Seminar Topic – Non-linear electrokinetic flow and ion transport near/in the nanofluidic devices: Insights using molecular dynamics simulations

Speaker – Manikandan D

Abstract – Nanochannels and nanopores are widely used nanofluidic devices. Integrating the nanofluidic
devices with the microfluidic devices leads to complex physics ion concentration polarization
(ICP) near the interface of these devices. This ICP effect leads to nonlinear I-V
characteristics resulting in three regions, Ohmic region, limiting resistance region (LRR) and
overlimiting resistance region (OLR). Many experimental investigations have been conducted
to understand the ion transport mechanism behind this nonlinear I-V behaviour. However, the
mechanism responsible for the transition between these regions has been in debate for the last
three decades.
In this talk, we report for the first time overlimiting current near a nanochannel using all-atom
molecular dynamics (MD) simulations. Here, the simulated system consists of a silicon
nitride nanochannel integrated with two reservoirs. The reservoirs are filled with 0.1 M
potassium chloride (KCl) solution. A total of ~1.1 million atoms are simulated with a total
simulation time of ~1μs over ~30,000 CPU hours using 128 core processors (Intel(R) E5-
2670 2.6 GHz Processor). With the help of these large scale MD simulations, we investigate
the nonlinear electrokinetic flow near the nanofluidic devices and the ion transport
mechanism behind the nonlinear I-V characteristics. Further, we provide a new way of
studying noise in the ionic current oscillations inside the solid-state nanofluidic devices.

Seminar Topic – Thermal boundary conduction at nanoscale solid -liquid interface

Speaker – Abhijith Anandakrishnan

Abstract – Thermal boundary resistance (TBR), also known as Kapitza resistance, occurs at the
interface between two dissimilar materials while a heat current flows across it. Recent
years have seen a surge in heat transfer literature investigating the mechanism of TBR
owing to its potential applications in quantum cascade lasers, light-emitting diodes, phase
change memory, high power electronic cooling, targeted drug delivery, photothermal
cancer therapy, and thermoelectrics. Despite the efforts, the physics of nanoscale TBR at
the solid-liquid interface is still debated. The TBR measured across well-characterized
interfaces such as Silicon-Water or Graphene-water exceeded the theoretical predictions
by one order of magnitude. We investigated the TBR models based on the liquid layering
phenomenon for organic coolants. The long-chain molecules, like perfluorohexane, retain
the liquid layering even at a higher temperature than water. Water, on the other hand,
increases its mobility at higher temperatures. As a consequence, in water, the contribution
of molecular diffusion to heat transfer increases compared to the increase in vibrational
carrier transport. To account for the various factors and develop a universal approach to
predict the TBR, we employed classical machine learning algorithms and investigated the
simultaneous influence of system geometry, work of adhesion, and interfacial liquid
structuring on TBR. The TBR is modeled in a high-dimensional feature space with eight
different predictor variables. The feature significance in ensemble-based algorithms
attributes the highest weightage to interfacial liquid structuring. The best performing
machine learning model predicts TBR with an accuracy 30% higher than the conventional
hyperbolic model correlating hydration layer density and TBR. Our study reveals that the
careful design of interfaces with calculated thermodynamic conditions like temperature,
pressure, surface free energy, and tailored geometric features will help achieve precise
values of TBR at the interface and introduce machine learning as a robust alternate
strategy to explore the optimal design parameters.

Seminar Title: Study of some soft matter systems using optical tweezers

Speaker: Rahul Vaippully

Abstract:

Optical tweezers is a very useful tool in physics, chemistry and biology. Although translational motion of trapped particles have been extensively studied, rotations are also being studied more recently. Of the rotations, in-plane or yaw motion has been developed over the last couple of decades. In this presentation, we explore yaw motion first and then move on to explore the first out-of-plane rotation which we call pitch motion in the nomenclature of the airlines.

We discuss our new method to generate yaw rotations with low ellipticity beams. Then, we use the yaw rotation to study adhesively of surfaces. We move on to detect pitch motion at high resolution and explore cell biological applications. Lastly, we explore strategies for calibration of optical tweezers inside the cell.

Seminar Topic: Open surface passive droplet manipulation

Speaker:  Imdad Chowdhury

Abstract:

Passive droplet manipulation on open surfaces such as mixing, transport, and splitting has a broad range of applications, including condensation, electronic chip cooling, Lab-On-a-Chip (LOC) systems, and Point-Of-Care (POC) diagnostics. We have performed the numerical modeling of a few passive droplet manipulation techniques such as a) wettability patterning, b) texture gradient, and c) shape gradient of surfaces. We have focused on the wettability patterning and demonstrated a standalone power-free technique for transporting and splitting a droplet on an open surface using continuous wettability-gradients. A Y-shaped wettability-gradient track – laid on a superhydrophobic background – is used to investigate the dynamics of the splitting process. A 3D phase-field Cahn-Hilliard model for interfaces and Navier-Stokes equations for transport are employed and solved numerically using the finite element method (FEM). Numerical results are used to decipher the motion and splitting of the droplet at the Y-junction using the principle of energy conservation. The droplet splitting ratio (ratio of the sizes of daughter droplets) can be controlled by manipulating the widths of the Y-branches. The physics of the droplet transport, flow pattern inside the droplet, and the splitting mechanisms have been explained through detailed numerical studies and scaling analysis. We also studied the effect of wettability confinement on droplet transport. The study provides the required theoretical underpinnings to achieve autonomous transport and splitting of droplets on open surfaces, which has clear potential for applications in surface fluidic devices.

Title: 2D Membrane for Renewable Energy

Speaker: DR. Prahalad K. Barman

Abstract:
The blue energy (salinity gradient energy) identified as a promising non-intermittent renewable energy source. However, this membrane-based technology is facing major limitation for large-scale viability, primarily due to the poor membrane performance. The atomically thin 2D nano porous material with high surface charge density resolving the bottle neck and leading to a new class of membrane material for the salinity gradient energy.

Although the 2D nano porous membrane are showing extremely high performance in terms of energy generation through single pore, but the fabrication and technical challenge (like ion concentration polarization) making the nano porous membrane a non-viable solution. On the other hand, the meso and macro porous structures in 2D membrane are showing improved energy generation capacity. The laser assisted(femtosecond and ultrafast laser) technique making the fabrication of these pores is quick, low complex and hence making the membrane technology viable. In this talk, the details fabrication of these 2D membranes along with creation of macro pores in these membranes for blue energy generation will be discussed.

Seminar Topic: Molecular and supramolecular structure design for applications in Biomedical arena.

Speaker: Prof. Muraleedharan K. M
Dept. of Chemistry, IITM.

Abstract: Design of organic systems with pre-defined properties requires proper control at electronic-, conformational- or supramolecular levels. As part of our interest in this area, we are working on different types of compounds, which include both rigid three-dimensional frameworks as well as relatively flexible ones. Electronic control of redox stability in di hydroquinolines to identify new anticancer leads, folding preferences & controlled conformational transitions in synthetic peptides, modular design of drug delivery systems, and design of chemical probes for selective detection & quantification of gaso transmitters are some areas we are focusing at the moment. This presentation is intended to share the latest results with MNBF team so that areas of overlapping interest can be identified for collaborative research.

Seminar Topic:
Particle migration under combined acoustic relocation and acoustophoretic force

Speaker: Amal Nath
PhD Scholar, Fluid Systems Laboratory

Abstract
Bulk transport of fluid streams is observed when a co-flow of heterogeneous fluids is subjected to a standing bulk acoustic wave inside a microchannel. For most applications like particle sorting or cell washing, this bulk transport (‘acoustic fluid relocation‘) is prevented by ensuring that the co-flowing fluid streams have a negligible difference in density or compressibility. Here we demonstrate the behavior of dilute suspensions under acoustic relocation, by flowing a suspension of relatively lower acoustic impedance through the channel center flanked by side streams of high acoustic impedance. Under acoustic actuation, the low-impedance suspension stream gets transported (or relocated) to the sides. The particles may remain within the original suspending stream at the sides or enter the central stream and their dynamics is governed by the combined effect of relocation-induced drag and acoustic primary radiation force. Depending on the final configuration of the suspended particles, we characterize the different regimes in terms of the relevant timescales of advection, relocation and acoustophoretic migration. The operational parameters are non-dimensionalized and a general phase diagram is developed which provides some guidelines in developing relocation-based cell sorters and medium exchange devices. Numerical model predicting the complete/partial migration or non-migration of particles from the suspension to the relocated side stream is developed, in agreement with the experimental observations. Using the combined technique, we also experimentally demonstrate the medium exchange and size-based sorting of biological cells, which shows the potential application of the study in biochemical assays

Seminar Topic:
Computational modelling of red blood cell mechanics

Speaker: SAINATH. H.
PhD Scholar, Micro and Nanoscale Transport Laboratory.

Abstract
Hematological diseases affect millions of people annually. They include genetic disorders like hereditary spherocytosis, G6PD deficiency, and conditions related to HIV, sickle cell disease, in addition to blood cell cancers. Explicit modeling of blood has enormous importance in studying different cell sorting techniques, phenomena such as aggregation, hemostasis and hemolysis. Fundamental understanding of the intricate dynamics showcased by the cells would help us in disease detection and even provide vital information regarding the pathophysiology of the disease. Recently, there has been a tremendous interest in identifying biomarkers for cell-based diseases. Furthermore, microfluidic platforms and miniaturized lab-on-a-chip devices have made a considerable impact on point-of-care blood analysis, leading to effective diagnosis. Here, we focus on the numerical modeling of red blood cells (RBCs) in health and disease. A three dimensional, high fidelity in-silico RBC model capable of capturing hemodynamics has been developed. Dissipative particle dynamics ( DPD) and the theories of statistical mechanics are implemented to analyze the cell behaviour and morphology in microcirculation. After the completion of the rigorous model validation process, an in-depth comparison of cell mechanics in different pathological states are examined.