Tailoring neutron-shielding boron-metakaolin geopolymers with B4C filler: surfactant-driven interfacial and microstructural control

The incorporation of boron (B) as a neutron absorber into metakaolin-based geopolymers for the remediation of radioactive debris following nuclear accidents has attracted considerable attention. In this study, boron carbide (B4C) was employed as a functional filler, while cetyltrimethylammonium bromide (CTAB) acted as both a dispersant and a stabiliser to enhance the neutron shielding properties of metakaolin-based geopolymers. Although the addition of B4C improved processability via a “roller-ball” effect and had no discernible impact on the geopolymerisation process, its weakly polar, negatively charged surface led to the formation of a loose, weak-shell interfacial transition zone (ITZ) between the filler and the matrix, thereby reducing mechanical strength and chemical stability. In contrast, CTAB self-assembled into an interdigitated monolayer on the B4C surface, reversing its surface charge to positive and promoting its uniform dispersion within the matrix. While CTAB slightly inhibited the dissolution of metakaolin, it preferentially interacted with B4C, thereby mitigating the adverse effects on the geopolymerisation process. Moreover, CTAB promoted gelation within the ITZ surrounding B4C, facilitating the development of a dense, potassium-deficient, yet electrostatically stabilised microstructure. This synergistic interaction enhanced interfacial bonding between the filler and the matrix, enabled efficient stress transfer, and significantly improved mechanical performance and chemical stability. Furthermore, the B4C–CTAB-modified geopolymers demonstrated enhanced neutron shielding performance. Overall, this work offers a promising approach for engineering high-performance, multifunctional geopolymer composites for nuclear and environmental applications.