A Synergistic Approach to Atmospheric Water Scavenging.

An abundant supply of fresh water is one of the leading challenges of the 21st century (UNESCO. The United Nations World Water Development Report 2018: Nature-Based Solutions for Water;UNESCO: Paris, France, 2018; p 154). Here we describe a new approach to scavenge atmospheric water that employs a hierarchically ordered porous material with embedded particles (Lash, M. H.; Jordan, J. C.; Blevins, L. C.; Fedorchak, M. V.; Little, S. R.; McCarthy, J. J.Non-Brownian Particle-Based Materials with Microscale and Nanoscale Hierarchy. Ang. Chem. Int. Ed.201554, 5854-5858). This composite uses structure to amplify native material performance to realize synergy between the capture and storage and to ultimately qualitatively change the adsorption behavior of the hydrogel (from unfavorable to favorable). In this way we can capture moisture at significantly lower relative humidities than would otherwise be feasible with the native materials. Not only does this approach pose the potential for a cheap and low-energy source of clean water but it could also be modified for application across a variety of condensable vapor reclamations.

Transport analogy for segregation and granular rheology.

Here, we show a direct connection between density-based segregation and granular rheology that can lead to insight into both problems. Our results exhibit a transition in the rate of segregation during simple shear that occurs at I∼0.5 and mimics a coincident regime change in flow rheology. We propose scaling arguments that support a packing fraction criterion for this transition that can both explain our segregation results as well as unify existing literature studies of granular rheology. By recasting a segregation model in terms of rheological parameters, we establish an approach that not only collapses results for a wide range of conditions, but also yields a direct relationship between the coordination number z and the segregation velocity. Moreover, our approach predicts the precise location of the observed regime change or saturation. This suggests that it is possible to rationally design process operating conditions that lead to significantly lower segregation extents. These observations can have a profound impact on both the study of granular flow or mixing as well as industrial practice.

Non-Brownian particle-based materials with microscale and nanoscale hierarchy.

Colloidal crystals are interesting materials owing to their customizable photonic properties, high surface area, and analogy to chemical structures. The flexibility of these materials has been greatly enhanced through mixing particles with varying sizes, compositions, and surface charges. In this way, distinctive patterns or analogies to chemical stoichiometries are produced; however, to date, this body of research is limited to particles with nanoscale dimensions. A simple method is now presented for bottom-up assembly of non-Brownian particle mixtures to create a new class of hierarchically-ordered materials that mimic those found in nature (both in pore distribution as well as stoichiometry). Additionally, these crystals serve as a template to create particle-based inverted crystalline structures with customizable properties.

Fabrication and characterization of non-Brownian particle-based crystals.

Particle-based crystals have been explored in the literature for applications in molecular electronics, photonics, sensors, and drug delivery. However, much of the research on these crystals has been focused on particles of nano- and submicrometer dimensions (so-called colloidal crystals) with limited attention directed toward building blocks with dimensions ranging from tens to hundreds of micrometers. This can be attributed, in part, to the fact that the underlying thermal effects in these larger systems typically cannot naturally overcome kinetic barriers at the meso- and macroscales so that many of the methods used for nanoscale particle assembly cannot be directly applied to larger components, as they become kinetically arrested in nonequilibrium states. In this work, ultrasonic agitation is being explored as a means of allowing large, non-Brownian microparticles (18-750 µm) to overcome the kinetic barriers to packing in the creation of close-packed, highly ordered, crystalline structures. In addition, we study how the energy input affects bulk particle behavior and describe several new ways to characterize particle-based crystals made from microparticles.

Accurate amorphous silica surface models from first-principles thermodynamics of surface dehydroxylation.

Accurate atomically detailed models of amorphous materials have been elusive to-date due to limitations in both experimental data and computational methods. We present an approach for constructing atomistic models of amorphous silica surfaces encountered in many industrial applications (such as catalytic support materials). We have used a combination of classical molecular modeling and density functional theory calculations to develop models having predictive capabilities. Our approach provides accurate surface models for a range of temperatures as measured by the thermodynamics of surface dehydroxylation. We find that a surprisingly small model of an amorphous silica surface can accurately represent the physics and chemistry of real surfaces as demonstrated by direct experimental validation using macroscopic measurements of the silanol number and type as a function of temperature. Beyond accurately predicting the experimentally observed trends in silanol numbers and types, the model also allows new insights into the dehydroxylation of amorphous silica surfaces. Our formalism is transferrable and provides an approach to generating accurate models of other amorphous materials.