Polyelectrolyte Complexes as Valuable Ingredients for Nonequilibrium Micelles

Non-equilibrium self-assembled nanostructures hold promise for stimulated transitions at otherwise constant conditions. The reliable formation of these structures can be a challenge.[1,2] This is true when considering the delicate balance between kinetic trapping of micelles for long term stability and otherwise implementing the possibility to induce morphological transitions toward the equilibrium structure by applying minute deflections from metastability.

Having started with a temperature-responsive, basically uncharged polymer-based system, which meets both demands[3] but lacks facile recyclability in terms in regaining the initial nonequlibrium morphologies, we aimed to investigate polyelectrolyte-containing micellar systems. In all cases, considerable changes of the material properties can occur upon triggering the nonequilibrium micelles by help of various stimuli. E.g. low viscosity dispersions of spherical micelles can be transformed on their way toward equilibrium to a network of worm-like micelles forming a gel. These transformations take place at basically constant conditions upon application of a temporary trigger. Hence, the system remembers the history of the sample, like a past heat wave. As mentioned, the non-equilibrium nature of interpolyelectrolyte complex micelles can be principally recycled after approaching equilibrium.[4] Here, the interplay between addition/removal of salt as plasticizer and a temperature-responsive polymer gives a handle to modulate the hydrophilic/hydrophobic balance while freezing and melting the internal micellar structures (glassy interpolyelectrolyte complexes). Hence, micellar morphologies obtained at certain conditions can be conserved for other conditions, where the morphology of these micelles is not the equilibrium one. Eventually, we present a micellar system, which memorizes heat above a certain threshold temperature, as it turns turbid upon suffering high temperatures.[5] We present also a system, which has opposite temperature behavior.[3] In the former case, Smoluchowski-type aggregation kinetics were observed. Besides the history monitoring of exceeding such a temperature, it can also be switched to a system that only senses the current temperature. 

In summary, we present different systems,[6] where minute changes in the conditions lead either to irreversible or sometimes reversible changes in the colloidal properties. In the latter case, certain measures need to be taken to shift the system back…

[1] D.J. Pochan et al., Science 2007, 317, 647.

[2] F.S. Bates et al., Science 2017, 356, 520.

[3] F.A. Plamper et al., Adv. Mater. 2017, 29, 1703495.

[4] F.A. Plamper et al., ACS Macro Lett. 2018, 7, 341.

[5] F.A. Plamper et al., ACS Appl. Mater. Interfaces 2023, 15, 57950.

[6] S.D.P. Fielden, J. Am. Chem. Soc. 2024, 146, 18781.