We study the deposition mechanisms of polymer from a confined meniscus of volatile liquid. In particular, we investigate the physical processes that are responsible for qualitative changes in the pattern deposition of polymer and the underlying interplay of the state of pattern deposition, motion of the meniscus, and the transport of polymer within the meniscus. As a model system we evaporate a solution of poly(methyl methacrylate) (PMMA) in toluene. Different deposition patterns are observed when varying the molecular mass, the initial concentration of the solute, and temperature; these are systematically presented in the form of morphological phase diagrams. The modi of deposition and meniscus motion are correlated. They vary with the ratio between the evaporation-driven convective flux and the diffusive flux of the polymer coils in the solution. In the case of a diffusion-dominated solute transport, the solution monotonically dewets the solid substrate by evaporation, supporting continuous contact line motion and continuous polymer deposition. However, a convection-dominated transport results in an oscillatory ratcheting dewetting-wetting motion of the contact line with more pronounced dewetting phases. The deposition process is then periodic and produces a stripe pattern. The oscillatory motion of the meniscus differs from the well documented stick-slip motion of the meniscus, observed as well, and is attributed to the opposing influences of evaporation and Marangoni stresses, which alternately dominate the deposition process.
The capacity of nanoparticles to self‐arrange to various structures and their unique physical properties has made these building blocks essential in a broad range of applications and scientific disciplines. In this work, the manipulation of particulate structures that appear from binary dispersions is demonstrated, comprising same size particles of two different chemistries, following the evaporation of an electrolyte solution carrier. By varying the ionic strength and pH in the solutions, the balance between attractive and repulsive surface forces is tuned, that is, electrical double layer, Van der Waals, hydrophobic, and hydrophilic forces, in the binary particle mixtures. Hence, the corresponding potential energy barriers are tuned to particle attachments to each other and to the underlying substrate and alter the nanoscopic arrangement of the different types of particles in the microscopic particulate structures, which appear by convective pattern formation. Hence, by realizing the physical mechanisms which govern the potential energy contributions to the pattern formation of particulate structures at the nanometer scale, the 3D morphology of binary mixtures of same size particles is rendered homogeneous, layered, or phases separated. This is a useful approach toward the top‐down fabrication of nonhomogeneous colloidal structures.
We employ a theoretical model to explain the wetting–dewetting motion of the contact line by incorporating opposing evaporation and Marangoni induced flows in the deposition process.
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