A conventional surfactant becomes CO_2-responsive in the presence of switchable water additives

摘要

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 CO_2 is used as the stimulus but becomes CO_2-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 CO_2. 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 CO_2 and switchable water can result in aggregation of polystyrene (PS) latexes; the later removal of CO_2 neutralizes the DMEA and decreases the ionic strength allowing for the aggregated PS latex to be redispersed and recovered in its original state. Switched on: Whereas CO_2-triggered switchable surfactants are known, commonly-used conventional surfactants, such as sodium dodecyl sulfate (SDS), are not switchable. In the presence of an additive, "switchable water" (an aqueous solution of switchable ionic strength), SDS can be made CO _2-responsive in a new benign method of reversibly breaking emulsions and latexes (see figure).