arXiv subjects

Sunando DasGupta

Publications and source records attributed to Sunando DasGupta.

13 recordsLinked to original sources

arXiv2026

Two-dimensional clay channels for tunable nanofluidic memristor

Dynamic reconfiguration of charge carriers in confined ion-channels under electrical stimulation produces memory effects, where the internal resistance depends on history of the electric field. Vermiculite nanofluidic devices harness this effect to store and process information within a single component. We report switching between distinct memory loops by tuning ion transport pathways, governed by asymmetrical device architecture and intrinsic surface-charge. Polarity-dependent memory switching between crossing-1 and crossing-2 loops is achieved solely by altering electrode configurations, without modifying electrolyte, channel surface chemistry or device structure: providing mechanistic insights into ionic memristors through a straightforward, experimental strategy. The memristive characteristics are demonstrated in both in-plane and out-of-plane channel configurations with channel lengths spanning from centimeters to micrometers length scales using re-stacked vermiculite membranes and further investigated for miniaturization with devices of nanometer scale channel lengths, fabricated via ultramicrotomy method. Furthermore, we demonstrate neuromorphic functionalities, including synaptic potentiation-depression and programmable memory retention, highlighting potential for bio-inspired computing systems. Cost-effective and scalable fabrication solution processed vermiculite membrane memristors pave the way for practical integration of nanofluidic memristors for neuromorphic computing applications.

cond-mat.mtrl-sci↗

arXiv2019

Temperature-gradient induced massive augmentation of solute dispersion in viscoelastic micro-flows

Enhancing solute dispersion in electrically actuated flows has always been a challenging proposition, as attributed to the inherent uniformity of the flow field in absence of surface patterns. Over the years, researchers have focused their attention towards circumventing this limitation, by employing several fluidic and geometric modulations. However, the corresponding improvements in solute dispersion often turn out to be inconsequential. Here we unveil that by exploiting the interplay between an externally imposed temperature gradient, subsequent electrical charge redistribution and ionic motion, coupled with the rheological complexities of the fluid, one can achieve up to one order of magnitude enhancement of solute dispersion in a pressure-driven flow of an electrolyte solution. Our results demonstrate that the complex coupling between thermal, electrical, hydro-dynamic and rheological parameters over small scales, responsible for such exclusive phenomenon, can be utilitarian in designing novel thermally-actuated micro and bio-microfluidic devices with favorable solute separation and dispersion characteristics.

physics.flu-dyn↗

arXiv2019

Nanoparticles modulate contact angle hysteresis in electrowetting

The pinning of the contact line adversely influences the electrowetting performance of sessile liquid droplets. In this paper, we report the electrowetting hysteresis characteristics of 100 mM aq. KCl sessile liquid droplet placed on a hydrophobic PDMS surface. The effect of nanoparticles on the contact angle hysteresis under the imposed electric potential is further investigated. This study reveals that the contact angle hysteresis decreases beyond a certain threshold value of nanoparticles concentration. Therefore, nanoparticle suspension in the liquid droplet can be used to enhance or suppress the electrowetting hysteresis and consequentially rate of heat transfer during hot spot cooling.

cond-mat.soft↗

arXiv2019

Electroosmotic flow of viscoelastic fluids in deformable microchannels

The electroosmotic flow of non-Newtonian fluids in deformable microchannels is fundamentally important in the understanding of the hydrodynamics in physiological flows. The performance of these microchannels is governed by the load bearing capacity indicating the maximum amount of load that the device can withstand. While significant research efforts are aimed towards the coupling of electrokinetics with substrate deformability, the corresponding enhancement in the performances still remains elusive. Towards this, employing an intricate coupling between substrate compliance, hydrodynamic, and electrokinetic modulations, we have analyzed the possible sources of alterations in the flow physics in a deformable microchannel under the rheological premises of viscoelastic fluids which have a close resemblance with biological fluids typically used in several bio and micro-fluidic applications. The present study reveals that by operating under favorable regimes of parameters like the concentration and molecular weight of the polymer, the quality of the Newtonian solvent, and the concentration of electrolyte, one can achieve substantial augmentation in the load carrying capacity of a deformable microchannel for viscoelastic fluids as compared to its Newtonian counterpart. We believe that the present theoretical framework can be extremely important in the designing of electro-kinetically modulated bio-mimetic microfluidic devices.

cond-mat.soft↗

arXiv2018

Pitcher Plant Inspired Biomimetic Liquid Infused Slippery Surface Using Taro Leaf

Bio-inspired anti-wetting surfaces, such as lotus leaf or pitcher plant, have led to the development of stable liquid infused slippery surfaces for various scientific applications. The present work demonstrates the use of biomimetic superhydrophobic surface (inspired from taro leaf) for fabrication of a stable air-liquid film. The taro leaf replica is fabricated on PDMS using two step soft-molding technique, where microstructures of the replicated surface are used to retain silicone oil layer to form a stable slippery surface. The fabricated surface exhibits a low contact angle hysteresis (CAH) of 2°, with sliding angle (SA) of 1.1°, which further affirms the super-slippery nature of the surface. Furthermore, it also shows excellent self-repairing ability, thermal stability and long-term durability of the oil coating against high shear rates, high impact droplets etc. We thus envisage that the present method of fabrication of slippery surface is simple and economical, and thus useful for various applications such as water drag reduction, self-cleaning, anti-fogging, anti-fouling etc.

cond-mat.soft↗

arXiv2018

Electrowetting of a nano-suspension on a soft solid

The wetting of solid surfaces can be manoeuvred by altering the energy balance at the interfacial region. While electric field acts favourably to spread a droplet on a rigid surface, this tendency may be significantly suppressed over soft surfaces, considering a part of the interfacial energy being utilized to deform the solid elastically by capillary forces. Here, we bring out a unique mechanism by virtue of which addition of nano-particles to the droplet brings in a favourable recovery of the electro-spreading characteristics of a soft surface, by realizing an alteration in the effective dielectric constant of the interfacial region. Our experiments further demonstrate that this mechanism ceases to be operative beyond a threshold volume fraction of the particle suspension, due to inevitable contact line pinning. We also develop a theory to explain our experimental observations. Our findings provide a non-contact mechanism for meniscus spreading and droplet control, bearing far-reaching implications in biology and engineering.

cond-mat.soft↗

arXiv2018

An electrokinetic route to giant augmentation in load bearing capacity of compliant microfluidic channels

The performances of lubricated systems widely used in natural, biological, and artificial settings are traditionally dictated by their load bearing capacities. Here we unveil that, by exploiting a unique coupling between interfacial electro-mechanics, hydrodynamics and substrate compliance, it is plausible to realize a massive augmentation in the load bearing capacities ofcompliant microfluidic channels. Our analysis demonstrates that the interplay between wettability and charge modulation in association with the solution chemistry and surface compliance results in this remarkable phenomenon. These results are likely to open up novel design paradigms of augmenting the load bearing capacities of miniaturized bio-mimetic units through the realization of a symmetry breaking phenomenon triggered by asymmetries in electromechanical and hydrodynamic transport over interfacial scales.

physics.flu-dyn↗

arXiv2018

Water under the Ridge: Evaporation, Translation, Crumpling and Encapsulation of a Water Droplet atop a Liquid Polymeric Film

The intriguing dynamics of a compound liquid-system comprising of water and (uncured) poly-dimethylsiloxane is explored in the present work. The viscoelastic nature of the film, coupled with the dynamics of evaporation, triggered a self-propulsion in the droplet, which gradually segued into the crumpling of the film, and finally culminated in the encapsulation of the water droplet by the polymer. The physics of the hitherto unreported phenomena has been explained via the development of an analytical model, by taking into account all the germane forces. It is conjectured that this symbiotic and self-sustained dynamics, aided with the non-requirement of any complex fabrication procedures, would pave the path for the development of precision drug-delivery, unmediated flow-focusing, self-mixed microreactors, the study of micro-swimmers, surface encapsulation, and photonics, to name a few.

cond-mat.soft↗

arXiv2017

Liquid crystal induced elasto-capillary suppression of crack formation in thin colloidal films

Drying of colloidal droplets on solid, rigid substrates is associated with a capillary pressure developing within the droplet. In due course of time, the capillary pressure builds up due to droplet evaporation resulting in the formation of a colloidal thin film that is prone to crack formation. In this study, we show that introducing a minimal amount of nematic liquid crystal (NLC) can completely suppress the crack formation. The mechanism behind the curbing of the crack formation may be attributed to the capillary stress-absorbing cushion provided by the elastic arrangements of the liquid crystal at the substrate-droplet interface. Cracks and allied surface instabilities are detrimental to the quality of the final product like surface coatings, and therefore, its suppression by an external inert additive is a promising technique that will be of immense importance for several industrial applications. We believe this fundamental investigation of crack suppression will open up an entire avenue of applications for the NLCs in the field of coatings, broadening its already existing wide range of benefits.

physics.flu-dyn↗

arXiv2016

Electrically Modulated Wetting of Drops on Soft Dielectric Films

The inter-connection between the elasticity of a dielectric film and the wetting of a sessile drop on the same, under an applied electrical voltage, remains unaddressed. Here, we report the electrowetting-on-dielectric (EWOD) behaviour of sessile drops on dielectric elastomer films of varying elasticities- from an apparently rigid dielectric film to a soft, deformable dielectric film. Our results reveal that the elasticity of the underlying dielectric film provides an additional control over the droplet electrowetting behaviour, which may be best addressed from free energy based consideration, leading to a modification of the classical Lippman-Young paradigm. We also provide an explanation on the displacement profiles for the deformation of the soft dielectric surface, due to the interfacial electro-elastocapillary interaction triggered by the electrowetted sessile droplet. These results can be of profound importance in various emerging applications, ranging from the development of soft liquid lenses to drug delivery.

physics.flu-dyn↗

arXiv2015

Molecular Dynamic Approach of Enhanced Self-Propelled Nano-Droplet Motion on Wettability Gradient Surfaces

Droplet motion over a surface with wettability gradient has been simulated using molecular dynamics (MD) simulation to highlight the underlying physics. GROMACS and Visual Molecular Dynamics (VMD) were used for simulation and intermittent visualization of the droplet configuration respectively. The simulations mimic experiments in a comprehensive manner wherein micro-sized droplets are propelled by surface wettability gradient against a number of retarding forces. The liquid-wall Lennard-Jones interaction parameter and the substrate temperature were varied to explore their effects on the three-phase contact line friction coefficient. The contact line friction was observed to be a strong function of temperature at atomistic scales, confirming the experimentally observed inverse functionality between the coefficient of contact line friction and increase in temperatures. These MD simulation results were successfully compared with the results from a model for self-propelled droplet motion on gradient surfaces.

physics.flu-dyn↗

arXiv2015

Electrically modulated dynamic spreading of drops on soft surfaces

The intricate interaction between the deformability of a substrate and the dynamic spreading of a liquid drop on the same, under the application of an electrical voltage, has remained far from being well understood. Here, we demonstrate that electrospreading dynamics on soft substrates is dictated by the combined interplay of electrocapillarity, the wetting line friction and the viscoelastic energy dissipation at the contact line. Our results reveal that during such electro-elastocapillarity mediated spreading of a sessile drop, the contact radius evolution exhibits a universal power law in a substrate elasticity based non-dimensional time, with an electric potential dependent spreading exponent. Simultaneously, the macroscopic dynamic contact angle variation follows a general power law in the contact line velocity, normalized by elasticity dependent characteristic velocity scale. Our results are likely to provide the foundation for the development of a plethora of new applications involving droplet manipulations by exploiting the interplay between electrically triggered spreading and substrate-compliance over interfacial scales.

physics.flu-dyn↗

arXiv2014

Wettability Induced Crack Dynamics and Morphology

Substrate wettability alteration induced control over crack formation process in thin colloidal films has been addressed in the present study. Colloidal nanosuspension (53nm, mean particle diameter) droplets have been subjected to natural drying to outline the effects of substrate surface energies over the dry-out characteristics with emphasis on crack dynamics, crack morphology and underlying particle arrangements. Experimental findings indicate that number of cracks formed decreases with increase in substrate hydrophobicity. These physical phenomena have been explained based on the magnitude of stress dissipation incurred by the substrate. DLVO predictions are also found to be in tune with the reported experimental investigations.

physics.flu-dyn↗