Single-Sided NMR for Real-Time Tracking of Porous Structure Formation of Acrylate Copolymer Waterproof Composites during Erosion

The failure mechanism of acrylate copolymer waterproof composite films under sulfuric acid treatment is elucidated by time- and depth-resolved low-field single-sided nuclear magnetic resonance (NMR). The high depth sensitivity (10 μm) and large detection region (14 × 14 mm 2 ) of single-sided NMR enable in situ tracking of porous structure formation under aqueous conditions. Both the pore size and interior surface wettability can be obtained through the proper selection of probe molecules, that is, water and ethanol, with different molecular sizes and surface tensions. A two-step erosion process is discovered over 7 days of treatment: Phase I (initial 4 days) primarily features calcite-to-gypsum transformation along with pore generation, and Phase II (final 3 days) involves slowing of pore propagation and copolymer matrix swelling. Numerical modeling confirms that such erosion inhibition arises from the interfacial stress concentration due to heterogeneous swelling of the acrylate copolymers.