Micellar growth: Role of molecular geometry and intermolecular hydrogen bonding

The hydroxyl-substituted gemini surfactants, 2-hydroxyl-butanediyl-α,ω-bis(dimethyl-dodecylammonium bromide), and 2,3-hydroxyl-butanediyl-α,ω-bis(dimethyldodecylammonium bromide) that are referred to as 12-4(OH)-12 and 12-4(OH)2-12, respectively, were synthesized and their viscoelastic properties in aqueous solution were studied using steady-state and dynamic frequency sweep rheological measurements. Compared with the unsubstituted butanediyl-α,ω-bis(dimethyldodecylammonium bromide) (12-4-12), the hydroxyl-substituted surfactants obviously promoted the micellar growth, especially for 12-4(OH)2-12. However, the solution viscoelasticity of 12-4(OH)2-12 was always far poorer than that of 12-3(OH)-12 (2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecylammonium bromide)). The present results indicated that the molecular geometry is still an essential and indispensable condition and the hydrogen bonding interactions may be only a supplementary (reinforcing) contribution for the formation of long wormlike micelles. The addition of salts can adjust the molecular geometry but weakened the contribution of the electrostatic energy to the growth of wormlike micelles.