Directing convection to pattern thin polymer films

Abstract

Convection can be harnessed in elegant ways to pattern surfaces, often using uncomplicated equipment and materials, providing an interesting platform for future technological developments in thin film topographic assemblies. This manuscript contains a brief review of thin polymer film patterning methods that rely on directing convection, such as ''coffee ring'' patterning, lithographically induced self-assembly, and electrohydrodynamic patterning. These techniques are described in the context of a recent approach explored in our group for generating topographic patterns by photochemically directing Marangoni flow in thin polymer films with subtle gradients in surface energy. Aspects unique to this process are highlighted so that they may facilitate new developments in manufacturing technologically impactful patterned surfaces. For example, the features produced by photochemically directed Marangoni-driven flow are preprogrammed in the solid state, thermally developed and can be formed in multilayer films.

Photoinitiated Marangoni flow morphing in a liquid crystalline polymer film directed by super-inkjet printing patterns

“…At all temperatures, θ gly on cis-isomerized PAz was smaller than that of PBMA- b -PAz. These facts strongly suggests that the driving mechanism of the above photoinitiated migrations is the surface tension driven flow by the Marangoni effect, as has been suggested in former studies using photopatterned amorphous polymer films upon heating above T g 12–16 . The rate of mass migration in this work was notably fast compared with those of these previous examples.…”

“…Proposals by Ellson et al . 12–16 and this work further present a new direction to induce surface morphing by utilizing the Marangoni effect.…”

“…If the flow-induced deformation of polymer surfaces can be controlled as designed, this will provide a powerful tool for surface microfabrication. In this regard, Ellison and coworkers 12–16 have proposed the pioneering concept of arbitrary inscription of polymer surfaces based on the Marangoni flow via photopatterning on the free surface. A melt-flow is induced according to photopatterns upon annealing above the glass transition temperature ( T g ) of the base polymer.…”

Surface energy gradient driven convection for generating nanoscale and microscale patterned polymer films using photosensitizers

“…Since interdiffusion weakens the surface energy pattern that drives Marangoni flow, capillary forces favoring a flat film surface eventually dominate and the height variations start dissipating. 49 This study strengthens the argument that the feature formation mechanism is from Marangoni convection that occurs on a shorter time scale than self-diffusion, with features decaying at longer annealing times as the surface energy gradient diminishes with polymer self-diffusion.…”

Morphologies and Thermal Variability of Patterned Polymer Films with Poly(styrene-co-maleic anhydride)

“…Polymer films are likely prepared by spin-coating or dip-coating and classified as ultrathin films with a thickness < 100 nm or thin films with a thickness of 100 to 10,000 nm [1]. Due to the (visco-)elasticity of polymer films, the morphology can be influenced by interactions with the substrate or by external effects such as, e.g., temperature [2], humidity [3], pressure [4], electricity [5], light [6] or direct convection [7]. The adaptable morphology and response to external stimuli provides an excellent way for in situ handling of the morphology and properties of the polymer film.…”