Hyperbranched polymer composed of G1
polyamidoamine (PAMAM) and branched with poly (propylene oxide) (PPO)-block-poly (ethylene oxide) (PEO) was
investigated to interact with sodium dodecyl sulfate (SDS) and di-dodecyl dimethyl ammonium
bromide (DDAB), respectively, by the methods of turbidity titration and
analysis, rheology measurements, dynamic light scattering (DLS) and
transmission electron microscopy (TEM). It was noticeable that even at extremely
low concentration of SDS (even far from the critical micelle concentration
(cmc)), the system exhibits high turbidity, indicating that SDS molecules can
insert into cationic amine groups and hydrophobic microenvironment, resulting
in the formation of polymer-SDS complexes with large size. At the SDS
concentration range of below 0.1 mM, the
turbidity and cloud point (CP) temperature of the system keep almost invariable,
mostly because of the repulsion between SDS molecules and the complexes. And,
therefore, the size of the mixed aggregates retains almost constant. In the
case of vesicle system of DDAB, the aggregates are in the size of 100 nm - 200
nm and 500 nm - 3000 nm at the concentrations of 30 mM
and 100 mM, respectively. However,
in the mixture of hyperbranched polymer with DDAB, by comparison, the size is
smaller in a binary system than that of in DDAB system. So it is reasonable to
infer that DDAB molecules remove from multilamellar vesicles of DDAB to the
hydrophobic microenvironment of hyperbranched polymer aggregates, with the
addition of the hyperbranched polymer. It leads to the destruction of the
gel-like conformation in DDAB system, leading to the shear thinning of the
mixture and, as a result, the viscoelastic character of the system is lost in a
large degree.