A system of electrolytes using water as a solvent was successfully used to support a typical lithium-ion battery chemistry that operates at 3.7V-4.2 V using standard ultraviolet-cured acrylic-based polymers as hydrophobic barriers. The aqueous electrolyte is contained in a system of poly(ethylene glycol) acrylate polymers crosslinked to produce an electrolyte gel that has electrochemical properties similar to that of the liquid phase component. The electrolyte gels have elastic moduli in the kPa range, making them soft enough to tolerant flexing, cutting, and blunt force impacts while keeping the electrodes covered and safe from shorting. While batteries based on water-in-salt electrolyte provides intrinsic safety that is otherwise unavailable from typical non-aqueous electrolytes, acrylate-based aqueous gel electrolytes offer the potential of large-scale manufacturing owing to the relatively low volatility of the electrolyte components and the low complexity of the proposed manufacturing process.

Highly concentrated solutions of lithium salts in water have made sweeping strides from the time in the early 2010s where aqueous electrolytes could operate a battery within an electrochemical window no more than 1.5V wide. In this presentation, we discuss the construction of a lithium ion battery using graphite as the anode and LiCoO2 as the cathode to make a cell with a 4.2V potential. The primary electrolyte is a water:trimethylphosphate hybrid with a water mole fraction of 0.44 and LiTFSI salt at a concentration of 9 molal. This aqueous hybrid electrolyte can be formed into a gel electrolyte by directly polymerizing acrylate-based monomers and crosslinkers dissolved in the electrolyte. We demonstrate that by protecting the graphite anode using an acrylate gel with a fluoroethylene carbonate-based liquid electrolyte, the battery cell can be cycled repeatedly between 3.0V and 4.2V just like a cell using organic carbonate electrolytes. The advantage of the aqueous hybrid electrolyte is that it is non-flammable, and a cell using aqueous gel electrolytes can withstand damage and even be cut open while operating with no risk of fire or explosion. The manufacturing and performance characteristics of the aqueous 4V battery will be discussed as well as the interfacial issues that come about with the use of aqueous gel electrolytes in a 4V-capable battery system.

Application of electric field has become one of the most promising actuation tools in bio-microfluidics for cell deformation, poration and manipulation. However, electric field guided cell deformation process is still not well understood due to its complex multiphysics nature. In this paper, we present an electric field induced cell deformation study using hybrid immersed interface-immersed boundary method where both electric and hydrodynamic forces are evaluated with interface resolved approach Immersed interface method is employed to evaluate electric field in fluids with submerged cells while immersed boundary method is used to study hydrodynamics with flexible immersed boundaries. Electric field induced force is calculated using Maxwell's stress tensor approach. The results show that the deformation process depends on the electrical properties of fluid as well as cells, the direction of applied electric field and nature of electric field induced forces. When electrical conductivity of cell is less than that of fluid medium, cell experiences compressive force and deformation rate is faster. The response of fluids to the deformation process is also depend on the relative electrical properties of cell and fluid medium. This study provides critical insight of the transient cell deformation mechanism and better understanding which can help in designing experimental studies and exploring new applications of electric field guided cell deformation.

Deformation of flexible vesicles suspended in a fluid medium due to an applied electric field can provide valuable insight into deformation dynamics at a very small scale. In an electric field, the response of the vesicle membrane is strongly influenced by the conductivity of surrounding fluid, vesicle size and shape, and the magnitude of applied field. We studied the electrodeformation of vesicles immersed in a fluid media under a DC electric field. An immersed interface method is used to solve the electric field over the domain with conductive or non-conductive vesicles while an immersed boundary method is employed to solve fluid flow, fluid-solid interaction, membrane mechanics and vesicle deformation. Initial force analysis on the membrane surface reveals almost linear influence of vesicle size, but the vesicle size does not affect the long-term deformation which is consistent with experimental evidence. Highly nonlinear effect of the applied field as well as the conductivity ratios inside and outside of the vesicle are observed. Results also point towards an early linear deformation regime followed by an equilibrium stage for the membranes. Modeling results suggest that electrodeforming vesicles can create unique external flows for different conductivity ratios. Moreover, significant influence of the initial aspect ratio of the vesicle on the force distribution is observed across a range of conductivity ratios.

Many biological settings involve complex fluids that have non-Newtonian mechanical responses that arise from suspended microstructures. In contrast, Newtonian fluids are liquids or mixtures of a simple molecular structure that exhibit a linear relationship between the shear stress and the rate of deformation. In modeling complex fluids, the extra stress from the non-Newtonian contribution must be included in the governing equations.In this study we compare Lagrangian mesh and Oldroyd-B formulations of fluid-structure interaction in an immersed boundary framework. The start-up phase of planar Poiseuille flow between two parallel plates is used as a test case for the fluid models. For Newtonian and Oldroyd-B fluids there exist analytical solutions which are used in the comparison of simulation and theoretical results. The Lagrangian mesh results are compared with Oldroyd-B using comparable parameters. A regridding algorithm is introduced for the Lagrangian mesh model. We show that the Lagrangian mesh model simulations with regridding produce results in close agreement with the Oldfoyd-B model.

Recent experimental studies report that the understanding of dielectrophoretic (DEP) interactions and chaining of irregularly shaped particles, particularly ellipsoidal shaped particle, are critical for development of smart materials, engineered biological cellular structure and tissue formation. This paper presents a comprehensive numerical investigation of direct current (DC) dielectrophoretic (DEP) chaining and interactions of ellipsoidal particles in a microchannel. A hybrid immersed boundary-immersed interface method is employed to explain the fundamental mechanism of DEP interactions and chaining of ellipsoidal particles. Electric field equations are solved by the immersed interface method while the immersed boundary method is employed to solve fluid equations. The DEP force was estimated by using Maxwell’s stress tensor (MST) and the Cauchy stress tensor (CST) was employed to evaluate hydrodynamic force. The results show that the electrical properties of fluid and particles are the main deciding factor on the final orientation of ellipsoidal particles. However the size, shapes and initial positions and orientations have significant impact on interaction time spans. Results also show that if the interacting particles are electrically similar i.e. having same electrical conductivity then they always form a chain parallel to the applied electric field, otherwise they form a chain which is orthogonal to the applied electric field. In parallel chaining, particles rotate in a clockwise direction, while in orthogonal (to the applied electric field) chaining, particles rotate in counter-clockwise direction to reach to the final orientation. Results also indicate that the ellipsoidal particles go through an electro-orientation process if initially the major axis of the ellipsoidal particles is not in perfect alignment with the applied electric field. The electro-orientation and DEP interaction take place simultaneously to reach to final stable orientation. This study provides critical insight on the mechanism of DEP interactions and chaining of ellipsoidal shaped particles.

Mammalian cells respond in a variety of ways to concentrations of activated transforming growth factor (TGF) in the extracellular domain via intracellular Smad signaling pathways. TGF-β/Smad interaction is prevalent in a wide range of tumor environments with both autocrine and paracrine mechanisms driving temporal evolution. TGF-β has been reported to exhibit both pro- and antagonistic roles in tumor progression and survival. It has been argued that tumor cells upregulate TGF-β production by modifying the TGF-β/Smad pathway. Although several numerical studies of the tumor microenvironment have been conducted, most are based on PDEs where the cells are represented as a continuum or on discrete agent-based methods. Here, we develop a hybrid/cells-based model for the tumor microenvironment with cells represented as discrete entities in which diffusion and reaction in the extracellular environment as well as protein/receptor surface interactions are described using immersed interface methods. We develop a model for the cellular TGF-β/Smad pathways with the intracellular processes represented by systems of ODE's. In this study, we investigate the variation in cellular response with different levels of TGF-β in the extracellular environment. Our numerical results show that the model can account for experimental results on tumor cell lines when intracellular production and secretion of TGF-B based on activated Smad concentrations are included in the model system. Additionally, we studied the intracellular and surface levels of TGF-β in two different types of cells and observed variation in the extracellular domain.

This paper presents a comprehensive numerical study of dielectrophoretic (DEP) interactions and assembly of particles with various size, shape and electrical properties. A hybrid immersed boundary-immersed interface method is employed to solve coupled electric field and fluid flow equations. DEP forces are estimated from Maxwell⿿s stress tensor. Results show that the final orientation depends on the electrical properties of the particles and fluid media. Particles that are identical in their electrical conductivities form an assembly parallel to the applied electric field regardless of their sizes, shapes and initial orientations. On the other hand, particles with dissimilar electrical conductivities (i.e. combination of more and less conductivities than the fluid media) form an assembly perpendicular to the electric field regardless of their sizes, shapes and initial positions. However, the interaction time span depends on the particles size and shape. In parallel assembly, particles rotate in a clockwise direction, while in perpendicular assembly particles rotate in counter-clockwise direction to reach to the final orientation. The simulation results qualitatively match with the experimental observation. This study provides critical insight on DEP interactions and assembly for a class of particles.

This paper presents a comprehensive numerical study of dielectrophoretic (DEP) interactions and assembly of particles with various size, shape and electrical properties. A hybrid immersed boundary-immersed interface method is employed to solve coupled electric field and fluid flow equations. DEP forces are estimated from Maxwell's stress tensor. Results show that the final orientation depends on the electrical properties of the particles and fluid media. Particles that are identical in their electrical conductivities form an assembly parallel to the applied electric field regardless of their sizes, shapes and initial orientations. On the other hand, particles with dissimilar electrical conductivities (i.e. combination of more and less conductivities than the fluid media) form an assembly perpendicular to the electric field regardless of their sizes, shapes and initial positions. However, the interaction time span depends on the particles size and shape. In parallel assembly, particles rotate in a clockwise direction, while in perpendicular assembly particles rotate in counter-clockwise direction to reach to the final orientation. The simulation results qualitatively match with the experimental observation. This study provides critical insight on DEP interactions and assembly for a class of particles. (C) 2016 Elsevier B.V. All rights reserved.

Dielectrophoresis (DEP) has become one of the most popular mechanisms for label free particle manipulations and transport in microfluidics. The efficacy of this mechanism is greatly dependent on the understanding and control of DEP interactive motion among particles. In this study, we performed a systematic investigation to understand the effect of particles size and electrical properties on DC DEP interactions among particles using in-house hybrid immersed boundary – immersed interface numerical method. Immersed boundary method is employed to predict flow field and immersed interface method is used to simulate electric field. The numerical model utilizes Maxwell’s stress tensor to obtain DEP forces, while solving transient Navier-Stokes equation it determines the hydrodynamic interaction between each of the particles and the fluid containing them. By varying the number of particles as well as the particles’ size, electrical properties and initial orientations, a number of possibilities were considered. Results indicate that the particles with similar electrical conductivities attract each other and tend to align themselves parallel to the external electric field regardless of sizes. If electrical conductivity of particles is lower than that of the fluid medium then the particle-particle interactions is caused by the negative DEP. If electrical conductivity of particles is higher than that of the fluid medium then the interactive motions of particle is attributed to the positive DEP. On the other hand, electrically dissimilar particles still attract each other but tend to align perpendicular to the electric field. Both negative and positive DEP contributes in interactions between electrically dissimilar particles. Numerical simulation also shows that the identical sized particles move at the same speed during interaction. In contrast, smaller particles moves faster than the larger particle during the interactions. This study explains the effect of size and electrical properties on DEP interactive motions of particles and can be utilized to design microfluidic devices for DEP particle manipulations.

In recent years, there are significant interests in the manipulation of bipolar Janus particles. In this article, we investigate the transient behavior of the electro‐orientation process and particle–particle interaction of ellipsoidal bipolar Janus particles in the presence and absence of a DC electric field. The bipolar particle dynamics is modeled with a body force term in the fluid flow equations based on the Maxwell stress tensor. This force is due to presence of bipolar surface charges on the particles as well as their interactions with an imposed field. An interface resolved numerical scheme that consider the finite size of the particle is adopted for computation of the electric and flow fields. Our numerical results show that in the absence of an electric field, particles can undergo self‐orientation to reach an equilibrium position. The time taken to reach a stable orientation depends on the initial configuration and inter‐particle separation distance. Bipolar particles experience forces only on their polar ends, a phenomena that is difficult to capture with noninterface resolved methods. When bipolar particles are exposed to an external electric field, they rotate to align along the external electric field direction. Depending upon the initial configuration, particles orient via clockwise or counter clockwise rotations to form head to tail chains. The time required to form particle assembly strongly depends on particle size and bipolar charge density. The present numerical algorithm can be applied to a wider class of dual‐faced Janus particles.

Dielectrophoresis, a nonlinear electrokinetic transport mechanism, has become popular in many engineering applications including manipulation, characterization and actuation of biomaterials, particles and biological cells. In this paper, we present a hybrid immersed interface–immersed boundary method to study AC dielectrophoresis where an algorithm is developed to solve the complex Poisson equation using a real variable formulation. An immersed interface method is employed to obtain the AC electric field in a fluid media with suspended particles and an immersed boundary method is used for the fluid equations and particle transport. The convergence of the proposed algorithm as well as validation of the hybrid scheme with experimental results is presented. In this paper, the Maxwell stress tensor is used to calculate the dielectrophoretic force acting on particles by considering the physical effect of particles in the computational domain. Thus, this study eliminates the approximations used in point dipole methods for calculating dielectrophoretic force. A comparative study between Maxwell stress tensor and point dipole methods for computing dielectrophoretic forces are presented. The hybrid method is used to investigate the physics of dielectrophoresis in microfluidic devices using an AC electric field. The numerical results show that with proper design and appropriate selection of applied potential and frequency, global electric field minima can be obtained to facilitate multiple particle trapping by exploiting the mechanism of negative dielectrophoresis. Our numerical results also show that electrically neutral particles form a chain parallel to the applied electric field irrespective of their initial orientation when an AC electric field is applied. This proposed hybrid numerical scheme will help to better understand dielectrophoresis and to design and optimize microfluidic devices.

A mathematical model and numerical techniques are proposed to study AC electric field induced cellular assembly in a microfluidic device. In the mathematical model, the Maxwell stress tensor is used to calculate the dielectrophoretic force acting on particles by considering the physical effect of particles in the computational domain. Thus, the proposed model eliminates the approximations used in point dipole methods for calculating dielectrophoretic force. The numerical method is based on hybrid immersed boundary-immersed interface methods. An immersed boundary method is used for the fluid equations and particle transport, while an immersed interface method is employed to obtain the AC electric field in a fluid media with suspended particles. For the immersed interface method, an iterative algorithm is developed to solve the complex Poisson equation using a real variable formulation. The decoupled algorithm for solving complex differential equations converges rapidly. The hybrid method is used to investigate the physics of AC dielectrophoresis in a cross-channel junction. The numerical results show that with proper design and appropriate selection of applied potential and frequency, global electric field minima can be obtained to facilitate multiple particle trapping by exploiting the mechanism of negative dielectrophoresis.

The production of hydrogen from water with semiconductor photocatalysts can be promoted by adding small amounts of metals to their surfaces. The resulting enhancement in photocatalytic activity is commonly attributed to a fast transfer of the excited electrons generated by photon absorption from the semiconductor to the metal, a step that prevents deexcitation back to the ground electronic state. Here we provide experimental evidence that suggests an alternative pathway that does not involve electron transfer to the metal but requires it to act as a catalyst for the recombination of the hydrogen atoms made via the reduction of protons on the surface of the semiconductor instead.