Developing the ability to 3D print various classes of materials possessing distinct properties could enable the freeform generation of active electronics in unique functional, interwoven architectures. Achieving seamless integration of diverse materials with 3D printing is a significant challenge that requires overcoming discrepancies in material properties in addition to ensuring that all the materials are compatible with the 3D printing process. To date, 3D printing has been limited to specific plastics, passive conductors, and a few biological materials. Here, we show that diverse classes of materials can be 3D printed and fully integrated into device components with active properties. Specifically, we demonstrate the seamless interweaving of five different materials, including (1) emissive semiconducting inorganic nanoparticles, (2) an elastomeric matrix, (3) organic polymers as charge transport layers, (4) solid and liquid metal leads, and (5) a UV-adhesive transparent substrate layer. As a proof of concept for demonstrating the integrated functionality of these materials, we 3D printed quantum dot-based light-emitting diodes (QD-LEDs) that exhibit pure and tunable color emission properties. By further incorporating the 3D scanning of surface topologies, we demonstrate the ability to conformally print devices onto curvilinear surfaces, such as contact lenses. Finally, we show that novel architectures that are not easily accessed using standard microfabrication techniques can be constructed, by 3D printing a 2 × 2 × 2 cube of encapsulated LEDs, in which every component of the cube and electronics are 3D printed. Overall, these results suggest that 3D printing is more versatile than has been demonstrated to date and is capable of integrating many distinct classes of materials.

Surface coatings and patterning technologies are essential for various physicochemical applications. In this Letter, we describe key parameters to achieve uniform particle coatings from binary solutions: First, multiple sequential Marangoni flows, set by solute and surfactant simultaneously, prevent non-uniform particle distributions and continuously mix suspended materials during droplet evaporation. Second, we show the importance of particle-surface interactions that can be established by surface-adsorbed macromolecules. To achieve a uniform deposit in a binary mixture, a small concentration of surfactant and surface-adsorbed polymer (0.05 wt% each) is sufficient, which offers a new physicochemical avenue for control of coatings. PACS numbers:An evaporating liquid drop, either single or multicomponent, containing solutes or particulates leaves a deposit whose form is determined by various parameters, for instance internal flow fields [1][2][3], liquid compositions [4][5][6][7][8][9][10], and interactions between suspended particles and a solid substrate [11][12][13][14], which are crucial for coating processes. In particular, control of the deposit uniformity and thickness can be important in surface patterning [15][16][17], ink-jet [4,18,19] and 3D printing technologies [20]. These processes are complex because of physicochemical dynamics that arise from Marangoni effects [2, 5-10, 12, 21, 22] and particle deposition mechanisms [11,12,14,23]. In fact, although a binary mixture is used quite often to achieve uniform particle deposition from droplets smaller than 100 µm [4,18,19], to our best knowledge such coatings have not been achieved for larger droplets. Furthermore, while the wetting and dewetting behaviors of binary mixture drops have been investigated [24,25], the relation between the deposition pattern and the evaporatively driven flow field in a binary mixture droplet is incomplete (Table S1, Supporting Information (SI)) [26].In this Letter, to achieve a uniform coating, we identify key characteristics of a multicomponent solution, which consists of a binary mixture, surface-active surfactant, and surface-adsorbed polymer. We were motivated to pursue the ideas here from examining a whisky droplet after drying on an ordinary glass where it creates a relatively uniform particle deposit (see Fig. 1), which is in contrast to the well-known 'coffee-ring stain' [1]. Based on our understanding of the drying and coating mechanisms of binary liquid droplets, whisky droplets, and more complex solution droplets, we design a model liquid that yields nearly uniform deposits by taking the approach that whisky is an ethanol-water mixture containing diverse dissolved molecules, which contribute to the * Electronic address: hastone@princeton.edu complexity of the system, the flows, and the final particle deposits.We begin with a few remarks about whisky, since it serves as a model complex mixture, where nearly uniform particle deposits are observed after drying. Whisky is an alcoholic liquid (ethanol:water, 35:65 % b...

Embedded three-dimensional (EMB3D) printing is an emerging technique that enables free-form fabrication of complex architectures. In this approach, a nozzle is translated omnidirectionally within a soft matrix that surrounds and supports the patterned material. To optimize print fidelity, we have investigated the effects of matrix viscoplasticity on the EMB3D printing process. Specifically, we determine how matrix composition, print path and speed, and nozzle diameter affect the yielded region within the matrix. By characterizing the velocity and strain fields and analyzing the dimensions of the yielded regions, we determine that scaling relationships based on the Oldroyd number, Od, exist between these dimensions and the rheological properties of the matrix materials and printing parameters. Finally, we use EMB3D printing to create complex architectures within an elastomeric silicone matrix. Our methods and findings will both facilitate future characterization of viscoplastic matrices and motivate the development of new materials for EMB3D printing.

Control and stabilization of viscous fingering of immiscible fluids impacts a wide variety of pressure-driven multiphase flows. We report theoretical and experimental results on a time-dependent control strategy by manipulating the gap thickness b(t) in a lifting Hele-Shaw cell in the power-law form b(t)=b(1)t(1/7). Experimental results show good quantitative agreement with the predictions of linear stability analysis. By choosing the value of a single time-independent control parameter, we can either totally suppress the viscous fingering instability or maintain a series of nonsplitting viscous fingers during the fluid displacement process. In addition to the gap thickness of a Hele-Shaw cell, time-dependent control strategies can, in principle, also be placed on the injection rate, viscosity of the displaced fluid, and interfacial tension between the two fluids.