"We found that spontaneous vertical alignment of liquid crystals was induced by adding nanoparticles of polyhedral oligomeric silsesquioxanes in the liquid crystal layer," team member Chia-Wei Kuo told nanotechweb.org. "The technique could be used to make the next generation of thinner, more flexible displays."
The new method means that substrates of plastic-polymer films or other bendable materials could be used instead of glass to make such displays. In general, flexible substrates need to be processed at low temperatures to prevent the substrate becoming deformed. Nanoparticle-induced vertical alignment allows just this.
Kuo and colleagues obtained their results by first mixing the polyhedral oligomeric silsesquioxane nanoparticles and liquid crystals together in an ultrasonic bath for 15 minutes. Next, they heated the mixture to remove the solvent in which the mixture had been dispersed. They then loaded the composite into a test cell – called the nanoparticle-doped hybrid-aligned nematic (HAN) cell.
The researchers measured the optical characteristics of the HAN cell using a diode laser between crossed polarizers. "We found that the nanoparticle-doped HAN cells were very similar to conventional HAN cells made by traditional methods," said Kuo. "This implies that liquid crystals can be effectively aligned by doping them with nanoparticles."
The team will now be busy perfecting its technique. One drawback to overcome is the slow response time and high viscosity of the nanoparticle-doped liquid crystals. But the researchers already have an idea of how to solve this problem: "We will try adding a monomer additive into the liquid crystal/nanoparticle mixture to form polymer-stabilized liquid crystals in the test cell," explained Kuo. "In this way, the test cell will be divided by the polymer chain and the response time of the liquid crystals should be reduced."
The work was reported in Appl. Phys. Lett.