Water-induced damage revolution of the carbon nanotube reinforced poly (methyl methacrylate) composites

Polymer matrixed nanocomposites commonly suffer from mechanical degradation when employed in a watery environment, but the destructive moisture effect and the impact of nano fillers lacks an integrated understanding. In this work, we investigate the water-induced defects of carbon nanotube (CNT) filled poly (methyl methacrylate) (PMMA) composite at the microscopic level. Three damage modes are detected and the corresponding damage mechanisms are verified to be involved in the microstructural evolution: i) hydrogen bonds tend to form efficiently between H₂O and polymer atoms at the beginning of moisture absorption; ii) H₂O aggregation in micro-pores induces polymer chain stretching and bulk volume expansion; iii) inconsistent response of CNT and polymer chains on water absorption dominates interfacial degradation. We find that CNTs plays a waterproofing role by reducing free volume and providing zigzagging diffusion paths for water molecules. This study discloses the mechanism of water-induced deterioration in nanocomposites, facilitating improvement of their underwater mechanical properties.