Stabilization mechanisms of foams enhanced by xanthan gum and sodium carboxymethyl cellulose: Rheology–bubble structure interplay and predictive criteria for drainage delays

Investigating the stabilization mechanisms of foams is critical for diverse industrial applications. In this study, xanthan gum (XG) and sodium carboxymethyl cellulose (CMC) were employed to prepare foams. The results revealed that the expansion ratio was governed by the gas–liquid Reynolds number. When the liquid Reynolds number was less than 9, the expansion ratio was less than 5. The bubble diameter strongly depended on the liquid capillary number and the gas Reynolds number. For industries that need delicate foam, a high liquid capillary number and a high gas Reynolds number are needed. In addition, a linear relationship between the foam yield stress and bubble size was observed, along with a negative quadratic dependence on the expansion ratio. Furthermore, when the bubble diameter was less than the critical value (the foam yield stress exceeded the local stress within the plateau border), no liquid flowed out of the foam (drainage delay). A predictive model for the critical bubble diameter and delayed drainage time was developed (with a deviation of 25 % between the predicted and experimental values), incorporating zero-shear-rate viscosity, expansion ratio, and bubble size. This research provides theoretical guidance for the application of foam in different industrial scenarios.