Directional Assembly of Large-Area Silica Nanorod Film Using the Electric-Field-Assisted Capillary Channel Method

Theself-assembly of colloidal particles, especially colloidalparticles with anisotropic geometry, is important for applicationsin the construction of many functional materials. Compared with theself-assembly of colloidal particles with isotropic geometries, notonly does the geometric orientation among neighboring anisotropicparticles need to be considered for the reduction of Gibbs free energy,the orientations of the particles are best to be externally influenced.Because of this, the preparation of assembled nanorod arrays withuniform alignment across a large area is still a significant challenge.In this work, an electric-field-assisted capillary channel methodis reported, using an external electric field to influence the orientationof silica nanorods or FeOOH ellipsoids during assembly. By applicationof an external electric field, the alignment of the nanorods is effectivelycontrolled. The capillary channel method provides continuous replenishmentof a colloidal solution containing nanorods or spheres for assemblyof large-area films. The area of the formed films was influenced bythe assembly temperature, channel width, colloidal solution concentration,and solvent surface tension. The competition between the thermal Brownianmotion and torque generated by the external electric field impactedthe nanorod array quality in the film. While increasing the intensityof the electric field improved nanorod alignment, applying a potentialgreater than 6 V also produced a heating effect, negatively affectingthe quality of the nanorod arrays. The nematic order parameter S which characterizes the degree of alignment of FeOOH ellipsoidswith smaller length is significantly lower than the one for silicananorods due to the higher critical field strength and the increasedsusceptibility to the effects of thermal motion. The assembly of silicananorods at 35 & DEG;C under an effective potential of 4-6V provides a compromise between achieving uniform nanorod orientationand maximizing the coverage area of the colloidal film.

Automated summary

The self-assembly of anisotropic colloidal particles is crucial in the construction of functional materials. The orientation among neighboring particles needs to be considered, and external influence is necessary for optimal results. This study presents a method using an electric field to control the alignment of silica nanorods or FeOOH ellipsoids during assembly, providing a solution for large-area film formation.