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The suspending appearance of poly(acrylic acid)-based rheology modifier in high-content surfactant: The effect of polymer structure and molecular weight on the rheological properties of the complex systems

Zhengyun Xie,Kai Li,Wei Tang,Shulan Yang,Yanlin Sun

The “all in one” multifunctional and concentrated daily chemical products are required by the market, such as the long-term release of anti-bacterial, medical, or perfume agents. These functions mainly rely on the microcapsules, which could encapsulate these functional and unstable molecules, and then release them in the long term. To stabilize these functional solid particles in a high-content surfactant, it is necessary to add a suspending rheological modifier. The poly(acrylic acid) (PAA)-based rheology modifier is one of the most common additives in the industry of daily chemicals, for thickening or suspending. In this paper, linear PAA, and branched PAA polymers (Carbomer 941 and Carbomer 940) were selected to study the suspending ability of PAA-based rheology modifier in high-content surfactant and to investigate the effect of PAA polymer structure and M w on the complex solution's rheological properties. The yield and viscosity test of the complex solutions of linear PAA and high-content surfactant revealed that the addition of linear PAA could lead to lower yield stress and viscosity, and failed to suspend the polystyrene (PS) model microspheres due to its smaller mean square radius of gyration. The branched PAA polymer, Carbomer 940 and Carbomer 941 were more stable than the linear PAA in these two kinds of surfactant. More specifically, Carbomer 940 with a higher M w, would exhibit higher yield stress and viscosity than Carbomer 941 with a lower M w in nonionic surfactant alcohol polyoxyethylene ether (AEO) solvent with content less than 5 wt%. When the content was higher than 5 wt%, Carbomer 941 presented higher yield stress and viscosity than Carbomer 940, and successfully suspended PS microspheres in the 20 wt% AEO solution. This could depend on the polymer chain's elongation state of these two PAA-based branched rheology modifiers. The same trend happened in the appearance of Carbomer 940 and Carbomer 941 in alcohol ether sulphate (AES) solution. However, the electrostatic repulsive force between the AES and PAA-based rheology modifier could further make the polymer chain curl up and restrain the suspending ability in a lower content surfactant solution. Therefore, this fundamental research could guide the application of the anionic polyelectrolytes in the concentrated daily chemical product for stable suspending particles.