Institute of Physics , Science Park 904 , Amsterdam 1098 XH , The Netherlands.
Max Planck Institute for Polymer Research , Ackermannweg 10 , Mainz 55128 , Germany.
Langmuir. 2018 Oct 16;34(41):12344-12349. doi: 10.1021/acs.langmuir.8b02874. Epub 2018 Oct 2.
Surface active agents (surfactants) are commonly used to improve the wetting of aqueous solutions on hydrophobic surfaces. The improved wettability is usually quantified as a decrease of the contact angle θ of a droplet on the surface, where the contact angle θ is given by the three surface tensions involved. Surfactants are known to lower the liquid-vapor surface tension, but what they do to the two other surface tensions is less clear. We propose an improved Zisman method for quantifying the wetting behavior of surfactants at the solid surface. This allows us to show that a number of very common surfactants do not change the wettability of the solid: they give the same contact angle as a simple liquid with the same liquid-vapor surface tension. Surface-specific sum-frequency generation spectroscopy shows that nonetheless surfactants are present at the solid surface. The surfactants therefore change the solid-liquid and solid-vapor surface tensions by the same amount, leading to an unchanged contact angle.
表面活性剂（surfactants）通常用于改善水相溶液在疏水性表面上的润湿性。润湿性的改善通常通过测量液滴在表面上的接触角θ来定量表示，其中接触角θ由涉及的三个表面张力给出。众所周知，表面活性剂会降低液体-蒸汽表面张力，但它们对另外两个表面张力的影响不太清楚。我们提出了一种改进的 Zisman 方法来定量描述表面活性剂在固体表面上的润湿行为。这使我们能够表明，许多非常常见的表面活性剂不会改变固体的润湿性：它们与具有相同液体-蒸汽表面张力的简单液体给出相同的接触角。表面特定的和频发生光谱表明，尽管如此，表面活性剂仍存在于固体表面。因此，表面活性剂使固-液和固-气表面张力等量变化，导致接触角不变。
