Evaluation of jet performance in drop-on-demand (DOD) inkjet printing

Inkjet printing has been widely used in many applications and has been studied for many years. However, there are not many systematic researches on the mechanism of jet formation, nor is there any reliable platform that enables us to evaluate jet performance. In this study, an approach to practically evaluate the jet stability of the dropon-demand (DOD) inkjet printing has been proposed, based on which the transient behavior of the DOD drop formation has been studied experimentally for Newtonian liquids with a range of different viscosities (1.0–11 cp) but of a comparable surface tension. For more viscous liquids, the rate of the jet retraction after a pinch-off from the nozzle was found to increase as the thread motion became more sharp and conical as a result of the shape effect. The break-up time of the jet also increased because the rate of capillary wave propagation was lower for more viscous liquids. The jet stability graph, which can be drawn in terms of jet retraction and break-up time, was employed to characterize the jetting stability, and the degree of satellite drop generation was quantitatively evaluated by two critical jet speeds. The effect of an electric pulse imposed on a piezoelectric plate inside the printhead was also studied. The single-peak electric pulse was used in this experiment for simple analysis, and the jet speed variation was measured under different operating conditions. Both the optimal dwell time and the maximum stable jetting frequency were affected by viscosity and they were explained in terms of the propagation theory.     

Development of method for estimating drop diameter in the manufacturing process of functional O/W microcapsules

A new method for preparing functional O/W microcapsules using a process involving O/W/O emulsion as particle formation was developed. Coenzyme Q10 (CoQ10) or reduced coenzyme Q10 (QH) was used as the core substance. QH oxidized fast when exposed to air. O/W microcapsules were manufactured by conventional liquid phase drying method (LPD). The purpose of this study is to develop a simple method of estimating drop diameter which is possible to evaluate immediately the mean drop diameter during the microencapsulation process without the usual photographic measurement. This developed estimation is possible to predict a Sauter mean diameter by measuring the amount of inner CoQ10 released from O/W emulsion droplet. The amount of inner oil phase released from O/W emulsion has correlation with increased total surface area of O/W emulsion droplet caused by breaking droplet. Released rate of CoQ10 from O/W emulsion droplet to outer continuous phase under different rotational speed and emulsion viscosity was measured with an absorption spectrometer. As a result of the changes of released inner CoQ10 amount, droplet breakage under low emulsion viscosity was promoted by agitation speed. It is concluded that droplet dispersion state during manufacturing of O/W microcapsules was evaluated well by applying the developed estimation method.     

Activity, stability and inhibition of a bioactive paper prepared by large-scale coating of laccase microcapsules

Enzyme immobilization on paper by large-scale processes may play a valuable role in the development of economical and widely distributed biosensors. In this study, we report on the coating of laccase from Trametes versicolor on papers using a laboratory coater (Cylindrical Laboratory Coater) that simulates realistic conditions similar to those obtained with industrial coaters. In order to achieve an efficient retention of laccase in the coating, the enzymes were incorporated in poly(ethyleneimine) microcapsules. The microcapsules were suspended in a starch-based coating suspension, applied on paper by blade coating at a rate of 500 and 800 m/min thereupon dried by evaporation using an IR lamp at 36 kW. A technique based on the colorimetric reaction between the laccase and its substrate, p-phenylenediamine (PPD), was developed to evaluate the activity of the immobilized enzyme. Our results show that the use of microencapsulation allows for better activity retention in papers over time at room temperature (50% loss after 28 days) compared to papers modified with free laccase (50% loss after 4 days). Microcapsules also decrease the inhibition of laccase by azide.     

Influence of process parameters on microcapsules loaded with n-hexadecane prepared by in situ polymerization

A series of melamine–formaldehyde microcapsules containing n-hexadecane were synthesized by in situ polymerization from partial etherified melamine–formaldehyde resins. This research was conducted to clarify the influence of different parameters on the encapsulation process, i.e. during the emulsion formation step and during the shell formation using surface tension measurement, Fourier-transform infrared spectroscopy and differential scanning calorimetry. By carefully analyzing the influencing factors including phase volume ratio, types of surfactants and content, stirring rate and time, pH, reaction time, feeding weight ratio of core/shell pre-polymer, the optimum synthetic conditions were found out. The results indicated that a binary mixture of Tween-20 and Brij-35 was found suitable emulsifier at low pH. Furthermore, formaldehyde/melamine (F/M) mole ratio influenced not only the shell formation mechanism but also the particle size distribution, microcapsule morphology and resin conversion rate.     

Application of flow-focusing to the break-up of an emulsion jet for the production of matrix-structured microparticles

Powder behaviour and performances are intimately related to particle attributes defined by the size, shape and structure of the individual particles making up the powder. The heterogeneous nature of the vast majority of powders reflected in the broad distribution of these particle attributes gives rise to the well-known difficulties in the prediction of powder behaviours. To achieve a better predictability and ultimate control of the performances, significant research efforts have recently been made towards the production of particles with controlled attributes, i.e. structured particles with a very narrow size distribution. This paper presents a new method for the production of monodisperse matrix-structured microcapsules using a simple in-house designed and fabricated macroscopic flow cell. The method combines flow-focusing with laminar jet break-up of a water-in-oil emulsion jet in a bulk water phase that produces monodisperse water-in-oil-in-water dispersion templates. The templates are then converted into solid microcapsules with a matrix structure by solvent evaporation. Results presented in the paper confirm a transition of flow regime from jetting to dripping when the outer to inner flow rate ratio reaches a critical value, accompanied by an increase in the size of the resultant droplets from the break-up. Importantly, the transition imposes a limit to the smallest size of monodisperse droplets each flow cell can produce through flow-focusing. The smallest monodisperse microcapsules produced from the flow cell used in this study through flow-focusing are in diameter.     

用于细颗粒分离的水力旋流器的压力特性研究

对用于细颗粒分离的水力旋流器的压力特性 (压力降及压降比 )与流量、分流比、旋数、溢流口和底流口直径及气液比等主要参数之间的关系进行了深入的研究与分析。研究发现 ,水力旋流器内部压力降分别随流量、分流比、旋数及气液比的提高而加大 ,压降比则分别随流量、分流比、旋数的提高而降低。随着溢流口直径的加大 ,水力旋流器的溢流压力降减小 ,而压降比也随之降低 ;随着底流口直径的加大 ,底流压力降减小 ,压降比随之升高。分析可知 ,减少旋流器能耗的有效方法是降低旋数 ,或者减少混合介质中的气液比     

Polystyrene Suspension Polymerization: The Effect of Polymerization Parameters on Particle Size and Distribution

Effects of polymerization parameters are studied to better understand interactions between parameters in stirred-tank polymerization reactors and to derive a regression model correlating polymer particle size and particle-size distribution with agitator speed, agitator diameter, tricalcium phosphate, dodecyl benzene sodium sulfonate concentrations, and mass cycle period. The derived equations give way to prediction of the polymerization conditions in order to obtain desired particle size and particle-size distributions which covers particle sizes between 0.3 and 5 mm. The roles of some other parameters and limiting agitation parameters are also investigated.     

偏氯乙烯—丙烯酸甲酯悬浮共聚树脂颗粒特性的研究

在5升釜中进行偏氯乙烯—丙烯酸甲酯悬浮共聚.研究了分散剂浓度、搅拌转速、聚合温度以及水油比等因素对树脂颗粒特性(平均粒径及分布、表观密度)的影响.     

Synthesis of NiO-YSZ composite particles for an electrode of solid oxide fuel cells by spray pyrolysis

NiO-YSZ (YSZ: Y₂O₃-stabilized ZrO₂) composite particles for a Ni-YSZ cermet anode in solid oxide fuel cells (SOFCs) were synthesized via spray pyrolysis (SP). The formation mechanism of the composite particles by this process was analyzed. The internal microstructure of the particles synthesized during SP processing was observed at each heating temperature of 200, 300, 400 and 1000 °C, and then the formation mechanism of the composite structure was discussed. As a result, it was found that NiO-YSZ composite particles were formed through the following steps. Firstly, during the evaporation stage up to 200 °C, a filled particle with Ni(CH₃COO)₂ and YSZ fine grains were formed from the atomized droplet containing Ni ion and dispersed YSZ sol by volume precipitation. Secondly, during the continuous thermolysis stage up to 400 °C, YSZ grains were formed and moved to the surface of the composite particle by the outgas and the oxidation of Ni(CH₃COO)₂. Finally, the NiO-YSZ composite particle that has NiO grains uniformly covered with fine YSZ grains was formed after the final sintering stage up to 1000 °C.     

Effect of compatibilization on the deformation and breakup of drops in step-wise increasing shear flow

Drop deformation and breakup were investigated in the presence of a block copolymer in step-wise simple shear flow using a home-made Couette cell connected to an Anton Paar MCR500 rheometer. Polyisobutylene (PIB) was used as the matrix, while five different molecular weights of polydimethylsiloxane (PDMS) were selected to provide drops with a relatively wide range of viscosity ratio. A block copolymer made of PDMS-PIB was used for interfacial modification of the drop-matrix system. The copolymer concentration was 2 wt% based on the drop phase. The experiments consisted in analyzing the drop shape and measuring the variation of the length to diameter ratio, L/D, both in steady state and in transient regimes till breakup. This allowed revising of the classical Grace curve that reports the variation of the critical capillary number for breakup as a function of viscosity ratio and providing also a new one for blends compatibilized with an interfacial active agent with a given molecular weight.     

Effect of precursor composition on the activation of pitchbased carbon fibers

Pure and silver-containing carbon fibers were prepared from isotropic pitch precursors supplied by Conoco, Inc., and a Korean research team and activated in carbon dioxide to varying degrees of burn-off. The specific activation rates for the carbon fibers were measured as well as the nitrogen adsorption characteristics of the activated carbon fibers. Scanning electron microscopy was used to investigate the surface morphology and the behavior of silver particles during the activation process. Molecular composition of the two pitch precursors was determined using a gas chromatograph mass spectrometer and a MALDI TOF mass spectrometer. Results showed that specific surface area increased with the burn-off, and the trends were similar for the pure and silver-containing fibers formed from both isotropic pitch precursors. However, the catalytic behavior of silver during activation, the activation rate, and even the pore characteristics of the activated fiber were found to be dependent on the molecular composition of the precursor pitch.     

Coating and Drying in Spouted Bed: Influence of the Liquid-Particle Work of Adhesion

The aim of this work is to analyze the resulting process: coating or drying, and the respective fluid dynamic behavior, by bottom-spraying polymeric suspensions on a spouted bed of inert particles. Glass beads, ABS®, polypropylene (PP), and polystyrene (PS) were chosen as inert particles and were analyzed and characterized by their physicochemical properties. The polymeric suspensions were characterized by density, surface tension, rheology, and wettability. The fluid dynamic behavior of the bed was correlated with the particles and suspensions characteristics for each process: coating and drying. Each process performance was correlated with the polymeric suspension-particle work of adhesion.     

Coating and Drying in Spouted Bed: Influence of the Liquid-Particle Work of Adhesion

The aim of this work is to analyze the resulting process: coating or drying, and the respective fluid dynamic behavior, by bottom-spraying polymeric suspensions on a spouted bed of inert particles. Glass beads, ABS®, polypropylene (PP), and polystyrene (PS) were chosen as inert particles and were analyzed and characterized by their physicochemical properties. The polymeric suspensions were characterized by density, surface tension, rheology, and wettability. The fluid dynamic behavior of the bed was correlated with the particles and suspensions characteristics for each process: coating and drying. Each process performance was correlated with the polymeric suspension-particle work of adhesion.     

Application of ultrasound spectroscopy for nanoparticle sizing in high concentration suspensions: A factor analysis on the effects of concentration and frequency

Ultrasound is an attractive technique for nanoparticle sizing as it offers non-invasive, suitable for highly turbid and concentrated samples, and potentially no sample dilution needed features. This paper presents a factor analysis method for the determination of the concentration range and frequency domain for the use of ultrasound techniques for particle sizing when ECAH (Epstein, Carhart, Allegra and Hawley) model is applied. The advantage of using this method is by dealing with experimental data, some practically useful information, which the current theory cannot be employed to produce, may be identified, for instance, the critical volume concentration of particles below which sound attenuation is linearly dependent on particle concentration and the frequency domain in which frequencies have higher contribution to the attenuation than those outside the domain.To use this method, each data matrix is constructed by ultrasound attenuation data with frequency as variables and concentration as observations. Attenuation data are obtained with the measurements of ultrasound spectroscopy of oil/water emulsions and solid/water suspensions at different concentrations.As a result of the factor analysis, for emulsions up to 40%vol concentration, the linear dependence of attenuation on concentration and a same level contribution of frequency ranging from 1 to 120 MHz are found. However, for solid suspensions, attenuation appears to be nonlinearly related to solid concentration and the critical concentration value at which attenuation is turning into nonlinear from a linear trend can also be calculated. It is also found that in solid suspensions, frequencies less than 10 MHz have less contribution to attenuation than that of higher than 10 MHz. Therefore, for ultrasound particle sizing using ECAH model, before the inversion of attenuation to particle size distribution takes place, using this method the range of concentration and frequency to which the use of ECAH model is valid can be determined.     

Effect of Selected Additives on Microencapsulation of Anthocyanin by Spray Drying

Microencapsulation of anthocyanin pigment present in Garcinia indica Choisy was carried out with maltodextrin of various dextrose equivalents (DE 06, 19, 21, and 33) and other additives such as gum acacia and tricalcium phosphate to enhance the stability of the pigment. The microencapsulated pigment containing 5.0% maltodextrin DE 21, 0.25% gum acacia, and 0.25% tricalcium phosphate was found to have lowest hygroscopic moisture content (4.38%), highest antioxidant activity (69.90%), and highest anthocyanin content (485 mg/100 g). The glass transition temperature was 44.59°C. The sorption isotherms for microencapsulated powder showed that the samples were stable up to water activity less than 0.43. The scanning electron microscope structures depicted that the particle size ranged from 5 to 50 μm with smooth spheres. Storage at 4°C increased the half-life twofold compared to that of the spray-dried product kept at ambient temperature (25°C).     

Visualization of compound drops formation in multiphase processes for the identification of factors influencing bubble and water droplet inclusions in oil drops

An innovative methodology for visualizing and identifying some mechanisms by which complex structures such as air-in-oil-in-water (A/O/W) and water-in-oil-in-water (W/O/W) may be formed inside mixing tanks dispersing various phases is described. In the case of A/O/W inclusions, isolated inclusion events could be observed by the first time with an experimental setup designed to produce sudden turbulence in a small confined space simulating a three-phase fermentation system. It was observed that high-energy direct-collisions of the bodies are not required for inclusions to occur; rather, a gentle contact between the phases was needed. Then, by maintaining an oil drop in a fixed position while it was impacted by single air bubble, it was feasible to calculate the percentage of air-bubble inclusions into oil drops for different compositions of the continuous phase. By adding biomass as a solid phase, the inclusion occurrence reached 61%; likely this was caused by a mechanical effect of the added biomass (making the interface breakable or unstable) with a minor contribution by the decreased surface tension. In the case of W/O/W, a basic mechanism by which the inclusion of water droplets in oil drops may occur is described. This was derived from the analysis of the hydrodynamic process of the formation of a water drop inside a volume of oil where the differential pressures occurring along the water–oil interface were mapped. This is the first time that factors influencing water and air inclusions in oil drops are identified, and possible mechanisms behind their occurrence are proposed, based on visual evidence.     

Effect of nozzle geometry and processing parameters on the formation of nanoparticles using FSP

Two numerical models were developed to simulate the sauter mean diameter (SMD) of the droplets during atomization and the growth of particles inside the flame by coagulation and sintering. These models were linked to CFD to simulate flame spray pyrolysis (FSP) process. The effects of reactor geometries and processing parameters on the temperature and velocity profiles, droplet evaporation and particle growth were predicted using the validated computation models. The results show that increasing the oxidant gap size (from 0.1 mm to 0.5 mm) by keeping the dispersion gas pressure drop constant at 1 bar (transonic regime ∼310–315 m/s) across the nozzle tip increased the gas to liquid mass ratio (GLMR) by a factor of 6. This reduced the flame height and lowered the residence time of the particles in the high temperature zone of the flame, thus, decreased the sintering rate and the growth of nanoparticles. The results also showed that decreasing the oxygen content of the dispersion gas helped to decrease the peak temperature of the flame and reduced the particle size. The simulation results can be used for the FSP equipment design and process optimization.     

Nickel molybdate as precursor of HDS catalysts: Effect of phase composition

Sulfided and -NiMoO₄ have been employed as model HDS catalysts, aiming to investigate the effect of phase composition of the precursor mixed oxide on the physicochemical characteristics and activity of the sulfides. Both sulfides are highly amorphous or microcrystalline, and could not be differentiated by means of XRD. The differences in BET area were also found to be minimal. However, it was found by means of TPR that the stable -isomorph is reduced at lower temperatures than the unstable -phase in both the oxidic and sulfided states. Sulfided -NiMoO₄ was found to be a better catalyst for the HDS of thiophene than the sulfided -isomorph. This could be related to the higher stability of the former in H₂, as decomposition of the active, amorphous Ni-Mo-S structures results in less active and more crystalline phases, as found by XRD.