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

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 ...

We demonstrate the use of a microfluidic stagnation point flow to trap and extend single molecules of double-stranded (ds) genomic DNA for detection of target sequences along the DNA backbone. Mutant EcoRI-based fluorescent markers are bound sequence-specifically to fluorescently labeled ds λ-DNA. The marker-DNA complexes are introduced into a microfluidic cross slot consisting of flow channels that intersect at ninety degrees. Buffered solution containing the marker-DNA complexes flows in one channel of the cross slot, pure buffer flows in the opposing channel at the same flow rate, and fluid exits the two channels at ninety degrees from the inlet channels. This creates a stagnation point at the center of a planar extensional flow, where marker-DNA complexes may be trapped and elongated along the outflow axis. The degree of elongation can be controlled using the flow strength (i.e., a non-dimensional flow rate) in the device. Both the DNA backbone and the markers bound along the stretched DNA are observed directly using fluorescence microscopy and the location of the markers along the DNA backbone is measured. We find that our method permits detection of each of the five expected target site positions to within 1.5 kb with standard deviations of <1.5 kb. We compare the method’s precision and accuracy at molecular extensions of 68% and 88% of the contour length to binding distributions from similar data obtained via molecular combing. We also provide evidence that increased mixing of the sample during binding of the marker to the DNA improves binding to internal target sequences of dsDNA, presumably by extending the DNA and making the internal binding sites more accessible.

Various ceria and colloidal silica polishing slurries were used to polish fused silica glass workpieces on a polyurethane pad. Characterization of the slurries' particle size distribution (PSD) (using both ensemble light scattering and single particle counting techniques) and of the polished workpiece surface (using atomic force microscopy) was performed. The results show the final workpiece surface roughness is quantitatively correlated with the logarithmic slope of the distribution function for the largest particles at the exponential tail end of the PSD. Using the measured PSD, fraction of pad area making contact, and mechanical properties of the workpiece, slurry, and pad as input parameters, an Ensemble Hertzian Gap (EHG) polishing model was formulated to estimate each particle's penetration, load, and contact zone. The model is based on multiple Hertzian contact of slurry particles at the workpiece-pad interface in which the effective interface gap is determined through an elastic load balance. Separately, ceria particle static contact and single pass sliding experiments were performed showing~1-nm depth removal per pass (i.e., a plastic type removal). Also, nanoindentation measurements on fused silica were made to estimate the critical load at which plastic type removal starts to occur (P crit~5 3 10 À5 N). Next the EHG model was extended to create simulated polished surfaces using the Monte Carlo method where each particle (with the calculated characteristics described above) slides and removes material from the silica surface in random directions. The polishing simulation utilized a constant depth removal mechanism (i.e., not scaling with particle size) of the elastic deformation zone cross section between the particle and silica surface, which was either 0.04 nm (for chemical removal) at low loads (

P crit ). The simulated surfaces quantitatively compare well with the measured rms roughness, power spectra, surface texture, absolute thickness material removal rate, and load dependence of removal rate.

A microfluidic four-roll mill device that can cover the entire spectrum of flow types including purely rotational flow was designed using pseudo-three-dimensional simulations. In experiments using high aspect ratio devices etched in silicon, the authors observed the whole range of flow type by changing only the flow rate ratio. This microfluidic four-roll mill device can be applied to examining microdrop deformation and the dynamics of single molecules in a mixed flow or to enhancing mixing efficiency by sinusoidal changes of the inlet flow rate.

The “High-Foot” platform manipulates the laser pulse-shape coming from the National Ignition Facility laser to create an indirect drive 3-shock implosion that is significantly more robust against instability growth involving the ablator and also modestly reduces implosion convergence ratio. This strategy gives up on theoretical high-gain in an inertial confinement fusion implosion in order to obtain better control of the implosion and bring experimental performance in-line with calculated performance, yet keeps the absolute capsule performance relatively high. In this paper, we will cover the various experimental and theoretical motivations for the high-foot drive as well as cover the experimental results that have come out of the high-foot experimental campaign. At the time of this writing, the high-foot implosion has demonstrated record total deuterium-tritium yields (9.3×1015) with low levels of inferred mix, excellent agreement with implosion simulations, fuel energy gains exceeding unity, and evidence for the “bootstrapping” associated with alpha-particle self-heating.

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.

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