Cationic Gemini surfactants based on adamantane: Synthesis, surface activity and aggregation properties

A series of novel cationic Gemini surfactants based on adamantane, namely 1,3-bis(alkyldimethylammonioethoxycarbonyl) adamantane dibromide ([CnE-Ad-ECn], n = 12, 14, 16) were synthesized from 1-adamantanecarboxylic acid. The surface activity and aggregation properties of the resultant surfactants were investigated by using surface tension, electrical conductivity, dynamic light scattering (DLS), steady-state fluorescence and fluorescence quenching technique. These surfactants have been found to have low critical micelle concentrations (CMC) and large minimum surface area per molecule (Amin) values as compared to other categories of cationic Gemini surfactants. A series of thermodynamic parameters such as standard free energy ( Δ G m 0 ), enthalpy ( Δ H m 0 ), and entropy ( Δ S m 0 ) of micellization were evaluated from electrical conductivity measurements in the temperature range of 288–308 K. In addition, the micropolarity and the micelle aggregation number (Nagg) were studied by fluorescence measurements. Particular performances of [CnE-Ad-ECn] such as low CMC, large Amin, and small Nagg, should be attributed to the lipophilic, rigid and bulky adamantane spacer.