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Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

Gvozdovskyy I., Kurioz Y., Reznikov Y.

Opto-Electronics Review

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2009

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Vol. 17, No. 2

116-119

EN

We report on first studies of wetting of liquid crystal on photoaligning surface. We observed strong light-induced variations of a contact angle of a liquid LC 5CB on a photoaligning surface of fluoro-polyvinyl-cinnamate (PVCN-F) and we connected these variations with changes of PVCN-F polarity. We also present drastic changes of the contact angle of a nematic liquid crystal (MLC-6080) on the PVCN-F surface in a vicinity of temperature anchoring transition of liquid crystal from homeotropic orientation to planar one. We did not find any peculiarities in temperature dependence of the contact angle of isotropic liquid (glycerol) on PVCN-F and of nematic liquid crystal on pure glass in the same temperature range. It allows us to suggest that rearrangement of LC molecules and flexible fragments in the LC-polymer interface are responsible for the change of surface tensions both of LC and polymer and the observed jump of the contact angle.

2

Formation and dynamics of easy orientation axis in magnetic field on PVCN-F surface

Buluy O., Reznikov Y., Slyusarenko K., Nobili M., Reshetnyak V.

Opto-Electronics Review

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2006

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Vol. 14, No. 4

293-297

EN

We describe the experiments on a magnetically-induced drift of the easy axis on a soft surface of photoaligning material fluoro-polyvinyl-cinnamate. We found unexpected partial relaxation of the drift of the easy axis after switching the magnetic field off. This relaxation cannot be explained in a framework of the existing models and requires additional assumptions about the drift process. We propose a model that explains the experimental data suggesting elastic-like behaviour of the polymer fragments during the drift of the easy axis.

3

Sticking of liquid crystal on photosensitive polymer layers

Gerus I., Glushchenko A., Kurioz Y., Reznikov Y., Tereshchenko O.

Opto-Electronics Review

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2004

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Vol. 12, No. 3

281-284

EN

The sticking effect on photoaligning surfaces was investigated. We demonstrated that additional irradiation of photoaligning polymers with cinnamoyl side groups with not-polarized UV-light strongly decreases their sticking parameter. We associate this effect with cross-linking of the flexible side-groups by UV light and, as a consequence, with light-induced strengthening of the photoaligning surface. Restriction of mobility of the flexible groups on the photoaligning surface (surface strengthening) resulted in depressing the sticking effect. The method of the decrease of the sticking effect by the light-induced strengthening is rather general, and it can be applied for any photoaligning materials undergoing a light-induced cross-linking of polymer fragments. For poly(vinyl 4-fluorocinnamate) the light-induced strengthening allowed us to get the record value of the sticking parameter, S₀= 0.2%, which is better than traditional rubbed polyimide surfaces provide. Such a value of the sticking parameter along with other aligning characteristics allows considering poly(vinyl 4- fluorocinnamate) as very prospective material for modern liquid crystal display technologies.