Porous Polymer Films Templated by Marangoni Flow-Induced Water Droplet Arrays

Abstract

In this article, we report the development of a novel, simple, and cost-effective method for fabricating porous polymer films with controllable interpore distances, pore sizes, and arrangements using water droplets induced by Marangoni flow as templates. First, a spread-thin ethanol film on a partially water-wettable substrate is exposed to a humid airflow, facilitating the evaporation and recession of the ethanol film. Meanwhile, water in the airflow condenses on the ethanol film and accumulates near the receding contact line, which induces the formation of water fingers at the receding contact line and, finally, ordered arrays of water droplets after detachment. The formation of the hexagonal and square arrays of water droplets is due to the pinning and sliding of the water fingers on the silicone oxide (SiOx) and silicon (Si) substrates, respectively. By varying the thickness of the ethanol film spread on the Si substrate, the sliding velocity of water fingers can be tuned, subsequently leading to the fabrication of other arrangements. The interdroplet distance and droplet size can be dependently controlled by tuning the humidity of the airflow. The ordered arrays of water droplets on the substrate are then utilized to fabricate porous polymer films by dip-coating the substrate with a polystyrene solution. Films with hexagonal and square (and other arrangements) arrays of pores are fabricated on the silicon oxide (SiOx) and silicon (Si) substrates, respectively. The pore size can also be independently tuned by further condensation or evaporation of formed water droplets, leading to porous polymer films with both close- and non-close-packed arrays of pores. The ordered porous polymer films can be further used as templates for fabricating metal post patterns.

Anticholinesterase furocoumarins from Heracleum platytaenium, an endemic species to Idea mountains

“…In this method, not only hexagonal arrays but also square and other types of arrangements of pores in the films can be achieved and this opens a new way to manufacture highly ordered porous structures in a wide diversity for use in lithography masks, biomolecular patterning, and metal or metal oxide patterning. 166 Kojima et al investigated the effect of interfacial tension between water and polymer solution for the control of the honeycomb pattern structure by using PS and amphiphilic copolymers. The physical properties of these amphiphilic copolymers play a critical role in the stabilization of the condensed water droplets and structure of the honeycomb patterned films.…”

Marangoni-induced deformation of evaporating liquid films on composite substrates

“…Equation 6 expresses the no-penetration and no-slip conditions and Eqs. 7, 8 express the continuity of temperature and heat flux at the solid-liquid interface, respectively.…”

“…The expressions of the type (15) are substituted into the non-dimensionalized system (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). The governing equations and boundary conditions are expanded in series of ε.…”

“…Evaporation of liquid films and drops is a key phenomenon in many modern technological processes, including ink-jet printing [1], drying of paint films [2,3], and self-assembly of nanoparticles and porous layers [4][5][6]. The dynamics of evaporating films and drops is governed by various physical mechanisms, including surface tension, gravity, wettability, and phase change.…”

Characterization and electrochemical behaviors of honeycomb-patterned poly(N-vinylcarbazole)/polystyrene composite films

“…One of the many methods for fabricating porous polymer films [7][8][9][10] is the breath-figure formation, which is a simple and useful technique [11,12]. Through this method, porous films from many kinds of substrates, including star polymers, block copolymers, proteins, and polymer composites, have been fabricated under humid conditions [13,14].…”