Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan, Shandong 250100, PR China.
School of Chemical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.
J Colloid Interface Sci. 2021 Sep;597:383-392. doi: 10.1016/j.jcis.2021.04.003. Epub 2021 Apr 5.
Responsive surfactant systems based on dynamic covalent bond exhibit an unsatisfactory foamability and foam stability, despite their documented functionality in emulsions. As such we anticipate that the foaming performance should be improved by introducing Pickering effect, which is possible when the responsiveness of the dynamic covenant bonds controls not only the hydrophobicity of polymers but also their aggregation behavior (to form nanoparticles).
Here we created surface active nanoparticles made from self-aggregated polymers consisting of PAH (polyallylamine hydrochloride)-BA (benzaldehyde). The covalent imine bonds between originally hydrophilic PAH and hydrophobic BA are dynamic in that their formation and breakage is a function of solution pH, confirmed by H NMR and dynamic interfacial tension measurement.
At pH 7.4, a stable foam is achieved in the PAH-BA (amino to aldehyde ratio at 1:0.2) solution; while at pH 2.5, it defoams due to breakage of dynamic bonds corresponding to the measured diminishing surface activity. The reversibility of foaming-defoaming has been demonstrated by alternatively changing pH for multiple cycles, with the foaming performance persistent. The foam stability can be improved by more hydrophobic compounds e.g. at a lower amino to aldehyde ratio or using PAH-cinnamaldehyde (CA). The reversible and responsive foaming demonstrated in a Pickering system provides a new method to create novel foaming systems with properties desirable to many applications.
尽管基于动态共价键的响应性表面活性剂系统在乳液中具有已记录的功能，但它们的起泡性和泡沫稳定性并不令人满意。因此，我们预计引入 Pickering 效应可以改善起泡性能，当动态共价键的响应性不仅控制聚合物的疏水性，还控制其聚集行为（形成纳米颗粒）时，就有可能实现这种效应。
在这里，我们创建了由自聚集聚合物组成的表面活性纳米颗粒，这些聚合物由 PAH（盐酸聚烯丙基胺）和 BA（苯甲醛）组成。最初亲水的 PAH 和疏水的 BA 之间的共价亚胺键是动态的，其形成和断裂是溶液 pH 的函数，这通过 H NMR 和动态界面张力测量得到了证实。
在 pH 7.4 下，在 PAH-BA（氨基与醛基的比例为 1:0.2）溶液中可实现稳定的泡沫；而在 pH 2.5 下，由于动态键的断裂，相应的表面活性降低，导致泡沫消泡。通过交替改变 pH 值进行多次循环，已经证明了起泡-消泡的可逆性，并且起泡性能保持不变。通过添加更疏水的化合物（例如，降低氨基与醛基的比例或使用 PAH-肉桂醛（CA））可以提高泡沫稳定性。在 Pickering 系统中展示的可逆和响应性起泡为创建具有许多应用所需特性的新型起泡系统提供了一种新方法。
