McKee Clayton T, Ducker William A
Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, USA.
Langmuir. 2005 Dec 20;21(26):12153-9. doi: 10.1021/la051008v.
We have studied the refractive index of a thin aqueous film between microscopic hydrophobic surfaces using evanescent wave atomic force microscopy (EW-AFM). An evanescent wave, generated at a solid-liquid interface, is scattered by AFM tips or glass particles attached to AFM cantilevers. The scattering of this wave is used to determine the refractive index as a function of separation between these surfaces. Measurements were performed on surfaces that were rendered hydrophobic with octadecyltrichlorosilane, which produces solid-water contact angles in excess of 90 degrees. For AFM tips, the average refractive index in the thin film was always equal to that of water when the film was thicker than approximately 100 nm. At smaller separations, the refractive index was always greater than or equal to that of water. This is inconsistent with the formation of air or vapor films and consistent with a small amount of organic material between the surfaces. For colloidal spheres (R approximately 10 microm), we were not able to detect changes in the refractive index of the thin film between the sphere and plate.
我们使用倏逝波光原子力显微镜（EW-AFM）研究了微观疏水表面之间薄水膜的折射率。在固液界面产生的倏逝波被附着在AFM悬臂上的AFM针尖或玻璃颗粒散射。利用该波的散射来确定折射率与这些表面之间间距的函数关系。测量是在使用十八烷基三氯硅烷使其具有疏水性的表面上进行的，该物质会产生超过90度的固水接触角。对于AFM针尖，当薄膜厚度大于约100纳米时，薄膜中的平均折射率始终等于水的折射率。在更小的间距下，折射率始终大于或等于水的折射率。这与空气或蒸汽膜的形成不一致，而与表面之间存在少量有机材料一致。对于胶体球（半径约为10微米），我们无法检测到球与平板之间薄膜折射率的变化。
