Printing technologies have been demonstrated to be highly efficient and compatible with polymeric materials (both inks and substrates) enabling a new generation of flexible electronics applications. Conductive flexible polymers are a new class of materials that are prepared for a wide range of applications, such as photovoltaic solar cells, transistors molecular devices, and sensors and actuators. There are many possible printing techniques. This chapter provides an opportunity to review the most common printing techniques used at the industrial level, the most commonly used substrates and electronic materials, giving an overall vision for a better understanding and evaluation of their different features. Several technological solutions (contact/noncontact) and its critical challenges are also presented. Inkjet Printing Technology (IPT) has been receiving a great attention and therefore higher focus is given to this technology. An overview of IPT is presented to evidence its importance and potential as a key-technology on the research field for printed electronics development, as well as on large scale industrial manufacturing. A background and a review on prior work are presented along with used materials, developed applications and potential of IPT technology. The main features of the different printing technologies, advantages and main challenges are also compared.

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Filaments in a planar chemical garden grow following tortuous, erratic paths. We show from statistical mechanics that this scaling results from a self-organized dispersion mechanism. Effective diffusivities as high as...

A deep knowledge of the hydrodynamics of two-phase flow in millichannels and microchannels is relevant to the design and control of micro structured equipment. While there is plenty of work published in this area, there is a lack of studies over a wide range of dimensionless numbers and some factors have not been properly addressed, such as the role of the Reynolds number, the features of recirculation regions in the liquid slug and the liquid film development length. Therefore, a wide range parametric study of isolated gas Taylor bubbles flowing in co-current with liquid in circular milli- and microchannels is presented, in a wide range of Capillary (CaB) (0.01–2) and Reynolds numbers (ReB) (0.01–700). The shape and velocity of the bubbles are, together with the flow patterns in the flowing liquid, analyzed and compared with numerical and experimental correlations available in the literature. For low values of CaB, the streamlines (moving reference frame (MRF)) in the liquid slug show semi-infinite recirculations occupying a large portion of the cross-section of the channel. The mean velocity of the fluid moving inside the external envelope of the semi-infinite streamlines is equal to the bubble velocity. For high values of CaB, there are no recirculations and the bubble is moving faster or at least at the velocity of the liquid in the center of the tube; this flow pattern is often called bypass flow. The results also indicate that the liquid film surrounding the bubbles is for low CaB and ReB numbers almost stagnant, and its thickness accurately estimated with existing correlations. The stagnant film hypothesis developed provides an accurate approach to estimate the velocity of the bubble, in particular for low values of CaB. The asymptotic behavior of the studied parameters enables the extrapolation of data for CaB lower than 0.01. In addition to the simulations of isolated bubbles, simulations with two consecutive bubbles were also carried out; coalescence was only observed in very specific conditions. The results obtained in this study are directly applicable to co-current slug flow in milli- and microchannels for 0.1 < ReB < 1000 and 0.02 < CaB < 2.

Slug flow is a multiphase flow pattern characterized by the occurrence of long gas bubbles (Taylor bubbles) separated by liquid slugs. This multiphase flow regime is present in many and diversified natural and industrial processes, at macro and microscales, such as in eruption of volcanic magmas, oil recovery from pre-salt regions, micro heat exchangers, and small-sized refrigerating systems. Previous studies in the literature have been mostly focused on tubular gas bubbles flowing in Newtonian liquids. In this work, results from several numerical simulations of tubular gas bubbles flowing in a shear thinning liquid in microchannels are reported. To simulate the shear thinning behavior, carboxymethylcellulose (CMC) solutions with different concentrations were considered. The results are compared with data from bubbles flowing in Newtonian liquids in identical geometric and dynamic conditions. The numerical work was carried out in computational fluid dynamics (CFD) package Ansys Fluent (release 16.2.0) employing the volume of fluid (VOF) methodology to track the volume fraction of each phase and the continuum surface force (CSF) model to insert the surface tension effects. The flow patterns, the viscosity distribution in the liquid, the liquid film thickness between the bubble and the wall, and the bubbles shape are analyzed for a wide range of shear rates. In general, the flow patterns are similar to those in Newtonian liquids, but in the film, where a high viscosity region is observed, the thickness is smaller. Bubble velocities are smaller for the non-Newtonian cases.