Abstract
In this paper we report the new experimental results on the rise of a liquid crystal in flat capillaries with inner photosensitive surfaces. The capillaries with different surface orientations were prepared by the use of the photo-alignment technique. Such a surface treatment makes it possible to eliminate the noncontrollable influence of a nanorelief on the wetting process, which takes place in the rubbing treatment technique previously used in similar experiments. The dynamics of the capillary rise of a nematic liquid crystal 5CB (4-cyano-4′-pentylbiphenyl) in vertical plane capillaries with photo-aligned substrates were studied for the first time. It was found that the stationary value of a contact angle weakly depends on the direction of a planar surface orientation relative to the direction of a capillary rise. It has been shown that the application of strong electric fields resulted in a decreasing of the contact angle. The results, obtained for the nematic liquid crystal, are compared with the results of an investigation of the capillary flow in a shock-free ferroelectric smectic phase.
Highlights
The investigation of the wetting of solid surfaces by different liquids is an interesting issue, both from an academic and a technological point of view [1,2]
The ITO coating on one of the glass substrates was partly deleted to provide the application of alternating electric voltage U of frequency f to one of the two local capillaries with the same surface orientation. This revealed the effect of the electric field on the wetting and viscosity properties of liquid crystals
The inner surfaces of the plates were thoroughly cleaned to establish strongly water-wet glass surfaces and spin coated by 0.5% solution of azo sulphiric dye (SD-1) in dimethyl formamide (DMF) and baked at 90 ◦ C for a 1 h to provide a thin nanometer layer of a dye
Summary
The investigation of the wetting of solid surfaces by different liquids is an interesting issue, both from an academic and a technological point of view [1,2]. It is important to explore the dynamics of the director reorientation in a nematic liquid crystal (LC) phase confined to thin or ultrathin channels or capillaries [1,3]. These processes were investigated using different experimental methods, for example by the study of liquid (isotropic and anisotropic) drops spreading over both isotropic and anisotropic surfaces [4,5,6,7,8], including those with the micro (nano) relief [7]. The alternative well-established technique is based on the arising of liquids in vertical capillaries with different cross sections. It should be noted that both experimental and theoretical studies of the capillary rise of isotropic liquids have a long history [9,10,11,12]
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