Centimeter-scale mesoporous silica monoliths were synthesized by a multi-step fabrication process by combining cooperative and evaporation-induced self-assembly with high-pressure compaction. The fabricated monoliths were highly permeable with a surface area exceeding 270 m2/g from a continuous SBA-16 cubic mesoporous matrix. This new type of mesoporous solids exhibits excellent mechanical stability comparable to sedimentary rocks, despite having a low density of only ~ 1.1 g/cm3.

Stave assemblies at the Large Hadron Collider and other high-energy physics experiments require radiationresistant adhesives composed of light elements with high thermal conductivity and low interfacial resistance. Porous carbon foams are currently bonded to carbon fiber faceplates with graphite-filled epoxy. Low-viscosity epoxies are used to increase the amount of filler in order to double the thermal conductivity without impacting the properties of the material under irradiation. Promising new adhesive formulations showed no degradation in thermal conductivity after exposure to a fluence of 10(16) n/cm(2) (>0.1 MeV neutrons) or 10 Gy gamma radiation, but showed variable degradation, compared to the currently used adhesive, after exposure to a fluence of 10(15) p/cm(2) (1 MGy, 67.5 MeV protons). Adhesives with more than double the irradiated thermal conductivity of the baseline material showed marked improvement in thermal transport in graphite/epoxy/foam/epoxy/ graphite structures based on thermal diffusivity measurements. Silicon carbide particles can be added to graphite to stiffen the modulus of the filled epoxy. When spherical AlN was used as a filler, the degradation in thermal conductivity under proton irradiation varied based on the size of the ceramic filler. Options for improving the thermal performance of irradiated adhesives for high-energy physics experiments are discussed.

Magnesium-based alloy WE43 is a state-of-the-art bioresorbable metallic implant material. There is a need for implants with both complex geometries to match the mechanical properties of bone and refined microstructure for controlled resorption. Additive manufacturing (AM) using laser powder bed fusion (LPBF) presents a viable fabrication method for implant applications, as it offers near-net-shape geometrical control, allows for geometry customization based on an individual patient, and fast cooling rates to achieve a refined microstructure. In this study, the laser–alloy interaction is investigated over a range of LPBF-relevant processing conditions to reveal melt-pool dynamics, pore formation, and the microstructure of laser-melted WE43. In situ X-ray imaging reveals distinct laser-induced vapor depression morphology regimes, with minimal pore formation at laser-scan speeds greater than 500 mm/s. Optical and electron microscopy of cross-sectioned laser tracks reveal three distinct microstructural regimes that can be controlled by adjusting laser-scan parameters: columnar, dendritic, and banded microstructures. These regimes are consistent with those predicted by the analytic solidification theory for conduction-mode welding, but not for keyhole-mode tracks. The results provide insight into the fundamental laser–material interactions of the WE43 alloy under AM-processing conditions and are critical for the successful implementation of LPBF-produced WE43 parts in biomedical applications.

Nanoconfined water plays a pivotal role in a vast number of fields ranging from biological and materials sciences to catalysis, nanofluidics and geochemistry. Here, we report the freezing and melting behavior of water (D2O) nanoconfined in architected silica-based matrices including Vycor glass and mesoporous silica SBA-15 and SBA-16 with pore diameters ranging between 4–15 nm, which are investigated using differential scanning calorimetry and 2H nuclear magnetic resonance spectroscopy. The results provide compelling evidence that the extreme dynamical heterogeneity of water molecules is preserved over distances as small as a few angstroms. Solidification progresses in a layer-by-layer fashion with a coexistence of liquid-like and solid-like dynamical fraction at all temperatures during the transition process. The previously reported fragile-to-strong dynamic transition in nanoconfined water is argued to be a direct consequence of the layer-by-layer solidification.

The integral membrane protein, bacteriorhodopsin (BR) was encapsulated in sol-gel derived porous silica gel monoliths in native purple membrane (BR-PM) and synthetic lipid nanodisc (BR nanodisc) environments. BR nanodiscs were synthesized by solubilizing purple membrane in discoidal phospholipid bilayer stabilized by amphipathic Styrene-Maleic Acid (SMA) copolymer. UV-vis absorbance spectroscopy and dynamic-light scattering indicated the formation of BR monomers solubilized in lipid nanodiscs 10.2 +/- 0.7 nm in average diameter. Fluorescence and absorbance spectroscopic techniques were utilized to probe conformational, environmental, and rotational changes associated with the tryptophan residues and the covalently-bound retinal moiety of BR upon entrapment in the silica matrix. We show that the immobilized BR in both membrane environments retained its bound retinal cofactor and the ability of the cofactor to undergo conformational changes upon light illumination necessary for BR's activity as a proton transporter. For purple membrane fragments, the results indicated that the local pH in the pores around BR after encapsulation was important for its stability at temperatures higher than 50 degrees C. Under the same buffering conditions, retinal was released from silica-encapsulated BR-PM and BR nanodiscs beginning at 80 degrees C (without a conformational change) and 50 degrees C (with a conformational change), respectively, reflecting differences in protein-protein (trimeric vs. monomeric) and protein-lipid interactions.

Spatiotemporal heterogeneity is one of the hallmarks of the relaxation dynamics associated with the glass transition. A key question in this regard is whether the dynamical heterogeneity has a structural origin. We report differential scanning calorimetry (DSC) data that reveal the presence of extreme spatial heterogeneity in the freezing dynamics of water (D2O) and the glass transition dynamics in the supercooled molecular liquid ortho-terphenyl (OTP), when these liquids are confined in nano-architected mesoporous silica with interconnected pores of different geometry. The results demonstrate, for the first time, that despite connectivity between the pores, nanoconfined water and OTP display distinct freezing/melting points and glass transition temperatures characteristic of each pore type. Viewed as a whole, these experimental results point to the coexistence of strong spatial heterogeneities over length scales of a few nanometers in the structure and dynamics of these liquids, suggesting a close mechanistic connection between them.

CONSPECTUS: Core principles of chemistry are ubiquitously invoked to shed light on the nature of molecular level interactions in nanoconfined fluids, which play a pivotal role in a wide range of processes in geochemistry, biology, and engineering. A detailed understanding of the physicochemical processes involved in the flow, structural transitions, and freezing or melting behavior of fluids confined within nanometer-sized pores of solid materials is thus of enormous importance for both basic research and technological applications. This Account provides a perspective on new insights into the thermodynamic and kinetic transitions of nanoconfined fluids in their stable and metastable forms. After briefly introducing the unique properties of mesoporous silicas from the SBA, MCM, and FDU families that serve as the confinement matrices, combining highly ordered single and bimodal mesopore architectures with tunable pore sizes in the similar to 2-15 nm range and narrow size distributions, recent studies on melting/freezing behavior of water confined in these host matrices are reviewed. While differential scanning calorimetry (DSC) reveals a linear relationship between melting point depression and pore size (independent of the pore shape), as predicted by the Gibbs-Thomson relation, variable temperature H-2 wide-line nuclear magnetic resonance (NMR) spectroscopy studies confirm the core-shell model of water and give evidence for a layer-by-layer freezing mechanism, which gives rise to an apparent fragile-to-strong transition in the solidification dynamics. In contrast to the freezing/melting behavior of water, the effect of nanoconfinement on the glass transition of supercooled liquids is nonuniversal and the glass transition temperature T-g can either increase or decrease with the dimensionality and extent of confinement. This nonuniversal behavior is exemplified by the two glass-forming molecular liquids, glycerol and ortho-terphenyl (OTP). While glycerol shows an increase in T-g and a pronounced slowdown of the rotational dynamics of the constituent molecules due to a change in the molecular packing between the bulk and the confined liquid, OTP displays a linear and confining-mediadependent depression of T-g with increased confinement that is strongly influenced by the pore-liquid interface characteristics. This Account concludes with a focus on recent experimental evidence of extreme spatial and dynamical heterogeneity in both freezing and glass transition processes. This discovery was enabled by the unique mesoporous structures of SBA-16 and FDU-5, possessing bimodal architectures with two interconnected pore types of different size and shape (spherical and cylindrical). For the very first time, two melting points for water and two glass transitions for supercooled OTP, corresponding to a specific pore type, were observed. Collectively, these observations strongly suggest a close mechanistic connection between the local fluctuations in the structure and dynamics of nanoconfined liquids. While the findings reviewed in this Account provide new insights into thermodynamic and kinetic transitions of fluids, there remain many unanswered questions regarding the effects of nanoconfinement on the fundamental properties of fluids, which offer exciting future opportunities in chemical research.

Solid-liquid interactions in nanoconfinement often differ from their bulk counterparts. One such interaction is speciation on a material surface within an electrolyte solution. It remains unclear if surface speciation differs in nanoconfinement due to EDL overlap, material composition, pore structure, or combinations thereof. Different materials have shown varying degrees of surface speciation changes in nanoconfinement, from negligible up to 87% difference [1, 2]. This potential change in surface chemistry can affect adsorption of metals and wetting characteristics of NAPLs and oils, major processes considered in environmental management and resource exploration fields [1, 2, 3]. Constraining which combinations of aforementioned conditions cause changes in surface speciation will help predict types of solid-liquid interactions that may occur given system-specific characteristics. Synthesized amorphous silica aerogel with an average pore diameter of 19 nm and cylindrical pores is used to study effects of nanoconfinement on amorphous silica surface speciation with a known pore geometry. Potentiometric titrations are performed on 0.1 g of crushed aerogel in 0.001, 0.01, 0.1, and 1 M KNO 3 solutions at 20ºC and 0.8 bar. Solutions are titrated from pH 11 to 2 with 0.1 M HNO 3 . Surface charge density is calculated from titration data and fitted to CCM and CEM surface complexation models to derive surface protonation constants. These values will be compared between models and to those of bulk silica.

1Geology & Geophysics, U. of Wyoming, Laramie, WY, (*correspondence: ajacobs8@uwyo.edu) 2Mechanical Engineering, Pennsylvania State, University Park, PA 3School of Energy Resources, U. of Wyoming, Laramie, WY 4Materials Science & Engineering, UC-Davis, Davis, CA 5Chemical Engineering, U. of Utah, Salt Lake City, UT 6Chemistry, U. of Utah, Salt Lake City, UT 7Metallurgical Engineering, U. of Utah, Salt Lake City, UT

Hydrogen fuel has become a popular option for a future fuel source to replace dwindling natural resources. Despite this push, the bulk of today's hydrogen fuel is still produced from fossil fuels, tethering production to non-renewable sources and further release of greenhouse gases. The use of photocatalytic semiconductors for solar-driven water-splitting offers a clean solution to hydrogen fuel production. Titanium dioxide sensitized to visible light represents a simple and promising system for application in hydrogen fuel production as well as for the generation of energy in photovoltaics. Sol-gel synthesis methods allow for the development of titanium dioxide with highly tunable properties while providing a simple method for inclusion of sensitizing agents without the use of additional fixing agents or lengthy adsorption stages. Rather than using conventional dyes to sensitize the titanium dioxide for visible light photocatalysis, the creation of a biohybrid material through the encapsulation of proteins enables us to take advantage of the natural functionality of such proteins to further improve on the photoactivity of titanium dioxide. By harnessing naturally occurring proteins from our environment and sol-gel chemistry, we are capable of fabricating novel materials in order to address the mounting need for clean, renewable fuel and energy production.

Microstructural refinement of magnesium (Mg) alloys is beneficial for mechanical and corrosion properties, both of which are critical for their successful application as temporary implant materials. One method of achieving a refined microstructure is through rapid solidification via gas-atomization-powder production. In this study we investigated spark plasma sintering (SPS) as a potential processing method for maintaining this refined microstructure while achieving a range of porosities up to full densification. We characterized the microstructural evolution as a function of sintering temperature from 250 to 450 °C for the alloy WE43 using multi-scale correlative microscopy techniques, including light microscopy and scanning and transmission electron microscopy-based methods. The spatial distribution of the two major alloying elements, neodymium (Nd) and yttrium (Y), was determined and the intermetallic phases they form identified using energy dispersive X-ray spectroscopy in conjunction with electron diffraction. The gas-atomized powder microstructure consists of Mg-rich dendrites and a percolating interdendritic Mg-Nd-Y ternary phase with structure Mg14Nd2Y, surrounded by a high Nd and Y content in solid solution. This microstructure is maintained up to a sintering temperature of 350 °C, while with higher sintering temperatures segregation of Nd and Y dominates. The percolating ternary phase breaks up into faceted globular precipitates with structure Mg5Nd, which is isomorphous to Mg14Nd2Y. Y comes out of solution and migrates to previous powder-particle surfaces, possibly forming Y2O3. Sample densities ranged from 64 to 100% for sintering temperatures of 250 to 450 °C, respectively, and the grain size remained constant at about 10 µm. SPS is demonstrated to be an attractive alternative method for processing Mg alloys to a wide range of porosities and fine microstructures. The microstructural refinement achieved by SPS holds the potential for slow and homogeneous corrosion. STATEMENT OF SIGNIFICANCE: This study presents the impact spark plasma sintering (SPS) has on the microstructure of WE43, a magnesium alloy used for biodegradable implants. SPS is of great interest in this context as it is scalable, rapid, and has the potential for tuning density while maintaining a refined microstructure. The microstructure and density are explored from the gas-atomized powder to the densified material using electron microscopy and chemical mapping from the macro- to the nano-level. The insights gained reveal an original evolution of rare-earth element distribution with an isomorphous chemistry change, while the microstructure develops from the non-equilibrium state (powder) towards an equilibrium structure upon sintering. This study, including measurements of mechanical performance, sets the premises of SPS for the fabrication of Mg-based implants with tunable characteristics.

Mullite is the only stable intermediate phase in the alumina–silica system at atmospheric pressure. Although this solid solution phase is commonly found in human-made ceramics, only rarely does it occur as a natural mineral. Yet mullite is a major component of aluminosilicate ceramics and has been found in refractories and pottery dating back millennia. As the understanding of mullite matures, new uses are being found for this ancient material in the areas of electronics and optics, as well as in high temperature structural products. Many of its high temperature properties are superior to those of most other metal oxide compounds, including alumina. The chemical formula for mullite is deceptively simple: 3Al 2 O 3 .2SiO 2 . However, the phase stability, crystallography, and stoichiometry of this material remain controversial. For this reason, research and development of mullite is presented in an historical perspective that may prove useful to engineers and scientists who encounter this material under nonequilibrium conditions in their work. Emphasis is placed on reviewing studies where the primary goal was to create single-phase mullite monoliths with near theoretical density.

We study bacteriorhodopsin (BR) in its native purple membrane encapsulated within amorphous titanium dioxide, or titania, gels and in the presence of titania sol particles to explore this system for hydrogen production. Förster resonance energy transfer between BR and titanium dioxide sol particles was used to conclude that there is nanometer-scale proximity of bacteriorhodopsin to the titanium dioxide. The detection of BR-titania sol aggregates by fluorescence anisotropy and particle sizing indicated the affinity amorphous titania has for BR without the use of additional cross-linkers. UV-vis spectroscopy of BR-titania gels shows that methanol addition did not denature BR at a 25 mM concentration presence as a sacrificial electron donor. Additionally, confinement of BR in the gels significantly limited protein denaturation at higher concentration of added methanol or ethanol. Subsequently, titania gels fabricated through the sol-gel process using a titanium ethoxide precursor, water, and the addition of 25 mM methanol were used to encapsulate BR and a platinum reduction catalyst for the production of hydrogen gas under white light irradiation. The inclusion of 5 μM bacteriorhodopsin resulted in a hydrogen production rate of about 3.8 μmol hydrogen mL-1 h-1, an increase of 52% compared to gels containing no protein. Electron transfer and proton pumping by BR in close proximity to the titania gel surface are feasible explanations for the enhanced production of hydrogen without the need to cross-link BR to the titania gel. This work sets the stage for further developments of amorphous, rather than crystalline, titania-encapsulated bacteriorhodopsin for solar-driven hydrogen production through water splitting.

Bacteriorhodopsin was encapsulated within amorphous titanium dioxide gel in order to sensitize the bulk material to visible light and promote mass transfer of protons within the pore of the gel for the purpose of hydrogen production through photocatalytic-driven water-splitting. The dynamics of the bacteriorhodopsin within the gel matrix were investigated through spectroscopic techniques to determine the stability and functionality of the protein under confinement and in the presence of ethanol. Ethanol concentrations within the gel pores varied up to 11.4 M with evidence of the presence of properly folded bacteriorhodopsin in gels with ethanol concentrations up to 6.4 M with no indications of protein loss over the course of two weeks. Under visible light irradiation, entrapped bacteriorhodopsin retained the ability to make reversible conformational changes associated with the initiation of the protein's photocycle necessary to perform as a proton pump. In response to increasing temperatures, the bacteriorhodopsin was also able to achieve the same level of secondary structure shifts in the gel as in solution. The amorphous titanium dioxide without encapsulated protein was shown to achieve a comparable level of photocatalytic activity to commercial crystalline nanoparticles under UV-only irradiation and the inclusion of bacteriorhodopsin to increase this activity and make the material more applicable for solar-driven photocatalysis is promising. This sets the stage for the development of a bio-nanocomposite material for renewable hydrogen production.

To understand the role of α-Fe/TaC interface on the clustering behavior of helium (He) atoms inside castable nanostructured alloys under irradiation, we built two models (Ta13C14@Fe215 and {1 0 0} 〈1 1 0〉 Fe//{1 0 0} 〈1 0 0〉 TaC interface) and perform systemical ab initio calculations to investigate the energetics of point defects (vacancy, anti-site defect and He), substitutional defect clusters CrFem (1 ≤ m ≤ 4), and Hen (1 ≤ n ≤ 4) clusters, the migration behavior of He atom as well as the effect of Cr atoms and vacancies on the stability of Hen clusters. Vacancy and He at the α-Fe/TaC interface of the Ta13C14@Fe215 are more stable than that in Ta13C14 cluster and Fe matrix. Ta atom at this interface escapes from the lattice site more easily than C atom. In addition, the Cr atoms substituting Fe sites are more stable than Fe vacancies, which reduces the formation energies of Hen clusters in α-Fe/TaC on the Ta13C14@Fe215. Both formation energy and migration energy of He atom in {1 0 0} 〈1 1 0〉 Fe//{1 0 0} 〈1 0 0〉 TaC interface are lower than those in bulk TaC and α-Fe. Hence, {1 0 0} 〈1 1 0〉 Fe//{1 0 0} 〈1 0 0〉 TaC interface as a sink can trap more helium atoms and vacancies than α-Fe matrix.