Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H02: Self-assembly of Nanomaterials: Porous MaterialsFocus
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Sponsoring Units: DCP Chair: Marjolein Dijkstra, Utrecht University Room: LACC 150B |
Tuesday, March 6, 2018 2:30PM - 3:06PM |
H02.00001: Controlling Nucleation and Growth of 2D Covalent Organic Frameworks Invited Speaker: William Dichtel Covalent organic frameworks (COFs) are two or three-dimensional polymer networks with designed topology and chemical functionality, permanent porosity, and high surface areas. These features are potentially useful for a broad range of applications, including catalysis, optoelectronics, and energy storage devices. But current COF syntheses offer poor control over the material’s morphology and final form, generally providing insoluble and unprocessable microcrystalline powder aggregates. COF polymerizations are often performed under conditions in which the monomers are only partially soluble in the reaction solvent, and this heterogeneity has hindered understanding of their polymerization or crystallization processes. Homogenous polymerization conditions for boronate ester-linked, two-dimensional COFs that inhibit crystallite precipitation, resulting in stable colloidal suspensions of 2D COF nanoparticles will be presented. The hexagonal, layered structures of the colloids are confirmed by small angle and wide angle X-ray scattering (SAXS/WAXS), and kinetic characterization provides insight into the growth process. The colloid size is modulated by solvent conditions, and the technique is demonstrated for four 2D boronate ester-linked COFs. The diameter of individual COF nanoparticles in solution is monitored and quantified during COF growth and stabilization at elevated temperature using in situ variable-temperature liquid cell TEM (VT-LCTEM) imaging, a new characterization technique that complements conventional bulk scattering techniques. The use of these colloids to obtain larger crystals through a seeded growth approach will be presented. |
Tuesday, March 6, 2018 3:06PM - 3:18PM |
H02.00002: Molecular Simulation of Covalent Organic Framework Formation Vu Nguyen, Michael Grunwald Covalent-organic frameworks (COFs) are porous crystalline materials with promising applications from energy storage to separations. The main synthetic challenge associated with COFs is their poor long-range order; typical sizes of crystal domains do not exceed a few tens of nanometers. Here, we develop a model of the molecular constituents of COF-5 and follow the early stages of its assembly dynamics from dilute solution. Our simulations indicate that under typical experimental conditions COF-5 formation happens far from equilibrium through spinodal decomposition. This rapid assembly mode produces large concentrations of defects that are difficult to anneal and are likely responsible for the limited crystallinity observed in the synthesis of many COFs. We analyze the driving forces for COF-5 formation and find that stacking interactions between aromatic molecular constituents are too strong. When these interactions are weakened, assembly proceeds through single nucleation events followed by slow growth. The COF-5 crystallites obtained in this way are essentially defect-free. |
Tuesday, March 6, 2018 3:18PM - 3:54PM |
H02.00003: Controlled Assembly of Nanoporous Materials: Addressing the Voids in our Understanding of Zeolite Crystallization Invited Speaker: Jeffrey Rimer The unique properties of nanoporous zeolites find use in a variety of applications spanning ion exchange and separations to catalysis and drug delivery. The ability to selectively control zeolite synthesis to achieve desired physicochemical properties relies upon detailed understandings of the thermodynamic and kinetic factors regulating crystal nucleation and growth, which are generally lacking. Designing innovative approaches to tailor zeolite crystallization and exploit unique structure-performance relationships has the potential to produce materials with superior properties beyond what is achievable by conventional routes. In this talk, I will discuss efforts to elucidate the complex mechanisms of zeolite crystallization, which occur by nonclassical pathways [1] involving the self-assembly and structural evolution of amorphous precursors. There is still much that we do not understood regarding the role of precursors in nucleation and the influence of growth conditions on the selection of crystal topology, which underscores the need for molecular-level studies of zeolite crystallization. Our group addresses these challenges using a broad range of techniques that include the use solvothermal atomic force microscopy to capture time-resolved images of growing zeolite surfaces in real time.[2] This technique has led to the first in situ characterization of zeolite growth with the capability of resolving surface dynamics at the spatiotemporal scales necessary to elucidate mechanistic pathways of crystallization. Based on our findings, we observe that growth occurs via multiple (cooperative) pathways that differ from one material to the next. In this talk, we will summarize our findings for several zeolite structures. |
Tuesday, March 6, 2018 3:54PM - 4:06PM |
H02.00004: Nanoscale Control of Homoepitaxial Growth on a Two-Dimensional Zeolite Meera Shete, Manjesh Kumar, Donghun Kim, Neel Rangnekar, Dandan Xu, Jeffrey Rimer, Michael Tsapatsis Zeolites, crystalline microporous solids are of interest for a variety of applications including catalysis, adsorption, ion-exchange, separation membranes etc. Advances in the understanding of zeolite synthesis and crystallization have facilitated the development of core-shell catalysts, hierarchical materials, exfoliated two-dimensional nanosheets and thin films. Thus control of zeolite growth at a scale approaching single-unit-cell dimension is important to tailor their microstructure for performance optimization. However growth studies focusing on nanoscale control are still in their infancy. |
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H02.00005: A Molecular Dynamics Model for ZIF-8 Formation Carlos Chu-Jon, Michael Grunwald Metal-organic frameworks are a class of highly porous materials suitable for applications in energy storage and conversion, catalysis, and separations. Despite the large number of different MOF structures that have been discovered experimentally, little is known about their formation mechanisms. Here we present a simple computational model for ZIF-8 that utilizes an implicit solvent and coarse-grained interactions to elucidate the early stages of crystallization. Utilizing molecular dynamics we find that ZIF-8 nucleation is a multi-step process that is preceded by a metastable liquid-like phase that undergoes rearrangement and an increase in coordination number subsequent to the nucleation event. Furthermore, our model predicts the existence of a short lived gyroid-like structure that forms prior to ZIF-8 nucleation. Our simulation rationalize recent spectroscopic results that suggested the formation of a population of non-crystalline clusters prior to ZIF-8 growth. |
Tuesday, March 6, 2018 4:18PM - 4:54PM |
H02.00006: Self-assembly of mesophases and zeolitic crystals from nanoparticles Invited Speaker: Valeria Molinero Recent years have seen an explosion in the number of crystalline and quasi-crystalline structures formed by assembly of nanoparticles. To date, however, it has been difficult to assemble nanoparticles into mesophases such as those formed by block copolymers and surfactants. This presentation will discuss recent work in which we demonstrate that simulations of binary mixtures of unbound particles with simple short ranged pair interactions produce the same mesophases as block copolymers and surfactants, including lamellar, hexagonal, gyroid, body-centered cubic, face-centered cubic, perforated lamellar, and semicrystalline phases [Kumar and Molinero, J. Phys. Chem. Lett. 2017, 8, 5053-5058]. We will further discuss how the addition of anisotropic interactions to one type of particle in the mixture can result in the fast formation of zeolitic crystals, and the role of the mesophases in facilitating the formation of almost defect-free complex structures. The experimental realization of the interparticle interactions of this work would provide a distinc route to produce complex zeolitic crystals and liquid crystalline mesophases from nanoparticles. |
Tuesday, March 6, 2018 4:54PM - 5:06PM |
H02.00007: Non-contact Atomic Force Microscopy of Ordered Porous Materials Zachery Enderson, Alex Elder, Thomas Orlando, Phillip First Ordered porous materials (OPMs) are of scientific and technological |
Tuesday, March 6, 2018 5:06PM - 5:18PM |
H02.00008: Tracing Polymerization in Calcium Silicate Hydrates using Si Isotopic Fractionation Romain Dupuis, Jorge Dolado, José Surga, Andres Ayuela Silicate-chains polymerization is a crucial process in calcium silicate hydrate minerals, with large relevance for improving the durability and reducing the environmental impact of cement-based materials. To better understand the evolutionary mechanisms underlying the polymerization of silicate-chains in layered calcium silicate hydrates, we propose to trace the evolution of the polymerization degree by using silicon isotopes[1 ]. We show that the Isotopic fractionation tool is able to discern not only between the polymerization order of calcium silicate hydrate minerals but even between cement gels suffering calcium leaching[2]. Silicon isotopic fractionation can, therefore, be used to improve the sustainability of concrete along its lifetime in the quest for green cement[3]. |
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