Using particle-based Monte Carlo simulations and continuum modeling, we study the self-assembly of asymmetric diblock copolymers in the course of solvent evaporation. We examine the effects of evaporation rate and solvent selectivity on the structure formation, especially the alignment of the cylindrical domains of the minority block. The comparison of the two simulation techniques facilitates identifying general trends upon parameter variation, while their inherent differences help us to understand the role of single-chain dynamics, fluctuations, and additional model details. In both cases, the simulation models feature a liquid and a gas phase with an explicit surface, across which solvent evaporates. We propose a "layer evolution model" that links processing parameters to the final morphology via the time dependence of layers, in which characteristic microphases, for example, spherical or cylindrical, can form. The evolution of these layers varies with the processing conditions and determines the morphology. This allows us to discuss the interplay of various experimentally accessible parameters, which we support by respective simulations. Our results single out two main factors to ensure the formation of minority-block cylinders, perpendicular to the film surface: (i) Fast evaporation rates induce a steep gradient in the polymer-density profile; that is, the polymer density immediately beneath the gas− liquid surface rapidly exceeds the critical value for cylinder formation. This confines cylinder formation into a layer that is thinner than the actual cylinder diameter, forcing a perpendicular alignment. (ii) A certain selectivity of the gas phase for the matrix-forming, majority block is necessary to disrupt an otherwise entropically favored surface layer of the minority block that would lead to parallel cylinder alignment.

Despite the presence of strong fluctuations, many turbulent systems such as Rayleigh-Bénard convection and Taylor-Couette flow display self-organized large-scale flow patterns. How do small-scale turbulent fluctuations impact the emergence and stability of such large-scale flow patterns? Here, we approach this question conceptually by investigating a class of pattern forming systems in the presence of random advection by a Kraichnan-Kazantsev velocity field. Combining tools from pattern formation with statistical theory and simulations, we show that random advection shifts the onset and the wave number of emergent patterns. As a simple model for pattern formation in convection, the effects are demonstrated with a generalized Swift-Hohenberg equation including random advection. We also discuss the implications of our results for the large-scale flow of turbulent Rayleigh-Bénard convection.Many turbulent systems show a remarkable degree of large-scale coherence, despite the presence of strong fluctuations. Large-scale convection patterns in the atmosphere and in the oceans are among the most fascinating examples. Rayleigh-Bénard convection (RBC) [1][2][3][4], the flow between two plates heated from below and cooled from above, is a prototypical model for such flows and displays a range of phenomena-the emergence of laminar large-scale rolls close to the onset of convection, transitions to increasingly complex flow patterns as the temperature difference is increased, and finally, the emergence of turbulence. Close to onset, techniques like linear stability analysis as well as amplitude and phase equations explain the emergence and stability of convection patterns [5][6][7][8][9][10][11]. Further away from the onset of convection, the flow becomes increasingly difficult to describe, especially when it becomes turbulent. Both experiments and, in particular, numerical simulations have provided insights into these complex flow regimes [1][2][3]. Remarkably, coherent large-scale flow patterns, so-called turbulent superstructures, have been reported in the presence of small-scale turbulence [12][13][14][15][16][17][18]. Using suitable averaging techniques, the topology and dynamics of the superstructures have been extracted from the turbulent flow fields, demonstrating, e.g.,large-scale dynamics reminiscent of spiraldefect chaos [16]. Extensive experimental and numerical investigations revealed that the length scale of the emerging patterns increases as a function of Rayleigh and Prandtl numbers as the flow becomes increasingly unsteady [19][20][21] and, finally, turbulent [14,18]. Investigations of RBC close to onset suggest that there is no universal scale selection mechanism, see, e.g., [22,23] for an overview. As soon as turbulence sets in, the issue is even more delicate: so far there is no conclusive explanation for the increased wavelength of turbulent superstructures. Interestingly, similar issues remain in explaining turbulent Taylor Couette flow [24], i.e. the flow between two rotating cylinders. Also here, the ...