Abstract
Hybrid nanomaterials possess complex architectures that are driven by a self-assembly process between an inorganic element and an organic ligand. The properties of these materials can often be tuned by organic ligand variation, or by swapping the inorganic element. This enables the flexible fabrication of tailored hybrid materials with a rich variety of properties for technological applications. Liquid-liquid interfaces are useful for synthesizing these compounds as precursors can be segregated and allowed to interact only at the interface. Although procedurally straightforward, this is a complex reaction in an environment that is not easy to probe. Here, we explore the interfacial crystallization of mithrene, a supramolecular multi-quantum well. This material sandwiches a well-defined silver-chalcogenide layer between layers of organic ligands. Controlling mithrene crystal size and morphology to be useful for applications requires understanding details of its crystal growth, but the specific mechanism for this reaction remain only lightly investigated. We performed a study of mithrene crystallization at an oil-water interfaces to elucidate how the interfacial free energy affects nucleation and growth. We exchanged the oil solvent on the basis of solvent viscosity and surface tension, modifying the dynamic contact angle and interfacial free energy. We isolated and characterized the reaction byproducts via scanning electron microscopy (SEM). We also developed a high-throughput small angle X-ray scattering (SAXS) technique to measure crystallization at short reaction timescales (minutes). Our results showed that modifying interfacial surface energy affects both the reaction kinetics and product size homogeneity and yield. Our SAXS measurements reveal the onset of crystallinity after only 15 min. These results provide a template for exploring directed synthesis of complex materials via experimental methods.
Highlights
Exchanging out the organic solvent resulted in shifting reaction kinetics, mithrene edge morphology, and overall product yield and size as compared to the toluene synthesis
We believe that the slow diffusion of the DMSO into the aqueous layer overtime still allowed for mithrene crystals to form at an interface, but the reducing interfacial surface tension caused the polymer raft to break and the products sunk to the bottom of the vial
Altering solvent viscosity and the interfacial surface tension provides a tool for studying some aspects of the interfacial environment without having to resort to such methods
Summary
The metal-organic chalcogenolates (MOCHas) of coinage metals (Cu, Ag, Au) and simple organic ligands have attracted interest as a class of hybrid nanostructured materials (Dance et al, 1984; Dance and Fisher, 1994; Yeung et al, 2020; Hu et al, 2009; Laibinis et al, 1991; Lavenn et al, 2016) with interesting optoelectronic properties (Veselska et al, 2019; Yan et al, 2017; Mak et al, 2010), mechanochemistry (Jodlowski et al, 2016; Yan et al, 2018), and intrinsic chemical tunability (ChengInterfacial Synthesis of Mithrene et al, 2014; Kumar et al, 2013). Silver (I) benzeneselenolate, is a well understood example of this material class It is a direct gap semiconductor with a large exciton binding energy, that exhibits optical properties similar to transition metal dichalcogenide monolayers like MoS2 (Chen et al, 2017; Trang et al, 2018; Maserati et al, 2020; Yao et al, 2020). We examined the role of reagent concentration and temperature on its interfacial crystallization (Schriber et al, 2018; Forster et al, 2002) and their role in the assembly of both the target crystals and an amorphous byproduct (Schriber et al, 2018; Popple et al, 2018) These studies focused on modifying external components to the interfacial synthesis, as opposed to affecting the interface itself
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