A Conventional Surfactant Becomes CO₂‐Responsive in the Presence of Switchable Water Additives

Abstract

We have developed a new benign means of reversibly breaking emulsions and latexes by using "switchable water", an aqueous solution of switchable ionic strength. The conventional surfactant sodium dodecyl sulfate (SDS) is not normally stimuli-responsive when CO2 is used as the stimulus but becomes CO2 -responsive or "switchable" in the presence of a switchable water additive. In particular, changes in the air/water surface tension and oil/water interfacial tension can be triggered by addition and removal of CO2 . A switchable water additive, N,N-dimethylethanolamine (DMEA), was found to be an effective and efficient additive for the reversible reduction of interfacial tension and can lower the tension of the dodecane/water interface in the presence of SDS surfactant to ultra-low values at very low additive concentrations. Switchable water was successfully used to reversibly break an emulsion containing SDS as surfactant, and dodecane as organic liquid. Also, the addition of CO2 and switchable water can result in aggregation of polystyrene (PS) latexes; the later removal of CO2 neutralizes the DMEA and decreases the ionic strength allowing for the aggregated PS latex to be redispersed and recovered in its original state.

CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications

“…Replacing them with CO 2 -responsive surfactants could be problematic because of higher surfactant cost and the need to reformulate well-established processes and formulations. 54 Redispersion is achievable using gentle hand shaking rather than sonication (sonication was required for the redispersion of most CO 2switchable latexes reported in this review). Su et al added DMEA as a CO 2 -switchable additive to a dodecane/water emulsion, which had been prepared using SDS surfactant.…”

“…54 The process was reversible and removal of CO 2 resulted into the creation of a stable emulsion (Fig. Replacing them with CO 2 -responsive surfactants could be problematic because of higher surfactant cost and the need to reformulate well-established processes and formulations.…”

“…147,156,182 SHS can be separated from a hydrophobic product by extraction with carbonated water. 54 For instance, when a CO 2 -switchable ionogen is in its neutral form, the ionic strength of the aqueous solution is low, but after the introduction of CO 2 , the ionic strength increases (Fig. 147 SHS can be used in the recycling of polystyrene foam.…”

Preparation and characterization of CO2-responsive poly(amino acid) derivatives with guanidine group

“…Particle size and zeta potential measurements Zeta potential and laser particle size analysis measurements are used as an efficient way to detect the molecular morphological changes of molecules [32,33]. Therefore, to investigate the molecule existing form of PolyAspAm(OA/Larg) in aqueous solution and its molecular microstructure variation during the cycle of treatment with CO 2 followed by N 2 , size and zeta potential of the nanoparticles were employed by testing the dispersion via dynamic light scattering (DLS) at 25°C.…”

CO2-based Solvents

“…Addition of CO 2 to a suspension of fine clay particles in SW causes much faster and more complete settling of the particles. 117 SW can be used as a draw solution for the recovery of fresh water from wastewater or sea water using forward osmosis. 117 Emulsions stabilized by non-switchable surfactants in SW can be broken by CO 2 addition.…”