From polyethyleneimine hydrogels to Pickering-like smart "On/Off" emulgels switched by pH and temperature.

Hypothesis: According to the so-called colloidal tectonic concept, we assumed that a single self-complementary polymer-based tecton could be used to design self-assembled emulsions. The polymer must be of high-molecular weight with balanced bipolar properties generating those of rigidity and flexibility. Linear polyethyleneimine (LPEI, 25 kDa) was used because it acts as a buffer by continuous protonation/deprotonation of the amine groups.

Experiments: The relationships between the physicochemical properties of LPEI (protonation, charge, size, aggregation and gelation) and emulsions (type, droplet size, rheological behavior and stability) were investigated to highlight the self-assembly and stabilization mechanisms during the construction events as well as the inherent properties of emulsions (responsiveness to external stimuli).

Findings: In aqueous solution, after a first heat and cool cycle, the adequate and spontaneous self-assembly of hydrophobic and hydrophilic sections leads to hydrogels by the formation of a 3D network where the crystallized hydrophobic domains act as knots. In the presence of various oils, the hydrogels provide long-term stable Pickering emulgels. The as-prepared emulsions are highly controllable due to their self-assembled nature (up to 10 consecutive runs). Consequently, this new approach provides a facile route to construct self-assembled, reversible and dynamics Pickering-like emulsions by simplifying the colloidal tectonics concept.