Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves

Three-dimensional (3D) printing is becoming an increasingly common technique to fabricate scaffolds and devices for tissue engineering applications. This is due to the potential of 3D printing to provide patient-specific designs, high structural complexity, rapid on-demand fabrication at a low-cost. One of the major bottlenecks that limits the widespread acceptance of 3D printing in biomanufacturing is the lack of diversity in “biomaterial inks”. Printability of a biomaterial is determined by the printing technique. Although a wide range of biomaterial inks including polymers, ceramics, hydrogels and composites have been developed, the field is still struggling with processing of these materials into self-supporting devices with tunable mechanics, degradation, and bioactivity. This review aims to highlight the past and recent advances in biomaterial ink development and design considerations moving forward. A brief overview of 3D printing technologies focusing on ink design parameters is also included.

Designing Biomaterials for 3D Printing

The shape of deposits obtained from drying drops containing colloidal particles matters for technologies such as inkjet printing, microelectronics, and bioassay manufacturing. In this work, the formation of deposits during the drying of nanoliter drops containing colloidal particles is investigated experimentally with microscopy and profilometry, and theoretically with an in-house finite-element code. The system studied involves aqueous drops containing titania nanoparticles evaporating on a glass substrate. Deposit shapes from spotted drops at different pH values are measured using a laser profilometer. Our results show that the pH of the solution influences the dried deposit pattern, which can be ring-like or more uniform. The transition between these patterns is explained by considering how DLVO interactions such as the electrostatic and van der Waals forces modify the particle deposition process. Also, a phase diagram is proposed to describe how the shape of a colloidal deposit results from the compet...

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Self-assembly of colloidal particles from evaporating droplets: role of DLVO interactions and proposition of a phase diagram.

In recent years, wearable electronics have experienced tremendous development due to their promising applications in fields such as portable, flexible/stretchable human-interactive sensors, displays, and energy devices. To effectively fabricate wearable electronics, a high-efficient, cost-saving, and eco-friendly manufacture technology is required. Inkjet printing, which rapidly, precisely, and reproducibly deposits a broad variety of functional materials in a non-impact, addictive patterning, and maskless approach, serves as an effective tool for the fabrication of wearable electronics. In this review, the recent advances in inks, strategies, and the applications of inkjet-printed wearable electronics are summarized. Based on uniform and high-resolution patterns, well-compatible functional inks can be deposited to fabricate flexible/stretchable and durable wearable electronics. Perspectives on the remaining challenges and future developments are also proposed.

Inkjet printing wearable electronic devices

https://repository.tudelft.nl/islandora/object/uuid%3Ab12d4d79-67af-4177-b03c-88bfaa8b622d/datastream/OBJ/download

A review on suppression and utilization of the coffee-ring effect.

The shape of deposits obtained from drying drops containing colloidal particles matters for technologies such as inkjet printing, microelectronics and bioassay manufacturing. In this work, the formation of deposits during the drying of nanoliter drops containing colloidal particles is investigated experimentally with microscopy and profilometry, and theoretically with an inhouse finite-element code. The system studied involves aqueous drops containing titania nanoparticles evaporating on a glass substrate. Deposit shapes from spotted drops at different pH values are measured using a laser profilometer. Our results show that the pH of the solution influences the dried deposit pattern, which can be ring-like or more uniform. The transition between these patterns is explained by considering how DLVO interactions such as the electrostatic and van der Waals forces modify the particle deposition process. Also a phase diagram is proposed to describe how the shape of a colloidal deposit results from the competition between three flow patterns: a radial flow driven by evaporation at the wetting line, a Marangoni recirculating flow driven by surface tension gradients, and the transport of particles towards the substrate driven by DLVO interactions. This phase diagram explains three types of deposits commonly observed experimentally, such as a peripheral ring, a small central bump, or a uniform layer. Simulations and experiments are found in very good agreement.

Self-assembly of colloidal particles from evaporating droplets: role of DLVO interactions and proposition of a phase diagram

An efficient way to precisely pattern particles on solid surfaces is to dispense and evaporate colloidal drops, as for bioassays The dried deposits often exhibit complex structures exemplified by the coffee ring pattern, where most particles have accumulated at the periphery of the deposit In this work, the formation of deposits during the drying of nanoliter colloidal drops on a flat substrate is investigated numerically and experimentally A finite-element numerical model is developed that solves the Navier–Stokes, heat and mass transport equations in a Lagrangian framework The diffusion of vapor in the atmosphere is solved numerically, providing an exact boundary condition for the evaporative flux at the droplet–air interface Laplace stresses and thermal Marangoni stresses are accounted for The particle concentration is tracked by solving a continuum advection–diffusion equation Wetting line motion and the interaction of the free surface of the drop with the growing deposit are modeled based on criteria on wetting angles Numerical results for evaporation times and flow field are in very good agreement with published experimental and theoretical results We also performed transient visualization experiments of water and isopropanol drops loaded with polystyrene microspheres evaporating on glass and polydimethylsiloxane substrates, respectively Measured evaporation times, deposit shapes and sizes and flow fields are in very good agreement with the numerical results Different flow patterns caused by the competition of Marangoni loops and radial flow are shown to determine the deposit shape to be either a ring-like pattern or a homogeneous bump

/pdf/pattern-formation-during-the-evaporation-of-a-colloidal-ohwmdoy6im.pdf

Pattern formation during the evaporation of a colloidal nanoliter drop: a numerical and experimental study

An efficient way to precisely pattern particles on solid surfaces is to dispense and evaporate colloidal drops, as for bioassays. The dried deposits often exhibit complex structures exemplified by the coffee ring pattern, where most particles have accumulated at the periphery of the deposit. In this work, the formation of deposits during the drying of nanoliter colloidal drops on a flat substrate is investigated numerically and experimentally. A finite-element numerical model is developed that solves the Navier-Stokes, heat and mass transport equations in a Lagrangian framework. The diffusion of vapor in the atmosphere is solved numerically, providing an exact boundary condition for the evaporative flux at the droplet-air interface. Laplace stresses and thermal Marangoni stresses are accounted for. The particle concentration is tracked by solving a continuum advection-diffusion equation. Wetting line motion and the interaction of the free surface of the drop with the growing deposit are modeled based on criteria on wetting angles. Numerical results for evaporation times and flow field are in very good agreement with published experimental and theoretical results. We also performed transient visualization experiments of water and isopropanol drops loaded with polystyrene microsphere evaporating on respectively glass and polydimethylsiloxane substrates. Measured evaporation times, deposit shape and sizes, and flow fields are in very good agreement with the numerical results. Different flow patterns caused by the competition of Marangoni loops and radial flow are shown to determine the deposit shape to be either a ring-like pattern or a homogeneous bump.

Xiaohua Fang

Papers

Self-assembly of colloidal particles from evaporating droplets: role of DLVO interactions and proposition of a phase diagram.

Self-assembly of colloidal particles from evaporating droplets: role of DLVO interactions and proposition of a phase diagram

Pattern formation during the evaporation of a colloidal nanoliter drop: a numerical and experimental study

Pattern formation during the evaporation of a colloidal nanoliter drop: a numerical and experimental study