Tetrasiloxane room temperature ionic liquids: adsorption and aggregation properties in aqueous solution

The adsorption and aggregation behavior of three tetrasiloxane surface active room temperature ionic liquids, N-(2-aminoethyl)-3-aminopropyltetrasiloxane carboxylic acid ammonium, [Si(4)N(2)-2CA(n) (n = 1, 2, 3)], have been studied on the basis of static/dynamic surface tension, conductivity, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The static surface tension of the Si(4)N(2)-2CA(n) aqueous solutions measured at the critical aggregation concentration (CAC) is observed to be significantly lower than that of amide-functionalized ILs and is comparable to those reported for trisiloxane RT-SAILs, N-(2-aminoethyl)-3-aminopropyltrisiloxane carboxylic acid ammonium and 3-aminopropyltrisiloxane carboxylic acid ammonium. The dynamic surface tension results indicate that adsorption process is a mixed diffusion-kinetic adsorption mechanism. DLS and TEM analysis of Si(4)N(2)-2CA(n) solutions reveal that they can self-assemble into vesicles with an average diameter in the range of 70-500 nm.