arXiv subjects

Dinesh Kumar Sahu

Publications and source records attributed to Dinesh Kumar Sahu.

7 recordsLinked to original sources

arXiv2026

Designing corrugated surfaces to guide colloidal self-assembly

The self-assembly of colloidal particles enables the creation of structured materials with programmable functionalities; however, controlling interaction specificity and aggregate morphology in a reversible and scalable manner remains a major challenge. Here, we investigate the selective depletion-induced self-assembly of 3D-printed flat polygonal colloids, where nanoscale surface topography is engineered through precise modeling in two-photon polymerization. By designing anisotropic lateral surfaces, we direct specific interactions that govern aggregate morphology, yielding dimers, chains, zigzag, and honeycomb structures depending on the surface configuration. The specificity of interaction is tuned by varying the length scale of the topographic surfaces, the depletant concentration and the ionic strength of the solution, revealing a transition from selective to non-selective aggregation regimes. The relative placement of lateral interacting surfaces on the colloids enables assembly into aggregates spanning a broad range of sizes, while tuning the interaction strength selectively stabilizes distinct structural motifs. We demonstrate this interplay between geometric arrangement and interaction energy experimentally and corroborate through both theory and simulations for specifically hexagonal shaped colloids. This study establishes a versatile framework for programming colloidal interactions via micro-architectural design, offering new routes for fabricating reconfigurable and functional soft materials.

cond-mat.soft↗

arXiv2023

Light-responsive nematic colloids and colloidal crystals

Rational control over the periodic arrangement of particles by means of external stimuli is a technologically important aspect of colloidal science with important physical underpinnings. Here, a robust structural control of particle assemblies in a nematic liquid crystal (NLC) is demonstrated by dissolving trace amounts of light-responsive azo-dendrimer molecules which spontaneously get adsorbed on the particle surface. The azo-dendrimer molecules in the presence of external UV irradiation undergo conformational change (trans-cis); as a result, they transmit the mechanical torque to surrounding LC molecules and alter the near-field director orientation. The director re-orientation at the surface of the particles causes topological defect transformation which involves elastic dipoles, quadrupoles and hexadecapoles. The defect transformation can be emulated in colloidal assemblies towards different purposes such as rotation of chains and restructuring of 2D colloidal crystals. In this study, various topological aspects of light-activated defect transformation and its application in the collective manipulation of colloidal assemblies are presented.

cond-mat.soft↗

arXiv2022

Electrophoresis of metal-dielectric Janus particles with dipolar director symmetry in nematic liquid crystals

We study electrophoretic mobility of metal-dielectric Janus particles with dipolar director profile in two nematic liquid crystals (LCs) having same (positive) conductivity anisotropy and opposite dielectric anisotropy. The applied ac electric field is parallel and perpendicular to the director for the positive and negative dielectric anisotropy LCs, respectively. The velocity of the Janus particles in both LCs is significantly higher than that of the non-Janus particles. We map the electroosmotic flow fields surrounding the particles using microparticle image velocimetry ($μ$-PIV) and show that the flows on the metal hemisphere is stronger than that on the dielectric hemisphere and the pumping of LC along the direction of motion of the Janus particles is more than that of the non-Janus particles. For a given liquid crystal, particles with asymmetric surface properties is useful for enhancing their electrophoretic mobility and activity.

cond-mat.soft↗

arXiv2022

Defect-polymorphism controlled electrophoretic propulsion of anisometric microparticles in a nematic liquid crystal

Nontrivial shape of colloidal particles create complex elastic distortions and topological defects in liquid crystals and play a key role in governing their electrophoretic propulsion through the medium. Here, we report experimental results on defects and electrophoretic transport of anisometric (snowman-shaped) dielectric particles subjected to an alternating electric field perpendicular to the director in a nematic liquid crystal. We demonstrate that the shape asymmetry gives rise to defect-polymorphism by nucleating point or ring defects at multiple locations on the particle and controls the direction as well as the magnitude of the electrophoretic propulsion. Our findings unveil a novel degree of freedom in translocating microparticles in liquid crystals for applications in microfluidics, controlled transport and assembly.

cond-mat.soft↗

arXiv2021

Electric field driven controllable motility of metal-dielectric Janus particles with boojum defects in a nematic liquid crystal

In a sharp contrast to the response of silica particles we show that the metal-dielectric Janus particles with boojum defects in a nematic liquid crystal are self-propelled under the action of an electric field applied perpendicular to the director. The particles can be transported along any direction in the plane of the sample by selecting the appropriate orientation of the Janus vector with respect to the director. The direction of motion of the particles is controllable by varying the field amplitude and frequency. The command demonstrated on the motility of the particles is promising for tunable transport and microrobotic applications.

cond-mat.soft↗

arXiv2020

A novel method for measuring electric field induced dipole moments of metal-dielectric Janus particles in nematic liquid crystals

Janus particles are special types of nano or micro particles possessing at least two surfaces with distinct physical or chemical properties. The most studied Janus particles are the metal-dielectric particles, in which half surface of dielectric particles is coated with a very thin layer of metals. The external electric field induces dipole moment, and consequently the particles exhibit self-assembled dynamic structures in concentrated aqueous suspensions. Here, we study metal-dielectric Janus particles in a nematic liquid crystal under AC electric field and demonstrate a novel method for measuring effective induced dipole moments of the particles, through competition between elastic and electrostatic (Coulomb) forces of the two particles. The calculated polarisability of the particles based on a simple model agrees well with the effective polarisability measured in the experiments. Our findings have important bearing on functional materials based on metal-dielectric Janus particles dispersed in an anisotropic medium.

cond-mat.soft↗

arXiv2020

Omnidirectional transport and navigation of Janus particles through a nematic liquid crystal film

We create controllable active particles in the form of metal-dielectric Janus colloids which acquire motility through a nematic liquid crystal film by transducing the energy of an imposed perpendicular AC electric field. We achieve complete command over trajectories by varying field amplitude and frequency, piloting the colloids at will in the plane spanned by the axes of the particle and the nematic. The underlying mechanism exploits the sensitivity of electro-osmotic flow to the asymmetries of the particle surface and the liquid-crystal defect structure. We present a calculation of the dipolar force density produced by the interplay of the electric field with director anchoring and the contrasting electrostatic boundary conditions on the two hemispheres, that accounts for the dielectric-forward (metal-forward) motion of the colloids due to induced puller (pusher) force dipoles. These findings open unexplored directions for the use of colloids and liquid crystals in controlled transport, assembly and collective dynamics.

cond-mat.soft↗