Understanding the driving forces for crystal growth by oriented attachment through theory and simulations
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BUILDING HIERARCHICAL MATERIALS VIA PARTICLE AGGREGATION
Understanding the driving forces for crystal growth by oriented attachment through theory and simulations Maria L. Sushko1,a) 1
Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. a)
Received: 28 February 2019; accepted: 5 April 2019
Oriented attachment (OA) is a particle-based crystallization pathway in which nanocrystals self-assemble in solution and attach along certain crystallographic direction often forming highly organized three-dimensional crystal morphologies. The pathway offers the potential for a general synthetic approach of hierarchical nanomaterials, in which multiscale structural control is achieved by manipulating the interfacial nucleation and self-assembly of nanoscale building blocks. Here, the current status of the development of a predictive theoretical framework for modeling crystallization by OA is reviewed. A particular emphasis is made on recent developments in understanding the microscopic details of solvent-mediated forces that drive nanocrystal reorientation and alignment for face-selective attachment. Interactions arising from the correlated solvent dynamics at particle interfaces emerge as the main sources of long-range face-specific interparticle forces and short-range torque for fine particle alignment into lattice matching configuration. These findings shift the focus of the experimental and theoretical research of OA onto the detailed study of interfacial solvent structure and dynamics.
Introduction Mounting experimental evidence point to a significant complexity of crystallization processes. Often crystal do not grow via monomer addition but undergo multiple transformation and assembly processes. One class of such alternative pathways involves crystallization by attachment of oriented crystals, known as oriented attachment (OA) [1, 2, 3]. The idea of crystal growth through the attachment of aligned small crystals was first suggested more than a 100 years ago based on observations of the assembly of pre-existing crystals in saturated solution into single or twinned crystals [4]. In these early experiments, crystallization of lead nitrate under slow evaporation of the solvent produced single crystals of octahedral habit. By contrast, stirring the solution of pre-existing crystals yielded the formation of spinel twins [5]. A more direct evidence of OA was obtained using transmission electron microscopy (TEM), which revealed a persistent crystallographic alignment of nanocrystals. The nanocrystals formed single crystal chains through the attachment along a specific crystal face [6, 7]. Subsequently many
ª Materials Research Society 2019
materials were shown to exhibit similar crystallization behavior in a geological environment, under controlled synthesis conditions and in biological systems [3, 8]. Most of the conclusions about the OA pathwa
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