Using the Interplay of Particle and Substrate Roughness to Modulate Particle Arrangements in Non-Close-Packed...

Arranging colloidal particles on surfaces with tunable interparticle distances, like in non-close-packed structures (NCPS), is important for many applications. However, controlling their formation remains challenging. Although particle and substrate roughness, along with electrostatic repulsion, affect colloidal interactions, their combined effect on colloidal arrangement remains poorly understood. Therefore, model silica particles with smooth, medium-rough, and rough, virus-like morphologies were synthesized. Virus-like particle synthesis was optimized for controlled roughness (R _q = 1.4-5.1 nm) and low polydispersity (∼5%). Amine-functionalized particles dispersed in water and aqueous LaCl₃ solutions were transferred onto gold substrates of two different roughnesses to form NCPS. Only the two roughest particle types (R _q = 4.3 and 5.0 nm) formed three-dimensional aggregates on rough substrates, likely due to pre-aggregation in dispersion, which could be driven by roughness-mediated mechanical interlocking. By varying ionic strength, the effect of electrostatic repulsion on interparticle distances of differently rough particles (R _q = 0.3-2.1 nm) is investigated. The rougher the particles, the less an increasing ionic strength reduces interparticle distances. At low ionic strengths, interparticle distances of rough particles (R _q = 2.1 nm) are independent of ionic strength. Smoother substrates promote lateral mobility for all particles, reducing interparticle distances more strongly for smooth particles. However, aggregation of particles with R _q = 2.1 nm remains almost the same on both substrates (R _q = 0.57 and 1.62 nm), while it increases significantly for smoother particles, suggesting that roughness-induced frictional forces are more important at short distances. These findings reveal that adjusting surface roughness can facilitate controlled particle arrangements.