Model of Ion Solvation in Liquid Crystal Cells

Abstract

The leading display technology, active matrix display requires very high reliability. Characteristic parameters for high reliability are, for instance, voltage holding ratio and residual DC values. Both parameters show a strong deterioration if some charge carrier or contamination is present in active matrix display cells, and this leads to an inacceptable contrast value of the display. The physicochemical understanding of such contamination causes, origin or solvation, still remain unclear. A model is presented in this paper, using a simple simulation method called `sparkle' whose results are in very good agreement with the experimental results.

Terminal end‐group efficiency for the nematic phase using model bicyclo[2.2.2]octanes

“…A series of new terminal polyfluorinated substituents, such as trifluoromethyl and trifluoromethoxy groups, have been used to induce a positive dielectric anisotropy in nematic mixtures for use in LCDs with active matrix addressing. These polyfluorinated end groups do not solvate ions in the boundary layers of LCDs and leach ions from these layers into the nematic mixture [4,8]. We now report an empirically updated order of terminal group efficiency for substituents in a terminal position for the nematic phase including these groups.…”

“…The latter requirement precludes the use of cyano groups in a terminal position, as they dissolve and solvate ions, e.g. from the alignment layers on the inside of the LCD [8]. The presence of these ions leads to a low voltage holding ratio.…”

Nematic Liquid Crystals with Negative Dielectric Anisotropy: Molecular Design and Synthesis

“…As one possible reason for the low holding ratio, the complexation and solvation of ionic contaminants by nitrogen containing components of liquid crystal mixtures is discussed. 25 Since the AMD is developing towards the major LCD technology standard, materials like the fluoropyridines cannot be used, in spite of their otherwise highly interesting properties.…”

Super‐Fluorinated Liquid Crystals: Towards the Limits of Polarity

“…There are also some limitations in the toolbox of the designer of liquid crystals for AM LCDs: nitrogen heterocycles or nitrile groups that would enhance the molecular dipole moment should not be used, because they either promote photochemical degradation of the LC mixture or cause image sticking in the LCD panel as a result of their strong affinity towards ionic trace impurities. This leaves three possible strategies for the design of very polar materials, and these methods involve the use of: (1) extremely polar fluorinated terminal groups, such as CF 3 or SF 5 , [6] enhanced by laterally fluorinated aromatic ring structures; [7] (2) intrinsically polar bridge structures, such as CF 2 O bridges [8] and (3) polar aliphatic oxygen heterocycles. [9] Strategies (1) and (2) alone are usually not sufficient, and the use of 1,3-dioxane building blocks (strategy 3) often causes reliability problems under oxidative or hydrolytic stress.…”