Aggregation Properties of a Novel Class of Amphiphilic Cationic Polyelectrolytes Containing Gemini Surfactant Segments

Abstract

A novel class of amphiphilic cationic polyelectrolytes, poly(A-co-G)s, comprising of gemini type surfactant segment 1,3-bis(N,N-dimethyl-N-dodecylammonium)-2-propylacrylate dibromide (G) and acryloyloxyethyl trimethyl ammonium chloride (A), were synthesized. Their aggregation properties were investigated by employing fluorescence spectroscopy, dynamic light scattering, transmission electron microscopy, and ζ-potential measurements. For comparison, a series of polyelectrolytes containing a traditional single alkyl chain surfactant unit (acryloyloxyethyl-N,N-dimethyl-N-dodecylammonium bromide (D)), poly(A-co-D)s, were also synthesized and investigated. It was found that the critical aggregation concentration (cac) of poly(A-co-G)s is much lower than that of poly(A-co-D)s. The huge interpolymer aggregates (with a hydrodynamic radius of >450 nm) occur in poly(A-co-G)s aqueous solution, and the size of aggregates increases with the increase of the molar content of the gemini-type surfmer segment and the concentration of the copolymer. The size of aggregates in poly(A-co-D)s aqueous solution is much smaller than poly(A-co-G)s, which also increases with the increase of the molar content of the single alkyl chain surfmer segment and the concentration of the copolymer. The results of aggregation number and charge density of aggregate in poly(A-co-G)s and poly(A-co-D)s indicate that the copolymers have a strong tendency toward interpolymer aggregation and the aggregates in poly(A-co-G)s are much more compact than those of poly(A-co-D)s. These results are interpreted in terms of the synergistic effects of double hydrophobic chains on the gemini surfactant unit.