Creating Regular Matrices of Aligned Silica Nanohelices: Theory and Realization

Abstract

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 is challenging, but desirable to optimize the performance of biomimetic structures, nano-sensors (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 the 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.

Tuning the Chiroptical Properties of Elongated Nano-objects via Hierarchical Organization

“…4 A number of strategies to assemble these nanoobjects are developed. The proposed strategies rely on physical approaches based on controlled evaporation or shear force (dip-coating, doctor blade coating, microfluidic, spraying…), 5,6,7,8,9 or on incorporation in matrices, for example by formation of lyotropic mineral liquid crystals or in polymer networks. 10,11,12,13 In order to control the interaction between materials and light, they need to be structured on a length scale smaller than the wavelength of the exciting electromagnetic field, i.e.…”

Controlling disorder in self-assembled colloidal monolayers via evaporative processes

“…using polymers, very small nanoparticles, or electrostatic repulsion from the substrate), will increase the degree of order in their packing. 102,167 We used convective assembly to control the disorder in bands of tightly packed silica helices having a wire-like structure. 102 Ordered assembly was possible in both the Landau-Levich and convective assembly regimes (Fig.…”

“…102,167 We used convective assembly to control the disorder in bands of tightly packed silica helices having a wire-like structure. 102 Ordered assembly was possible in both the Landau-Levich and convective assembly regimes (Fig. 7).…”

“…The shearing induced by draining can lead to vertically striped deposition patterns under some conditions. 102 In the formation of Landau–Levich films, the viscous, gravitational, and surface tension forces in the trapped fluid layer exist in equilibrium. The Landau–Levich equation can be used to describe the thickness of this fluid layer, h 0 : where γ is the air–liquid surface tension, and ρ is the density of the solvent.…”

“…using polymers, very small nanoparticles, or electrostatic repulsion from the substrate), will increase the degree of order in their packing. 102,167 …”