Synthesis and aqueous solution properties of PAMAM dendron surfactants bearing a quaternary ammonium focal group and sugar terminal groups

Poly(amidoamine) (PAMAM) dendron surfactants bearing a focal quaternary alkyldimethylammonium group and terminal sugar groups (Cmqb-GnLac; m = 12, 18, 22; n = 0, 1) have been synthesized. Solution properties of these dendron surfactants were investigated by means of static surface tension, electric conductivity, fluorescence probing with pyrene, dynamic light scattering (DLS) and static light scattering (SLS). In the surface tension profiles all Cmqb-GnLac systems indicate a clear break point corresponding to the critical micelle concentration (cmc). The cmc decreases with increasing length of alkyl chain, from 8.2 × 10−3 (C12) to 4.5 × 10−6 mol dm−3 (C22) for G0Lac, from 1.0 × 10−2 (C12) to 3.7 × 10−5 mol dm−3 (C22) for G1Lac systems. Unlike conventional cationic surfactants, the surface tension at cmc (γcmc) significantly increases with increasing alkyl chain length, associated with a slight increase in the molecular occupied area. Degree of counter ion (Br−) binding to the micelles is found to be very low due to an effective charge shielding by bulky non-ionic headgroups. In all Cmqb-GnLac systems the micellar size decreases above a certain concentration. In the higher concentration regime, formation of micelles with a very small number of (at most a few) molecules is suggested from DLS data.