Geoffrey Alan Ozin talks with
ScienceWatch.com and answers a few questions about
this month's Emerging Research Front Paper in the field of
Materials Science. The author has also sent along
several images of his work.
Article: Colloidal crystal films: Advances in
universality and perfection
Authors: Wong, S;Kitaev,
Journal: J AM CHEM SOC, 125 (50): 15589-15598 DEC 17
Addresses: Univ Toronto, Mat Chem Res Grp, Dept Chem, 80 St
George St, Toronto, ON M5S 3H6, Canada.
Univ Toronto, Mat Chem Res Grp, Dept Chem, Toronto, ON M5S
Why do you think your paper is highly
Our work paved the way for other researchers to reliably prepare
high-quality colloidal crystal films for various applications in diverse
research areas. We have demonstrated major advances in preparation of
colloidal crystal films in two important directions: quality of
microspheres, where monodispersity was improved to below 2%, and
development of reliable universal procedure for preparation of high-quality
films using arbitrary sizes of colloidal particles.
Importantly, the developed procedure is really facile and versatile, since
it uses only simple laboratory equipment, so it can be readily implemented
in different research laboratories. Furthermore, the developed procedure
features all the necessary elements to be relatively
Finally, it was our decision to present the developed methodology in a form
of clear well-detailed protocols for others to reproduce and build upon,
rather than patenting the results. In this respect, it is pertinent to
mention that one reviewer's critical comments on our manuscript was that
the article feels and reads as a patent, which was actually the highest
compliment given to us.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
Compared to prior advances in the field (especially those made by Vicki L.
Colvin of the Department of Chemistry, Rice University, Houston, TX, and
David J. Norris of the NEC Research Institute in Princeton, NJ), we have
developed a universal procedure to form colloidal crystal films out of
arbitrary sizes of colloidal particles (from less than 100 nm to more than
Optical microphotographs of several attempts to
deposit colloidal crystals on photonic fibers
resulting in a donut and a bean, illustrating the
beautiful colors of opals so formed. The diameter
of the donut and the thickness of the bean are
approximately 125 microns (300X
accompanying four slides and
We have clearly established the parameters necessary for reliable colloidal
crystal film formation. These parameters included: i) most importantly, the
quality of the microspheres, which happened to be extremely sensitive to
the impurities within the largest sizes; ii) sufficient temperature and the
geometry of the vessel to sustain required convection patterns; iii) the
concentration of microspheres in dispersions which precisely control the
thickness of the films.
The reported procedure has been demonstrated to be robust and reliable, so
it can be repeated several times (e.g., Fig. 2), used for binary systems,
scaled, etc., to produce virtually any type of colloidal crystal films to
satisfy just about every requirement of the diverse fields of science that
could benefit from the applications of advanced functional properties of
colloidal crystal films.
Would you summarize the significance of your paper in
Similar to how oranges can be packed neatly in grocery stores, we mastered
the packing of tiny spheres with the size of 1/100 of a human hair into
perfectly ordered arrangements (Figs. 1,2). In addition, we have worked out
how to make those spheres precisely the same—we did not want any
bananas placed alongside our oranges.
The procedure for the sphere packing that we have developed is really
straightforward. In a nutshell: the spheres are placed in a solvent, which
is brought very close to its boiling point, so the liquid starts to
evaporate quickly, and under the right conditions, these perfectly packed
films grow upon evaporation.
While we—or other scientists doing similar work prior to
us—would have liked to claim the credit for the novelty of these
prepared materials, we certainly could not, as Nature had already prepared
such materials long before. The opal, one of the earth's most lustrous
gemstones, originated in Australia over 100 million years ago in
silica-laden sediment deposited along the shoreline of the Artesian Basin.
Opal is one of the few gemstones sedimentary in origin and contains 6 to
10% water from the ancient sea.
What we could take great pride in is that, with our control over sphere
sizes and the way they pack, we could prepare opals of every possible color
and shade! It may be curious to note that the best scientific samples had
rather monotonous (if not to say relatively boring) colors (Fig. 3). At the
same time, the scientific failures always had a silver lining of
breathtaking colors (Fig. 4).
How did you become involved in this research and were
any particular problems encountered along the way?
The research was initiated in 2001 by a postdoctoral fellow and later
research associate, Dr. Vladimir Kitaev, in a project on photonic crystal
applications in optics. Vladimir started to work on the perfection of
colloidal microspheres and their deposition under different conditions. The
high-T setup was constructed and then an industrious undergraduate student,
Sean Wong, came and put his energy to work along with Vladimir's on a
project which later became a major part of the paper.
We are pleased to state that no specific problems were encountered along
the way, but it is also instructive to note that we needed to take
advantage of the extensive time needed to get everything just right and
doubly checked before putting everything together to describe a reliable,
highly reproducible procedure which others could easily adopt and utilize
for their own diverse research activities.
Where do you see your research leading in the
How we see it is, most importantly, that we have opened the way for other
researchers to reliably prepare high-quality colloidal crystal films and to
use them in their diverse areas of interest.
For us, this work served as a backbone for successful research on colloidal
crystals, photonic crystals, sensors, and templating media, which resulted
in a series of high-profile publications and the spin-off of a
Toronto-based company, Opalux, whose mission is the development and
commercialization of bottom-up active photonic crystal products that
target electrically and mechanically tuneable full color coatings for
applications exemplified by displays and battery state-of-charge
monitors, along with banknote anti-counterfeit and
Do you foresee any social or political implications for
We evaluate this only in terms of the indirect scientific and technological
impact of the proposed methodology, along with the reliable preparation of
diverse high-quality colloidal films, which provide a versatile tool for
further research within the diverse areas of chemistry, physics, materials
science, engineering, biology, and medicine with direct applications in
photonics and sensors, displays and security devices, membranes, and
Geoffrey Alan Ozin
Dept. of Chemistry
University of Toronto
Toronto , Canada