Study on salt thickening mechanism of the amphiphilic polymer with betaine zwitterionic group by β-cyclodextrin inclusion method

A method based on host-guest inclusion system was used to investigate the salt thickening mechanism of poly [acrylamide-co-N, N′-dimethyl (methylmethacryloyl ethyl) ammonium propane sulfonate-co-cetyl dimethyl allyl ammonium chloride] (PADC). The salt thickening behavior of PADC solution was studied by rotational viscometer, and its average hydrodynamic diameter ( D h ) was characterized by dynamic light scattering (DLS). The formed host (β-cyclodextrin)-guest (hydrophobic groups of PADC) inclusion system was confirmed by scanning electron microscopy (SEM). A method of characterizing the hydrophobic association strength and determining the hydrophobic association contribution rate (HACR) was introduced by the inclusion of β-cyclodextrin (β-CD). The results showed that the apparent viscosity and the D h of PADC solution increased with the increase of salt concentration. In addition, the types of salt also affected the thickening property of PADC solution. Moreover, the results of HACR indicated that the hydrophobic association strength of PADC solution was enhanced in the presence of salts, which was confirmed by fluorescent method. Thus, it could be concluded that the salt thickening of PADC solution was caused by the destruction of ionic bonds in betaine monomer and the enhancement of hydrophobic association strength.