Characterization of quaternized poly(amidoamine) dendrimers of generation 1 with multiple octyl chains

A quaternized dendrimer-type surfactant with 16 octyl chains and 16 ammonium groups (refer to C8qbG1) has been synthesized by the reaction of poly(amidoamine) dendrimer of generation 1 with glycidyldimethyloctylammonium bromide, and its physicochemical properties have been characterized by measuring surface tension, fluorescence spectroscopy of pyrene, specific conductivity, dynamic light-scattering (DLS) and electrophoretic light-scattering (ELS). The surface tension of C8qbG1 decreases gradually with increasing concentration, and reaches two break points, probably indicating that the quaternized dendrimers adsorb and saturate at the air/water interface, and then interact strongly with them being at the interface. The concentrations at two break points coincide with those obtained by the electrical conductivity method. The fluorescence intensity ratio of the first to the third band in the emission spectrum of pyrene for C8qbG1 continues to decrease slowly from 3-fold-concentration of first break point obtained by the surface tension method. In addition, the results of DLS and ELS show that C8qbG1 forms large aggregates with positive ζ-potentials in the solution, and these sizes become large with the concentration. One of the reasons for such a bulk behavior may be caused by the attractive interaction between multiple hydrocarbon chains of C8qbG1.