A Method for Producing a Polymer Film with an Array of Cavities Therein

A method for producing an array of cavities (2) in a polymer film (1) comprises preparing a polymer/solvent solution and drop casting a thin film (6) of the solution on a substrate. The film solution (6) is subjected to three gas flows. An initial gas flow of a relatively low relative humidity is passed over the film solution (6) to evaporate solvent from the polymer/solvent solution (6) to reduce the surface temperature of the film solution (6) below the dew point temperature of the next gas flow, namely, an intermediate gas flow. The intermediate gas flow of relatively high relative humidity forms droplets on the surface of the film solution (6) which grow into the film solution to form the cavities (2) therein. A final gas flow evaporates droplets from the formed cavities (6) as well as further solvent from the film solution (6), but maintains the level of solvent in the film solution (6) at a level, when the droplets have been evaporated to the extent that they no longer influence the formation of the cavities (2), so that the glass transition temperature of the polymer/film solution adjacent the cavities (2) is below the temperature of the film solution (6) in order to permit local polymer flow adjacent the cavities (2) to determine the final shape of the cavities (2).

WO 2,011,045,777


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