arXiv subjects

Abhinav Naga

Publications and source records attributed to Abhinav Naga.

5 recordsLinked to original sources

arXiv2026

When and how particles are removed by drops

Particulate contaminants decrease the power output of solar panels, the transparency of windows, and are detrimental to microelectronics, where even a single particle can induce a short circuit. Despite significant research on particle adhesion and self-cleaning, it remains unclear when and how a drop can remove a particle from a surface, thus efficiently cleaning the surface. Here, by combining lattice Boltzmann simulations and confocal microscopy experiments, we show that at least six different scenarios arise from the complex interplay between capillary and friction forces when a drop collides with a particle on a surface. Notably, the capillary force plays a dual role in particle removal: while its tangential component always drives removal, its normal component can also hinder it. We introduce a dimensionless capillary capture parameter that successfully predicts particle removal across a wide range of particle and surface properties. Our results reveal that the design of easy-to-clean surfaces should not focus only on maximizing hydrophobicity, but also on minimizing the particle-surface friction.

cond-mat.soft↗

arXiv2026

Modelling droplet-particle interactions on solid surfaces by coupling the lattice Boltzmann and discrete element methods

We develop a three-dimensional numerical scheme for investigating interfacial flows coupled with frictional solid particles. Our approach combines the lattice Boltzmann method (LBM) to model the dynamics of a two-component fluid, and the discrete element method (DEM) to model normal reaction, sliding friction, and rolling friction between solid particles and between particles and solid surfaces. Key to the coupling between the fluid and particle dynamics are the momentum exchange method to transfer hydrodynamic forces between the fluids and particles, a geometric boundary condition to tune particle wettability, and a capillary force model describing surface tension forces between particles and liquid-fluid interfaces. We rigorously validate the contact forces by investigating the dynamics of a particle bouncing off a solid surface and rolling down an inclined plane, the hydrodynamic force by the Segrè-Silberberg effect, and the capillary force by particle detachment from a liquid-fluid interface. Motivated by the self-cleaning properties of lotus leaves, we apply the method to investigate how drops remove contaminant particles from surfaces. We successfully reproduce scenarios reported experimentally by Naga et al. (Soft Matter (2021) 17(7):1746-1755) by tuning the particle friction. Furthermore, the LBM-DEM approach allows us to systematically explore the effects of particle friction coefficients, drop size, and speed. Our method opens opportunities to study numerous phenomena involving particle dynamics interacting with interfacial flows, including soil erosion, capillary-driven colloidal self-assembly, and how raindrops transport microplastics in the environment. It also makes it possible to control parameters that are difficult to tune independently in experiments, including contact angles, surface tension, and friction coefficients.

physics.flu-dyn↗

arXiv2026

Understanding the Dynamics of Evaporation-Driven Colloidal Self-Assembly

Complex colloidal cluster morphologies are desirable for the fabrication of advanced materials, such as photonic crystals and meta-materials, and can be formed through evaporation-driven packing. By coupling lattice Boltzmann and discrete element methods, here we elucidate the rich interplay between fluid and particle dynamics during evaporation-driven self-assembly of spherical colloidal particles. We construct a regime diagram for a wide range of evaporation rates, interparticle friction coefficients, and particle numbers, identifying parameter regimes for open, closed, and minimal moment of inertia cluster configurations. Analyzing the competition between capillary, hydrodynamic, normal, and friction forces, we show that interparticle friction can exert a disproportionately strong influence on the final packing outcome despite being considerably smaller in magnitude than other forces at play. Our simulation results further highlight the potential for tuning colloidal cluster configurations via their dynamic trajectories.

cond-mat.soft↗

arXiv2024

Wetting on Silicone Surfaces

Silicone is frequently used as a model system to investigate and tune wetting on soft materials. Silicone is biocompatible and shows excellent thermal, chemical, and UV stability. Moreover, the mechanical properties of the surface can be easily varied by several orders of magnitude in a controlled manner. Polydimethylsiloxane (PDMS) is a popular choice for coating applications such as lubrication, self-cleaning, and drag reduction, facilitated by low surface energy. Aiming to understand the underlying interactions and forces, motivated numerous and detailed investigations of the static and dynamic wetting behavior of drops on PDMS-based surfaces. Here, we recognize the three most prevalent PDMS surface variants, namely liquid-infused (SLIPS/LIS), elastomeric, and liquid-like (SOCAL) surfaces. To understand, optimize, and tune the wetting properties of these PDMS surfaces, we review and compare their similarities and differences by discussing (i) the chemical and molecular structure, and (ii) the static and dynamic wetting behavior. We also provide (iii) an overview of methods and techniques to characterize PDMS-based surfaces and their wetting behavior. The static and dynamic wetting ridge is given particular attention, as it dominates energy dissipation, adhesion, and friction of sliding drops and influences the durability of the surfaces. We also discuss special features such as cloaking and wetting-induced phase separation. Key challenges and opportunities of these three surface variants are outlined.

cond-mat.soft↗

arXiv2021

Enhancing condensation on soft substrates through bulk lubricant infusion

Soft substrates such as polydimethylsiloxane (PDMS) enhance droplet nucleation during the condensation of water vapour, because their deformability inherently reduces the energetic threshold for heterogeneous nucleation relative to rigid substrates. However, this enhanced droplet nucleation is counteracted later in the condensation cycle, when the viscoelastic dissipation inhibits condensate droplet shedding from the substrate. Here, we show that bulk lubricant infusion in the soft substrate is a potential pathway for overcoming this limitation. We demonstrate that even 5% bulk lubricant infusion in PDMS reduces viscoelastic dissipation in the substrate by more than 30 times and more than doubles the droplet nucleation density. We correlate the droplet nucleation and growth rate with the material properties controlled by design, i.e. the fraction and composition of uncrosslinked chains, shear modulus, and viscoelastic dissipation. Through in-situ, microscale condensation on the substrates, we show that the increase in nucleation density and reduction in pre-coalescence droplet growth rate is insensitive to the percentage of lubricant in PDMS. Our results indicate the presence of a lubricant layer on the substrate surface that cloaks the growing condensate droplets. We visualize the cloaking effect and show that lubricant infusion in PDMS significantly increases the rate of cloaking compared to PDMS without any lubricant infusion. Finally, we show that the overall enhanced condensation due to bulk lubricant infusion in PDMS leads to more than 40% increase in dewing on the substrate.

cond-mat.soft↗