Pseudo hydrophobically associative polymer with CO2-switchable viscosity

Abstract

Smart materials with switchable viscosity-enhancing properties are used in different fields, and are constantly being researched and expanded. Due to its plenty of advantages, such as richness and greenness, CO2 has been continuously used as a trigger for switchable viscosity-enhancing materials in recent years, and endows the material with the performance of multiple reversible switching. Herein, Polyethyleneimine (PEI) and sodium dodecyl sulfate (SDS) are formulated as aqueous solutions with CO2-switchable viscosity. In the presence of CO2, PEI and SDS produce structures comparable to hydrophobically associative polymers in aqueous solution to increase viscosity; in the absence of CO2, structures like hydrophobically associative polymers disappear, reducing reversibly viscosity of aqueous solution with PEI and SDS. Compared with the real hydrophobically associative polymer, the more complicated synthesis process is omitted. Using rotational rheometer and 1H NMR, the CO2-switchability and pH-switchability of the SDS/PEI mixture solution were compared, and it was proved that the viscosity-enhancing behavior of the mixture solution was related to both SDS and PEI; at the same time, the effects of SDS/PEI ratio, concentration, salinity and temperature on the viscosity-enhancing behavior of SDS/PEI mixture solution were studied, and the influence mechanism of each factor on the viscosity-increasing behavior was discussed. Finally, using dynamic light scattering, fluorescence spectroscopy and confocal microscopy, the CO2-switchable viscosity-enhancing mechanism of SDS/PEI mixture solution was explored. Under the stimulation of CO2, the protonation of PEI and the resulting electrostatic interaction, hydrophobic association, form a physical cross-linked network in the mixed aqueous solution to achieve the viscosity enhancement.