Electrophoretic Deposition for National Security Applications

Please click Additional Files below to see the full abstract

COLLOIDAL ADDITIVE MANUFACTURING USING PROJECTION BASED LIGHT DIRECTED ELECTROPHORETIC DEPOSITION

Electrophoretic deposition (EPD) has been used industrially for nearly century for deposition of paint and barrier coatings. Traditionally, it has been used to create unpatterned thin films of various materials such as metals, ceramics, and polymers. Recently, we have demonstrated the ability to use a photoconductive electrode system to create millimeter scale patterns and structures in electrophoretically deposited films, the first steps to turning EPD into an additive manufacturing technique. Here, we present improvements to the technique that increase overall resolution and material set as well decrease feature size to 10s of microns by using a novel projection system. We also detail the our attempts at applying LD-EPD to creating microarchitected materials. Prepared by LLNL under Contract DE-AC52-07NA27344

MODELING APPROACHES IN ELECTROPHORETIC DEPOSITION

Electrophoretic deposition (EPD) occurs when electric-field-driven colloidal particles suspended in a fluid migrate toward an electrode or liquid−liquid interface where they assemble into a deposit. The deposition rate depends on many parameters, such as the applied field strength, volume fraction of colloids, and electrophoretic mobility. Enhanced control of the shape, composition, and performance of functional materials fabricated via EPD can benefit from computationally feasible models that predict transient formation and resulting morphology of colloidal depositions. Here we discuss a broad range of EPD modeling approaches, their applicability and predictive capabilities. The majority of available models provide continuum level descriptions of EPD [1] that inherently neglect inter-colloidal interactions. Such models predict mass deposition rates that depend (at least) on the electrophoretic velocity, electrode surface area, and fraction of colloids that stick to the deposit. Film thickness models suggest nonuniform deposits occur when the colloidal particle permittivity exceeds that of the suspension or near electrode edges where electric field singularities locally enhance deposition rates. Alternative particle level modeling of EPD is still nascent, but promises to offer more detailed predictive information about deposit formation and packing morphology than traditional approaches. To this end, we also present and evaluate a particle-based model of colloidal suspensions that undergo electrophoretic motion and deposition [2] using an extensive set of mesoscale simulations that characterize experimentally relevant colloidal suspensions. Since the model explicitly computes inter-colloidal interactions, it is uniquely poised to elucidate how deposition conditions influence defect structures and particle rearrangement within EPD colloidal crystals. We use the model to investigate how empirical parameters, such as electric field strength and electrolyte concentration, can be tuned in order to control the degree of colloidal ordering versus non-ordering that occurs during EPD. It is straightforward to configure the model to study how various preparations of the interface, e.g. a bare surface, a lattice of particles, an amorphous monolayer, etc., and also annealing schemes influence the deposit microstructure. [1] Ferrari, B.; Moreno, R. EPD Kinetics: A Review. Journal of European Ceramic Society. 2010 (5), pp 1069-1078. [2] Giera, B.; Zepeda-Ruiz, L. A.; Pascall, A. J.; Weisgraber, T. H. Mesoscale Particle-Based Model of Electrophoretic Deposition. Langmuir. 10.1021/acs.langmuir.6b04010 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA2734

ELECTROPHORETIC DEPOSITION OF B4C/AL CERMETS IN A 3D GEOMETRY WITH GREATER CURVATURE FOR APPLICATIONS IN ARMOR SYSTEMS

Armor technology in aircraft, vessels, vehicles, and personnel are improved by increasing performance, operational supportability, and survivability. Industrial production of armor is facilitated when coupled with a flexible and affordable manufacturing process (such as EPD). Ceramic/metal composite materials are attractive for armor applications for they combine the hardness of ceramics and the toughness of metals. Armor shaped by ceramic tiles and concave plates are in service. Yet ceramic armor is largely ‘flat’ when compared to the curvature required to provide additional protection of soldier extremities; or enable 3D geometries in air, land, and sea vehicle parts that are both functional and structural. Boron carbide is one of the lightest and hardest ceramics known. Introducing Al into the microstructure of boron carbide creates an ideal low porosity armor that is lightweight, hard, and tough. The conformal nature of the EPD process enables ceramic parts to be made that take the shape of the working electrode. High green body densities of EPD processed parts translate to less reduction in volume during sintering; thus enabling the formation of near net shaped B4C/Al cermet armor parts. These parts can then be incorporated into armor systems for increasing performance, operational supportability, and survivability of both service personnel and vehicles. We report the creation of B4C/Al cermets in simple 3D geometries produced by EPD to demonstrate how it can be used to make shaped parts of greater curvature for armor applications. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LL

Additively manufacturable micro-mechanical logic gates.

Early examples of computers were almost exclusively based on mechanical devices. Although electronic computers became dominant in the past 60 years, recent advancements in three-dimensional micro-additive manufacturing technology provide new fabrication techniques for complex microstructures which have rekindled research interest in mechanical computations. Here we propose a new digital mechanical computation approach based on additively-manufacturable micro-mechanical logic gates. The proposed mechanical logic gates (i.e., NOT, AND, OR, NAND, and NOR gates) utilize multi-stable micro-flexures that buckle to perform Boolean computations based purely on mechanical forces and displacements with no electronic components. A key benefit of the proposed approach is that such systems can be additively fabricated as embedded parts of microarchitected metamaterials that are capable of interacting mechanically with their surrounding environment while processing and storing digital data internally without requiring electric power

Numerical Advances in Electrophoretic Deposition in Flow Cells

Please click Additional Files below to see the full abstract

DYNAMIC MESOSCALE MODEL OF REVERSIBLE ELECTROPHORETIC DEPOSITION

We present and evaluate a particle-based model of colloidal suspensions that undergo electrophoretic motion and repetitive deposition and resuspension using an extensive set of mesoscale simulations that characterize experimentally relevant colloidal suspensions. In particular, we explore resuspension kinetics under a variety of conditions: electric field strength and cycling frequency, suspension viscosity and electrolyte concentration, and colloid properties, e.g. size and surface potential distributions, non-spherical shapes, and bulk volume fraction. Such studies can reveal the process by which particles accumulate at electrodes and form thin deposits as well as provide insights into the “sticking parameter”[1] that accounts for the fraction of colloids that irreversibly incorporate into the deposit. The model explicitly accounts for inter-colloidal interactions and operates within experimental time and length scales. Thus, simulations can be compared directly against experiment to elucidate reversible electrophoretic deposition systems. [1] Ferrari, B.; Moreno, R. EPD Kinetics: a Review. Journal of the European Ceramic Society 2010. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

Modelling of Electrophoretic Deposition (EPD) of soft particles and experimental verification

Please click Additional Files below to see the full abstract

Field responsive mechanical metamaterials.

Typically, mechanical metamaterial properties are programmed and set when the architecture is designed and constructed, and do not change in response to shifting environmental conditions or application requirements. We present a new class of architected materials called field responsive mechanical metamaterials (FRMMs) that exhibit dynamic control and on-the-fly tunability enabled by careful design and selection of both material composition and architecture. To demonstrate the FRMM concept, we print complex structures composed of polymeric tubes infilled with magnetorheological fluid suspensions. Modulating remotely applied magnetic fields results in rapid, reversible, and sizable changes of the effective stiffness of our metamaterial motifs