In many applications of polyelectrolyte/surfactant (P/S) mixtures, it is difficult to fine-tune them after mixing the components without changing the sample composition, e.g. pH or the ionic strength. Here we report on a new approach where we use photoswitchable surfactants to enable drastic changes in both the bulk and interfacial properties. Poly(diallyldimethylammonium chloride) (PDADMAC) mixtures with three alkyl-arylazopyrazole butyl sulfonates (C_nAAP) with -H, -butyl and -octyl tails are applied and E/Z photoisomerization of the surfactants is used to cause substantially different hydrophobic interactions between the surfactants and PDADMAC. These remotely controlled changes affect significantly the P/S binding and allows for tuning both the bulk and interfacial properties of PDADMAC/C_nAAP mixtures through light irradiation. For that, we have fixed the surfactant concentrations at values where they exhibit pronounced surface tension changes upon E/Z photoisomerization with 365 nm UV light (Z) and 520 nm green (E) light and have varied the PDADMAC concentration. The electrophoretic mobility can be largely tuned by photoisomerisation of C_nAAP surfactants and P/S aggregates, which can even exhibit a charge reversal from negative to positive values or vice versa. In addition, low colloidal stability at equimolar concentrations of PDADMAC with C_nAAP surfactants in the E configuration lead to the formation of large aggregates in the bulk which can be broken up by irradiation with UV light when the surfactant's alkyl chain is short enough (C₀AAP). Vibrational sum-frequency generation (SFG) spectroscopy reveals changes at the interface similar to the bulk, where the charging state at air–water interfaces can be modified with light irradiation. Using SFG spectroscopy, we interrogated the O–H stretching modes of interfacial H₂O and provide qualitative information on surface charging that is complemented by neutron reflectometry, from which we resolved the surface excesses of PDADMAC and C_nAAP at the air–water interface, independently.

中文翻译：

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光响应芳基氮杂吡唑表面活性剂/PDADMAC混合物：可逆控制体积和界面性质

在聚电解质/表面活性剂（P/S）混合物的许多应用中，在混合各组分后，在不改变样品组成（例如pH或离子强度）的情况下很难对其进行微调。在这里，我们报告了一种新方法，其中我们使用光可切换表面活性剂来实现体积和界面性质的巨大变化。应用聚（二烯丙基二甲基氯化铵）（PDADMAC）与三种带有-H、-丁基和-辛基尾部的烷基芳基偶氮吡唑丁基磺酸盐（C _n AAP）的混合物，并使用表面活性剂的E / Z光异构化来引起之间显着不同的疏水相互作用。表面活性剂和PDADMAC。这些远程控制的变化显着影响 P/S 结合，并允许通过光照射调节 PDADMAC/C _n AAP 混合物的体积和界面特性。为此，我们将表面活性剂浓度固定在在 365 nm 紫外光 ( Z ) 和 520 nm 绿光 ( E ) 光的E / Z光异构化作用下表现出明显表面张力变化的值，并改变了 PDADMAC 浓度。电泳迁移率可以通过 C _n AAP 表面活性剂和 P/S 聚集体的光异构化来很大程度上调节，甚至可以表现出从负值到正值的电荷反转，反之亦然。此外，等摩尔浓度的 PDADMAC 与E构型的 C _n AAP 表面活性剂的胶体稳定性较低，导致在本体中形成大的聚集体，当表面活性剂的烷基链足够短时（C ₀ AAP）。振动和频发生（SFG）光谱揭示了与本体相似的界面变化，其中空气-水界面的充电状态可以通过光照射来改变。使用 SFG 光谱，我们询问了界面 H ₂ O的 O-H 拉伸模式，并提供了表面充电的定性信息，并辅以中子反射计，从中我们解决了空气-水界面处PDADMAC 和 C _n AAP 的表面过量问题，独立。