Creating Regular Matrices of Aligned Silica Nanohelices: Theory and Realization

Here, we exercise nanoscale control over the assembly of highly anisotropic silica helices using convective flow by using the physical properties occurring during evaporation-induced self-assembly. Organizing and patterning such chiral elongated objects over large surfaces in a controllable and reproducible fashion are challenging but desirable to optimize the performance of biomimetic structures, nanosensors (mechanical properties of helices), or optical materials (chiral objects have asymmetric interactions with light as absorption is different for left- and right-handed polarization). The coupling of evaporation forces and physicochemical solution properties induce specific helix alignment, and the stick–slip phenomenon produces a periodical deposition of bands with controllable and regular spacing. Helix orientation, packing density, and spacing can then be tuned. We observe the effect of polymer additives, silica helix concentration, and substrate withdrawal speed on the quality and orientation of the helix deposition. Theoretical modeling based on capillary hydrodynamics is developed to describe the relationship between evaporative conditions and pitch distance, the band width of the stick region, and the helix orientation