Browsing by Author "Swarn Lata Singh"

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Crystallization of fluids: Free-energy functional for symmetry breaking first-order freezing transition
(2009) Swarn Lata Singh; Yashwant Singh
A free-energy functional for a crystal that contains both the symmetry conserved and symmetry broken parts of the direct pair correlation function is developed. To test how accurately this free-energy functional describes the symmetry breaking first-order phase transition of freezing, we use it to investigate the crystallization of fluids interacting via the inverse power potential; u(r)=ε(σ/r)n. In agreement with simulation results we find that under the fluid-solid co-existence the f.c.c. structure is more stable for n=12, whereas for soft repulsions (n≤6) the b.c.c. structure is more stable. Copyright © 2009 EPLA.
Durability of Slippery Liquid-Infused Surfaces: Challenges and Advances
(MDPI, 2023) Divyansh Tripathi; Prauteeto Ray; Ajay Vikram Singh; Vimal Kishore; Swarn Lata Singh
Slippery liquid-infused porous surfaces (SLIPS) have emerged as a unique approach to creating surfaces that can resist fouling when placed in contact with aqueous media, organic fluids, or biological organisms. These surfaces are composed of essentially two components: a liquid lubricant that is locked within the protrusions of a textured solid due to capillarity. Drops, immiscible to the lubricant, exhibit high mobility and very-low-contact-angle hysteresis when placed on such surfaces. Moreover, these surfaces are shown to resist adhesion to a wide range of fluids, can withstand high pressure, and are able to self-clean. Due to these remarkable properties, SLIPS are considered a promising candidate for applications such as designing anti-fouling and anti-corrosion surfaces, drag reduction, and fluid manipulation. These collective properties, however, are only available as long as the lubricant remains infused within the surface protrusions. A number of mechanisms can drive the depletion of the lubricant from the interior of the texture, leading to the loss of functionality of SLIPS. Lubricant depletion is one challenge that is hindering the real-world application of these surfaces. This review mainly focuses on the studies conducted in the context of enhancing the lubricant retention abilities of SLIPS. In addition, a concise introduction of wetting transitions on structured as well as liquid-infused surfaces is given. We also discuss, briefly, the mechanisms that are responsible for lubricant depletion. © 2023 by the authors.
Free-energy functional for freezing transitions: Hard-sphere systems freezing into crystalline and amorphous structures
(2011) Swarn Lata Singh; Atul S. Bharadwaj; Yashwant Singh
A free-energy functional that contains both the symmetry-conserved and symmetry-broken parts of the direct pair correlation function has been used to investigate the freezing of a system of hard spheres into crystalline and amorphous structures. The freezing parameters for fluid-crystal transition have been found to be in very good agreement with the results found from simulations. We considered amorphous structures found from molecular dynamics simulations at packing fractions η lower than the glass close packing fraction ηJ and investigated their stability compared to that of a homogeneous fluid. The existence of a free-energy minimum corresponding to a density distribution of overlapping Gaussians centered around an amorphous lattice depicts a deeply supercooled state with a heterogeneous density profile. © 2011 American Physical Society.
Intrusion of liquids into liquid-infused surfaces with nanoscale roughness
(American Physical Society, 2022) Swarn Lata Singh; Lothar Schimmele; S. Dietrich
We present a theoretical study of the intrusion of an ambient liquid into the pores of a nanocorrugated wall w. The pores are prefilled with a liquid lubricant that adheres to the walls of the pores more strongly than the ambient liquid does. The two liquids are modeled as a binary liquid mixture of two species of particles, A and B. The mixture can decompose into a liquid rich in A particles, representing the ambient liquid, and another one rich in B particles, representing the liquid lubricant. The wall is taken to attract the B particles more strongly than the A particles. The ratio w-A/w-B of these interaction strengths is changed in order to tune the contact angle θAB formed by the A-rich/B-rich liquid interface between the two fluids and a planar wall, composed of the same material as the one forming the pores. We use classical density functional theory in order to capture the effects of microscopic details on the intrusion transition, which occurs as the concentration of the minority component or the pressure in the bulk of the ambient liquid is varied, moving away from bulk liquid-liquid coexistence within the single-phase domain of the A-rich bulk ambient liquid. These liquid structures have been studied as a function of the contact angle θAB and for various widths and depths of the pores. We also studied the reverse process in which a pore initially filled with the ambient liquid is refilled with the liquid lubricant. The location of the intrusion transition, with respect to its dependence on the contact angle θAB and the width of the pore, qualitatively follows the corresponding shift of the capillary-coexistence line away from the bulk liquid-liquid coexistence line, as predicted by a macroscopic capillarity model. Quantitatively, the transition found in the microscopic approach occurs somewhat closer to the bulk liquid-liquid coexistence line than predicted by the macroscopic capillarity model. The quantitative discrepancies become larger for narrower cavities. In cases in which the wall is completely wetted by the lubricant (θAB=0) and for small contact angles, the reverse transition follows the same path as for intrusion; there is no hysteresis. For larger contact angles, hysteresis is observed. The width of the hysteresis increases with increasing contact angle. A reverse transition is not found inside the domain within which the ambient liquid forms a single phase in the bulk once θAB exceeds a geometry-dependent threshold value. According to the macroscopic capillarity theory, for the considered geometry, this is the case for θAB>54.7∘. Our computations show, however, that nanoscale effects shift this threshold value to much higher values. This shift increases strongly if the widths of the pores become smaller (below about ten times the diameter of the A and B particles). © 2022 authors. Published by the American Physical Society.
Multifunctional Nanoscale Pigments: Emerging Risks and Circular Strategies for a Sustainable Future
(John Wiley and Sons Inc, 2025) Ajay Vikram Singh; Preeti Bhardwaj; Vimal Kishore; Sunil Choudhary; Akihiko Hirose; Neha Gupta; Madleen Busse; Swarn Lata Singh; Christopher J. Osgood
The substantial penetration of nanoscale pigments into a range of sectors has changed the dynamics of industries such as medical, material science, and many more. Nonetheless, their persistence in the environment and probable adverse impacts on health require that an assessment of such risks be formulated considering the One Health perspective. This viewpoint considers the crossing of boundaries of progress in the nanotechnology of nanoscale pigments with environmental, animal, and human health and emphasizes the significance of collaborative activity. Traditional perspectives explain the distribution of pigment history, while the nanotechnology of today's accessibility poses problems regarding utilization, toxicities, and interactions with the environment. Through discussions of environmental pathways, health determinants, and regulatory insufficiencies, this work makes evident that pigments are critical both as emerging contaminant's and as innovation drivers. The necessary advancements in exposure minimization and sustainable practices are discussed as well, giving insight on benign-by-design techniques and circular economy solutions. Expanding the discussion of the existing knowledge and the gap where the ´One Health´ concept can be applied in physiochemical properties of pigments as well as governance, this work offers an approach to enabling risk while enhancing invention. It urges timely global action for sustainable, beneficial nanoscale pigment futures. © 2025 The Author(s). Small Science published by Wiley-VCH GmbH.
Pair correlation functions and a free energy functional for the nematic phase
(American Institute of Physics Inc., 2007) Pankaj Mishra; Swarn Lata Singh; Jokhan Ram; Yashwant Singh
In this paper we have presented the calculation of pair correlation functions in a nematic phase for a model of spherical particles with the long-range anisotropic interaction from the mean spherical approximation (MSA) and the Percus-Yevick (PY) integral equation theories. The results found from the MSA theory have been compared with those found analytically by Holovko and Sokolovska [J. Mol. Liq. 82, 161 (1999)]. A free energy functional which involves both the symmetry conserving and symmetry broken parts of the direct pair correlation function has been used to study the properties of the nematic phase. We have also examined the possibility of constructing a free energy functional with the direct pair correlation function which includes only the principal order parameter of the ordered phase and found that the resulting functional gives results that are in good agreement with the original functional. The isotropic-nematic transition has been located using the grand thermodynamic potential. The PY theory has been found to give a nematic phase with pair correlation function harmonic coefficients having all the desired features. In a nematic phase the harmonic coefficient of the total pair correlation function h (x1, x2) connected with the correlations of the director transverse fluctuations should develop a long-range tail. This feature has been found in both the MSA and PY theories. © 2007 American Institute of Physics.
Polymer Translocation and Nanopore Sequencing: A Review of Advances and Challenges
(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Swarn Lata Singh; Keerti Chauhan; Atul S. Bharadwaj; Vimal Kishore; Peter Laux; Andreas Luch; Ajay Vikram Singh
Various biological processes involve the translocation of macromolecules across nanopores; these pores are basically protein channels embedded in membranes. Understanding the mechanism of translocation is crucial to a range of technological applications, including DNA sequencing, single molecule detection, and controlled drug delivery. In this spirit, numerous efforts have been made to develop polymer translocation-based sequencing devices, these efforts include findings and insights from theoretical modeling, simulations, and experimental studies. As much as the past and ongoing studies have added to the knowledge, the practical realization of low-cost, high-throughput sequencing devices, however, has still not been realized. There are challenges, the foremost of which is controlling the speed of translocation at the single monomer level, which remain to be addressed in order to use polymer translocation-based methods for sensing applications. In this article, we review the recent studies aimed at developing control over the dynamics of polymer translocation through nanopores. © 2023 by the authors.
Polymer translocation: effects of periodically driven confinement
(Royal Society of Chemistry, 2024) Manish Dwivedi; Swarn Lata Singh; Sanjay Kumar
We study the influence of confinement on the dynamics of translocation of a linear polymer chain in a good solvent through a cone-shaped pore. Using the Langevin dynamics simulations, we calculate both the first attempt time and translocation time as a function of the position of the back wall and apex angle α. As the in vivo confining environment is inherently dynamic, we extended the present study to explore the consequences of a periodically driven back wall and apex angles on the translocation dynamics. Our findings reveal that the translocation time initially decreases as the driving frequency increases, but increases after a certain frequency. The frequency at which the translocation time is found to be minimum is referred to as the resonance activation. Analyzing the distribution of translocation times around this frequency renders interesting information about the translocation process. We further explore the translocation dynamics by calculating the residence time of individual monomers, shedding light on the microscopic aspects of the process. © 2024 The Royal Society of Chemistry.
Self-Assembly of DNA-Grafted Colloids: A Review of Challenges
(MDPI, 2022) Manish Dwivedi; Swarn Lata Singh; Atul S. Bharadwaj; Vimal Kishore; Ajay Vikram Singh
DNA-mediated self-assembly of colloids has emerged as a powerful tool to assemble the materials of prescribed structure and properties. The uniqueness of the approach lies in the sequence-specific, thermo-reversible hybridization of the DNA-strands based on Watson–Crick base pairing. Grafting particles with DNA strands, thus, results into building blocks that are fully programmable, and can, in principle, be assembled into any desired structure. There are, however, impediments that hinder the DNA-grafted particles from realizing their full potential, as building blocks, for programmable self-assembly. In this short review, we focus on these challenges and highlight the research around tackling these challenges. © 2022 by the authors.