We report a method for fabricating optical quality silica and silica-titania glasses by additive manufacturing, or 3D printing. Key to this success was the combination of sol-gel derived silica and silica-titania colloidal feedstocks, 3D direct ink writing (DIW) technology, and conventional glass thermal processing methods. Printable silica and silica-titania sol inks were prepared directly from molecular precursors by a simple one-pot method, which was optimized to yield viscous, shear-thinning colloidal suspensions with tuned rheology ideal for DIW. After printing, the parts were dried and sintered under optimized thermal conditions to ensure complete organic removal and uniform densification without crystallization.Characterizations of the 3D-printed pure silica and silica-titania glasses show that they are This article is protected by copyright. All rights reserved. 2 equivalent to commercial optical fused silica (Corning ® 7980) and silica-titania glasses (Corning ULE ® 7972). More specifically, they exhibit comparable chemical composition, SiO 2 network structure, refractive index, dispersion, optical transmission, and coefficient of thermal expansion. 3D printed silica and silica-titania glasses also exhibited comparable polished surface roughness and meet refractive index homogeneity standards within range of commercial optical grade glasses. This method establishes 3D printing as a viable tool to create optical glasses with compositional and geometric configurations that are inaccessible by conventional optical fabrication methods. † denotes value determined by LA-ICP-MS; a-SiO 2 used to represent amorphous SiO 2

We present a new class of architected materials that exhibit rapid, reversible, and sizable changes in effective stiffness.

molding have been demonstrated for fabricating complex glass structures. [11][12][13][14][15][16][17][18] However, there are limitations to these methods. In binder jetting, the sintered glasses can be fragile and appear opaque due to incomplete densification. Methods to print glass directly (e.g., fused deposition or filament feed) require high temperatures to melt the silica feedstock, resulting in filaments that are potentially vulnerable to thermal stresses and unable to completely merge into the desired structure, which may limit the printing speed and resolution of the printed parts. Soft replication molding cannot be used to produce gap-spanning features, and pseudo-3D objects (i.e., stacked assemblies of thin molded sheets) can only be formed by precisely aligning layers that must then be bonded during heat treatment. None of these methods have been shown to produce glasses that are simultaneously transparent, free form, and 3D with sub-millimeter features.We have developed a two-part process (forming and sintering) which uses direct ink writing (DIW) for the 3D printing of optically transparent glass structures with sub-millimeter features. DIW is a layer-by-layer assembly technique in which shear-thinning inks are extruded through a nozzle in a programmable pattern, upon which the inks rapidly solidify via gelation, evaporation, or temperature-induced phase change. [19] DIW has been used in a wide range of applications such as polymeric optical wave guides, complex scaffolds, 3D periodic graphene aerogels, and self-healing materials. [6,[20][21][22][23][24] Our process first relies on DIW printing of colloidal silica suspensions to form silica green bodies (porous, low density structures) of the desired shape. A key feature of this process is the ability to control yield stress and shear thinning to obtain ink properties best suited for specific applications of the printed glass. Second, the printed structures are dried and heated to temperatures below the melting point of silica to sinter the green body into a fully dense, amorphous, transparent solid structure (Figure 1). In contrast to direct 3D printing of molten glass, this two-step approach does not require high temperatures during printing and allows for higher resolution features, due to both the ability to extrude thinner filaments and the shrinkage that occurs during the densification stage.The critical challenges in formulating a suitable ink for formation of the silica green bodies toward glass structures are: i) the ink must possess the desired rheological behavior for printing and shape retention, and ii) the ink must be able to dry without cracking while still maintaining open porosity that Silica inks are developed, which may be 3D printed and thermally processed to produce optically transparent glass structures with sub-millimeter features in forms ranging from scaffolds to monoliths. The inks are composed of silica powder suspended in a liquid and are printed using direct ink writing. The printed structures are then dried and sintered ...

No abstract

We explore the phase diagram and mechanical properties of molecular gels produced from mixing water with a dimethyl sulfoxide (DMSO) solution of the aromatic dipeptide derivative fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF). Highly soluble in DMSO, Fmoc-FF assembles into fibrous networks that form gels upon addition of water. At high water concentrations, rigid gels can be formed at Fmoc-FF concentrations as low as 0.01 wt %. The conditions are established defining the Fmoc-FF and water concentrations at which gels are formed. Below the gel boundary, the solutions are clear and colorless and have long-term stability. Above the gel boundary, gels are formed with increasing rapidity with increasing water or Fmoc-FF concentrations. A systematic characterization of the effect of Fmoc-FF and water concentrations on the mechanical properties of the gels is presented, demonstrating that the elastic behavior of the gels follows a specific, robust scaling with Fmoc-FF volume fraction. Furthermore, we characterize the kinetics of gelation and demonstrate that these gels are reversible in the sense that they can be disrupted mechanically and rebuild strength over time.

The electrosynthesis of value‐added multicarbon products from CO2 is a promising strategy to shift chemical production away from fossil fuels. Particularly important is the rational design of gas diffusion electrode (GDE) assemblies to react selectively, at scale, and at high rates. However, the understanding of the gas diffusion layer (GDL) in these assemblies is limited for the CO2 reduction reaction (CO2RR): particularly important, but incompletely understood, is how the GDL modulates product distributions of catalysts operating in high current density regimes > 300 mA cm−2. Here, 3D‐printable fluoropolymer GDLs with tunable microporosity and structure are reported and probe the effects of permeance, microstructural porosity, macrostructure, and surface morphology. Under a given choice of applied electrochemical potential and electrolyte, a 100× increase in the C2H4:CO ratio due to GDL surface morphology design over a homogeneously porous equivalent and a 1.8× increase in the C2H4 partial current density due to a pyramidal macrostructure are observed. These findings offer routes to improve CO2RR GDEs as a platform for 3D catalyst design.

We demonstrate an additive manufacturing approach to produce gradient refractive index glass optics. Using direct ink writing with an active inline micromixer, we three-dimensionally print multimaterial green bodies with compositional gradients, consisting primarily of silica nanoparticles and varying concentrations of titania as the index-modifying dopant. The green bodies are then consolidated into glass and polished, resulting in optics with tailored spatial profiles of the refractive index. We show that this approach can be used to achieve a variety of conventional and unconventional optical functions in a flat glass component with no surface curvature.

Dipeptide derivative molecules can self-assemble into space-filling nanofiber networks at low volume fractions (<1%), allowing the formation of molecular gels with tunable mechanical properties. The self-assembly of dipeptide-based molecules is reminiscent of pathological amyloid fibril formation by naturally occurring polypeptides. Fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) is the most widely studied such molecule, but the thermodynamic and kinetic phenomena giving rise to Fmoc-FF gel formation remain poorly understood. We have previously presented evidence that the gelation process is a first order phase transition characterized by low energy barriers to nucleation, short induction times, and rapid quasi-one-dimensional crystal growth, stemming from solvent-solute interactions and highly specific molecular packing. Here, we discuss the phase behavior of Fmoc-FF in different solvents. We find that Fmoc-FF gel formation can be induced in apolar solvents, in addition to previously established pathways in aqueous systems. We further show that in certain solvent systems anisotropic crystals (nanofibers) are an initial metastable state, after which macroscopic crystal aggregates with no preferred axis of growth are formed. The molecular conformation is sensitive to solvent composition during assembly, indicating that Fmoc-FF may be a simple model system to study complex thermodynamic and kinetic phenomena involved in peptide self-assembly.