Reversible stability of colloids switched by CO 2 based on polyhexamethylene guanidine.

The stability of a colloid, including emulsion and polymer latex, can be destroyed irreversibly by the addition of salt. Using the CO 2 stimulus, amines can be converted into organic ammonium salts reversibly, which can access the switching of colloids. Polyhexamethylene guanidine (PHMG), was chosen as a switchable amine. The conductivity of PHMG aqueous solution switched by adding and removing CO 2 . Surface tension measurements verified that, under CO 2 , the critical micelle concentration of sodium dodecyl benzene sulfonate (SDBS) decreased from 1.0 × 10 -3 to 5.0 × 10 -4 M with the addition of PHMG. The crude oil emulsion containing SDBS and PHMG was destroyed and restored reversibly by the treatment with CO 2 and N 2 . The polystyrene latex also occurred an obvious stratification after sparging with CO 2 and returned a homogeneous phase upon bubbling N 2 . This study is intended to pave the way for colloids which has reversible stability in response to CO 2 stimulation.