Aggregation behavior of surfactants with cationic and anionic dendronic head groups.

HYPOTHESIS

Ionic dendronic head groups possess very different structural features than simple surfactant head groups. Accordingly, their self-assembly behavior is expected to differ from that of conventional surfactants. The number of generations of the headgroup should play a particularly relevant role.

EXPERIMENTS

A novel type of surfactants with different dendronic head groups (cationic and anionic) was studied in this work. A systematic variation of the number of generations of the head group (n = 1, 2, and 3), of the head group charge (cationic and anionic), and of the length of the hydrophobic chain (hexanoyl and hexadecanoyl chains) was performed and the self-assembly behavior probed by means of small-angle neutron scattering (SANS) in order to obtain detailed structural insights.

FINDINGS

The analysis of the scattering data shows that the general packing parameter concept applies also to dendrimeric surfactants and a larger head group results in smaller aggregates. However, in contrast to conventional surfactants, increasing the head group size results in a stronger tendency to self-aggregate, as a consequence of the head group's partly hydrophobic character. Another peculiarity of the self-assembled aggregates, is the low aggregation numbers and the high water content within the micelle, as a result of the highly branched head group.