/pdf/new-approaches-to-nanofabrication-molding-printing-and-other-9d730ga5zp.pdf

New approaches to nanofabrication: molding, printing, and other techniques.

Inkjet printing is viewed as a versatile manufacturing tool for applications in materials fabrication in addition to its traditional role in graphics output and marking. The unifying feature in all these applications is the dispensing and precise positioning of very small volumes of fluid (1–100 picoliters) on a substrate before transformation to a solid. The application of inkjet printing to the fabrication of structures for structural or functional materials applications requires an understanding as to how the physical processes that operate during inkjet printing interact with the properties of the fluid precursors used. Here we review the current state of understanding of the mechanisms of drop formation and how this defines the fluid properties that are required for a given liquid to be printable. The interactions between individual drops and the substrate as well as between adjacent drops are important in defining the resolution and accuracy of printed objects. Pattern resolution is limited by the extent to which a liquid drop spreads on a substrate and how spreading changes with the overlap of adjacent drops to form continuous features. There are clearly defined upper and lower bounds to the width of a printed continuous line, which can be defined in terms of materials and process variables. Finer-resolution features can be achieved through appropriate patterning and structuring of the substrate prior to printing, which is essential if polymeric semiconducting devices are to be fabricated. Low advancing and receding contact angles promote printed line stability but are also more prone to solute segregation or “coffee staining” on drying.

/pdf/inkjet-printing-of-functional-and-structural-materials-fluid-417wq0279u.pdf

Inkjet Printing of Functional and Structural Materials: Fluid Property Requirements, Feature Stability, and Resolution

Purpose – The purpose of this paper is to systematically and critically review the literature related to process design and modeling of fused deposition modeling (FDM) and similar extrusion-based additive manufacturing (AM) or rapid prototyping processes. Design/methodology/approach – A systematic review of the literature focusing on process design and mathematical process modeling was carried out. Findings – FDM and similar processes are among the most widely used rapid prototyping processes with growing application in finished part manufacturing. Key elements of the typical processes, including the material feed mechanism, liquefier and print nozzle; the build surface and environment; and approaches to part finishing are described. Approaches to estimating the motor torque and power required to achieve a desired filament feed rate are presented. Models of required heat flux, shear on the melt and pressure drop in the liquefier are reviewed. On leaving the print nozzle, die swelling and bead cooling are ...

https://forums.reprap.org/file.php?1,file=42240,filename=A_review_of_melt_extrusion_additive_manufacturing_processes_Process_design_and_modeling.pdf

A review of melt extrusion additive manufacturing processes: I. Process design and modeling

We demonstrate inkjet printing as a viable method for large-area fabrication of graphene devices. We produce a graphene-based ink by liquid phase exfoliation of graphite in N-methylpyrrolidone. We use it to print thin-film transistors, with mobilities up to ∼95 cm2 V–1 s–1, as well as transparent and conductive patterns, with ∼80% transmittance and ∼30 kΩ/□ sheet resistance. This paves the way to all-printed, flexible, and transparent graphene devices on arbitrary substrates.

/pdf/inkjet-printed-graphene-electronics-57uspbuxaf.pdf

Inkjet-printed graphene electronics.

We have studied inkjet-printed drops of a conductive polymer. We show how varying drop spacing and temperature lead to several different printed line morphologies and offer a simple geometric explanation for these various forms. Also, by controlling the evaporation profile of drying drops and lines, we demonstrate control of the coffee ring effect by which solute is transferred to the rim. Under appropriate conditions, we are able to enhance or eliminate the coffee ring effect in our drying features.

http://pubs.acs.org/doi/pdf/10.1021/la7026847

Inkjet-printed line morphologies and temperature control of the coffee ring effect.

The velocity and shape of rising bubbles, with an equivalent radius of 0.33–1.00 mm, in ‘hyper clean’ water, have been experimentally determined. For the small bubbles there is perfect agreement with theory, proving that this water can be considered as pure (no surfactants). For the larger bubbles there is a small discrepancy due to an overestimation in the theory.

The rise velocity and shape of bubbles in pure water at high Reynolds number

We have studied the stability of ink-jet printed lines of liquid with zero receding contact angle on a homogeneous substrate. Such lines can become unstable by forming a series of liquid bulges, at various wavelengths, connected by a ridge of liquid. The instability was studied with a simple dynamic model. It was shown that the line becomes unstable when the contact angle of the liquid with the substrate is larger than the advancing contact angle. This condition, however, is not a sufficient condition. When the transported flow rate is sufficiently small compared to the applied flow rate a printed line can be shown to be stable, i.e. the width of the printed line is constant. This was found to depend on the advancing contact angle of the liquid over the substrate.

The stability of ink-jet printed lines of liquid with zero receding contact angle on a homogeneous substrate

Experiments and numerical simulations of rising spherical bubbles in quiescent surfactant solutions are presented. The rise velocities versus the concentration in the bulk are measured using three surfactants, Triton X100, Brij30 and SDS for different bubble sizes, between 0.4 and 1 mm equivalent radius. We also present a brief description of the finite‐difference numerical method developed to solve the full Navier‐Stokes equations around the contaminated bubble for Reynolds numbers ranging from 50 to 200. The distributions of the tangential velocity, the vorticity, the pressure and the surfactant concentration on the bubble surface are calculated. In the case of high Peclet numbers surfactant molecules, which adsorb on the surface are convected and collected at the rear part of the bubble forming a stagnant cap where the no‐slip condition holds. The concentration on the bubble interface is obtained for surfactants having a desorption rate much slower than the convective rate. The sudden increase of the shear stress and pressure at the leading edge of the cap contributes mainly to decrease the rise velocity. This rapid slowdown of the bubble occurs when nearly half of the bubble surface is covered by the surfactant layer, and this is due to the particularly high values obtained for the shear stress and the pressure at the leading edge of this cap‐angle. Measured and calculated rise velocities for bubbles of 0.4 mm equivalent radius show good agreement when the sorption kinetics controls the surfactant exchange between the bulk and the surface. Calculated critical concentrations needed to cover completely the bubble agree with the measurements even for larger bubbles.

The effect of surfactant on the rise of a spherical bubble at high Reynolds and Peclet numbers

Preparation of monodisperse polymer particles and capsules by ink-jet printing

The encounter of bubble pairs of 0(1 mm) in both pure water and aqueous surfactant solutions was studied experimentally. In pure water, two equally sized bubbles were found to coalesce if the Weber number, W = ρV2 R/σ, based on the velocity of approach, V, was below a critical value, W cr = 0.18, where ρ and σ are the density and surface tension of the liquid respectively and R the equivalent radius of the bubbles. After coalescence bubbles perform volume and shape oscillations.

P. C. Duineveld

Papers

The rise velocity and shape of bubbles in pure water at high Reynolds number

The stability of ink-jet printed lines of liquid with zero receding contact angle on a homogeneous substrate

The effect of surfactant on the rise of a spherical bubble at high Reynolds and Peclet numbers

Preparation of monodisperse polymer particles and capsules by ink-jet printing

Bouncing and Coalescence of Bubble Pairs Rising at High Reynolds Number in Pure Water or Aqueous Surfactant Solutions