Inverse Opal Photonic Crystals - Department of Chemistry ...

FOREWARD
This laboratory guide was conceived during the summer of Y2001 at the University of
Minnesota Materials Research Science and Engineering Center (UMN MRSEC) by Nagalingam
Balakrishnan, a faculty member of the United Tribes Technical College who participated in the
UMN MRSEC summer research program with his student Anna Gopher. This team worked in
the research group of Professor Andreas Stein in the Department of Chemistry of UMN, studying
the synthesis of “inverse opals,” wherein uniformly sized polymer spheres are used as templates
for sol-gel condensation reactions to produce inorganic solid replicas with uniformly spaced
macropores. These materials are particularly intriguing because the uniform spacing of the
macropores and the large periodicities result in peculiar optical properties that prevent the
transmission of specific wavelengths of light. They are crystals in every sense of the word, but
with the crystal lattice defined by the macropores. One glance at these crystals reveals light
refraction identical to that observed in natural opals, which are simply crystals of uniformly
spaced silica spheres. This laboratory guide has been prepared with the intention of teaching
specific laboratory techniques – emulsion polymerization, templated sol-gel condensation,
sintering, and optical measurements – to undergraduate students, and possibly high school
students. We believe that the deep appreciation of jewelry and other artifacts, including opals,
by Native American communities makes this a particularly attractive laboratory module for
science instruction in tribal colleges.
Special thanks are due Dr. Frank Snowden, the Associate Direction of the UMN Education and
Human Resources program, for his coordination of the outreach activities that led to this guide.
This guide would not have been possible without the generous support of the National Science
Foundation, which provided funding for the UMN MRSEC and its summer research programs
for external participants.
Michael D. Ward
Director, UMN MRSEC
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