Nanostructured surfaces for liquid crystal applications (Abstract/Comunicazione in atti di convegno)

  • Nanostructured surfaces for liquid crystal applications (Abstract/Comunicazione in atti di convegno) (literal)
  • 2013-01-01T00:00:00+01:00 (literal)
Alternative label
  • Kieup Lee , Rossella Capasso , Martin Kuehnast , Lucia Petti and Giusy Scalia (2013)
    Nanostructured surfaces for liquid crystal applications
    in 13th International Meeting on Information Display (IMID2013), Daegu-Republic of Korea, August 26-29, 2013
  • Kieup Lee , Rossella Capasso , Martin Kuehnast , Lucia Petti and Giusy Scalia (literal)
  • Abstract (literal)
  • Graduate School of Convergence Science and Technology, Seoul National University, Suwon, 443-270, Korea; Martin Luther University Halle-Wittenberg, Halle, Germany; CNR (literal)
  • Nanostructured surfaces for liquid crystal applications (literal)
  • Liquid crystals are easily aligned by surface treatments and a simple rubbing can dictate the uniform orientation of liquid crystal molecules. The most common way to achieve planar alignment of liquid crystals is to unidirectionally rub a polyimide film, coating selected substrates. This method is a very effective way for choosing the desired, common, orientation for liquid crystal molecules but also for creating their stable, steady state once the switching field is turned off. Even if effective, the rubbed polyimide also has disadvantages, being a source of contamination, an additional process step in the display fabrication and a possible cause of deterioration of the overall display performance. Moreover, the control of fine structure is not easily implementable. Therefore, it would be desirable to find new ways to control the LC alignment, eliminating the layer of rubbed polymer. We propose the use of substrates nanostructured with suitable patterns for planar alignment. In addition, nanostructured substrates can also be used for confining liquid crystal in sub-micron cavities in which new behaviour can be observed, useful for novel electrical but also optical LC devices. In this work we present surfaces with nanostructures realized by electron-beam lithography (EBL). This technique allows the creation of very tiny structures at nanoscale with precise control of the geometrical parameters, carved into a suitable polymer. The created nanostructures can be used as a mother stamp for reproducing the pattern onto flexible substrates. We have designed the patterns for achieving planar alignment of the LC, uniformly but also towards different chosen orientations, and have evaluated the dependence on geometrical parameters of the structures. With such substrates we have realized typical sandwich cells for liquid crystals. By filling the cells, prepared with two nanopatterned substrates, with standard nematic mixtures, we could confirm the achievement of uniform planar alignment by polarizing optical microscopy. The alignment appears to occur independently to the width and distance of the channel realized in the present study. We have studied the stability of the alignment after passing through phase transitions and switching under the application of electric fields. In addition, we have also investigated the optical behaviour of cholesteric LC under nanoconfinment. (literal)
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