Crystallization under Nanoscale Confinement

New York University, New York NY

Investigators

Abstract

Non-technical Abstract: Crystallization, one of the largest unit operations in U.S. industry, is critical to the advancement of materials science as well as various technical sectors that rely on solid formulations, from the pharmaceutical industry to optical and electronic materials. Nonetheless, crystal growth remains a poorly understood phenomenon. Moreover, advanced technologies - from information storage to energy conversion - increasingly rely on materials design at the nanometer length scale. This project examines crystallization of materials in ultrasmall nanometer-scale pores that constrain the size of crystals to dimensions where properties that are central to key technological sectors depart from the ordinary. The unique environment provided by the nanopores in refractory monoliths will be used to evaluate the properties and reactivity of magnesium salts, which have been implicated as water reporters on Mars. Composites consisting of large ensembles of nanocrystals in free-standing monoliths that can be handled readily and are anticipated to have unusual properties, will be investigated. The project also will support education activities aimed at widening the STEM pipeline for emerging young scientists, including the creation of teams of NYC middle and high-school students who will compete in the US Crystal Growth Competition, concurrent with a curriculum on structure and properties of crystals. The principal investigator also will operate a Material World workshop for faculty from minority-serving institutions designed to introduce new interdisciplinary curricula to college classrooms, and he will host the 24th biannual International Conference on the Chemistry of the Organic Solid State in 2019. These activities will augment substantial existing STEM activities at the New York University Materials Research Science and Engineering Center. Technical Abstract: This project will investigate crystallization in nanoscale pores of inert monoliths, providing an approach to narrow the knowledge gap in nucleation and growth by confining crystallization at a length scale that typically is impenetrable to study. The pore dimensions are comparable to the critical size regime where crystallization outcomes are determined, providing an opportunity to examine the influence of size on polymorph selectivity during crystallization as well as size-dependent polymorph stability rankings for confined crystals, effectively adding size as a variable on the phase diagram. The project will unravel the correspondence between size-dependent thermal properties, polymorph stability ranking, and critical sizes estimated from 2D X-ray diffraction. The nanosized pores provide an ideal environment to examine the role of stereochemical auxiliaries on polymorph selectivity and stability, which is thought to involve binding at specific crystal faces of incipient nuclei at the early stages of crystal growth. Characterizing the behavior of magnesium salt hydrates, confined in pores to emulate intergrowths, may inform on recent hydrated phases on Mars. Free-standing composite materials based on large ensembles of aligned functional nanocrystals (> 1010 crystals/cm2), which can obviate the need for bulk single crystals, also will be explored. Collectively, the project will provide much-needed insight into nucleation and crystal growth at critical length scales where crystallization can be deterministic while also providing a pathway to new hybrid materials. Students working on this project will acquire expertise in advanced X-ray diffraction methods, crystal structure analysis, polymorphism, molecular modeling, spectroscopy and near-field microscopies, and they will be trained in materials concepts that impact critical technological sectors, including pharmaceutical and electronic materials.