colloidal probe and the breakthrough distance remained approximately 3.5 nm in all cases. Gradient mapping, a variant of force mapping, was also implemented on the three surfaces and resulted in a new technique for visualizing adsorbed surfactant in situ. The resulting maps showed patches of adsorbed surfactant below the CMC and revealed that with increasing concentration, the size of the patches increased resulting in full coverage near and above the CMC. These results are, to our knowledge, the first time force mapping has been used to spatially track patches of adsorbed surfactant. Finally, layers of surfactants on an AFM tip were investigated by collecting a force map on a single AFM tip using the tip of a separate AFM probe. A breakthrough event was observed between the tips, indicating that a layer of surfactant was present on at least one, if not both tips.