Self-assembled structures of anionic hydrophobically modified polyacrylamide with star-shaped trimeric and hexameric quaternary ammonium surfactants.

The self-assembly of a 1% hydrophobically modified and 30% hydrolyzed polyacrylamide (C12PAM) with cationic star-shaped oligomeric surfactants has been investigated by isothermal titration microcalorimetry, turbidimetry, ζ potential, scanning electron microscopy, and 1H NMR techniques. The oligomeric surfactants are composed of quaternary dodecyldimethylammonium ions with three or six hydrophobic chains connected by a polyamine spacer at the headgroup level, abbreviated as DTAD and PAHB, respectively. DTAD/C12PAM and PAHB/C12PAM mixed systems undergo the same aggregate transitions with increases in surfactant concentration from soluble networklike aggregates to precipitated denser and more cross-linked structures and then to soluble spherical aggregates. The networklike aggregates are generated at very low surfactant concentration. However, at the corresponding surfactant concentration without C12PAM, DTAD cannot form aggregates and PAHB forms only networklike aggregates with a very loose structure. The s...