1. SNM: Physics Guided Innovation of Integrated Flash-Light-Sintering, Continuous Nanomaterial Synthesis and Roll-To-Roll Deposition Processes
The objective of this proposal is to investigate the fundamental multiscale and multiphysical phenomena underlying a transformational and highly-scalable Nanoparticle-ink (NP-ink) sintering process, i.e., Flash-Light-Sintering (FLS). This fundamental research will guide the creation of novel processes that combine FLS with equally scalable Microreactor-Assisted Nanoparticle Synthesis (MANS), developed by the PI for continuous in-situ synthesis of NP-inks, and Roll-to-Roll (R2R) NP-ink deposition (Fig. 1). These processes will possess unmatched capabilities for low-cost, high-throughput and multimaterials-capable manufacturing of patterned and continuous thin-films with controlled nanoscale density (Fig.2) over large-area flexible substrates.
These thin-films lie at the core of devices poised to make a disruptive impact in applications like pervasive RFID, wearable bio-monitoring, environmental sensing, energy efficient built environments, as well as energy conversion and storage. We will overcome the key bottleneck of high manufacturing costs for large volume production of these thin-films, which has inhibited ubiquitous deployment of these devices. The working principle of FLS is the incidence of pulsed, broad-spectrum and broad-area light from a flash lamp onto a layer or pattern of NP-ink. NP-inks consist of nanoparticles (NPs) suspended in a liquid. In FLS the NPs convert the light's energy to heat via plasmon resonance, heat and evaporate the liquid, and then fuse into a sintered structure.
FLS can sinter NP-inks over a few square inches in a few seconds, without energy intensive vacuum, and at equipment costs that are a fraction of conventional vapor and plasma deposition equipment. We will develop physics-based models to uncover new knowledge on: (1) the interdependent phenomena of plasmon resonance, heat transfer and densification in FLS; and (2) the effect of doping and UV pumping on FLS of multiple non-metallic NPs. This approach will enhance control of current FLS-R2R and the knowledge gained will guide the creation of three novel scalable processes with unconventionally superior capabilities including: (1) expanded materials capability for sintering binary, ternary and quaternary metallic as well as non-metallic NPs; (2) reduced manufacturing costs via integration of MANS with FLS-R2R using design approaches that ensure process scalability; (3) enhanced process flexibility and reduced tooling costs by eliminating the need for pattern-specific and expensive gravure rollers that are currently necessary to fabricate patterned thin-films with R2R deposition.
Our work till date has experimentally shown a previously unreported turning point in temperature evolution during IPL of Ag NP films. This turning point in temperature correlates to a levelling off in densification, that has been experimentally observed in literature and in our work. FEA of NP-EM wave interaction was explicitly linked with semi-analytical models of interparticle necking to show that optically induced heating in NP ensembles dynamically reduces with increasing interparticle necking during IPL. This nanoscale model was linked to a mesoscale model of heat transfer and densification to show that capturing the nanoscale coupling between optical absorption and densification is critical to predicting a temperature turning point, levelling off in densification and the dependence of density on IPL parameters and the dependence of density on IPL parameters. We have further shown that smaller nanoparticles results in faster sintering at lower temperature during IPL. Our ongoing work is further investigating the effect of nanoparticle size and shape distributions on densification via Molecular Dynamics modeling, and on optical absorption via electromagnetic FEA.
2. Additive Manufacturing of Conformal Solar Cells via Xenon-Light-Assisted Sintering
The goal of this project is to use desktop scale IPL for low-cost, ambient condition fabrication of conformal thin film solar cells on surfaces of objects. To control the integrated inkjet printing-IPL and aerosol jet printing-IPL processes the interaction between optical absorption, nanoscale mass transfer during sintering and temperature evolution are being computationally and experimentally examined. We have shown the ability of the developed setups (≈ $20,000 each) to sinter inkjetted patterns of Ag NPs on polymer substrates, as well as studied the temperature, density and damage evolution of the polymer. Our future work will focus on similar low-cost forms of IPL for aerosol jet deposited large-area films.
3. Dieless, Heat-less Incremental Forming of Thermoplastic Surfaces
Thermoplastic polymer surfaces are widely used in automobiles and airplanes, packaging and biomedical implants. The multimaterial, die-less and room-temperature forming capabilities of polymer IF have been demonstrated. Compared to conventional processes (e.g., molding, thermoforming) polymer IF can lower thermal costs, reduce tooling costs and expand process flexibility for prototyping and low volume production in the above applications. Our research till date has shown that (A) greater step-down in polymer SPIF increases formability contrary to the trend seen in IF of metals, but excessive ∆z causes a change in failure mode from tearing to wrinkling; (B) polymers formed with SPIF show greater toughness and a reorientation of polymer chains as compared to the unformed polymer; (C) polymer DSIF, explored for the first time, increases formability, enhances part accuracy and reduces void content in the formed material as compared to SPIF. Further, greater ∆z increases formability in polymer DSIF as well.
Key outcomes of this work include (A) the knowledge that the difference between polymer and metal deformation can create significant differences in the effect of process parameters, e.g., higher ∆z in polymer IF increases not just formability but throughput as well; (B) greater toughness of the formed polymer is a positive aspect of polymer IF since thermoplastics are used mostly in applications requiring high toughness; (C) The future research focus should be on polymer DSIF due to its significant advantages over SPIF. Our ongoing efforts focus on predicting formability and part accuracy as a function of the process parameters in polymer DSIF. Our efforts will develop finite strain constitutive models, along with micromechanical void coalescence models and molecular dynamics models of void nucleation, to capture sheet deformation and damage in polymer DSIF. Additionally, a dedicated DSIF machine will be developed for detailed experimental characterization of polymer DSIF.
4. Model Calibration-based Design Methodologies for Structural Design of Supercritical CO2 Compact Heat Exchangers under Sustained Cyclic Temperature and Pressure Gradients
Our goal is to develop a design method for rapid structural assessment of diffusion-bonded Hybrid Compact Heat Exchangers (H-CHX), for use as secondary heat exchangers in coupling Sodium Fast Reactors (SFRs) with supercritical CO2 (sCO2) Brayton power cycles. The use of H-CHX in nuclear power production can significantly reduce cost and increase efficiency, thus enabling a broader societal benefit by advancing carbon-free energy and energy diversification. However, a critical technological issue is the lack of a technical basis for a H-CHX specific ASME code case. Such a code case is needed to enable uniformity in design rule usage for structural design of H-CHX that are used in the above application. The deeper technical issue is the need for a method, based on recently developed EPP pressure vessel design techniques that accounts for the unique aspects of H-CHX while assessing cyclic creep induced failure under the elevated cyclic temperature and pressure gradients that the H-CHX is subjected to.
We will develop and validate a computationally rapid Equivalent-Solid Cohesive-Zone (EQS-CZM) method, based on EPP analysis, to account for the effect of (a) multiple complex micrometer-sized features and flow pathways; (b) temperature and pressure gradients; and (c) joints at the corners of the flow channels, on the stress-strain response of the H-CHX. Computational efforts will be complemented with experimental diffusion-bonding and thermal-pressure testing of test H-CHX articles. (2) Conventional limit load interaction diagrams (2D Bree diagrams) for cyclic loading, built using conventional EPP-FEA, account for cyclic thermal and pressure loads but not for the significant spatial temperature gradients that can occur along the length of the flow channel. This can result in unconservative designs. We propose Bree surfaces, which extend 2D Bree diagrams by including another axis to represent flow channel length. We will develop methods for (a) efficient construction of the Bree surfaces, by leveraging the EQS-CZM method and existing EPP techniques; (b) exploration of Bree surfaces to enable design of feasible structural design pathways for the H-CHX.
The project deliverables will be method-specific procedures and mathematical formulations necessary for the design engineer to (1) use EQS-CZM method for estimation of compliance with EPP method imposed strain limits for creep induced failure; (2) construct and use the proposed Bree surfaces to arrive at feasible structural design pathways that consider cyclic creep-induced failure. The outcome of this project will be the creation and validation of methods which form a technical basis for the development of an ASME code case for H-CHX, or other compact heat exchangers, that are exposed to elevated cyclic temperature and pressure gradients during their operation.
5. High-flux Microchannel Receiver Development
The objective of the proposed research is to develop a Microchannel Solar Receiver (MSR), culminating in an on-sun test of a commercial scale receiver module with a surface area of approximately 1 square meter. The MSR can be used with a range of heat transfer fluids such as molten salts and liquid metals in which incident fluxes up to 400 W/cm2, and receiver efficiencies of around 95% can be expected. However, this project is focused on the development of a receiver for heating sCO2 from 550°C to 720°C with an incident flux of at least 100 W/cm2 and receiver efficiency of 90%. As part of the project we will use simulation and experimental investigations to demonstrate that the MSR will have a lifetime of 10,000 cycles and can meet the receiver cost goals of $150/kWt. The goals of this task are to: 1) develop a computational model to predict joint failure in the MSR under cyclic temperatures and mechanical loads experienced during operation; and 2) combine that information with thermal fluid flow models to design the geometry of the MSR. The failure behavior of the joint will be predicted in Finite Element Analysis (FEA) using a cohesive zone model approach. The calibrated and validated joint behavior model will be integrated into a 3D representative model of the MSR that will model how the frequency and magnitude of 3D mechanical and thermal loading affects the bond strength. These models will be used for virtual testing to support design of geometric parameters for sub-scale and full-scale MSRs. The outputs of this task will be: 1) a validated FEA model to predict joint failure as a function of frequency and magnitude of thermo-mechanical loading; 2) integration of the joint failure model with 3D thermo-mechanical FEA models of a representative geometry of the MSR; and 3) geometric design of the microchannel receiver in support of sub-scale and full-scale MSR designs.
6. Environmentally conscious dyeing of fabrics using continuous digital printing and drying of Biopigment inks
Textile dyeing and printing causes about 20% of the global industrial water pollution via the use of toxic dyes and mordants, wastes about 6 trillion liters of water as untreatable effluent and uses 390 Billion KWh of thermal energy annually. The challenge facing this industry is to concurrently: (1) replace toxic dyes and mordants with nontoxic alternatives; (2) reduce water and thermal energy consumption; and (3) retain similar or higher throughput as compared to conventional dyeing/printing. Recent techniques like supercritical CO2 dyeing can reduce water and mordant usage. However, they are thermally intensive, need large capital investments ($ 3-4 Million) and still use toxic dyes.
Our goal is to develop and commercialize a fabric dyeing/printing process that solves the above challenge. We propose the use of colored biopigments, extracted from fungi, as coloring agents in a novel high-throughput and flexible process for fabric dyeing/printing. Key innovations in this project are: (1) Low-cost, scalable and energy-efficient extraction of biopigments of a varied color palette from fungi grown in batch reactors; (2) Synthesis of biopigment inks that are compatible with inkjet printing, using benign non-aquatic solvents; (3) Creation of a dyeing/printing system that integrates Roll-to-Roll fabric motion, inkjet-printing of the biopigment inks, and optically-induced flash-lamp drying of the printed biopigment inks.
The envisioned outcomes of this project on textile dyeing/printing will be (1) 100% reduction in toxic mordants and dyes; (2) Reduced cost of fabric coloring agents due to lesser energy/raw materials used and renewable nature of biopigment extraction; (3) Reduced water wastage due to use of non-aquatic solvents and on-demand digital inkjet printing of biopigment inks; (4) reduction in the thermal energy used for drying; (5) equipment cost of ≈ $260K, throughput of ≈ 300 yards/min, low cost for customized printed fabrics, and similar fabric quality as current dyeing/printing processes. To realize the proposed process we will combine our expertise in fungal biopigments, inkjet printing, flash-lamp drying and textile characterization. We envision that the proposed technology can be commercialized with 3-4 years of the start of the project. Towards this goal we will engage our industry partners Xerox and Nike to inform the technical and commercialization aspects of this project at every stage of the project. If successful, this project will create a disruptive cost-competitive incentive to bring the textile dyeing/printing industry back to the U.S.