Figure 1

(Color online) (a) A schematic of the experimental setup and scanning electron microscopy (SEM) images of colloidal ellipsoids with aspect ratios $\alpha =3.0$, 4.3, and 7.6. The scalebar is $10\mu \text{m}$. (b) Particles $\left(\alpha =3.0\right)$ orienting in the electric field for $E=99\text{V}/\text{cm}$ and $\omega =10\text{kHz}$. The Fourier transform power spectrum is shown in the inset. [(c) and (d)] At higher field strengths $\left(E\ge 180\text{V}/\text{cm}\right)$, chains form with a characteristic angle with respect to the field, $\theta$. Chain angles are observed for both $+\theta$ and $-\theta$. (e) Two chains combine laterally. (f) Further growth leads to arrays with a centered rectangular unit cell, shown by the white box. (g) At higher concentrations, long-range order occurs. The scale bar is $25\mu \text{m}$. The inset shows the image power spectrum with the lattice vectors ${\mathbf{a}}^{\ast }$ and ${\mathbf{b}}^{\ast }$. To the right is the magnitude of the power spectrum for line segments through the (11) peak parallel and perpendicular to the field. Smooth lines (blue) show the total fits to $I_{\parallel }$ and $I_{\perp }$. The lower red Gaussian curves show the anisotropic width of the peak with the corresponding standard deviations ${\sigma }_{\parallel }$ and ${\sigma }_{\perp }$.Reuse & Permissions

Figure 2

(Color online) Distribution of chain angles that three or more particles subtend with the applied field for three particle aspect ratios.Reuse & Permissions

Figure 3

(Color online) Calculated energy of a point dipole with ellipsoidal shape in the vicinity of an ellipsoidal particle. A schematic of the model is shown in the inset. The two particles maintain a point contact as the angle between them increases. The scaled interaction energy exhibits a minimum at nonzero angle with respect to the field. The dashed line denotes $U=0$.Reuse & Permissions

Figure 4

(Color online) The angle of the interaction energy minimum at contact for point dipoles centered in two ellipsoids and the electrostatic model compared to the experiments for colloidal ellipsoids (triangles).Reuse & Permissions