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Swollen Polymer
Matrices as a Scaffold
for Macroporous Inorganic Materials
Inorganic Networks via Swollen Polymer Matrices
This project began in the Fall of 2001. We swell an organic
polymer in a solvent, and allow an inorganic precursor to diffuse into
and polymerize in the polymer matrix. We have studied a variety
of polymers and solvents, and dissolved the polymer after growth of the
inorganic material. We have published one full paper and several conference
proceedings on this project, and a full paper is in preparation. Several
proposals for funding of this project are pending.
We want
to grow an insoluble inorganic material in a matrix (light green, Figure
1) that can subsequently be removed.
This calcination is akin to burning away the template of a zeolite
or mesoporous silica, or to dissolving the ccp lattice of inverse opal.
We obtain an inorganic negative of the original swollen polymer
with, in principle, structural control.
The approach is very simple, versatile, and could rapidly lead
to new discoveries and applications.
Figure
1.
Idealized reaction scheme; polymer is shown in green: (a)
Control of swelling in organic solvent (yellow), followed by metal alkoxide
coating (light blue) and filling (dark blue); (b) Swelling directly
in neat metal alkoxide liquid greatly simplifies the reaction sequence
into one step.
See reference:
D. P. Brennan, A. Dobley, P. J. Sideris, S. R. J. Oliver, “Swollen Polydimethylsiloxane
(PDMS) as a Template for Inorganic Morphologies”, Langmuir, 2005,
21, 11994-11998.
Double-layer TiO2 Thin Films via
Swollen Polymer Matrices for Dye-Sensitized Solar Cell
We use a rapid, inexpensive
method to fabricate porous TiO2 thin films using swollen polymers
as a sacrificial structure director.
Polymethylmethacrylate (PMMA) can be swollen in methyl ethyl ketone
(MEK). PMMA spheres were
dissolved in MEK, then mixed with Ti butoxide at varying ratios. The mixed solution was deposited on a FTO conductive glass
or Si wafer by spin coating or dip coating.
Double-layer orous TiO2 thin films were obtained after
calcination, which removes the polymer from the film. Scanning
electron microscope (SEM) shows top layer particle size range from 100
nm to 500 nm.
After ultrasonication in water, top layer is removed and bottom layer
is analyzed by atomic force microscope (AFM), revealing particle size
of ~25 nm. Electron dispersion spectroscopy confirmed that the pores are
void spaces surrounded with TiO2 networks.
The double-layer porous TiO2 thin film provides a large
surface area semiconductor for the adsorption of photo sensitized dye
coupled on bottom layer and efficient light scatter effect on top layer,
potentially increasing the efficiency of photo-electricity conversion.
See
reference: X. Fan, D. P. Demaree, J. M. St.
John, A. Tripathi, S. R. J. Oliver, "Double-layer porous TiO2 electrodes
for solid-state dye-sensitized solar cells", Appl. Phys. Lett., 2008,
92, 193108.
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