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| - Lamellar Structures of Anionic Poly(amido amine) Dendrimers with Oppositely ChargedDidodecyldimethylammonium Bromide
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| - The lamellar structures of anionic poly(amido amine) dendrimers possessing carboxylate terminal groups athalf-generations G = n.5 (G2.5 and G4.5) with the cationic surfactant didodecyldimethylammonium bromide(DDAB) were investigated by small-angle X-ray scattering (SAXS) at 25 °C. The incorporation of dendrimersinto the lamellar liquid crystals, at DDAB concentrations in the range of 4∼30 wt %, results in the transitionfrom a monophasic lamellar structure (Lα) to biphasic lamellar mixtures (Lα and LαD), at similar 2[DDAB]/[−COONa] ratios for the two dendrimers with the later and earlier generations (56 for the G4.5 dendrimer and62 for the G2.5 dendrimer). The Lα structure consists of DDAB bilayers and dendrimer molecules doped intothe water domains. The oppositely charged dendrimer preferably sticks to the DDAB bilayers, resulting inthe decrease in the domain size of the wide spaced Lα structure with increasing the dendrimer concentration.In the narrow spaced LαD structure, monolayers of collapsed dendrimers are adsorbed tightly between theDDAB bilayers. The thicknesses of the dendrimer monolayers are found to be 4.2 nm for the G4.5 dendrimerand 3.0 nm for the G2.5 dendrimer. These values are smaller than the diameters of the corresponding dendrimersfound in aqueous solution. It is also deduced from Gaussian fits of SAXS patterns that the G4.5 dendrimercan form more ordered LαD structures with domain sizes larger than those of the G2.5 dendrimer, due to thestronger electrostatic interaction between the cationic surfactants and the oppositely charged dendrimers withterminal groups located at shorter distances.
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