Study on the aggregation nature of sodium cocoyl glycinate and sodium hyaluronate mixture in aqueous and NaCl solutions

Abstract

The mixed system of sodium cocoyl glycinate and sodium hyaluronate (HA) with different mass concentrations and relative molecular weights was investigated by the surface tension method. All the curves of surface tension versus logarithm of concentration (γ-lgc curves) of sodium cocoyl glycinate-HA mixed system displayed the properties of double platform. The critical micelle concentration (cmc) of sodium cocoyl glycinate was 1.690 g/L at 25°C. The two inflection points of the γ-lgc curves corresponding to the cocoyl glycine-HA mixed system were cac (the critical aggregation concentration) and cmc_e (the extended cmc of sodium cocoyl glycinate), and cac < cmc_e < cmc. With the change of the mass concentration and relative molecular weight of HA, the cac values were almost constant. However, cmc_e increased with the increase of the mass concentration of HA at the same HA molecular weight. For the HA of molecular weight of 800 and 260000 Da, the mass concentration of HA increased from 0.05 to 0.4 g/L, and the cmc_e value increased from 1.199 to 1.390 g/L and 1.102 to 1.330 g/L, respectively. When the mass concentration of HA remained the same, the change in the relative molecular weight of HA had little effect on the cmc_e value. For the mixed system of sodium cocoyl glycine −0.1 g/L HA, when the concentration of NaCl was 2 g/L, the salt enhancement effect was dominant. When the concentration of NaCl was 4 to 8 g/L, the salt weakening effect was dominant. It is indicated that HA can improve the chemical properties of sodium cocoyl glycinate at a certain concentration, thus improving the cleaning, foaming, and foam stability of sodium cocoyl glycinate.