Plasma beam alignment of liquid crystal with improved alignment stability [LCD manufacture]
A method of plasma beam treatment providing liquid crystal (LC) aligning substrates of improved alignment stability is described. In this method the aligning substrates are obliquely treated with a plasma flux containing alignment and passivation agents simultaneously. This method is applicable for the substrates of organic and inorganic origin. During this treating process, good pretilt angle stability and alignment quality are much promised.
Planar and tilted uniform alignment of liquid crystals by plasma-treated substrates
We describe a new aligning technique that yields uniform planar or tilted orientation of a nematic liquid crystal at different organic and inorganic substrates. The method is based on the oblique irradiation of an aligning substrate with a partially collimated flux of accelerated plasma. The sheet-like plasma flux is produced by an anode layer thruster with a race track geometry of the discharge channel. For liquid crystals with a positive dielectric anisotropy the technique produces two modes of uniform alignment: (1) with the easy axis in the incident plane of the plasma beam; (2) with the easy axis perpendicular to the plane of incidence. Mode 1 transforms into mode 2 as the irradiation dose increases. In mode 1, the pretilt angle can be controlled by changing the parameters of irradiation such as incidence angle, current density and particle energy. In mode 2, the pretilt angle is zero (planar alignment). The azimuthal anchoring coefficient is relatively weak (W a∼10−6 J m−2) for the first type of alignment and strong (W a≥10−4 J m−2, comparable to rubbed polymer substrates) for the second type. The two-mode alignment feature can be used to control alignment properties and to create alignment patterns. The method is free from the usual shortcomings of the traditional rubbing technique. We discuss possible mechanisms of the two-mode alignment and show that plasma-induced modifications of the substrate topography might be an important factor in liquid crystal alignment.
Non-isothermal O2 plasma treatment of phenyl-containing polymers
A variety of phenyl-containing polymer surfaces have been oxidized using low pressure non-equilibrium O2 glow discharges. Characterization by X-ray photoelectron spectroscopy has shown that the level of oxygen incorporation can be correlated to the intensity of the C(1s) π−π* valence transition measured for the untreated parent polymer. In all cases, a globular surface texture is observed by atomic force microscopy following O2 plasma treatment. These chemical and topographical changes can be explained in terms of the susceptibility of phenyl groups contained within the parent polymer structure toward oxidative glow discharge attack.