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A conducting drop suspended in a viscous dielectric and subjected to a uniform DC electric field deforms to a steady-state shape when the electric stress and the viscous stress balance. Beyond a critical electric capillary number $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{Ca}$, which is the ratio of the electric to the capillary stress, a drop undergoes breakup. Although the steady-state deformation is independent of the viscosity ratio $\lambda $ of the drop and the medium phase, the breakup itself is dependent upon $\lambda $ and $\mathit{Ca}$. We perform a detailed experimental and numerical analysis of the axisymmetric shape prior to breakup (ASPB), which explains that there are three different kinds of ASPB modes: the formation of lobes, pointed ends and non-pointed ends. The axisymmetric shapes undergo transformation into the non-axisymmetric shape at breakup (NASB) before disintegrating. It is found that the lobes, pointed ends and non-pointed ends observed in ASPB give way to NASB modes of charged lobes disintegration, regular jets (which can undergo a whipping instability) and open jets, respectively. A detailed experimental and numerical analysis of the ASPB modes is conducted that explains the origin of the experimentally observed NASB modes. Several interesting features are reported for each of the three axisymmetric and non-axisymmetric modes when a drop undergoes breakup.

An unprecedented route of DIW 3D printing of a polymer-solvent-nonsolvent ternary system to fabricate 3D structures with controlled internal porosity in thermoplastics is demonstrated.

The deformation of a thin elastic capsule subjected to a uniform electric field is investigated in the Stokes flow regime. The electrohydrodynamic flow is analyzed using a perfect conductor and a perfect dielectric model for the capsule and the fluid phase, respectively. A theoretical analysis is carried out using an asymptotic expansion in the electric capillary number (Ca) (a ratio of the electric stress to the elastic tension) in the small deformation limit using the finite deformation Hooke's law. The analysis is used to determine the elasticity of polysiloxane capsules suspended in oil, the deformation of which is obtained using videography. The boundary element method is implemented to seek numerical solutions to the hydrodynamic, elastic, and electrostatics equations. The finite deformation Hooke's law, the Mooney-Rivlin, and Skalak's model for elasticity are employed. The effect of electric capillary number, unstressed geometry, and the type of membrane material on the deformation of a capsule is presented in the high Ca number limit using numerical simulation. Capsules synthesized with higher monomer concentration displayed electric stress induced wrinkling process at high electric field strengths. Burst of a capsule is characterized by poration of the polymer membrane, which could be symmetric or asymmetric at the two poles, depending upon the value of the capillary number. The results should be useful in understanding the response of elastic capsules such as red blood cells and polymerized membranes, to an electric field, in applications such as electrodeformation and electroporation. It also provides a theoretical framework for a possible way of determining the elastic parameters of a capsule. C 2014 AIP Publishing LLC. [http://dx.

Recent advances in three-dimensional (3D) printing technology has enabled to shape food in unique and complex 3D shapes. To showcase the capability of 3D food printing, chocolates have been commonly used as printing inks, and 3D printing based on hot-melt extrusion have been demonstrated to model 3D chocolate products. Although hot-melt extrusion of chocolates is simple, the printing requires precise control over the operating temperature in a narrow range. In this work, for the first time, we directly printed chocolate-based inks in its liquid phase using direct ink writing (DIW) 3D printer to model complex 3D shapes without temperature control. We termed this method as chocolate-based ink 3D printing (Ci3DP). The printing inks were prepared by mixing readily available chocolate syrup and paste with cocoa powders at 5 to 25 w/w% to achieve desired rheological properties. High concentrations of cocoa powders in the chocolate-based inks exhibited shear-thinning properties with viscosities ranging from 102 to 104 Pa.s; the inks also possessed finite yield stresses at rest. Rheology of the inks was analyzed by quantifying the degree of shear-thinning by fitting the experimental data of shear stress as a function of shear rate to Herschel-Bulkley model. We demonstrated fabrication of 3D models consisting of chocolate syrups and pastes mixed with the concentration of cocoa powders at 10 to 25 w/w%. The same method was extended to fabricate chocolate-based models consisting of multiple type of chocolate-based inks (e.g. semi-solid enclosure and liquid filling). The simplicity and flexibility of Ci3DP offer great potentials in fabricating complex chocolate-based products without temperature control.