Influence of the Crosslinker Hydrophobicity on the Swelling Kinetics of Poly(Acrylic Acid) Microgels

Superabsorbent polymer gels are widely used in commercial areas, such as in hygiene products. A key aspect in these and other applications is the gel swelling kinetics, and a key factor of influence on that is the hydrophobicity of the gel. This paper reports on the synthesis of superabsorbent polymer microgel particles with four differently hydrophobic crosslinkers: N,N’-methylenebisacrylamide (MBAA), N,N’-ethylenebisacrylamide (EBAA), N,N’-propylenebisacrylamide (PBAA), and N,N’-butylenebisacrylamide (BBAA). This work uses droplet-based microfluidics to produce uniform and well-defined microgel specimen and study the influence of the crosslinker hydrophobicity on the swelling kinetics. In particular, this work determines swelling constants and their dependencies on the temperature of the swelling medium as well as the activation energies of swelling in relation to the crosslinker hydrophobicity. This work finds two competing effects, leading to a narrow window in which the activation energy of the swelling of the microgels decreases with increasing crosslinker hydrophobicity.