By: Aaron Richardson
Simon Fraser University is at the cutting edge of research in advanced organic materials. The Williams Group, headed by Dr. Vance Williams in the chemistry department, is working on the development of organic materials with functions as semiconductors, molecular photoswitches, and birefringent materials. Molecular photo switches are molecules that convert between two or more states when exposed to different wavelengths of light, while birefringent materials are materials that refract light in different ways based on their orientation.
The primary focus of the group is on liquid crystalline (LC) materials which are used in applications such as liquid crystal displays, medical imaging, and organic electronics. Research in the Williams Group consists of the combination of small organic molecules and the characterization of their physical, chemical, optical, and electronic properties. The goal of these studies is to gain a better understanding of the structure-property relationships of LC materials so that they can be used more efficiently in the future.
The most common and well-known commercial use of LC materials are in liquid crystal displays (LCDs) which we probably all encounter every day in our smartphones, televisions, and laptop computers. The function of such LCDs is based on the switching of a layer of LC molecules between two orientations by an applied electric field.
In one state, the molecules transmit light and the pixel is illuminated, and in the other state, the molecules block the light and the pixel is dark. In combination with other layers such as a colour filters, this process can be used to create colour images as well. In the case of an LCD, a relatively fluid type of LC phase is used to achieve fast response times and thus a seamless moving picture or video.
A new and exciting research direction for LC materials is towards organic electronics. Historically, most electronics are made from inorganic materials. However, in the past 10 years or so, research has been in the process of developing organic materials that arguably parallel the function of inorganics at what seems to be a fraction of the processing cost.
One of the most important components of any electronic device is a semiconductor — which essentially regulates the flow of electricity. A major challenge in producing a high performance organic semiconductor is achieving a highly ordered material for efficient charge transfer. To address this problem, PhD student David Ester in the Williams Group is currently working on the development of LC organic semiconductors.
What makes LC materials unique and useful is that they form an intermediate state between solid and liquid. In crystalline solids, molecules are highly ordered, with their positions and orientations fixed, making them rigid. In liquids, molecules have much less order, and both their positions and orientations are free to change, making them fluid. In the LC phase, molecules have an intermediate degree of order, and their orientations and positions may be fixed in one or two, but not all three, dimensions. By combining features of both states, the LC phase allows chemists to exploit benefits of both solids and liquids simultaneously.
Another important factor is that LC materials exhibit ‘self-assembly’ — this means that molecules assume a certain order without any external stimuli, simply due to their inherent intermolecular interactions, a process which occurs spontaneously based on temperature. With these exceptional properties, LC materials give scientists the possibility to create materials with new functionality unprecedented for solids or liquids alone.
The picture shown above is a polarized optical microscope (POM) image taken by David Ester as part of his research. The picture is 1400 x 900 micrometers; just over a millimetre in length, and just under a millimetre in width. It is invisible to the human eye, but captured in all of it’s beauty by the POM.
POM is a commonly used tool in the characterization of LC materials, not only producing striking patterns with beautiful colours, but also providing vital information about the order of molecules in the sample being studied. The textures in this image helped the Williams Group identify the structure of the LC phase of this material. “This particular focal-conic fan-shaped texture consists of layers of hexagonally packed molecules, the kind of phases that are being targeted for high-performance organic semiconductors,” Ester explains.
The POM image is also a candidate in the Science Exposed photo contest put on by the National Science and Engineering Research Council of Canada (NSERC). NSERC, as one of the primary sources of scientific research funding in Canada, is also a key sponsor of research being done by the Williams Group.
The purpose of the photo contest is to promote scientific awareness and generate an interest in science across Canada through the use of visually striking and scientifically significant photos. Scientists from a variety of fields, and coming from all over Canada, have submitted images to the contest, and Ester’s has been chosen among the top 20 finalists.
The repeated conical pattern found in Ester’s image comes from the ways in which the molecules assemble themselves. The patterns are not forced upon them. Instead, when the molecules are placed in an environment of a particular temperature, the molecules self-assemble into this pattern. The fact that this is the pattern that the molecules arrange themselves in is important in figuring out how they function, and in finding the best ways to use them in modern technology.
