The multiparametric nature of nanoparticle self‐assembly makes it challenging to circumvent the instabilities that lead to aggregation and achieve crystallization under extreme conditions. By using non‐base‐pairing DNA as a model ligand instead of the typical base‐pairing design for programmability, long‐range 2D DNA–gold nanoparticle crystals can be obtained at extremely high salt concentrations and in a divalent salt environment. The interparticle spacings in these 2D nanoparticle crystals can be engineered and further tuned based on an empirical model incorporating the parameters of ligand length and ionic strength.

The solidification of hybrid perovskite (MAPbX3, X = I, Br, Cl) inks is studied in situ by A. Amassian and co‐workers in article 1604113, revealing a remarkably complex process mediated by strong solvent‐solute interactions, the outcome of which is halide‐dependent. The ink is shown to solidify within 15–20s of spinning, forming a highly solvated (60–70 vol%) precursor phase. Crystalline order of the precursor, or lack thereof, strongly impacts the morphological outcome of thermal conversion and the reproducibility of solar cells.

Time‐resolved grazing‐incidence smallangle X‐ray scattering is used to investigate the structural changes in a lamellar block copolymer thin film during solvent vapor treatment and drying. Drastic changes proceed at the film surface: During solvent vapor treatment, the film surface is covered by one of the blocks. During drying, this thin surface layer retracts, and protrusions of the other block are formed. Further details can be found in the article by J. Zhang, D. Posselt, A. Sepe, X. Shen, J. Perlich, D.‐M. Smilgies, and C. M. Papadakis* on page 1289.

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Cover: The article by Potemkin and coworkers provides free-energy considerations to explain the molar mass dependent morphology of lamellar diblock copolymer thin films of poly(styrene-b-butadiene). Atomic force microscopy (AFM) and grazing-incidence small-angle scattering (GISAXS) data were instrumental to establish the lamellar orientation as a function of the interaction parameter xN and the ratio of film thickness over lamellar thickness D red . The relevant free-energy contributions are discussed that determine the boundary between the observed orientational phases. Further details can be found in the article by