Electric field-driven post-EPD drying as a structure-directing stage for silica particle assembly

초록

Electrophoretic deposition (EPD) is generally considered to establish the final particle arrangement during deposition, whereas the subsequent drying stage is not usually regarded as influencing film structure. Here, we show that post-EPD drying under controlled electric fields can further influence particle packing and local ordering in silica particle films. Silica particles (∼224 nm) were deposited in a parallel-plate cell, and the drying stage was conducted under natural, AC-only, or combined AC-DC conditions. Compared with natural and AC-only drying, combined AC-DC drying produced the densest particle packing and the highest degree of local ordering within the analyzed regions. The DC component stabilized deposited particles, whereas the AC component promoted particle rearrangement during solvent evaporation. Together, they improved monolayer completion while suppressing premature multilayer stacking. In contrast, natural drying produced loose, non-uniform packing, whereas AC-only drying yielded only limited local ordering. Image-based analyses revealed enhanced local orientational ordering, more persistent positional correlations within the analyzed SEM regions, and improved surface coverage uniformity under AC-DC drying. Optical images showed a more uniform yellow-to-orange appearance under the optimized AC-DC condition. Electrode spacing also affected particle coverage, with a 1.0 mm gap producing more homogeneous packing than a 0.5 mm gap. Current measurements and structural observations indicate that residual liquid maintains electrical connectivity during drying, allowing field-assisted particle assembly to continue during solvent evaporation. These findings indicate that post-EPD drying can serve as a practical structure-directing stage for controlling particle packing and local ordering in colloidal particle films.

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