Method of forming micropatterned surface using irradiation on a moisture responsive multi-layer film and film used in such method
A film comprises an elastomeric or soft polymer substrate that is capable of converting light to heat a second layer comprising a hydrophilic polymer and nanosheets of layered inorganic material dispersed in the hydrophilic polymer. The substrate can comprise a photothermal particle. The film can be used in a method by irradiating the film to cause wrinkles and optionally further exposing the film to moisture with optional drying.
1 . A method comprising;
obtaining a film comprising an elastomeric substrate wherein the substrate comprises an elastomeric material and photothermally active particles; and
a layer directly or indirectly adhered to the substrate, the layer comprising a hydrophilic polymer and nanosheets of a layered inorganic material wherein a thickness of the layer is 100 to 600 nanometers,
irradiating the film with a source of radiation which the photothermally active particles convert to heat to cause thermal expansion to form wrinkles in a region of the film that was irradiated.
2 . The method of claim 1 further comprising exposing the irradiated film to moisture.
3 . The method of claim 2 further comprising drying the film wherein the wrinkles are removed by the exposure to moisture and/or by the drying and then exposing the film to radiation a second time to form new wrinkles.
4 . The method of claim 1 wherein the amount of the nanosheets of layered inorganic material in the layer is less than 30% by weight based on total weight of the layer.
5 . The method of claim 2 further comprising drying to remove the wrinkles and optionally re-moisturizing the film restores the wrinkles.
6 . The method of claim 1 wherein after irradiating, the wrinkles remain after exposure to moisture and optionally drying.
7 . The method of claim 5 wherein the amount of the nanosheets of layered inorganic material in the layer is at least 30%, by weight based on total weight of the layer.
8 . The method of claim 1 , wherein the layer is electrically conductive and/or there is an electrically conductive layer on the layer opposite the substrate and wherein upon exposure to moisture after irradiation the film becomes a conductor.
9 . The method of claim 1 wherein the layered inorganic material is laponite.
10 . The method of claim 6 wherein the amount of the nanosheets of layered inorganic material in the layer is at least 30% by weight based on total weight of the layer.
11 . The method of claim 8 wherein upon subsequent drying the film ceases to be a conductor.
12 . The method of claim 1 wherein the photothermally active particles comprise carbon black.
13 . The method of claim 1 wherein the hydrophilic polymer is a polyvinyl alcohol and the source of the radiation is a laser.
14 . The method of claim 1 wherein a weight ratio of the elastomeric material to the photothermally active particles is 5:1 to 500:1.
15 . The method of claim 1 wherein the elastomeric material comprises polydimethylsiloxane.
16 . The method of claim 1 wherein the hydrophilic polymer comprises repeat units of —(CH 2 —CHOH) m —, and —(CH 2 —CHOCOCH 3 ) n —.