Two-step crystallization and solid–solid transitions in binary colloidal mixtures

Abstract

Crystallization is fundamental to materials science and is central to a variety of applications, ranging from the fabrication of silicon wafers for microelectronics to the determination of protein structures. The basic picture is that a crystal nucleates from a homogeneous fluid by a spontaneous fluctuation that kicks the system over a single free-energy barrier. However, it is becoming apparent that nucleation is often more complicated than this simple picture and, instead, can proceed via multiple transformations of metastable structures along the pathway to the thermodynamic minimum. In this article, we observe, characterize, and model crystallization pathways using DNA-coated colloids. We use optical microscopy to investigate the crystallization of a binary colloidal mixture with single-particle resolution. We observe classical one-step pathways and nonclassical two-step pathways that proceed via a solid–solid transformation of a crystal intermediate. We also use enhanced sampling to compute the free-energy landscapes corresponding to our experiments and show that both one- and two-step pathways are driven by thermodynamics alone. Specifically, the two-step solid–solid transition is governed by a competition between two different crystal phases with free energies that depend on the crystal size. These results extend our understanding of available pathways to crystallization, by showing that size-dependent thermodynamic forces can produce pathways with multiple crystal phases that interconvert without free-energy barriers and could provide approaches to controlling the self-assembly of materials made from colloids.

Gas flow-assisted vacuum drying: identification of a novel process for attaining high-quality perovskite films

“…27,35 Secondly, the gas flow accelerates the removal of solvent vapors near the interface, which leads to locally increased concentration at the interface. Hence, the crystallization starts at the solvent/air interface where the gas flow hits the sample first, as mentioned by Chen et al 36 Thirdly, the gas flow induces a higher nucleation rate leading to the formation of a highly oriented metastable crystal phase distributed across the wet film surface, 37 from where crystallites grow homogeneously as indicated by the red-shift of the PL peak and the narrow PL peak full width half maximum (Fig. 2c and Fig.…”

Polymorphic self-assembly of helical tubules is kinetically controlled

“…The fraction of defective tubules increases as the bending modulus B decreases and the target diameter D 0 increases. To avoid conditions under which de- fective structures are too prevalent, we set the binding energy to 6 k B T and the monomer chemical potential to µ = −3 k B T , so that assembly is sufficiently reversible to allow monomer detachment and annealing [31][32][33][34]. With these parameters, the fraction of defective tubes is generally below 30%.…”

Programming Self-Assembled Materials With DNA-Coated Colloids

“…Rogers et al [62][63][64][65][66] further investigated the physical behavior of the assembly of DNA-coated colloids mediated by free DNA strands. They argued that encoding information into the sequence and concentration of the free strands instead of the grafted strands could overcome the problems conventional colloidal self-assembly suffers, including uncollaborative mutual interactions and a limited number of interactions.…”