Ink Dispersion Research Articles

Development of Efficient Ink Dispersion Process for Solid-State Electrolyte and Electrode Manufacturing

All-solid-state lithium batteries (ASSBs) have several advantages over lithium-ion batteries (LIBs) such as higher safety thresholds associated with solid electrolytes (SEs) and the possibility of using lithium metal or silicon anodes to achieve comparatively higher energy and power density. The SE can also prevent chemical interactions with dissolved active materials, and thus solve the issue of long-term instability of LIBs. However, there are also challenges associated with ASSBs manufacturing, such as local stress and contact-loss between SE and active materials in cathodes due to active material “breath”, poor contact and high ionic resistance at the SE-cathode interface, difficulty in fabricating thin SEs, and the absence of scalable and cost-effective manufacturing processes (J. Janek and W.G. Zeier, Nature Energy 8 (2023): 230-240). A key to tackling these issues begins with ink formulation for electrolyte and cathode coating, including ink compositions and rheological properties.In this study, we report the influence of ink preparation methods and conditions on the solid-state electrolyte and cathode coating qualities, where lithium lanthanum zirconium oxide (LLZO) and lithium nickel manganese cobalt oxide (NMC) are used as model systems. Various mixing methods, such as acoustic wave mixing, high-speed off-axis mixing, and thin film mixing, are compared. Their influence on ink viscosity and particle dispersion, coating thickness and microstructure uniformity, and electrolyte and electrode electrochemical properties will be discussed.

Enhancing proton exchange membrane water electrolysis performance: Impact of iridium oxide catalyst ink dispersing methodology

Iridium oxide (IrO2) is the most successful catalyst for triggering oxygen revolution reactions in proton exchange membrane water electrolyzers (PEMWE). However, conventional ultrasonic methods for ink dispersion often result in ink instability, catalyst aggregation, and sedimentation. To address these issues, we investigate the effects of the dispersion type, treatment time, and ionomer-addition sequence on the catalytic performance. Ball-milling procedure prepares a more stable catalyst ink and achieves a larger electrochemical surface area (ECSA) than ultrasonic method. Extending the ball-milling time to 12 h improves the ink stability (absorbance change rate ∼0.6 % h−1); however, over-processing causes the thickest catalyst layer, leading to an enhanced mass transport resistance. Moreover, treating an ionomer with IrO2 causes the substitution of sulfonic acid groups by carboxylic acid groups and reduces the repulsive force in colloidal particles, resulting in poor ink stability, low proton conductivity, and small ECSA. Therefore, adding ionomer after ball milling is recommended for the preparation of a stable ink with high catalytic performance. The membrane electrode assembly prepared using this procedure exhibits an improved performance of 1.70 A cm−2 at 1.7 V, compared with that prepared using ultrasonic methods. This work provides crucial guidance of ink preparation for large-scale production of PEMWEs.

Synthesis of Amphiphilic Block Copolymer and Its Application in Pigment-Based Ink.

Amphiphilic block copolymers-based aqueous color inks show great potential in the field of visual communication design. However, the conventional step-by-step chemistry employed to synthesize the amphiphilic block copolymers is intricate, with low yield and high economic and environmental costs. In this work, we present a novel method for preparing an amphiphilic AB di-block copolymer of PCL-b-PAA by employing a combined polymerization strategy that involves both cationic ring-opening polymerization (ROP) of the ε-caprolactone monomer and the reversible addition-fragmentation chain-transfer (RAFT) polymerization on the acrylic acid monomer simultaneously. The corresponding polycaprolactone (PCL) and polyacrylic acid (PAA) serve as the hydrophobic and hydrophilic units, respectively. The effectiveness of the amphiphilic AB di-block copolymer as the polymeric pigment dispersant for water-based color inks is evaluated. The amphiphilic AB di-block copolymer of PCL-b-PAA exhibits a molecular weight of 1400 g mol-1, which is consistent with the theoretical value and suitable for polymeric dispersant application. The high surface excess (Γmax) of the PCL-b-PAA in water indicates a densely packed molecular morphology at the water/air interface. Additionally, micelles can be stably formed in the aqueous PCL-b-PAA solution at very low concentrations by demonstrating a low CMC value of 10-4 wt% and a micelle dimension of approximately 30 nm. The model ink dispersion is prepared using organic dyes (Disperse Yellow 232) and the amphiphilic block copolymer of PCL-b-PAA. The dispersion demonstrates near-Newtonian behavior, which is highly favorable for the application as inkjet ink. Furthermore, the ink dispersion displays a low viscosity, making it particularly suitable for visual communication design and printing purposes. Moreover, the ink dispersion demonstrates an unimodal distribution of the particle size, with an average diameter of approximately 500 nm. It retains exceptional stability of dispersion and even conducts a thermal aging treatment at 60 °C for 5 days. This work presents a facile and efficient synthetic strategy and molecular design of AB di-block copolymer-based dispersants for dye dispersions.

Dual-Functional Electrochromic Smart Window Using WO3·H2O-rGO Nanocomposite Ink Spray-Coated on a Low-Cost Hybrid Electrode.

Electrochromic windows have gained growing interest for their ability to change their optical state in the visible and NIR ranges with minimal input power, making them energy-efficient. However, material processing costs, fabrication complexity, and poor electrochromic properties can be barriers to the widespread adoption of this technology. To address these issues, electrochromic material and fabrication processes are designed to realize their potential as a cost-effective and energy-efficient technology. In this work, an electrochromic composite material-based ink is synthesized consisting of WO3·H2O nanoplates supported on rGO (reduced graphene oxide) nanosheets (WH-rGO), wherein an optimized amount of rGO (0.05 to 0.5 wt %) is introduced for providing a higher conduction pathway for efficient charge transport without sacrificing the electrochromic performance of WO3·H2O nanoplates. The stable ink dispersion prepared in the study is deposited by spray coating on transparent conducting electrodes over large areas (25 cm2). The WH-rGO nanocomposite (0.4 wt %) results in 43% optical modulation at 700 nm, with bleaching and coloration times of 6 and 8 s, respectively. Interestingly, the device also possesses an electrochemical energy storage capability with an areal capacitance of 16.3 mF/cm2. The electrochromic composite material is successfully translated on tin doped indium oxide (ITO)-coated Al metal mesh hybrid electrodes (T = 80%, Rs = 40 Ω/□) to replace ITO. Finally, an electrochromic device of 5 × 5 cm2 is fabricated by spray-coating the ink on cost-effective ITO/Al-mesh hybrid electrodes. The device displays blue to colorless modulation with an excellent bleaching time of 0.43 s and a coloration time of 2.16 s, making it one among the fast-operating devices fabricated by complete solution processing. This work showcases the economical production of a dual-function electrochromic device, which can be a feasible option as an alternative to existing ITO-based devices in both automotive and infrastructure applications.

Preparation of PtAg/C catalysts for the oxygen reduction in PEM fuel cells: comparison of ultrasonical and mechanical methods as the catalyst ink dispersion technique

Preparation of PtAg/C catalysts for the oxygen reduction in PEM fuel cells: comparison of ultrasonical and mechanical methods as the catalyst ink dispersion technique

Characterization and performance of silicone modified Polylactic acid (PLA)-graphene nanoplatelet ink coatings for flexible elastomeric substrates

A polylactic acid (PLA)-graphene nanoplatelets (GnPs) based ink dispersion in an eco-friendly solvent (ethyl acetate/benzyl alcohol) was developed to prepare conductive coatings for porous and non-porous elastomeric surfaces. The ink dispersion remained highly stable over time and to induce conformability to the elastomeric substrates, the dispersion formulations were modified with glycerol triacetate and silicone (PDMS) for plasticisation and ductility. The ink was spray coated on nitrile rubber (non-porous) and a commercial stretchable fabric (porous). To help adhesion, the nitrile rubber surface was pre-treated with acetic acid and the fabric surface was coated with a thin polychloroprene primer adhesive layer. Coating conductivity was tested under several stretch-release cycles at 25 %. The coatings functioned and remained conductive during and after 150 cycles. Gradually, the coatings electrical resistance doubled over the cycles, but decreased to almost initial levels and stabilized before the full 150 cycles were completed. The mechanical behaviour of the uncoated and coated substrates was described by the Mullins effect (stress softening in rubbers). Upon termination of the cyclic stretch-release tests, the coating resistance recovered to its original value. This is attributed to the mechanical energy dissipated through the cycles within the coatings that triggered microstructural rearrangements establishing original physical connections among GnPs.

Predicting Fuel Cell Ink Aggregation

Polymer-electrolyte fuel cells (PEFCs) provide multisector decarbonization solutions including in transportation, manufacturing, and long-term energy storage. They have become increasingly popular in these areas due to their high efficiency, power density, and low (or zero) emissions compared to traditional fossil-fuel dependent processes. The PEFC catalyst layer is the most complex and key part of the cell, and is critical for optimizing PEFC performance. Several studies have explored the structure/function relationships of PEFC catalyst layers, yet the physics and interactions controlling its in-situ formation remain a mystery. PEFC catalyst layers are traditionally fabricated out of a catalyst supported on a carbon nanoparticle with an ionomer, traditionally perfluorosulfonic acids (PFSAs) such as Nafion, as a binder, which stabilizes the carbon suspensions in the ink dispersion. Recent studies demonstrated the importance of pH as an experimental parameter for both comparison and characterization of such systems.1 In this talk, we explore the interactions in the colloidal inks through detailed mathematical modeling. We propose a kinetics-based model representing species aggregation with pointwise interacting spheres that vary in charge through buried side chains for predicting the aggregation behavior of Nafion and carbon in solutions under varying conditions, such as solvent, Nafion wt% and carbon wt%. To demonstrate the accuracy and robustness of the model, we compare the results against a range of pH conditions and size distributions. The insights from the model help establish design criteria and guide future ink and process conditions.AcknowledgementsThis study was conducted under the Million Miles Fuel Cell Truck Consortium (M2FCT) funded by the Hydrogen and Fuel Cell Technologies Office in the Energy Efficiency and Renewable Energy Office of the U.S. Department of Energy under contract DE-AC02-05CH11231.References S. A. Berlinger, B. D. McCloskey, and A. Z. Weber, J. Phys. Chem. B, 122, 7790–7796 (2018).

Microstructure Characterization of Catalysis Layers during Ink Drying Process for Polymer Electrolyte Membrane Fuel Cells

A catalyst ink for proton exchange membrane fuel cells (PEMFCs) is generally prepared by various mixing methods by dispersing platinum or platinum alloy nanoparticles supported on carbon blacks with ionomers in a specific solvent or solvent combination. The catalyst ink is deposited on the surface of the membrane or diffusion media and is typically subjected to elevated temperatures to facilitate rapid removal of solvent. Large carbon agglomerates resulting from sub-optimal ink dispersion and drying conditions can limit catalyst utilization, inhibit mass transport in the catalyst layer, and damage the membrane and possibly also the gas diffusion media [1, 2]. Micro-structural evolution of the catalyst ink can be controlled by interactions of the ionomer in the catalyst-ionomer ink and by the effect of ink solvent composition on those interactions during the ink drying process. This presentation will describe the results of in-situ/ex-situ X-ray scattering studies of the evolution of the cathode catalyst layer during the ink drying process to determine the impact of solvent removal rates and solvent identity on the structural evolution of the cathode catalyst layer. These studies also included operando ink drying at room temperature, under an atmosphere containing the solvent, and a high temperature. Ultra-small angle X-ray scattering (USAXS) was used to measure the agglomerate size distribution during the ink drying. A small environmental chamber was used to examine drying phenomena of high solid-content inks and dispersions to determine structural evolution during ink drying. The effects of ionomer concentration, catalyst concentration, and solvent composition on the microstructure of the catalyst inks and electrode are correlated with the MEA performance and operando diagnostic data. The goal of these studies is to guide the MEA fabrication process to optimize MEA performance and durability.

Dual‐Mode Switching E‐Paper by Negative Electrorheological Fluid with Reversible Silica Networks

AbstractHuman–machine interaction will be revolutionarily different in the future Internet of Things (IoT) environments. Many displays will be adopted onto electronic devices to enhance human–device communication, even under a very bright sunlight ambience. Thus, power consumption and sunlight visibility are important attributes for this application. Electrophoretic displays (EPDs) have the inherent advantages of ultra‐low power consumption and high sunlight visibility, which are perfectly suitable for IoT applications. The low power consumption resulted from the balance of viscosity, gravity, and other complicated forces involved in the electrophoretic dispersion. This force balance is generally termed “bistability,” meaning the particle‐packing can be stable without external power at black and white image states. However, good bistability implies a slow image updating rate, significantly degrades users’ experience. In this work, a 3D network structure that undergoes disruption and reorganization with the particles’ movement is utilized in the electrophoretic ink dispersion. Dynamic viscosity modulation enables the bistable and fast‐response dual‐working modes. The newly developed design can increase the response speed of EPDs by a factor of 2.38, simultaneously maintaining the bistability. The electronic ink with this reversible network provides a promising solution for the future video‐rate e‐paper displays.

Crack evolution during the film drying process of fuel cell microporous layer ink

Study on the film crack formation process of microporous layer (MPL) in fuel cells is necessary as the size of cracks substantially affects fuel cell durability. In-situ characterization of crack evolution in the full MPL ink drying process is essential to understand the crack formation mechanism. In this work, quasi in-situ crack evolution in the full MPL ink drying process under different stages is comprehensively investigated using ESEM, PLM, and regular SEM. A crack formation with subsequent crack healing mechanisms is discovered. Physiochemical characterizations indicated that the crack formation process is related to the evaporation of isopropanol, whereas the crack healing process is related to the subsequent evaporation of water. Experiments on solvent composition further indicate that the final crack size depends on the ink dispersion during the drying process. Furthermore, the optimal 1/2 IPA/water weight ratio formulation is proposed for the resulting MPL with fewer cracks.

Slot die coating window for a uniform fuel cell ink dispersion

AbstractThe continuous roll‐to‐roll slot die coating technique has shown great potential for fuel cell electrode fabrication. It is essential to determine the particulate coating window to obtain a defect‐free film of uniform thickness and uniform particle dispersion. For this dual‐purpose, an additional upper operating limit has been proposed via a “flow field analysis scheme” that combines analysis and simulation. In this analysis, the fundamentals of flow pattern transition (Poiseuille–Couette–bubbly flow) behind coating limits are clarified. The Couette flow is advantageous for uniform shear rate and dispersion. Furthermore, phase‐field simulations systematically investigate the effect of fluid and geometrical parameters and quantitatively present the flow limit with explicit expression. Results reveal that the slope of the upper limit is inversely correlated with shear‐thinning index n while proportional to the coating gap H. Combining the bubble entrainment boundary, lower n and H are favorable for a larger particulate coating window.

Simple numerical simulation of catalyst inks dispersion in proton exchange membrane fuel cell by the lattice Boltzmann method

We used the lattice Boltzmann method (LBM) to simulate the dynamic behavior of catalyst particles during the ink dispersion process in a proton exchange membrane fuel cell. In the two-dimensional shear element, the single relaxation time lattice Boltzmann model, also called the lattice Bhatnagar–Gross–Krook model in the LBM, was used to simulate fluid flow, while the Lagrange model was used to simulate the motion of nanoparticles. The governing equation of particle motion includes fluid drag force, electrostatic repulsion, van der Waals force, ionomer force, and Brownian force. This model can be used to explore the effect of different shear strengths on the formation of agglomerates in inks. Our results showed that shear strength significantly influenced the formation and structure of agglomerates during the dispersion phase. Compared with a Reynolds number (Re) of 500 and 2000, a Re of 1000 achieved optimal dispersion and stability. When Re is 0, 500, 1000, and 2000, aggregate particles tend to form chain structure, packed structure, regular aggregate structure, and a large number of free particles and stacked particles, respectively.

Influence of the dispersion state of ionomer on the dispersion of catalyst ink and the construction of catalyst layer

The ionomer state in the catalyst ink of a proton exchange membrane fuel cell (PEMFC) plays a critical role in the formation of the catalyst/ionomer interface on the catalyst layer (CL). In this study, the effect of ionomer dispersion state on catalyst ink dispersion and the construction of a reasonable CL was investigated. The study of catalyst inks revealed that the dispersion of n-propanol (NPA) -ionomer dispersion or sonication could effectively reduce the catalyst particle size in inks. For shear-dispersion and homogenizer-dispersion inks, the catalyst particle size was reduced from 6.17 nm to 5.12 nm and from 5.12 nm to 4.67 nm, respectively. The ionomer dispersion was capable of significantly reducing the size of agglomerates in the ink, which resulted in a reduction in the particle size of agglomerates on the surface of the cathode CL and an improvement in its flatness. The pore size distributions of the MEA cathode catalyst layers showed that water bath ultrasonic treatment of the ionomer could result in a more reasonable pore structure for the catalyst layer. The single-cell test revealed that changing the ionomer's dispersion state could significantly increase the fuel cell's output voltage to 0.707 V at 1000 mA cm−2, and the cell's power density to 1028 mW cm−2 at 2000 mA cm−2.

Microstructure and macroscopic rheology of microporous layer nanoinks for PEM fuel cells

The microporous layer (MPL) is of significance to the PEM fuel cell performance and durability through water management. It is essential to gain insights into the MPL nanoink, a critical state determining the resulting MPL porous structure and function. In this work, a comprehensive investigation of ink microstructure and rheology with different PTFE loadings and solvent compositions has been conducted from a theoretical and practical level. Two different CB/PTFE interaction modes (i.e., covering and bridging) were revealed and the latter dominates with increasing PTFE loading. It was found a PTFE loading of 30% produces homogeneous ink dispersion and best stability. Besides, larger aggregates were found with increased IPA/water ratio using cryo-SEM. Furthermore, rheological measurements revealed that less shear-thinning indicates stable inks. Combining the ink preparation and slot-die coating processes, an optimal formulation of 30% PTFE loading and 1/2 IPA/water weight ratio was proposed for a uniform ink dispersion.

Evaluation of Inkjet-Printed Reduced and Functionalized Water-Dispersible Graphene Oxide and Graphene on Polymer Substrate-Application to Printed Temperature Sensors.

The present work reports on the detailed electro-thermal evaluation of a highly water dispersible, functionalized reduced graphene oxide (f-rGO) using inkjet printing technology. Aiming in the development of printed electronic devices, a flexible polyimide substrate was used for the structures’ formation. A direct comparison between the f-rGO ink dispersion and a commercial graphene inkjet ink is also presented. Extensive droplet formation analysis was performed in order to evaluate the repeatable and reliable jetting from an inkjet printer under study. Electrical characterization was conducted and the electrical characteristics were assessed under different temperatures, showing that the water dispersion of the f-rGO is an excellent candidate for application in printed thermal sensors and microheaters. It was observed that the proposed f-rGO ink presents a tenfold increased temperature coefficient of resistance compared to the commercial graphene ink (G). A successful direct interconnection implementation of both materials with commercial Ag-nanoparticle ink lines was also demonstrated, thus allowing the efficient electrical interfacing of the printed structures. The investigated ink can be complementary utilized for developing fully printed devices with various characteristics, all on flexible substrates with cost-effective, few-step processes.

Thickness/morphology of functional material patterned by topographical discontinuous dewetting

AbstractTopographical discontinuous dewetting (TDD) patterning is a nascent 2D printing technique explored for high‐throughput nanoscale patterning of functional material inks. However, variables affecting the z thickness and morphology of the deposited functional materials inside the patterned microchannels remain unexplored. We developed a theoretical model that can determine the thickness of the deposited functional material layers using the TDD patterning technique. We then confirmed the model with experimental data by depositing colloidal dispersions into microchannels using TDD patterning to systematically study the effects of different processing variables. The contribution of evaporation‐driven flow to the deposited layer thickness was significant, with the relationship of thickness to inking speed different to that previously determined for thin film blade coating of colloidal dispersions in the evaporative regime. Additionally, a viscosity dampening effect was observed, unique to TDD of microchannels, which slowed the evaporation‐driven flow due to local viscosity increase in the microchannels. Channel dimensions and ink dispersion concentration affected thickness as hypothesized. Internal flows in the microchannels normal to the sidewalls and perpendicular to the microchannel length (“coffee ring” effect capillary flow/Marangoni flow) were found to contribute significantly to the final morphology/thickness of the deposited layers for the systems/dispersions experimentally measured.

Inkjet printed patterns of polyamidoamine dendrimer functionalized magnetic nanostructures for future biosensing device application

Inkjet printing technology holds a great potential for fabrication of biosensor device. An optimized programmed printing makes the processing steps easier on a variety of substrates at low cost. The drop-on-demand piezoelectric mode of printing can construct a design pattern with low volume of material at specified position onto a suitable substrate. But to achieve this successfully, a formation of stable ink suspension remains the most challenging task. In recent times, nanoparticles are considered to pave a way for miniaturization of biosensing devices. Thus, we synthesized, characterized and investigated the stability of magnetic Fe3O4 nanoparticles stabilized by the polyamidoamine (PAMAM = N(CH2CH2C(O)NHCH2CH2NH2)(CH2CH2N(CH2CH2C(O)NHCH2CH2NH2)2)2) dendrimer (PAMAM@Fe3O4). A best stable ink dispersion of PAMAM@Fe3O4 nanoparticles was obtained in a solvent mixture of 70% ethylene glycol and 30% distilled water. The nanoparticle ink with surface tension of 57.47 mN/m and viscosity of 5.45 mPa/s formed a narrow and uniform printed pattern onto graphene paper. Further, as a model protein for future biosensing application, antibody against alpha-fetoprotein was conjugated onto the dendritic surface and printed onto graphene paper. The characterization of the printed pattern by TEM revealed spherical morphology, whereas SEM provided evidence of difference in printed line width and spacing of nanoparticles and antibody conjugated nanoparticles. As a proof-of-concept, the study demonstrated a printable ink dispersion based on PAMAM@Fe3O4 nanoparticles for future miniaturization of biosensing steps on a chip-based platform.

Self-Healable Inks Permitting 3D Printing of Diverse Systems towards Advanced Bicontinuous Supercapacitors

Targeting a string of pressing issues featuring limited choices of material systems applicable to 3D printing, harsh preparation conditions, and unsatisfactory charge storage originating from the notorious interfacial issue, a versatile strategy permitting 3D printing of multidimensional and multifarious functional materials with solid electrochemical performance is proposed. By harnessing the utility of a gelation process, rapid assembly of functional materials into a cellular network with desired rheological behaviors for consistent 3D printing at concentrations 8-20 times smaller than reported values can be realized, therefore considerably facilitating ink preparation and dispersion while preventing the aggregation of active materials. In addition, through developing bicontinuous pathways for express transportation of ionic/electronic species and instituting a self-healing mechanism to eliminate interfacial resistance, a printed electrode with outstanding loading density and areal capacitance up to 32.2 mg/cm2 and 2.9 F/cm2 could be readily realized, which translates to an excellent energy density of 0.18 mWh/cm2 for a symmetrical device. The obtainable performance metrics are orders of magnitude higher than those from conventional measures. The highlights in this work mark an important leap for 3D printing of electrochemical energy storage devices in light of the universality of this approach and the solution provided that resolves the critical and longstanding interfacial issue for additive manufacturing. The proposed measure holds a rosy future for the construction of truly meaningful high energy density devices catering for demanding applications in the next generation.

The Controllable Design of Catalyst Inks to Enhance PEMFC Performance: A Review

Typical catalyst inks in proton exchange membrane fuel cells (PEMFCs) are composed of a catalyst, its support, an ionomer and a solvent and are used with solution processing approaches to manufacture conventional catalyst layers (CLs). Because of this, catalyst ink formulation and deposition processes are closely related to CL structure and performance. However, catalyst inks with ideal rheology and optimized electrochemical performances remain lacking in the large-scale application of PEMFCs. To address this, this review will summarize current progress in the formulation, characterization, modeling and deposition of catalyst inks. In addition, this review will highlight recent advancements in catalyst ink materials and discuss corresponding complex interactions. This review will also present various catalyst ink dispersion methods with insights into their stability and introduce the application of small-angle scattering and cryogenic transmission electron microscopy (cryo-TEM) technologies in the characterization of catalyst ink microstructures. Finally, recent studies in the kinetic modeling and deposition of catalyst inks will be analyzed. The formulation and the deposition process of catalyst inks determine the formation of catalyst. The interaction between the components of the catalyst ink governs the microstructure and processability of the ink, thereby affecting the microstructure and performance of the CL.

Design, Synthesis, and Application of Colored Cobalt Pigments (Pink, Blue, Green)

The combination of white or colorless oxides (MgO, Al2O3, ZnO) with colorant ions (Co2+) generates colored pigments (pink, blue, green). The color is caused by the insertion of the colorant ion in the respective crystal lattices (periclase, alumina, wurtzite), as verified by X-ray diffraction. Absorption spectra in the visible region show analogous triplet behavior of the absorption bands for the doped alumina and wurtzite samples but a difference in tetrahedral distortion, which generates blue and green pigments. In contrast, cobalt-doped periclase has color-related parameters related to the pink color. Crystallite and particle sizes show nanometric dimensions in the range of 20-60 nm (magnesium), 20-180 nm (aluminum), and 40-220 nm (zinc). The color is related to the shape (crystalline phase), size, and presence of chromophore ions with absorption in the visible region. Colorimetric studies (CIE L*a*b*) show variations between colors as a function of the polysaccharide that is used (starch or pectin) as fuel. The color variation is subtle in some cases but is significantly noticeable in other cases. Commercial colorless ink dispersion (10% m/m) shows excellent compatibility with the maintenance of hues and a slight increase in color saturation (C*).