Complexation between Dendritic Polyelectrolytes and Amphiphilic Surfactants: The Impact of Surfactant Concentration and Hydrophobicity

JS Klos and J Paturej, MACROMOLECULES, 56, 5022-5032 (2023).

DOI: 10.1021/acs.macromol.3c00223

The solution structureof complexes composed of the cationic dendrimer,anionic surfactants, and their counterions is studied by moleculardynamics simulations using the bead-spring coarse-grained model.We identify that depending on the surfactant concentration and hydrophobicitythe system exists in three structural regimes. In the first regimesurfactant molecules are noncooperatively absorbed by the dendrimer.Here, the pervaded volume of the dendrimer and the bulk solution containloosely distributed unimeric surfactants and counterions. In the secondregime hydrophobic attractions between surfactant tails give riseto cooperative binding. The absorbed surfactants self-assembly intomultichain micellar-like aggregates, whereas the bulk solution consistsof separate unimers. In the third regime the surfactants form multichainaggregates both within the interior of the dendrimer and in the bulk.Our data indicate that self- assembly of the absorbed surfactants affectsthe dendrimer conformations as compared to its neutral counterpart.In the case of noncooperative binding the dendritic polyelectrolyteswells due to the osmotic pressure exerted by the absorbed unimersand counterions. In the regimes characterized by cooperative bindingand pronounced self-aggregation of the encapsulated surfactants swellingof the dendrimer is suppressed. This is attributed to a reductionof the osmotic pressure inside the macromolecule due to the ion exchangephenomenon appearing as a result of strong Coulomb attractions betweencharged monomers of the dendrimer and the encapsulated micellar aggregates.We also find that aggregate formation affects the overall charge accumulatedin the dendrimer. In particular, for the dendrimer loaded with massiveaggregates, we report the charge inversion effect which transformsthe cationic dendrimer into an anionic dendrimer-surfactantcomplex. Our results provide molecular insights into self-assemblyof supramolecular complexes and controlled absorption of guest surfactantmolecules in dendrimer-based host-guest systems.

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