Three-Dimensionally Ordered Array of Air Bubbles in a Polymer Film

Abstract

We report the formation of a three-dimensionally ordered array of air bubbles of monodisperse pore size in a polymer film through a templating mechanism based on thermocapillary convection. Dilute solutions of a simple, coil-like polymer in a volatile solvent are cast on a glass slide in the presence of moist air flowing across the surface. Evaporative cooling and the generation of an ordered array of breath figures leads to the formation of multilayers of hexagonally packed water droplets that are preserved in the final, solid polymer film as spherical air bubbles. The dimensions of these bubbles can be controlled simply by changing the velocity of the airflow across the surface. When these three-dimensionally ordered macroporous materials have pore dimensions comparable to the wavelength of visible light, they are of interest as photonic band gaps and optical stop-bands.

Square Packing and Structural Arrangement of ABC Triblock Copolymer Spheres in Thin Films

“…The other possible mechanism could be analogous to the widely observed breath figure (BF) formation on drop-cast polymer films. [62][63][64][65][66][67][68][69][70][71][72] In earlier publications, 41,42 we proposed the possibility that water condensation onto the PEO-based block copolymers leads to PEO domain ordering. After solvent annealing, the solvent evaporation causes the cooling of the film surface.…”

Mesoscopic Patterning in Thin Polymer Films Formed under the Fast Dip‐Coating Process

“…We varied the atmospheric humidity in our experiments over a wide range and did not observe any evidence of the humidity having impact on mesoscopic pattern formation. We want to emphasize that we deposited our films on vertical plates, whereas other groups worked with horizontal substrates; hence, the sinking of water droplets, discussed by Srinivasarao [12][13][14] et al, cannot be invoked for the explanation of the phenomenon.…”

“…In other terms, a cooling due to the evaporation has been rapidly compensated by the heat flux from outside the system. Srinivasarao has shown that high vapor pressure of the solvent and the velocity of air across the surface drive solvent evaporation, rapidly cooling the surface, this cooling to be as much as 25°C 12 It is possible to suggest that in the absence of such compensation the evaporation cooling would lead to a decrease of the diffusion coefficient and increase of the viscosity. Both of these factors are able to prevent formation of nontrivial mesoscopic structures.…”

“…Srinivasarao, Shimomura and Pitois have related the phenomenon to atmospheric humidity, which can favor the formation of the honeycomb films [8][9][10][12][13][14] . L. Weh related self-organization to mass and heat transfer processes, which take place in the thin polymer film under the dewetting procedure.…”

Fabrication of a micro-structured surface based on interfacial convection for drag reduction

“…Maruyama et al [22] proposed a solvent-casting method for the preparation of 2-dimensional submicron scale structures. Srinivasarao et al [23] reported a simple and robust method using evaporative cooling to fabricate ordered micro-porous polymer films.…”