pH-responsive pickering foam created from self-aggregate polymer using dynamic covalent bond

Hypothesis: 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). Experiments: 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-1 NMR and dynamic interfacial tension measurement. Findings: 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. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

The study found that the foamability of responsive surfactant systems based on dynamic covalent bonds can be improved by introducing the Pickering effect, which depends on the control of hydrophobicity and aggregation behavior of polymers by the dynamic bonds. Experiments showed that the reversible and responsive foaming in the system is achieved through the continuous formation and breakage of dynamic bonds.