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

Abstract

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, 25kDa) was used because it acts as a buffer by continuous protonation/deprotonation of the amine groups. 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). 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.