Insights into Carbopol gel formulations: Microscopy analysis of the microstructure and the influence of polyol additives

Carbopol is a family of high molecular weight cross‐linked poyacrylic acids widely used as thickening agents in several industrial applications. In this work, the structure of Carbopol 974P NF was investigated at pH 7.4 by means of capillary viscometry, dynamic rheology, fluorescence microscopy, and electron microscopy in the dilute and semi‐dilute (hydrogel) state. Especially, high‐pressure freezing technique has proved to be a technique of choice to visualize the Carbopol hydrogel microstructure through cryo‐scanning electron microscopy analysis without artifacts related to the formation of ice crystals. It has been shown that the Carbopol hydrogel has a hierarchical structure made of large spherical entities of a few micrometers in size packed together and composed of much smaller agglomerated microgel particles. In addition, fluorescence and electron microscopies have pointed out that the presence of polyol additives in the gel formulation favors the formation of more dense or jammed structure, probably through hydrogen bonding. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42761.