Surfactants play an important role in modifying the properties of water–air interfaces. Here, we combine information from molecular dynamics simulations, surface tensiometry, and vibrational sum-frequency generation spectroscopy to study the interfacial behavior of photoswitchable arylazopyrazole (AAP) surfactants. This combination of the experimental techniques allows a direct relation between surface tension and surface concentration rather than just the bulk concentration. Specifically, we conducted a comparison between two derivatives, one with an octyl terminal group (O-AAP) and the other without this group (H-AAP), focusing on their respective E and Z isomers. From the simulations of these four systems, we see that those with a stronger cluster formation, likely resulting from higher intermolecular attractive interactions, display higher surface tensions for the intermediate surface excess. In some cases, even a small but noticeable maximum in the surface tension isotherm is observed for systems with strong cluster formation. Such a maximum is not observed in the experiments, although such an observation would be compatible with the general properties of the Frumkin isotherm. We exclude that the peak is due to the finite width of the simulation box. Apart from this effect, the general features of the surface tension are consistent between the experiment and simulation. Evidence is also provided that it is primarily the interaction of the aromatic rings that determines the strength of the surfactant interactions.

中文翻译：

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水-空气界面处的光开关 Arylazopyrazole 表面活性剂：微观视角


表面活性剂在改变水-空气界面的特性方面发挥着重要作用。在这里，我们结合了来自分子动力学模拟、表面张力测定和振动和频产生光谱的信息，以研究可光开关芳氮吡唑 （AAP） 表面活性剂的界面行为。这种实验技术的组合允许表面张力和表面浓度之间的直接关系，而不仅仅是整体浓度。具体来说，我们对两种衍生物进行了比较，一种具有辛基末端基 （O-AAP），另一种没有该基团 （H-AAP），重点关注它们各自的 E 和 Z 异构体。从这四个系统的模拟中，我们看到那些具有更强团簇形成的系统，可能是由更高的分子间吸引力相互作用引起的，对于中间表面过剩，显示出更高的表面张力。在某些情况下，对于具有强团簇形成的系统，甚至可以观察到表面张力等温线的最小值但很明显的最大值。在实验中没有观察到这样的最大值，尽管这样的观察与 Frumkin 等温线的一般性质相容。我们排除了峰值是由于模拟框的有限宽度造成的。除了这种影响之外，表面张力的一般特征在实验和模拟之间是一致的。还提供了证据表明，主要是芳香环的相互作用决定了表面活性剂相互作用的强度。