Jeevanjyoti Chakraborty

Electrokinetically modulated peristaltic transport of power-law fluids.

The electrokinetically modulated peristaltic transport of power-law fluids through a narrow confinement in the form of a deformable tube is investigated. The fluid is considered to be divided into two regions - a non-Newtonian core region (described by the power-law behavior) which is surrounded by a thin wall-adhering layer of Newtonian fluid. This division mimics the occurrence of a wall-adjacent cell-free skimming layer in blood samples typically handled in microfluidic transport. The pumping characteristics and the trapping of the fluid bolus are studied by considering the effect of fluid viscosities, power-law index and electroosmosis. It is found that the zero-flow pressure rise is strongly dependent on the relative viscosity ratio of the near-wall depleted fluid and the core fluid as well as on the power-law index. The effect of electroosmosis on the pressure rise is strongly manifested at lower occlusion values, thereby indicating its importance in transport modulation for weakly peristaltic flow. It is also established that the phenomenon of trapping may be controlled on-the-fly by tuning the magnitude of the electric field: the trapping vanishes as the magnitude of the electric field is increased. Similarly, the phenomenon of reflux is shown to disappear due to the action of the applied electric field. These findings may be applied for the modulation of pumping in bio-physical environments by means of external electric fields.

Combining mechanical and chemical effects in the deformation and failure of a cylindrical electrode particle in a Li-ion battery

A general framework to study the mechanical behaviour of a cylindrical silicon anode particle in a lithium ion battery as it undergoes lithiation is presented. The two-way coupling between stress and concentration of lithium in silicon, including the possibility of plastic deformation, is taken into account and two particular cases are considered. First, the cylindrical particle is assumed to be free of surface traction and second, the axial deformation of the cylinder is prevented. In both cases plastic stretches develop through the entire cylinder and not just near the surface as is commonly found in spherical anode particles. It is shown that the stress evolution depends both on the lithiation rate and the external constraints. Furthermore, as the cylinder expands during lithiation it can develop a compressive axial stress large enough to induce buckling, which in turn may lead to mechanical failure. An explicit criterion for swelling-induced buckling obtained as a modification of the classical Euler buckling criterion shows the competition between the stabilising effect of radius increase and the destabilising effect of axial stress.

Role of streaming potential on pulsating mass flow rate control in combined electroosmotic and pressure-driven microfluidic devices

In the present study, we investigate the implications of streaming potential on the mass flow rate control in a microfluidic device actuated by the combined application of a pulsating pressure gradient and a pulsating, externally applied, electric field. We demonstrate that the temporal dynamics due to streaming potential effects may lead to interesting non‐trivial aspects of the resultant transport characteristics. Our results highlight the importance of an adequate accounting of the streaming potential effects for temporally tunable mass flow rate control strategies, which may act as a useful design artifice to augment mass flow rates in practical scenarios.

Combined influence of streaming potential and substrate compliance on load capacity of a planar slider bearing

In the present study, we investigate the combined interplay of streaming potential and substrate compliance with sliding dynamics on the load carrying capacity of a planar slider bearing. We relax previously utilized simplifying assumptions to model the electrokinetic effects and demonstrate that the streaming potential may augment the load carrying capacity of the bearing to a considerable extent. Interestingly, we also reveal that the electrokinetically augmented load carrying capacity exhibits strong dependencies on a combination of the compliance and the sliding dynamics, which have, hitherto, not been extensively explored. This rich interplay reveals certain parametric regimes of interest, which are significant from the viewpoint of practical design considerations.

Influence of streaming potential on the elastic response of a compliant microfluidic substrate subjected to dynamic loading

In the present study, we investigate the effect of streaming potential on the elastic response of a compliant surface subjected to dynamic loading conditions. For illustrating the pertinent physical phenomena, we analyze in particular the dynamical characteristics of the system on squeezing out of a liquid layer through a narrow gap formed between an elasticfluidicsurface and an incipient rigid oscillating sphere. We reveal that the streaming potential effects may amplify the elastic force response of the substrate to a considerable extent. Interestingly and nontrivially, this increment turns out not only to be a function of the pertinent electrokinetic parameters dictating the establishment of the streaming potential, but also a combined consequence of the oscillation frequency and the stiffness of the substrate, consistent with a dynamical interaction between interfacial electrochemical-hydrodynamics and structural responsive characteristics that has hitherto not been emphatically explored.

Influence of streaming potential on pulsatile pressure‐gradient driven flow through an annulus

We study pulsatile pressure‐gradient driven flow through an annular confinement under the influence of streaming potential. Our study considers zeta potentials beyond the traditional Debye–Hückel limits, and takes care against aphysical predictions stemming from traditional Boltzmann statistics through modifications involving the finite size of the ionic species (steric effects). With these considerations, we demonstrate, rather non‐intuitively, that an intrinsic asymmetry may be manifested in the velocity profile of the flow through the annulus, as a consequence of the streaming potential effects in presence of Steric interactions. Our findings are likely to provide a new design basis for micro‐ and nano‐scale flow devices involving annular geometries.

Electrohydrodynamics within the electrical double layer in the presence of finite temperature gradients.

A wide spectrum of electrokinetic studies is modeled as isothermal ones to expedite analysis even when such conditions may be extremely difficult to realize in practice. Going beyond the isothermal paradigm, we address here the case of flow induced electrohydrodynamics, commonly streaming potential flows, in a situation where finite temperature gradients do exist. By way of analyzing a model problem of flow through a narrow parallel-plate channel, we show that the temperature gradients applied at the channel walls may have a significant effect on the streaming potential, and, consequently, on the flow itself. Our model takes into consideration all the pertinent phenomenological aspects stemming from the imposed thermal gradients, such as the Soret effect, the thermoelectric effect, and the electrothermal effect, by a full-fledged coupling among the electric potential, the ionic species distribution, the fluid velocity and the local fluid temperature fields, without resorting to ad hoc simplifications. We expect this expository study to contribute significantly towards more sophisticated future endeavors in actual development of micro- and nano-devices for applications simultaneously involving thermal management and electrokinetic effects.

Influence of constraints on axial growth reduction of cylindrical Li-ion battery electrode particles

Abstract Volumetric expansion of silicon anode particles in a lithium-ion battery during charging may lead to the generation of undesirable internal stresses. For a cylindrical particle such growth may also lead to failure by buckling if the expansion is constrained in the axial direction due to other particles or supporting structures. To mitigate this problem, the possibility of reducing axial growth is investigated theoretically by studying simple modifications of the solid cylinder geometry. First, an annular cylinder is considered with lithiation either from the inside or from the outside. In both cases, the reduction of axial growth is not found to be significant. Next, explicit physical constraints are studied by addition of a non-growing elasto-plastic material: first, an outer annular constraint on a solid silicon cylinder, and second a rod-like inner constraint for an annular silicon cylinder. In both cases, it is found that axial growth can be reduced if the yield stress of the constraining material is significantly higher than that of silicon and/or the thickness of the constraint is relatively high. Phase diagrams are presented for both the outer and the inner constraint cases to identify desirable operating zones. Finally, to interpret the phase diagrams and isolate the key physical principles two different simplified models are presented and are shown to recover important qualitative trends of the numerical simulation results.

Relaxation characteristics of a compliant microfluidic channel under electroosmotic flow

We investigate the effect of electroosmotic flow on the temporal response of an initially deformed microfluidic channel wall as it relaxes to its undeformed state. Our results reveal that the electrokinetic effects significantly alter not just the quantitative response of the relaxation dynamics but also the qualitative nature of the relaxation profiles. Furthermore, the electrokinetics brings about a preferential asymmetry to the nature of the dynamical evolution of the relaxation characteristics. Overall, we unveil a rich interplay between the pertinent physico-chemical interactions, the compliance of the deformable channel walls and the geometry of the fluidic confinement, bearing non-trivial consequences towards optimal control of electroosmotic flow in narrow channels with deformable confining boundaries.

Streaming Potential in Microflows and Nanoflows

In this chapter, we discuss a wide variety of important effects due to streaming potential when fluid flow takes place through conduits of micro- and nanometric dimensions. We first introduce this as one of the four primary electrokinetic phenomena with suitable background, and describe its significance in numerous natural and engineered settings. Its practical usage and measurement being inordinately linked to predictive models, we present the theory behind streaming potential. In light of recent research findings, and recognizing their importance in micro- and nano-flows, we also highlight the influence of streaming potential when considered together with the consideration of hydrophobic, steric, and thermal effects.