Designing Superabsorbent Polymers for Rapid Water Absorption through Microparticle Assembly after Inverse Suspension...

Manufacturers employ inverse suspension polymerization to increase water absorption and absorption under the pressure of superabsorbent polymers (SAPs) used in personal hygiene products. Researchers have primarily focused on maximizing the water absorption capacity of SAPs when saturated, often by maximizing the swelling ratio. However, there is a scarcity of literature addressing the fast absorption properties necessary for user comfort and dryness in real-world applications. In this study, we assembled PAA-based SAP microparticles in two different sizes to produce a novel capillary diffusion effect, aimed at enhancing water retention capacity after 1 min of absorption (RCW-1), capable of absorbing more water before swelling. We prepared 30-40 μm SAP microparticles (SAP-1), showing high RCW-1 but very low absorption against a pressure of 0.3 psi (AAP-0.3). We removed the oil phase and added fresh reaction medium to continuously aggregate and grow SAP-1 into larger particles (SAP-2) with a high AAP-0.3 and low RCW-1. Using fluorescence microscopy analysis, we were surprised to find that the small gaps between different-sized SAP microparticles could form water channels, allowing water to diffuse among the internal SAP particles through capillary force, providing rapid water absorption. By mixing SAP-1 and SAP-2 in different proportions, we were able to assemble the SAPs into grape-like clusters, achieving an RCW-1 of 197.97 ± 8.08 g/g and an AAP-0.3 of 21.51 ± 1.85 g/g. The ratio of SAP-1 to SAP-2 could be adjusted to produce clusters with different properties, allowing us to customize them for a wider variety of applications.