View source for Assembly of large-area, highly ordered, crack-free inverse opal films

Birgit Hausmann

== Reference ==
[http://www.pnas.org/content/early/2010/05/14/1000954107.abstract B. Hatton et. al. "Assembly of large-area, highly ordered, crack-free inverse opal films" PNAS 107 (23) 2010]

== 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 converted to inverse opal films of other materials as porous Si and <math>TiO_2</math> while maintaining their morphology during the gas/solid displacement reaction.

== 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]]
Herein we demonstrate the evaporative coassembly of a sacrificial
colloidal template with a matrix material in a single step to
yield a colloidal composite, thereby avoiding the need for liquid
infiltration into a preassembled porous structure

[[Image:Hatton2010 2.png|400px|thumb|left|'''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>)]][[Image:Hatton2010 3.png|500px|thumb|right|'''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]]

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.  

[[Image:Hatton2010 4.png|300px|thumb|right|'''Fig. 4''' <math>SiO_2</math> inverse opal structures formed by colloidal coassembly. Schematics (left) vs. SEM images (right). (A) Synthesis of
multilayered, hierarchical films with different pore sizes by successive layer
deposition prior to template removal. (The top left and bottom left SEM images show the interface
between layers before and after calcination, respectively.) (B) <math>SiO_2</math> structures grown on topologically patterned
substrates (Left), SEM fractured cross section of inverse opals grown in
4 μm wide, 5 μm deep channels on a Si substrate (Right). (C) Coassembly onto curved surfaces (Left), and SEM images
(Right) of a <math>SiO_2</math> inverse opal film layer (shown magnified, Inset) deposited
onto a sintered, macroporous Ti scaffold structure.]]