Effect of atmospheric plasma and rubbing coprocessing on liquid crystal alignment on a polyimide layer

Influence of Periodic Non-Uniformities of Well-Structured Sapphire Surface by LIPSS on the Alignment of Nematic Liquid Crystal

“…Therefore, let us estimate the value of W B unst of the unstructured gaps, by taking into account the fact that surface roughness is about 6 nm, which can be considered as the depth, A, for Equation (1). Let us suppose, hypothetically, that a roughness has a certain periodicity of about 250 nm that is the same average period of grooves, obtained by the usage of traditional methods of LC alignment [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. Under these conditions, the value of the AE W B unst is about 0.97 × 10 −6 J/m 2 .…”

“…As a consequence, research on different surfaces as perspective candidates for high-quality alignment of LCs is still continuing. There are a number of various processing techniques allowing to obtain anisotropy on the surface using them as high-quality aligning layers with certain properties for LC orientation [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ].…”

“…The most commonly encountered method of orientation of LCs is the rubbing technique, widely used in LCD technology [ 1 , 2 , 3 , 4 ]. In addition, in the last two decades, both photoalignment [ 5 , 6 , 7 , 8 , 9 , 10 ] and the ion/plasma method [ 11 , 12 ] as alternatives to the rubbing technique were successfully studied. Furthermore, uniform alignment methods of LCs were also investigated and proposed in a number of different ways, for instance the usage of Langmuir-Blodgett film [ 13 ], e-beam lithography [ 14 ], atomic force microscopy (AFM) nano-rubbing [ 15 , 16 ], nano-imprint lithography [ 17 , 18 ], and photolithography [ 19 ], respectively.…”

“…It is assumed that the homogeneous orientation of LCs is mainly caused by anisotropy created on the substrate surface due to the periodical distribution of grooves, charges, or crosslinking/destruction of the used polymer [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. Unfortunately, each method of surface treatment referred to above has its own advantages and drawbacks [ 5 ].…”

“…However, one of the main shortcomings of the photoalignment technique is, on the one hand, the relatively small areas of treated polymer layers and, on the other hand, a significant degradation of the LCs orientation with time due to the gradual deterioration of the photosensitive polymer layers [ 5 ]. Ion/plasma beam treatment as a perspective method leads to the homogeneous planar and tilted orientation of LCs [ 11 , 12 ]. Unfortunately, this technique may result in the unwanted accumulation of static charges, photodestruction of the polymer layer, or deterioration of the polymer properties [ 5 ].…”