Department of Mechanical Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Early detection of infectious diseases by employing point-of-care (POC) technologies, which are highly sensitive and specific, user-friendly, and robust, would find great significance specifically in developing nations. Rapid and real-time detection of such diseases helps in proper treatment and useful in preventing transmission. With the advent of nanotechnology, a wide range of biological assays is developed by coupling nanosensors with microfluidics devices that are advantageous over traditional methods. One particular type of such integration of bio-nanosensors with microfluidics is the localized surface plasmon resonance (LSPR) biosensors (broadly nanoplasmonic) toolbox developed for biological applications such as drug discovery, rapid and clinical diagnosis, and further studies of biological cells or biomolecules. Further, nanoplasmonic sensors provide great versatility such as multiplexing, portable, and implantable, making them unique candidates for use as POC diagnostics devices. This chapter presents some of the recently developed on-chip biomarker detection devices by coupling LSPR biosensors with microfluidics platform for rapid diagnostics of infectious diseases. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

World University root node

Materials Horizons: From Nature to Nanomaterials

Localized Surface Plasmon Resonance Sensors for Biomarker Detection with On-Chip Microfluidic Devices in Point-of-Care Diagnostics

Fluid manipulation using surface acoustic waves (SAW) has been utilized as a promising technique in the field of microfluidics due to its numerous advantages, over other active techniques, such as low power requirement, facile fabrication methods, and non-invasive nature. Even though SAW-based generation of micron-sized droplets through atomization has been studied, the role of substrate wettability on the characteristics of the transferred droplets has not been explored to date. Here, we study the generation and effective transfer of micron-sized droplets using SAW onto wettable substrates whose water contact angles vary from 5° to 145°. The characteristics of transferred droplets after impacting the wettable substrates are characterized in terms of the contact line diameter and polydispersity index. A theoretical model is formulated to predict the initial average size of the transferred droplets on the wettable substrates of different contact angles. The variation of polydispersity and number density with contact angle is explained by considering droplet coalescence and bouncing. The relevance of the technique in biological assays is demonstrated by transferring droplets of streptavidin protein samples onto a substrate. © 2022 The Royal Society of Chemistry.

RSC Advances

Surface acoustic wave-based generation and transfer of droplets onto wettable substrates

Microwell arrays are ideal platforms for cell culturing, cell separation, and low-volume liquid handling. The ability to manipulate droplets in microwells could open up the opportunity for developing new biochemical assays. Here, we study the trapping of aqueous droplets in an oil-filled microwell driven by the application of nanometer amplitude vibrations called surface acoustic waves (SAW). We elucidate the dynamics of the droplet within the vortex toward the final trapping location and the physics of the trapping phenomenon using a theoretical model by considering the relevant forces. Our study revealed that the combined effect of acoustic radiation and hydrodynamic forces leads to droplet migration and trapping. We demarcate the trapping and nontrapping regimes in terms of the minimum critical input power required for the trapping of droplets of different sizes and densities. We find that the critical power varies as the square of the droplet size and is higher for a denser droplet. The effects of input power and droplet size on the trapping location and trapping time are also studied. © 2022 American Chemical Society.

Langmuir

Trapping of Aqueous Droplets under Surface Acoustic Wave-Driven Streaming in Oil-Filled Microwells

Disease detection, single-cell analysis, biochemical reactions, etc. are of profound interest in several biomedical and bioengineering applications. These important processes require several profound aspects, e.g., lower consumption of reagent, rapid reactions, rapid detection, high throughput, etc. needs to be satiated. Droplet microfluidics has addressed all the desired aspects needed to achieve these applications by providing a compatible environment for biosensing and bioengineering reactions, smaller footprint, rapid detection, quick reaction, etc. These advantageous features have made droplet microfluidics a potent high throughput platform for biomedical research and applications. In addition to this, droplet microfluidics facilitates encapsulation of cells, reagents, drugs, particle synthesis, which makes droplet microfluidics a promising tool for biosensing and bioengineering applications. In this chapter, we will discuss both open surface and in-channel droplet microfluidics and their role in several biomedical applications. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Droplet Microfluidics—A Tool for Biosensing and Bioengineering Applications

High piezoresistive smart nanocomposites strain sensors have attracted much attention because of their sensing ability to monitor structural integrity. Current nano-sensors have been successfully manufactured, but due to fabrication cost and inefficiency in multitasking, they are not in demand. This paper mainly focuses on the comparative study between advanced smart sensors called graphene nanoplatelets (GNP) and conventional ultrasound sensor in the context of SHM in stainless steel. Here, the electrical resistance of the smart GNP sensor with the propagation of crack growth shifts from its baseline with the application of spectrum loading, which is helpful in crack failure. The post-processing method by conventional ultrasound is only helpful after the post-failure but not during crack propagation, which can be replaced by the GNP-doped poly (methyl methacrylate) PMMA sensor. Stresses around the hole change their shape from circular to elliptic, which is explained with the help of 2D Extended Finite Element Method (XFEM) simulations and the crack opening mechanism by Abaqus 6.12. After 3* (1st spectrum loading), it was difficult to spot the crack location, which was monitored smartly with a graphene sensor. GNPs are highly sensitive to cyclic spectrum loading. Structural health monitoring (SHM) has been done by a graphene doped PMMA sensor having the highest gauge factor (GF) of 800Ω, that is 84. The electrical resistance’s baseline shifting was found to increase with crack growth. The GNPs spray-coated nano-sensor helps in the early detection of crack propagation before failure. Hence, this can save the cost and life of structural components, which ultrasound sensor cannot do during crack growth. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

Journal of Nondestructive Evaluation

Crack Monitoring Potential of Smart Graphene Nanoplatelet (GNP)- Doped Poly (methyl methacrylate) (PMMA) Spray-Coated Sensor Compared to Conventional Ultrasound in Simple Structures

We report hydrodynamic interaction between droplets and the interface of a pair of co-flowing immiscible streams in a microchannel revealing droplet migration and interfacial deformation. We find small droplets of confinement ratio, i.e., ratio of drop size to the suspending stream width, β<1, exhibit lateral migration - while smaller droplets of β<0.5 migrate towards the co-flow interface, unexpectedly larger droplets of 0.5<β<1 drift away from the interface. The size-based contrasting migration behavior is attributed to the interplay between the hitherto unexplored wall-directed negative lift force and the well-established center-directed noninertial lift force. We also find large droplets of β>1 cause deformation waves in an initially stable and flat interface that propagate downstream akin to traveling peristaltic waves. Numerical simulations reveal that interfacial deformation is a consequence of the distinctive pressure jumps across the co-flow interface at the upstream and downstream of a droplet. Our study reveals the amplitude of the deformation wave associated with a droplet grows spatially downstream but remains the same for a train of droplets crossing a fixed location, indicating convective instability. The effects of co-flow interfacial tension, viscosity contrast, confinement ratio, and droplet spacing on the deformation wave amplitude and its variation along the flow direction are studied. The experimental results are verified using a simple theoretical model. Our study presents an unexplored droplet-driven interfacial deformation wave that may find relevance in droplet microfluidics. © 2022 American Physical Society.

Physical Review Fluids

Interaction between droplets and co-flow interface in a microchannel: Droplet migration and interfacial deformation

Aircraft components exposed to high temperature are usually coated with an insulating layer to protect them from failure due to thermal fatigue. This thin layer, known as thermal barrier coating (TBC), has to be monitored regularly in order to check for its degradation and loss of thickness during operation. Inspection of such components poses a challenge owing to the chemical composition, unevenness, and porous nature of the coating. In this paper, the authors propose a methodology for the feasible implementation of the eddy current technique in order to perform a high-speed inspection of thermal barrier-coated components and evaluate their condition. A set of reference specimen with predetermined TBC thickness values is used for the trials. After preliminary simulation studies to select the optimum parameters, raster scanning is performed on the specimen using an experimental configuration assembled in-house. The results show a variation in TBC thickness within each specimen, which are validated using measurements from the THz time-domain spectroscopy (TDS) method. A thickness map of each specimen is generated after cross-correlation. Furthermore, this eddy current-based approach is implemented for quantitatively evaluating the condition of another batch of TBC samples that were subjected to varying in-service conditions. With a robust setup and proper calibration procedure, the proposed methodology has the potential to be implemented for the fast and reliable inspection of aircraft engine components to ensure structural integrity. © 2022, Indian Society for Non-destructive Testing.

Lecture Notes in Mechanical Engineering

Towards Rapid, in Situ Monitoring of Thermal Barrier Coating Degradation Using Eddy Current NDE Technique

The original article contained a mistake. The original version of the article contained a mistake wherein Mr. Siddharth Gopalakrishnan’s written consent was not obtained prior to acknowledging him in the manuscript. Mr. Siddharth’s name has now been removed from the journal paper as he wishes not to be acknowledged in the paper. © Springer-Verlag London Ltd., part of Springer Nature 2022.

Fulltext

International Journal of Advanced Manufacturing Technology

Correction to: Laser ultrasonic inspection of additive manufactured components (The International Journal of Advanced Manufacturing Technology, (2019), 102, 5-8, (2571-2579), 10.1007/s00170-018-3046-y)

This paper studies the performance of laser spot thermography (LST) in defect detection on a mild steel sample at different temperatures (30-600 °C). In laser spot thermography, a laser spot is used to scan over the surface of the sample and the thermal profile is monitored using a thermal camera. For checking the feasibility/capability of laser spot thermography in defect detection under higher temperatures, a three-dimensional numerical model is developed using a commercial FE software package. This FE model is used to understand the heat transfer phenomenon during defect detection at higher temperatures, even after oxidation temperature. The influence of the oxide layer formation (scale) at higher temperatures (above 500 °C) in defect detection is established using the validated model. The thermal properties and optical properties of this oxide layer are different from those of the base metal; this will lead to a drastic variation in the thermal profile after the oxidation temperature. An oxide layer at 600 °C is introduced in the improved numerical model as a thin resistive layer at the top surface with a thickness of 50 μm. The thermal properties of the layer are assigned as the scale properties. FE modeling results show better agreement with experimental results even at 600 °C. Thus, the applicability of LST in high temperatures is experimentally proved. © 2022 Author(s).

Journal of Applied Physics

Laser spot thermography for defect detection on mild steel at higher temperatures (30-600 °c)

Interfacial migration of droplets in microfluidic confinements has significant relevance in cell biology and biochemical assays. So far, studies on passive interfacial migration of droplets are limited to co-flow interfaces having small interfacial tension (IFT ∼1 mN/m). Here, we elucidate the migration and spreading of droplets (SiO-1000, SiO-100, FC40, and castor oil as phase 3, P3) across the interface between a pair of coflowing streams (PEG as P1, SiO-100, SiO-20, FC40, and olive oil as P2) having large IFT (∼10 mN/m), with the three different phases immiscible. Interfacial migration involving interfaces of large IFT is facilitated by confining droplets between the channel wall and coflow interface. We find that contact between droplets and the coflow interface is governed by the confinement ratio (i.e., the ratio of drop size to stream width) and the ratio of the capillary numbers of the coflowing streams. Depending on the sign of the spreading parameter (S) of the co-flowing phases, droplet migration or spreading at the interface is observed. While interfacial migration is observed for S1&lt; 0 and S2&gt; 0, droplet spreading is observed for S1&lt; 0 and S2&lt; 0, where S1and S2are P1 and P2 side spreading parameters, respectively. We investigate the droplet migration dynamics and time evolution of the contact line and the interface. Our results show that the speed of interfacial migration increases with increasing spreading parameter contrast between the coflowing phases. In the droplet spreading case, we experimentally study the variation in the spreading length with time, revealing three distinct regimes in good agreement with predictions from analytical scaling. Our study explores the interfacial transport of droplets involving high IFT interfaces, advancing the fundamental understanding of the topic that may find relevance in droplet microfluidics. © 2022 American Chemical Society. All rights reserved.