The desalting/salting pathway: a route to form metastable aggregates with tuneable morphologies and lifetimes

We investigate the formation/re-dissociation mechanisms of hybrid complexes made from negatively charged PAA2k coated {\gamma}-Fe2O3 nanoparticles (NP) and positively polycations (PDADMAC) in aqueous solution regime very high ionic strength (I). When building blocks are mixed at large (1M NH4Cl), electrostatic interaction is screened complexation does not occur. If then lowered down to a targeted Itarget, there critical threshold Ic = 0.62 M which occurs, that independent on charge ratio Z pathway used reduce salinity (drop-by-drop mixing or fast mixing). salt added back up 1M, transition reversible persistent out-of-equilibrium aggregates formed. The lifetimes such depends Itarget: closer Itarget is, more difficult it dissolve aggregates. Such peculiar behavior driven by inner structure formed after desalting. far below Ic, strong interactions induce formation dense, compact frozen can only poorly reorganize further with time, makes their dissolution upon resalting almost reversible. Conversely, when close open due weaker System thus rearrange time lower its free energy reach stable states dissociate resalting, even strength.