Control of the Anchoring Energy of Rubbed Polyimide Layers by Irradiation with Depolarized UV-Light

Abstract

PACS. 62.40+i -Anelasticity, internal friction, stress relaxation, and mechanical resonances. PACS. 64.70Kb -Solid-solid transitions. PACS. 66.30−h -Diffusion in solids.Abstract. -YBa2Cu3O x exhibits a second-order tetragonal-to-orthorhombic transformation, at least in wide temperature ranges. The order parameter is proportional to the orthorhombic strain or to the O population difference between ( 1 2 0 0) and (0 1 2 0) sites in the Cu(1) plane. Quasi-static anelasticity experiments were performed at 100 and 120 • C on YBa2Cu3O x samples with O concentrations x between 6.29 and 6.9. The experiments show a drastic increase of both relaxation strength and relaxation time near the tetragonal-to-orthorhombic transformation at x 6.4, thus demonstrating i) large amplitudes and ii) a (critical) slowing-down of the order parameter fluctuations.

Diffusion model of photoaligning in azo-dye layers

“…Previous theoretical investigations of azo-dyes photoinduced birefringence were mostly based on taking into account the photochemical transformations such as cross linking in poly (vinyl)cinnamate derivatives and photodegradation in polyimides [7][8][9][10][11][12][13][14] or cis-trans photoisomerization process in azobenzene side-chain polymers [15][16][17]. A similar model has already been applied to describe the photoinduced birefringence in azo-dye Langmuir Blodgett films [18].…”

A lifetime model for LCOS panels under intense illumination

“…2-4. It was found that all parameters remained nearly constant during the test, and it was only near the end of the life that they started to change relatively rapidly. The constancy of contrast ratio and the entire VTF suggested that, unlike UV-exposure, 6 visible light does not weaken azimuthal anchoring of the LC and the twist angle remains constant.…”

“…Although information on photo-chemical changes in the PI layer induced by visible light is rather scarce, 1,2 there are numerous reports on UV light effect. [6][7][8][9][10] The main focus of these publications was on the effectiveness of aligning liquid crystals by PI after illumination by polarized UV light. Non-polarized UV light may cause some changes in the liquid-crystal azimuthal anchoring energy.…”

Photoalignment of nematic liquid crystal on polyamic‐acid‐based soluble polyimide with no side fragments

“…The interaction between the unreacted moieties and LC molecules usually is stronger and the LC director usually aligns perpendicular with the polarization of UV light. 15,21 In our case, the PI films were illuminated by p-polarized UV light with wavelength λ = 254 nm near the band of absorption by cyclobutane fragments of K5. The source of UV light was a high-pressure Hg lamp and the intensity of the UV light in the substrate plane was about I UV ≈ 5 mW/cm 2 .…”

“…14 Later, a number of papers were devoted to the study of the properties and origin of the photoalignment of polyimide materials of different chemical compositions. [15][16][17][18][19][20][21][22][23][24][25] It was found that UV-induced deimidization, e.g., cleavage of photosensitive fragments of a main polymer chain, is responsible for the formation of the easy orientation axis in polyimides. It was also shown that the anchoring energy and the pretilt of LC on a polyimide layer can be effectively tuned by selecting a dose and polarization degree of the incident UV light.…”