Small-Angle Neutron Scattering and Fluorescence Quenching Studies of Aggregated Ionic and Nonionic Surfactants in the Presence of Poly(1,4-diaminobutane) Dendrimers

Abstract

Small-angle neutron scattering (SANS) measurements were carried out on the supramolecular complexes formed between sodium dodecylsulfate (SDS) and different generation poly(1,4-diaminobutane) dendrimers. For the first and second generation dendrimers, the scattering data are consistent with the existence of spherical SDS micelles bound to the dendrimers. The aggregation numbers of these bound micelles were determined. When these data are combined with reported data from binding isotherms, information on the molecular composition and structure of the complexes can be obtained. For the first generation dendrimers the complexes comprise three and four dendrimer molecules bound to an SDS micelle. The number of bound dendrimers decreases for the next generation poly(1,4-diaminobutane) dendrimers. The SANS data for the dendrimer/SDS complexes of the third and fourth generation dendrimers are not consistent with small spherical micelles. Indeed the intense scattering observed at low values of wave vector transfer is consistent with the formation of large aggregates. This result was confirmed from viscosity measurements. Fluorescence quenching measurements suggest that the bound SDS in these larger structures have aggregation number of twice those of normal SDS micelles. The overall data suggests that the basic building blocks in these complexes consists of surfactant aggregates linking different dendrimers. Finally SANS measurements were also carried out to study the micelles of hexaethyleneglycol monododecyl ether (C12EO6) in the presence of these dendrimers. The scattering data are consistent with spherical free C12EO6 micelles existing in solution.

Supramolecular Complex Induced by the Binding of Sodium Dodecyl Sulfate to PAMAM Dendrimers

“…It redispersed when SDS concentration exceeded 15 mM, suggesting that the complex underwent a structural reorganization in excess amounts Dynamic light scattering was carried out to further examine the complexation mechanism and structural transformation during the course of binding. Contrary to previous studies that focused on the complexation behavior at high SDS concentration (g20 mM), 13,15,28,32 the current study attempted to monitor the gradual formation of the complex over a concentration regime ranging from an extremely low SDS concentration (<0.002 mM) to saturation concentration (>18 mM). The dependence of hydrodynamic radius (R h ) and scattering intensity on the SDS concentration for 0.2 mM G3[EDA] PAMAM-NH 2 at pH of 2, 7.4, and 10 was plotted in Figure 4.…”

“…The existence of spherical SDS micelles on PAMAM dendrimer surface beyond the saturation concentration was confirmed by Wyn-Jones and co-workers based on the SANS results. 32 It is noted that the redispersion was encountered at SDS micelle concentration of 0.25 mM (under the assumption that the aggregation number of SDS is 60), 39 which equals approximately the concentration of G3[EDA] PAMAM-NH 2 , suggesting that at least one SDS micelle is required to stabilize one dendrimer molecule. This finding is in agreement with the previous study on the structure of poly(1,4-diaminobutane) dendrimer/SDS complex.…”

Convenient Synthesis and Properties of Polypropyleneimine Dendrimer‐Functionalized Polymer Nanoparticles

“…We have previously shown that the primary reactive NPs can be produced through polymerization in microemulsions using either anionic, nonionic, or cationic surfactants 11, 12. The formation of supramolecular auto‐assemblies through interactions of polyaminodendrimers with anionic and nonionic surfactants has been reported 32. Consequently, we chose to prepare the reactive initial NPs in the presence of a cationic surfactant to avoid attractive interactions between dendrimers and surfactant molecules during the post‐functionalization step that might cause interparticle linkages and, hence, colloidal destabilization through aggregation.…”

Dendrimer–surfactant interactions

“…[46][47][48][49] In comparison, non-ionic surfactants such as hexaethylene glycol monododecyl ether (C 12 EO 6 , Chart 1) exhibit extremely weak interactions with cationic and anionic dendrimers. 23,50 Interestingly, anionic surfactants such as SDS strongly interact with not only cationic dendrimers, but also neutral dendrimers with sugar and hydroxyl groups as surface functionalities. 35 The ionic interactions are stronger for high generation dendrimers due to higher charge density and more binding sites on the dendrimers.…”