Why does Carbomer act as a thickening agent?

Carbomer is a class of cross-linked polyacrylic acid polymers widely utilized in cosmetics, pharmaceuticals, and daily chemical products, where it serves as a highly effective thickening agent, suspending agent, and gel matrix. Typically appearing as a loose white powder, it swells extensively in water but does not readily dissolve. The fundamental principle underlying its thickening mechanism lies in the fact that Carbomer molecules contain a large number of carboxyl groups; under acidic conditions, the polymer chains remain in a coiled, contracted state, resulting in low viscosity. However, upon the addition of alkaline neutralizing agents—such as triethanolamine or sodium hydroxide—the carboxyl groups undergo dissociation, generating electrostatic repulsive forces that cause the coiled polymer chains to fully uncoil and extend. Simultaneously, the cross-linked structure entraps a significant volume of water molecules to form a three-dimensional network, thereby causing a rapid increase in the system's viscosity and the formation of a stable gel or viscous liquid, thereby achieving a pronounced thickening effect.

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