Difference between revisions of "Assembly of large-area, highly ordered, crack-free inverse opal films"
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== Results and Discussion == | == Results and Discussion == | ||
| − | [[Image:Hatton2010 1.png|200px|thumb|left|'''Fig. 1''' Schematic for inverse opal synthesis: 1) Colloids assemble from a sol-gel solution 2) template removal]] | + | [[Image:Hatton2010 1.png|200px|thumb|left|'''Fig. 1''' Schematic for inverse opal synthesis: 1) Colloids assemble from a sol-gel solution 2) template removal]] [[Image:Hatton2010 2.png|400px|thumb|right|'''Fig. 2''' Highly ordered I-<math>siO_2</math> films formed from PMMA/sol-gel coassembly (Left scale bar is <math>10\mu m </math> and right scale bar is <math>1\mu m </math>)]] |
| − | The advantage of the presented process is that the infiltration of a preassembled porous structure is avoided, thus preventing the film from cracking during the drying step. Indeed, the fabrication technique consists only of two steps (Fig. 1): 1) Polymer colloids (e.g. polystyrene (PS) or poly methyl methacrylate (PMMA)) assemble in a sol-gel precursor solution (e.g. <math> Si(OH_4), Ti(OH_4), Ge(OH_4)</math>) during an evaporative deposition resulting in an opal film. 2) The template is removed. | + | The advantage of the presented process is that the infiltration of a preassembled porous structure is avoided, thus preventing the film from cracking during the drying step. Indeed, the fabrication technique consists only of two steps (Fig. 1): 1) Polymer colloids (e.g. polystyrene (PS) or poly methyl methacrylate (PMMA)) assemble in a sol-gel precursor solution (e.g. <math> \mathrm {Si(OH_4), Ti(OH_4), Ge(OH_4)}</math>) during an evaporative deposition resulting in an opal film. 2) The template is removed. |
If the PMMA spheres are deposited from a hydrolyzed tetraethoxy silane (TEOS) solution, the interstitial spaces of the polymeric opal film are filled with silica gel matrix material which results in an inverse opal silica structure (I-SiO2). In that way defects as cracking, formation of domain boundaries and colloidal vacancies which are a main problem in conventionally assembled films can be omitted over a cm length scale. | If the PMMA spheres are deposited from a hydrolyzed tetraethoxy silane (TEOS) solution, the interstitial spaces of the polymeric opal film are filled with silica gel matrix material which results in an inverse opal silica structure (I-SiO2). In that way defects as cracking, formation of domain boundaries and colloidal vacancies which are a main problem in conventionally assembled films can be omitted over a cm length scale. | ||
| − | + | [[Image:Hatton2010 3.png|500px|thumb|left|'''Fig. 3''' A) The film thickness is directly proportional to the colloidal concentration. The threshold thickness for cracking is indicated. B) A 1.5cm I-<math>siO_2</math> film. C) A cleaved film reveals the growth direction along <110>. Inset: fcc-lattice model]] | |
Several observations were made: There's a critical TEOS-to-colloid ratio (approximately 0.15 mL TEOS | Several observations were made: There's a critical TEOS-to-colloid ratio (approximately 0.15 mL TEOS | ||
Revision as of 14:31, 13 September 2010
Birgit Hausmann
Reference
Keywords
Coassembly, colloidal assembly, crack-free films, inverse opals, nanoporous
Overview
A new synthesis of crack-free inverse opal films over cm length scales is presented. The two step process consists of a) an evaporative deposition of polymeric colloids in a hydrolyzed silicate sol-gel precursor solution and b) a colloidal/matrix coassembly. The preferential grwoth direction is <110>. The synthesis of multilayered hierarchical films are also demonstrated. Furthermore, the inverse opal films were replicated in other materials as porous Si and <math>TiO_2</math> while maintaining their morphology during the gas/solid displacement reaction.
Results and Discussion
The advantage of the presented process is that the infiltration of a preassembled porous structure is avoided, thus preventing the film from cracking during the drying step. Indeed, the fabrication technique consists only of two steps (Fig. 1): 1) Polymer colloids (e.g. polystyrene (PS) or poly methyl methacrylate (PMMA)) assemble in a sol-gel precursor solution (e.g. <math> \mathrm {Si(OH_4), Ti(OH_4), Ge(OH_4)}</math>) during an evaporative deposition resulting in an opal film. 2) The template is removed. If the PMMA spheres are deposited from a hydrolyzed tetraethoxy silane (TEOS) solution, the interstitial spaces of the polymeric opal film are filled with silica gel matrix material which results in an inverse opal silica structure (I-SiO2). In that way defects as cracking, formation of domain boundaries and colloidal vacancies which are a main problem in conventionally assembled films can be omitted over a cm length scale.
Several observations were made: There's a critical TEOS-to-colloid ratio (approximately 0.15 mL TEOS solution per 20 mL PMMA suspension) beyond which crackfree films can be expected. Figure 2 shows a highly ordered crackfree film which was fabricated in optimized conditions: 1) suspending a vertically oriented glass slide in a mixture comprised of 0.15 mL of a 28.6 wt% TEOS solution with a 20 mL suspension of 280 nm diameter PMMA spheres (approximately 0.125 vol%), 2) allowing the solvent to slowly evaporate at 65 °C (deposition rate = 2 cm/day), and 3) treating the composite structure at 500 °C for 5 h in air.
Cracking seems to occur along {111} planes for thin films, which is consistent with conventional evaporative deposited films, whereas thicker films seem to crack along {110} planes.
