liquid crystals aligned to enhance visibility
TRANSCRIPT
Nakanishi wins Welch Award in Chemistry
Koji Nakanishi, Centennial Professor of Chemistry at Columbia University, will receive the 1996 Robert A. Welch Award in Chemistry, honoring his lifetime achievements in bioorganic chemistry. The award—$300,000 and a gold medallion—will be presented to Nakanishi in October by the Welch Foundation, Houston.
Nakanishi's career has focused on
natural bioactive compounds—elucidating their structures, explaining their modes of action, and exploring their use to solve human problems. His research groups, notable for multi-disciplinary and often international collaborations, have characterized more than 180 natural products, including metal-sequestering compounds from sea squirt blood, toxins from wasps, and antimutagens from plants. Their work on visual pigments is helping to reveal the mechanism of vision.
Many of these compounds are available only in minute amounts—or exist only fleetingly. So his work has stressed isolation and purification, as well as innovative approaches to structure elucidation, notably circular dichroic spectroscopy.
The Welch Award adds to Nakanishi's long list of honors, which include, in 1990, the Imperial Prize of the Japan Academy and the American Chemical Society's Arthur C. Cope Award, and in 1994, the National Academy of Sciences Award in Chemical Sciences.
Maureen Rouhi
800,000-metric-ton-per-year ethylene unit will bring the site's total annual ethylene capacity to more than 1.6 million metric tons. Expected to start up in early 2000, the new unit will use natural gas liquids—propane and light naphtha—as feedstocks.
The expansion will also add 535,000 metric tons per year of polyethylene capacity and 410,000 metric tons per year of ethylene glycol capacity. And Yan-pet will build 260,000 metric tons per year of polypropylene capacity, using the propylene by-product from the new ethylene unit. The expansion will bring the site's annual ethylene-deriva-tive products capacity to more than 2 million metric tons per year.
Meanwhile, Mobil and another Saudi partner, Petromin—a state-owned firm—are building a 2 million-barrel-per-year lubricant basestock refinery at the Yanbu site. The refinery will go online in the first quarter of 1997.
George Peaff
Liquid crystals aligned to enhance visibility A team of Swiss researchers has developed a photopolymerization technique that improves the visibility of liquid-crystal displays by controlling the tilting and alignment of the liquid-crystal molecules.
Physicists Martin Schadt and Hubert Seiberle and organic chemist Andreas Schuster at liquid-crystal R&D firm Rolic Ltd., Basel, use linearly polarized ultraviolet radiation to simultaneously align and cross-link the polymer molecules of the thin film that coats substrates that sandwich liquid-crystal molecules in displays.
The resulting photoaligned polymer film orients the adjacent layer of liquid-crystal molecules parallel to the UV radiation's polarization direction. The film also tilts the long axes of the liquid-crystal molecules at an angle to the plane of the substrate surface [Nature, 381, 212 (1996)].
The technique is an important breakthrough, says Jos van Haaren, research scientist at Philips Research Laboratories, Eindhoven, the Netherlands. "The Rolic group has solved the problem of tilting liquid-crystal molecules," he tells C&EN. "This was lacking in previous photoalignment techniques." The
method may find industrial uses, he notes.
"We developed normal photopoly-mers that are sensitive to polarized light," says Schadt, Rolic's chief executive officer. "The molecules induce alignment in the liquid crystals adjacent to them. The direction depends on how we cross-link [the photopolymer molecules] with the light."
He adds that the method can align twisted nematic displays used in TV and computer screens, where the rodlike organic liquid-crystal molecules are arranged in a spiral-staircase configuration between the two substrates. The molecules in each picture element—pixel—of the display transmit linearly polarized light. When an electric field is applied perpendicular to the pixel substrates, the liquid-crystal molecules change orientation, cutting light transmission. To control this change, the molecules next to the substrate surface must be aligned and tilted out of plane before the electric field is switched on.
In current industrial uses, liquid-crystal molecule alignment and tilting are controlled by mechanically brushing the thin polymer films on the substrates with a velvet cloth. But this generates dust and can cause electrostatic
damage to transistors in the displays, van Haaren notes in a commentary in the same issue of Nature. The new technique overcomes these problems.
The mechanical alignment method also results in restricted viewing angles for liquid-crystal displays. The photoalignment technique can be used to widen the field of view by dividing a single liquid-crystal display pixel into four subpixels, each with a different twisted nematic configuration.
The researchers point out that photoaligned liquid-crystal displays are stable to both heat and light. They suggest that linear photopolymerization technology not only improves the performance of existing liquid-crystal displays—such as viewing properties— but it also opens the way to new display configurations and other types of optically anisotropic devices.
"The next step is to see if the photoalignment technique is technologically compatible with existing processes for making these displays," points out van Haaren. "For instance, the photopolymer has to be transparent, and it has to have a low contamination level of the liquid-crystal layer. Otherwise, it may adversely affect the switching performance."
Michael Freemantle
MAY 20,1996 C&EN 9