Electric Field‐Directed Convective Assembly of Ellipsoidal Colloidal Particles to Create Optically and Mechanically Anisotropic Thin Films

Abstract

A method of simultaneous field‐ and flow‐directed assembly of anisotropic titania (TiO2) nanoparticle films from a colloidal suspension is presented. Titania particles are oriented by an alternating (ac) electric field as they simultaneously advect towards a drying front due to evaporation of the solvent. At high field frequencies (ν > ∼25 kHz) and field strengths (E > 300 V cm−1), the particles orient with their major axis along the field direction. As the front recedes, a uniform film with thicknesses of 1–10 µm is deposited on the substrate. The films exhibit a large birefringence (Δn ≈ 0.15) and high packing fraction (ϕ = 0.75 ± 0.08), due to the orientation of the particles. When the frequency is lowered, the particle orientation undergoes a parallel–random–perpendicular transition with respect to the field direction. The orientation dependence on field frequency and strength is explained by the polarizability of ellipsoidal particles using an interfacial polarization model. Particle orientation in the films also leads to anisotropic mechanical properties, which are manifested in their cracking patterns. In all, it is demonstrated that the field‐directed assembly of anisotropic particles provides a powerful means for tailoring nanoparticle film properties in situ during the deposition process.

Phase behaviour of polarizable colloidal hard rods in an external electric field: A simulation study

“…Furthermore, it is well known that electric fields can be used to control not only the relative position, 1, 2 but also the orientation of such anisotropic particles. 7,8,[15][16][17][18] In the present paper, we focus on the phase behaviour of rod-like colloidal particles in the presence of an external electric field. The aim of this paper is the construction of a phase diagram corresponding to experiments recently carried out on systems of micron-sized silica rods.…”

“…The aim of this paper is the construction of a phase diagram corresponding to experiments recently carried out on systems of micron-sized silica rods. 19 From experiments 15,19 and theoretical calculations, 17 we know that polarizable rods align their symmetry axis in the direction of a strong external electric field. Here, we assume that this alignment with the field is perfect, i.e., that all spherocylinders are aligned in the direction of the field.…”

Interfacial electron and phonon scattering processes in high-powered nanoscale applications.

“…Films of titania particles are deposited on aluminum coated glass slide by flow coating. 121,122 Briefly, a stable colloidal suspension of the titania nanoparticles suspended in ultra-pure water (resistivity ≥18. translated by a computer controlled motorized stage at a velocity, v of (a) 125 μm/s, (b) 1500 μm/s, (c) 125 μm/s and (d) 1500 μm/s.…”

Temperature induced formation of particle coated non-spherical droplets

“…Non-spherical particles, which are different from spherical particles in packing density and symmetry [1] are increasingly significant in tailoring the photonic properties of colloidal assemblies [2,3], controlling their assembly at fluid interfaces [4][5][6], and even creating complex particle structures [7,8]. Lots of efforts have been made to synthesize or fabricate non-spherical particles, including seeded emulsion polymerization [9,10], stretching particle-embedded polymer films [11], photolithography [12], microcontact printing [13], and the use of microfluidic devices to deform emulsion droplets [14][15][16].…”