Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, USA.
Phys Chem Chem Phys. 2013 Sep 7;15(33):14037-46. doi: 10.1039/c3cp50444a. Epub 2013 Jul 16.
We used friction force microscopy measurements to determine the yield strength of several structurally similar Langmuir-Blodgett (LB) bilayer films deposited on a hydrophobic substrate. Film failure was initiated by increasing the load applied by the probe of the atomic force microscope in the course of continuous scanning at nominally the same location on the sample. This film failure was readily detected in friction versus load curves, as well as by imaging of trenches created due to removal of the film. The depths of the trenches formed in the course of these yield strength experiments were consistent with complete removal of these bilayer films, as evidenced by comparisons to film thicknesses measured by ellipsometry. The structure of the LB bilayer was modified by replacing a tetra-chain amphiphile bearing four quaternary ammonium groups with a polymeric surfactant resulting in little change in the yield strength. On the other hand, the addition of a polyanionic gluing layer at the central interface of the bilayers almost doubled the yield strength of the films. To uncover any possible structural effects created by changes in the terminal functionality, the hydrocarbon top layer of the bilayer was replaced with a perfluorinated capping layer. In spite of the changes in frictional properties, the yield strength of this film also appeared to be dominated by the presence of the glued interface.
我们使用摩擦力显微镜测量来确定几种结构相似的 Langmuir-Blodgett（LB）双层膜在疏水基底上的屈服强度。在样品的名义上相同位置的连续扫描过程中，通过增加原子力显微镜探针施加的负载来引发膜的失效。在摩擦力与负载曲线中，以及在由于膜的去除而形成的沟槽的成像中，很容易检测到这种膜的失效。在这些屈服强度实验过程中形成的沟槽的深度与这些双层膜的完全去除一致，这可以通过与椭圆测量法测量的膜厚度进行比较来证明。通过用带有四个季铵基团的四链两亲物代替聚合物表面活性剂来修饰 LB 双层膜的结构，导致屈服强度几乎没有变化。另一方面，在双层膜的中心界面添加聚阴离子胶层几乎使膜的屈服强度增加了一倍。为了揭示由于末端官能团变化而产生的任何可能的结构影响，将双层膜的烃顶层替换为全氟化封端层。尽管摩擦性能发生了变化，但该膜的屈服强度似乎也主要由胶接界面的存在决定。
