This paper presents an approach to overcome the current limitations associated with printing low viscosity polymeric materials with architectural freedom via additive manufacturing. The approach is based on a combinatorial library fabrication method that enables efficient optimization of material formulations amenable for additive manufacturing. The proof-of-concept is demonstrated by using a customized direct ink writing system involving two low viscosity polymeric pastes containing conductive filler particles. A static mixer is used to produce a wide range of mass ratios of the pastes from 1:9 to 9:1 of the two pastes to achieve electrically conductive networks. The approach allows for demonstration of rapid experimental characterization of nine different carbon-based stretchable electrode formulations at once and screening of electrical percolation behavior and elongation of the specimens via a high-throughput analysis. The same experimental set up enables experimental characterization of many samples, e.g., up to 100 at once. The study demonstrates the use of a mixed solvent system and pi-pi interactions between the conductive filler particles and the resin for achieving higher elasticity of the conductive pastes and shape stability of printed parts.

This work reports removal of emulsified water droplets from ultralow sulfur diesel (ULSD) fuel using high surface area aerogel filter media constructs. A synergistic combination of additive manufacturing and sol-gel chemistry is used for fabrication of the filter media constructs from high surface area (>200 m(2)/g) and high porosity (>90%) polyimide and syndiotactic polystyrene aerogels that are grown using sol-gel processes inside the loadbearing 3D-printed polymeric constructs of polyamide and high impact polystyrene respectively. This paper evaluates the roles of several factors on water separation efficiency, such as surface energy of polymer media on wetting, surfactant adsorption by the high surface area polymer media, and size exclusion of water droplets by smaller aerogel pores. The surfactant-stabilized water droplets in ULSD can be removed with a separation efficiency of up to 95% using these mechanically strong aerogel constructs.

This paper reports a new method of functional metamaterial structure fabrication based on ultra-porous aerogel skins introduced on the surfaces of solid tetrakaidecahedron lattices obtained via 3D-printing tools. The solid tetrakaidecahedron lattice shapes are first fabricated from acrylate resin systems using a stereolithography printer. The lattice is then coated with a skin of polyimide gel via sol–gel reaction process, post-curing, and solvent-aging. The aerogel skin is recovered from the gel using supercritical drying. The lattice is found uniformly coated with polyimide aerogel skin as confirmed from examination of surface morphology via scanning electron microscopy and X-ray tomography imaging. The concept is extended to coatings by silica and Kevlar aerogel systems. The mechanical and thermal properties of the resultant materials and a set of applications are discussed.

In this work, polyurethane aerogels are fabricated in re-entrant honeycomb forms to achieve auxeticity and much higher flexibility than corresponding aerogel monoliths. For this purpose, a set of re-entrant honeycomb-shaped hollow molds is first printed from high-impact polystyrene (HIPS) using a fused filament fabrication technique and subsequently filled with polyurethane sol synthesized from an aliphatic triisocyanate and a diol selected from among butanediol, pentanediol, hexanediol, or octanediol. A sol-gel transition process yields the gel in a re-entrant honeycomb shape, which is isolated by dissolving the HIPS mold and supercritically dried using carbon dioxide. The effects of diol chain length on the properties of aerogels, such as bulk density, pore size, and tensile properties are investigated. The auxetic aerogels show different deformation behavior and much higher elongation at break than dogbone-shaped aerogel monoliths. Such unique properties of auxetic structures can extend applications of aerogels as acoustic absorbers and smart bandages that require high porosity, tunable pore structures, and high flexibility.

From conventional liquid repellent performance to manipulating liquid motion on a planar substrate, “slippery surfaces” with designed liquid-confined patterns (patterned slippery surfaces) have shown great success in many fields including microfluidic devices, microarray formation, and liquid guiding technologies. However, the fabrication of patterned slippery surfaces is not simple, and most of these fabrication methods involve complex surface chemical modification and multiple steps, significantly reducing the practicality of patterned slippery surfaces. In this study, a facile and simple approach to generate patterned slippery surfaces without complex chemical functionalization is demonstrated. A superhydrophobic base film is produced via layer-by-layer assembly of branched polyethylenimine (BPEI) and Nafion, a perfluorinated polyelectrolyte, in methanol. After that, a concentrated BPEI patterning solution is applied to the surface to create hydrophilic regions. As these hydrophilic domains have a stronger affinity to aqueous media than to the lubricant, a slippery surface with a hydrophilic pattern which can constrain liquid motion is obtained after infiltrating lubricant in the surface. This approach not only offers an efficient way to prepare patterned slippery surfaces but also provides versatility for different applications such as transparent surface patterning and liquid manipulation. Moreover, the flexibility of incorporating a solvatochromic dye into the patterning solution has introduced the possibility for the use of patterned slippery surfaces in anticounterfeiting technology.

Optimization of three-dimensional (3D) print conditions for material extrusion of plastics by fused filament fabrication typically involves trade-offs between mechanical properties and dimensional accuracy due to their orthogonal requirements. Increased polymer mobility improves the mechanical properties by chain diffusion to strengthen the interfaces between printed roads, but flow associated with the high polymer mobility leads to inaccuracies. Here, we describe the application of a model core-shell geometry in filaments to address these trade-offs and understand the material requirements to achieve improved dimensional accuracy. Systematic variation of the core with commercial polycarbonate-based plastics and a common high-density polyethylene (HDPE) shell illustrates that tensile properties obtained with these filaments are relatively insensitive to printing conditions and selection of the core polymer, but the dimensional accuracy of the printed part improves markedly as the glass transition temperature of the core polymer increases. The impact resistance of the core-shell-based parts is dependent on the selection of the core polymer with a significant decrease in impact resistance for the lowest modulus core examined. Although warping can be mostly mitigated with the core-shell filaments, the printed object is generally smaller than the digital source due to large volume change associated with HDPE crystallization. The dimensional accuracy is dependent on the solidification temperature and mechanical properties of the polymers comprising the filament, print conditions, and the local geometry of the object as quantified by layer-by-layer analysis of 3D scanned images of the printed objects. Both processing changes and some structures in the digital object that can degrade the dimensional accuracy are identified through this analysis. The core-shell filament structure represents a model geometry to understand the potential for the printing of polymer blends where separation of solidification temperatures in cocontinuous blends could provide a route to improve performance.

A 3D-printing process is presented for the manufacturing of modular aerogel/acrylate bricks that are fully scalable and customizable for potential applications in thermal insulation. The use of 3D-printing tools in conjunction with a sol-gel method of aerogel synthesis circumvents the geometric limitations of fabrication of large size load bearing aerogel articles. In this study, two-component aerogel bricks are manufactured from the low thermal conductivity of aerogels and 3D-printed load-bearing polymer bricks. For this purpose, aerogels are synthesized from polyimide and partially crosslinked stereolithography acrylate (SLA) resins. The aerogel materials are held by mechanically strong LEGO®-like bricks derived from fully crosslinked SLA resin and fully cured epoxy resin. The transient temperature profiles on brick surfaces due to contact heating and flexural and compressive properties of bricks filled with aerogel materials are discussed.

Polyolefins dominate the market for commodity plastics due to their low cost and suitable properties, but polyolefins are rarely used in 3D printing due to issues with deformation of the printed structure during crystallization from the large volume change. Here, we demonstrate that filaments containing approximately 50% of either high density or low density polyethylene (HDPE/LDPE) as a shell with a polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blend core can be printed using standard fused filament fabrication methods with adequate to good dimensional accuracy, improved impact resistance, and enhanced elongation at break relative to samples printed with PC/ABS alone. The combination of lower crystallinity (28%) of LDPE in comparison to HDPE (62%) and lower crystallization temperature of LDPE (89 degrees C) than HDPE (117 degrees C) leads to improved dimensional accuracy of the printed part. However, the elastic modulus of the composite containing LDPE is only 48% of the part printed with only PC/ABS for flat (XY) orientations, whereas the reduction in modulus with the HDPE shell is significantly less. The mechanical behavior can be rationalized in terms of aligned fiber composite theory where anisotropic modulus is expected to be dependent on the angle between stretching direction and fiber axis. The low cost of LDPE and HDPE along with the ability to increase impact strength and extensibility of printed parts further demonstrate the promise of composite core-shell filaments for additive manufacturing.

A fused filament fabrication process is used for conversion of polyimide aerogels into bicontinuous gyroid structures to obtain enhanced elasticity. A sacrificial hollow mold in an inverse gyroid shape is first fabricated from high impact polystyrene and is filled with the polyimide sol. After the sol-gel transition, the mold is dissolved in a solvent to yield the gel structure of a gyroid shape. The gel is supercritically dried to recover a free-standing aerogel structure with ultrahigh porosity (98.9%) and low bulk density (0.0146 g/cm(3)). The bicontinuous gyroid structure of the aerogel offers significant elasticity and high elongation at break compared to an otherwise brittle monolithic aerogel of polyimide. The ability to create intricate aerogel structures opens up a large potential in applications such as sensor housing and acoustic barriers of arbitrary shape and size and load-bearing porous thermally insulating structures that allow breathing.