Exploitation of Zwitterionic Surfactant Systems in Synthetic and Separation Science Applications

Many zwitterionic surfactants are thermoresponsive in that their solutions display a liquid – liquid miscibility gap which show an upper critical solution temperature (UCST). That is, at elevated temperatures above their cloud point (CP), their solutions exist as a homogeneous isotropic liquid phase. However, if the temperature is lowered to below the CP, this solution separates into two liquid phases, namely a small volume surfactant-rich phase and a much larger volume surfactant-poor phase. This unique phase behavior has provided the basis for use of such zwitterionic surfactant aggregate systems in separation (extraction) applications as well as a medium for the synthesis of nanomaterials (metal nanoparticles and/or nanochains) at elevated temperature. In this presentation, the phase behavior as well as micellar properties of several zwitterionic sulfate-type surfactants, i.e., 3-(N-alkyl-N,N-dimethylammonio) propane sulfates, in their homogeneous one phase region above the UCST, will be described. In addition, their utilization in CP extraction schemes for a variety of analytes (organic and biological species and nanoparticles) in addition to their ability to function as a medium for the synthesis, extractive concentration, stabilization, and storage of nanomaterials will be summarized.