arXiv subjects

Manjesh K. Singh

Publications and source records attributed to Manjesh K. Singh.

5 recordsLinked to original sources

arXiv2026

Nano-Clay-Stabilized Water-in-Oil Colloidal Pickering Emulsions as Thixotropic Lubricant

The limitations of conventional mineral oil-based lubricants motivate the development of environmentally benign emulsions capable of providing lubrication and heat dissipation in demanding applications. In this study, nano-organoclay (Garamite 1958)-stabilized thixotropic water-in-oil Pickering emulsions are developed using sunflower oil as the base. The rheological and tribological properties of the emulsion system are systematically examined. Rheological findings reveal a pronounced increase in yield stress, shear thinning and thixotropic behavior on increasing Garamite loading percentage in the emulsion. The tribological performance is assessed against dry, water, and oil-lubricated conditions for a steel-steel interface under high contact pressure. The findings indicate that the tribological performance is significantly influenced by the microstructure and thixotropic behavior of the emulsions. The emulsion with the optimal nano-clay concentration demonstrates approximately 41\% and 84\% lower friction and approximately 80\% and 96\% lower wear than oil and water, respectively. The emulsion exhibits sensitivity to the sliding direction and displays load-responsive friction behavior with a memory effect owing to the reversible structuring of the clay-droplet network. This superior performance is attributed to the combined effects of thixotropy, anisotropic nanoclay morphology, and stable droplet armoring, which form a robust and adaptive interfacial film. This study advances the understanding of Pickering emulsions in metallic tribosystems by correlating the microstructure and rheology with tribological performance, thereby facilitating the design of high-performance, smart, and eco-conscious lubricants for metallic systems.

cond-mat.soft↗

arXiv2025

Computational study of Adhesion and Friction Behavior of Crosslinked Polymer Network

In this study, we have utilized a molecular dynamics simulation approach to understand adhesion and friction behaviour of crosslinked polymer networks. We have used breakable quartic bond to model crosslinked polymers. We explored the structural characteristics and evaluated the coefficient of friction (CoF) as a function of crosslinked monomer fraction (cross-linking bond density) in four-fold cross-linked polymer networks. To estimate CoF, a rigid indenter was inserted to different depths of indentation. Subsequently a constant sliding speed was applied while keeping the depths of indentation fixed. Normal and friction forces were calculated at each depth to estimate CoF through a linear curve-fitting. For adhesion studies, using the force vs. displacement curve we quantified adhesion through the forces during the separation of rigid indenter from surface of crosslinked polymeric materials while unloading after indentation into the sample. The results indicate that as the fraction of crosslinked monomers increases, the stiffness of the crosslinked network increases, while the force of adhesion and CoF decrease. Additionally, increasing the depth of indentation during friction leads to higher frictional forces.

cond-mat.soft↗

arXiv2025

Study of surface roughness modulation on the adhesion behavior of PDMS elastomer

Adhesion control at the interface of two surfaces is crucial in various applications, including the design of micro- and nanodevices such as microfluidic devices, triboelectric nanogenerators, biochips, and electronic sensors. Several factors influence adhesion, including sample preparation, surface energy, mechanical properties such as modulus of elasticity, and surface texture or roughness. This study specifically investigates the effect of surface roughness on the adhesion behavior of the elastomer polydimethylsiloxane (PDMS), focusing on a complementary interface with identical roughness. To create surface roughness, sandpapers with grit sizes ranging from N = 120 to N = 2000 were used during the molding process. The surface roughness of the PDMS elastomer was then characterized using a stylus profilometer. Interfacial adhesion was evaluated through wedge test experiments, which enabled the analysis of the relationship between surface roughness, work of adhesion, and equilibrium crack length. Furthermore, the study also explores the correlation between the real area of contact and the work of adhesion.

cond-mat.soft↗

arXiv2025

Nano-silica based Aqueous Colloidal Gels as Eco-friendly Thixotropic Lubricant

The environmental risks posed by traditional oil and grease-based lubricants can be significantly mitigated by adopting water-based alternatives engineered with superior rheological performance. In this work, we present a fundamentally new and environmentally sustainable aqueous thixotropic colloidal gel of silica nanoparticles formed in the presence of NaCl. We conducted a systematic and detailed investigation of their rheological and tribological characteristics. The tribological performance was evaluated against dry and water-lubricated conditions for steel-steel interface. Our experiments demonstrate that the tribological performance of the formulated nanoparticle gel can be optimized by tuning its rheological properties. A combination of super-low friction and negligible wear was observed. The friction coefficient reduced by up to 97.46% (from 0.63 to 0.016) compared to dry sliding, and by 97.04% (from 0.541 to 0.016) compared to water lubrication. Similarly, the specific wear rate decreased by up to 99.62% and 96.10% under dry conditions and water lubrication respectively. This performance is attributed to a thixotropic, chemically robust gel formed via van der Waals interactions between silica flocs, enabling self-repairing properties, continuous tribo-film formation, and a nano-bearing effect from silica nanoparticles. These attributes enable the gel to maintain and regain its structure during periods of non-shear while also forming a thin film with sufficiently low viscosity to slip into the interfacial contact zone and continuously replenish it with lubricant.

cond-mat.soft↗

arXiv2020

Why Do Elastin-Like Polypeptides Possibly Have Different Solvation Behaviors in Water-Ethanol and Water-Urea Mixtures?

The solvent quality determines the collapsed or the expanded state of a polymer. For example, a polymer dissolved in a poor solvent collapses, whereas in a good solvent it opens up. While this standard understanding is generally valid, there are examples when a polymer collapses even in a mixture of two good solvents. This phenomenon, commonly known as co-non-solvency, is usually associated with smart polymers. Moreover, recent experiments have shown that the elastin-like polypeptides (ELPs) show co-non-solvency behavior in aqueous-ethanol mixtures. In this study, we investigate the phase behavior of ELPs in aqueous binary mixtures using molecular dynamics simulations of all-atom and complementary explicit solvent generic models. The model is parameterized by mapping the solvation free energy obtained from the all-atom simulations onto the generic interaction parameters. For this purpose, we derive segment based generic parameters for four different peptides, namely proline (P), valine (V), glycine (G) and alanine (A). Here we compare the conformational behavior of two ELP sequences, namely VPGGG and VPGVG, in aqueous-ethanol and -urea mixtures. Consistent with recent experiments, we find that ELPs show co-non-solvency in aqueous-ethanol mixtures. Ethanol molecules have preferential binding with all ELP residues and thus driving the coil-to-globule transition. On the contrary, ELP conformations show weak variation in aqueous-urea mixtures. Our simulations suggest that the glycine residues dictate the overall behavior of ELPs in aqueous-urea, where urea molecules have a rather weak preferential binding with glycine, i.e., less than kT. While the validation of the latter findings will require more detailed experimental investigation, the results presented here may provide a new twist to the present understanding of cosolvent interactions with peptides and proteins.

cond-mat.soft↗