Three-dimensional alignment of mannan I microcrystals under a strong magnetic field

Magnetic alignment offers a noncontact approach for controlling the orientation of materials with anisotropic magnetic susceptibility, including carbohydrate crystals; however, its applicability to mannan I microcrystals remains unclear. This study aimed to elucidate the magnetic alignment behavior and magnetic susceptibility anisotropy of mannan I microcrystals. Mannan I microcrystals derived from ivory nut endosperm were prepared via recrystallization and subsequently surface-modified by TEMPO-mediated oxidation to enhance dispersibility while preserving their crystalline structure. Under strong static magnetic fields, the microcrystals exhibited preferential alignment with the magnetic easy axis along the b-axis, resulting in three-dimensional orientation when combined with flat-on deposition during drying. Quantitative analysis yielded an experimental magnetic susceptibility anisotropy (Δχ = χ_b - χ_a) of 5.83 × 10^-8 (SI). A calculated Δχ value based on Pascal's law of additivity, using a density functional theory-optimized crystal structure, was of the same order of magnitude (1.36 × 10^-7, SI) and indicated a diamagnetic susceptibility order of χ_c < χ_a < χ_b < 0. These findings establish magnetic alignment as an effective strategy for structural control in bio-based nanomaterials and provide insights for the design of high-strength, optically anisotropic polysaccharide-based materials.